Researcher Database

Researcher Profile and Settings

Master

Affiliation (Master)

  • Faculty of Science Chemistry Organic and Biological Chemistry

Affiliation (Master)

  • Faculty of Science Chemistry Organic and Biological Chemistry

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Profile and Settings

Degree

  • Doctor of Science, April 1988, Tohoku University(Tohoku University)

Profile and Settings

  • Name (Japanese)

    Suzuki
  • Name (Kana)

    Takanori
  • Name

    200901041847970754

Alternate Names

Achievement

Research Interests

  • 超分子   応答性分子   酸化還元系   エレクトロクロミズム   分子素子   酸化還元   安定ラジカル   色素   有機電導体   水素結合   分子不斉   両性多段階酸化還元   光誘起電子移動   動的酸化還元   単一成分有機電導体   レドックス系   開殻型分子   円二色性   C-H--O水素結合   渡環相互作用   シクロファン   応答性   電気化学   ホトクロミズム   単一分子メモリ   固相反応   共有結合   ホストゲスト   物性有機化学   有機電子材料   構造有機化学   Organic Materials Chemistry   Organic Reaction Chemistry   Structural Organic Chemistry   

Research Areas

  • Nanotechnology/Materials / Structural/physical organic chemistry
  • Nanotechnology/Materials / Functional solid-state chemistry
  • Nanotechnology/Materials / Synthetic organic chemistry
  • Manufacturing technology (mechanical, electrical/electronic, chemical engineering) / Electronic devices and equipment

Research Experience

  • 2006/04 - Today Hokkaido University Faculty of Science, Department of Chemistry
  • 2002/04 - 2006/03 北海道大学大学院理学研究科化学専攻 教授
  • 1995/01 - 2002/03 Hokkaido University School of Science
  • 1989/04 - 1994/12 Tohoku University Faculty of Science, Department of Chemistry
  • 1988/04 - 1989/03 JSPS PD (東北大学理学部化学科)

Education

  • 1986/04 - 1988/04  東北大学大学院理学研究科化学専攻博士後期課程(短縮修了)
  • 1984/04 - 1986/03  Tohoku University
  • 1980/04 - 1984/03  Tohoku University  Faculty of Science

Awards

  • 2019/03 The Chemical Society of Japan Academic Award
     
    受賞者: SUZUKI Takanori
  • 2004/09 第一回野副鉄男教授記念奨励賞
     
    受賞者: 鈴木 孝紀
  • 1996/03 日本化学会進歩賞
     
    受賞者: 鈴木 孝紀

Published Papers

  • Luyan Wu, Yili Liu, Wenhui Zeng, Yusuke Ishigaki, Sensen Zhou, Xingxing Wang, Yidan Sun, Yan Zhang, Xiqun Jiang, Takanori Suzuki, Deju Ye
    Journal of the American Chemical Society 2023/12/07
  • Kewei Sun, Kazuma Sugawara, Andrey Lyalin, Yusuke Ishigaki, Kohei Uosaki, Oscar Custance, Tetsuya Taketsugu, Takanori Suzuki, Shigeki Kawai
    ACS Nano 1936-0851 2023/12/04
  • Takashi Harimoto, Tomoki Tadokoro, Soichiro Sugiyama, Takanori Suzuki, Yusuke Ishigaki
    Angewandte Chemie International Edition 1433-7851 2023/11/28 
    Abstract The concept of a domino‐type reaction has been applied in a wide range of fields such as synthetic organic chemistry, material engineering, and life science. To extend the domino concept to redox chemistry, we designed and synthesized a dimeric quinodimethane (QD) with a nonplanar dithiin spacer. The domino‐redox properties can be activated by raising the temperature, based on a thermally equilibrated twisted conformation of QD, which has a higher HOMO level that is more readily oxidized. After one QD unit is oxidized (trigger), steric repulsion and electronic interaction between electrophores make the neighboring QD unit adopt a twisted conformation (domino process), which facilitates the following oxidation. Thus, a domino‐redox reaction was achieved for the first time by a change in the HOMO level due to a drastic change in the molecular conformation.
  • Yusuke Ishigaki, Takashi Harimoto, Takuya Shimajiri, Takanori Suzuki
    Chemical Reviews 0009-2665 2023/11/10
  • Takashi Harimoto, Yuka Sugai, Kazuma Sugawara, Takanori Suzuki, Yusuke Ishigaki
    CHEMISTRY-A EUROPEAN JOURNAL 0947-6539 2023/07 
    Most redox systems generally cannot avoid the involvement of open-shell species upon generating multiply charged species, which often reduces reversibility in multi-color electrochromic systems. In this study, we newly synthesized octakis(aminophenyl)-substituted pentacenebisquinodimethane (BQD) derivatives and their hybrids with alkoxyphenyl analogues. Thanks to apparent two-electron transfer accompanied by double dramatic changes in the structure of the arylated quinodimethane skeleton, the dicationic and tetracationic states were generated and isolated quantitatively because of the negligible steady-state concentration of intermediary open-shell species such as monocation or trication radicals. When two electrophores with different donating abilities are attached to the BQD skeleton, a dicationic state with a different color can be isolated in addition to the neutral and tetracationic states. For these tetracations, an interchromophore interaction induces a red-shift of the NIR absorptions, thus realizing tricolor UV/Vis/NIR electrochromic behavior involving only closed-shell states.
  • Soki Kawaguchi, Takuya Shimajiri, Tomoyuki Akutagawa, Takanori Fukushima, Yusuke Ishigaki, Takanori Suzuki
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 96 (7) 631 - 635 0009-2673 2023/07 
    Due to inherent structural instability, low-dimensional mate-rials often undergo the Peierls transition upon cooling, which suppressed by an increase in dimensionality of their solid-state electronic structures using secondary bonding interactions such as chalcogen bonds (ChB). We revealed here that ChB them-selves have an inherent structural instability when a chalcogen atom participates in simultaneous formation of two ChB, dem-onstrating for the first time a Peierls-like transition (chalcogen-Peierls transition) of ChB-based organic solids upon cooling. Thus, a lattice dimerization occurs at 220-230 K that changes the two-dimensional ChB network into an accumulated one-dimensional ribbon network in the tetracyanoquinodimethane fused with two [1,2,5]thiadiazoles (1). Negative cooperativity of two ChB formation is weakened on the Se atom due to greater polarizability. Thus, the selenadiazole analogues (2 and 3) undergo a similar chalcogen-Peierls transition at lower tem- peratures, such as at 160-170 K and at 110-120 K, respectively, depending on the number of Se atom incorporated (one or two, respectively).
  • Yuta Nishimura, Takashi Harimoto, Takanori Suzuki, Yusuke Ishigaki
    CHEMISTRY-A EUROPEAN JOURNAL 0947-6539 2023/07 
    A nitrogen-centered heptalene, azaheptalene, was designed as a representative of a new class of redox-responsive molecules with a large steric strain that originates from the adjacent seven-membered rings. The pentabenzo derivative of azaheptalene was efficiently synthesized by a palladium-catalyzed one-pot reaction of commercially available reagents. Bromination led to mono- and dibrominated derivatives, the latter of which is interconvertible with isolable radical cation species exhibiting near-infrared absorption. Since the azaheptalene skeleton shows configurationally stable helicity with a large torsion angle, enantiomers could be successfully separated. Thus, optically pure azaheptalenes with P- or M-helicity showed strong chiroptical properties (|g(abs)|& GE;0.01), which could be changed by an electric potential.
  • Takuya Shimajiri, Henri-Pierre Jacquot de Rouville, Valérie Heitz, Tomoyuki Akutagawa, Takanori Fukushima, Yusuke Ishigaki, Takanori Suzuki
    Synlett 0936-5214 2023/04/12 
    Studies on a series of tetracyanoquinodimethanes (TCNQs) fused with [1,2,5]chalcogenadiazole rings reveals that chalcogen bonds (ChBs), through E center dot center dot center dot=C (E = S or Se) contacts, are a decisive factor in determining their crystal structures, with the formation of one- or twodimensional networks in a lateral direction. For anion-radical salts generated by one-electron reduction, electron conduction occurs in the direction of the network due to intermolecular electronic interactions involving ChBs. Based on the reliable synthon E center dot center dot center dot N=C for crystal engineering, molecular recognition occurs so that solid-state molecular complexes are selectively formed with certain donors, such as xylenes, among their isomers by charge-transfer-type clathrate formation. The inclusion cavity of the clathrate might provide a reaction environment for photoinduced electron transfer in the solid state. The accommodation of multiple conformers of overcrowded ethylene exhibiting thermo/mechanochromism is another example of a novel function that can be realized by ChBs through E center dot center dot center dot N=C contacts. Therefore, these chalcogenadiazolo-TCNQs endowed with the ability to form ChBs are promising materials for the development of novel solid-state functions. 1 Introduction 2 Bis[1,2,5]thiadiazolo-TCNQ (BTDA) 2.1 Chalcogen Bonds in Crystal Structures of BTDA and its Se Analogues 2.2 Electronic Effects of Chalcogen Bonds in Organic Conductors Consisting of BTDA 2.3 Molecular Recognition by Chalcogen Bonds in Molecular Complexes of BTDA 2.4 Single-Crystalline-State Photoreactions of Molecular Complexes of BTDA 2.5 Overcrowded Ethylene Composed of a BTDA Substructure 3 TCNQ Analogues Fused with a [1,2,5]Chalcogenadiazole 3.1 Crystal Structures of Chalcogenadiazolo-TCNQs 3.2 Crystal Structures of Chalcogenadiazolo-TCNNQs: An E center dot center dot center dot N=C Chalcogen Bond versus a Weak C-H center dot center dot center dot N=C Hydrogen Bond 3.3 Molecular Recognition by Chalcogen Bonds in TCNNQ Derivatives 4 Outlook
  • Minh Anh Truong, Tsukasa Funasaki, Lucas Ueberricke, Wataru Nojo, Richard Murdey, Takumi Yamada, Shuaifeng Hu, Aruto Akatsuka, Naomu Sekiguchi, Shota Hira, Lingling Xie, Tomoya Nakamura, Nobutaka Shioya, Daisuke Kan, Yuta Tsuji, Satoshi Iikubo, Hiroyuki Yoshida, Yuichi Shimakawa, Takeshi Hasegawa, Yoshihiko Kanemitsu, Takanori Suzuki, Atsushi Wakamiya
    Journal of the American Chemical Society 145 (13) 7528 - 7539 0002-7863 2023/03/22 
    Hole-collecting monolayers have drawn attention in perovskite solar cell research due to their ease of processing, high performance, and good durability. Since molecules in the hole-collecting monolayer are typically composed of functionalized pi-conjugated structures, hole extraction is expected to be more efficient when the pi-cores are oriented face-on with respect to the adjacent surfaces. However, strategies for reliably controlling the molecular orientation in monolayers remain elusive. In this work, multiple phosphonic acid anchoring groups were used to control the molecular orientation of a series of triazatruxene derivatives chemisorbed on a transparent conducting oxide electrode surface. Using infrared reflection absorption spectroscopy and metastable atom electron spectroscopy, we found that multipodal derivatives align face-on to the electrode surface, while the monopodal counterpart adopts a more tilted configuration. The face-on orientation was found to facilitate hole extraction, leading to inverted perovskite solar cells with enhanced stability and high-power conversion efficiencies up to 23.0%.
  • Takashi Harimoto, Takanori Suzuki, Yusuke Ishigaki
    Chemistry – A European Journal 29 (23) 0947-6539 2023/03/16 
    Electrochromic systems capable of switching near-infrared (NIR) absorption are fascinating from the viewpoint of applications in the materials and life sciences. Although 11,11,12,12-tetraaryl-9,10-anthraquinodimethanes (AQDs) with a folded form undergo one-stage two-electron oxidation to produce twisted dicationic dyes exhibiting NIR absorption, there is a need to establish a design strategy that can enhance the NIR-absorbing abilities of the corresponding dicationic dyes. In this study, we designed and synthesized a series of AQD derivatives with various substituents introduced at the ortho-position(s) of the 4-methoxyphenyl group. X-ray and spectroscopic analyses revealed that NIR-absorbing properties can be changed by introduction of the ortho-substituents. Thus, control of the steric and electronic effects of the ortho-substituents on the 4-methoxyphenyl groups was demonstrated to be an effective strategy for fine-tuning of the HOMO and LUMO levels for neutral AQDs and twisted dications, respectively, resulting in the modification of electrochemical and spectroscopic properties under an "ortho-substitution strategy".
  • Yusuke Ishigaki, Takuya Tachibana, Kazuma Sugawara, Moto Kikuchi, Takanori Suzuki
    ChemPlusChem 88 (3) 2192-6506 2023/03 
    Macrocyclic dications 2(2+) composed of two triarylmethylium units were designed and synthesized. In contrast to the reference monocations 1(+), macrocyclic dications 2(2+) exhibited mechanochromic emission extending to the red region (-900 nm), since the luminescence color in a solid state can reversibly change due to their constrained structures granted by alkylene linkers and the choice of a proper counterion. X-ray diffraction and spectroscopic analyses revealed that such mechanochromic behavior was induced by the crystal-to-amorphous transition. A change in the intermolecular interaction of macrocyclic dications 2(2+) would be the key to realizing a change in the emission pattern, since the color of the molecules did not change by applying mechanical stimuli. These findings may suggest a design strategy for creating a variety of stimuli-responsive materials, especially for carbocation-based fluorescent materials.
  • Yuki Hayashi, Shuichi Suzuki, Takanori Suzuki, Yusuke Ishigaki
    Journal of the American Chemical Society 145 (4) 2596 - 2608 0002-7863 2023/02/01 
    A series of six dications composed of pure hydrocarbons with one to six non-substituted 9,10-anthrylene units end-capped with two dibenzotropyliums were designed and synthesized to elucidate the electronic properties of huge oligo(9,10-anthrylene) backbones. Their structures were successfully determined by X-ray analyses even in the case of eight planar 14π-electron units, revealing that all dications adopt almost orthogonally twisted structures between neighboring units. Spectroscopic and voltammetric analyses show that neither the significant overlap of orbitals nor the delocalization of electrons between 14π-electron units occurs due to the orthogonally twisted geometry even in solution. As a result, sequential oxidation processes were observed with the reversible formation of multivalent cations with the release of the same number of electrons as the number of anthrylene units. Upon two-electron reduction, a closed-shell butterfly-shaped form was obtained from the dication containing one anthrylene unit, whereas open-shell twisted biradicals were isolated as stable entities in the cases of derivatives containing three to six anthrylene units. Notably, from the derivative with two anthrylene units, a metastable open-shell isomer was obtained quantitatively and underwent slow thermal conversion to the most stable closed-shell isomer (Ea = 23.1 kcal mol-1). There is a drastic change in oxidation potentials between two neutral species (ΔE = 1.32 V in CH2Cl2). Since the present dications were regenerated upon oxidation of the isolated reduction products, these systems may contribute to the development of advanced response systems capable of switching color, magnetic properties, and oxidative properties by using a “cation-capped orthogonal geometry”.
  • Yuzu Kobayashi, Yasuyuki Yokota, Raymond A. Wong, Misun Hong, Jun Takeya, Saho Osawa, Fumitaka Ishiwari, Yoshiaki Shoji, Takashi Harimoto, Keisuke Sugimoto, Yusuke Ishigaki, Takanori Suzuki, Takanori Fukushima, Yousoo Kim
    Journal of Physical Chemistry C 127 (1) 746 - 758 1932-7447 2023/01/12 
    Tracking various chemical reactions, including electrochemical and photochemical reactions at the single-molecule level, is expected to yield a great deal of knowledge from both fundamental and applied aspects. In this study, we report on a methodology to track the electronic-state changes of redox reactions at the single-molecule level by using electrochemical scanning tunneling microscopy (EC-STM). EC-STM is powerful for single-molecule analysis of redox reactions, but previous studies have shown difficulties separating the structural and electronic contributions due to orientational changes during the redox reaction. Here, we visualize the electronic-state changes of a single ferrocene associated with redox reactions using EC-STM by synthesizing and fabricating a monolayer of structurally rigid tripodal molecules based on triptycene, which act as ideal anchors to preserve a constant distance between the electrode and the ferrocene moieties. This methodology paves the way for versatile single-molecule measurements of important phenomena at the solid-liquid interface, such as photochemistry and heterogeneous catalysis.
  • Su Gi Chong, Shuichi Suzuki, Takanori Suzuki, Yusuke Ishigaki
    Bulletin of the Chemical Society of Japan 96 (10) 1144 - 1149 0009-2673 2023 
    4-Methoxyphenyl-substituted di(2-thienyl)methyliums were designed and synthesized as a new class of cationic dyes exhibiting absorption in the visible (Vis) and near-infrared (NIR) region. Their cyanine-type π-conjugation was confirmed by alternation of positive charges along the polymethine chain as well as by a significant disappearance of bond alternation. Upon one-electron reduction of these cations, neutral radicals were generated, which could be isolated as stable entities when an anthryl-type substituent was attached to the central methine carbon while the secondary radical without any substituent quantitatively converted to a σ-bonded dimer. Since both the stable radical and the dimer regenerated the starting cyanine dyes upon oxidation, the present redox pairs can serve as electrochromic materials that exhibit a change in absorption in the Vis-NIR region.
  • Kazuma Sugawara, Toshikazu Ono, Yoshio Yano, Takanori Suzuki, Yusuke Ishigaki
    Materials Chemistry Frontiers 7 (8) 1591 - 1598 2023 
    Tetraazaanthraquinodimethanes can exhibit various colours and emissions depending on their multiple conformations, such as not only folded and twisted forms but also intermediate structures, e.g., planar and twisted-folded forms, in pseudopolymorphs.
  • Yujing Ma, Kazuma Sugawara, Yusuke Ishigaki, Kewei Sun, Takanori Suzuki, Shigeki Kawai
    Chemistry – A European Journal 0947-6539 2022/12/20 
    On-surface cyclodehydrogenation recently became an important reaction to planarize pi-conjugated molecules and oligomers. However, the high-activation barrier to cleave the C-H bond often requires high-temperature annealing, consequently restricting structures of precursor molecules and/or leading to random fusion at their edges. Here, we present a synthesis of pyrrolopyrrole-bridged ladder oligomers from 11,11,12,12-tetrabromo-1,4,5,8-tetraaza-9,10-anthraquinodimethane molecules on Ag(111) with bond-resolved scanning tunnelling microscopy. This non-dehydrogenative cyclization between pyrazine and ethynylene/cumulene groups has a low-activation barrier for forming intermediary dimeric oligomer containing dipyrazinopyrrolopyrrolopyrazine units, thus giving new insight into the strain-sensitive in ladder-oligomer formation.
  • Takuya Shimajiri, Yusuke Ishigaki, Yuta Kawakami, Soki Kawaguchi, Yuki Hayashi, Kazuto Hada, Takanori Suzuki
    Synlett 34 (10) 1147 - 1152 0936-5214 2022/10/11 
    A carbon-carbon (C-C) single bond longer than 1.7 Å shows unique bond flexibility, even though a C-C single bond is typically rigid and robust. We report here that the bond length of a flexible C-C single bond surrounded by bulky alkyl groups on novel hexaphenylethane-type hydrocarbons could be affected by even weak non-covalent interactions such as London dispersion. Thanks to London dispersion, an ultralong and flexible C-C single bond exhibits an obvious bond contraction. X-ray analyses and Raman spectroscopy provide direct information regarding the bond length and strength, and density functional theory calculations explain the bond contraction driven by London dispersion. An extremely elongated C-C bond with flexibility would be a good probe for quantifying even weak interaction, which is usually difficult to detect, as a change in bond length.
  • Yusuke Ishigaki, Reina Fukagawa, Kazuma Sugawara, Takashi Harimoto, Takanori Suzuki
    Chemistry – An Asian Journal 17 (22) e202200914  1861-4728 2022/09/30 
    Two tetraarylanthraquinodimethane (Ar4 AQD) derivatives having two different aryl groups (aminophenyl and methoxyphenyl) were prepared by sequential dibromomethylation and Suzuki-coupling reactions. X-ray analyses showed that they adopt a folded structure in the neutral state whereas the corresponding dications have a planar anthracene ring, to which diarylmethylium units are perpendicularly attached. Different from Ar4 AQD having the same substituents that undergoes facile two-electron transfer during interconversion with the dicationic state, the intermediary cation radical becomes long-lived in the newly prepared unsymmetric derivatives. The geometric and electronic structures of the open-shell intermediates were elucidated through electrochemical and theoretical investigation, with revealing that the cation radicals adopt the twisted geometry like dications. Upon electrolyses of the dications, the twisted cation radicals were involved in the electrochromism whereas their steady-state concentration is negligible in the oxidation process, thus realizing unique tricolor electrochromic behavior with a hysteretic pattern of color change (colorless -> purple -> blue -> colorless).
  • Yusuke Ishigaki, Masaki Takata, Takuya Shimajiri, Luyan Wu, Wenhui Zeng, Deju Ye, Takanori Suzuki
    Chemistry (Weinheim an der Bergstrasse, Germany) 28 (70) 0947-6539 2022/09/15 
    10,11-Bis[bis(4-dimethylaminophenyl)methylene]dibenzo[ bf ]thiepin ( 1 ) and -oxepin ( 2 ) were prepared as stable yellow crystalline compounds, which are the cyclic analogues of electron-donating hexaarylbutadienes. Upon two-electron oxidation, they are reversibly transformed into the title dications ( 1 2+ and 2 2+ ) exhibiting near-infrared (NIR) absorptions, which were also isolated as stable salts. These redox pairs can serve as new entries into less well-explored organic NIR-electrochromic systems, and the separation of redox peaks (electrochemical bistability) was attained for 1 / 1 2+ and 2 / 2 2+ , thanks to drastic geometrical changes between neutral and dicationic states, as revealed by a series of X-ray analyses. Thiepin- S,S -dioxide analogue ( 3 / 3 2+ ) exhibits quite similar redox behavior due to nonaromatic nature of the dibenzothiepin or -oxepin unit in 1 2+ and 2 2+ , whereas thiepin- S -oxide derivative ( 4 / 4 2+ ) does not exhibit bistability due to the less change in geometry upon electron transfer, showing that a subtle change of a bridging atom in the central seven-membered ring can modify the redox properties.
  • Luyan Wu, Wenhui Zeng, Yusuke Ishigaki, Junya Zhang, He Bai, Takashi Harimoto, Takanori Suzuki, Deju Ye
    Angewandte Chemie International Edition 61 (37) e202209248  1433-7851 2022/08/08 
    Reversible imaging probes that allow for the dynamic visualization of the redox cycle between hydroxyl radical ((OH)-O-center dot) and hydrogen sulfide (H2S) are vital to probe the redox imbalance-involved pathological process in vivo. Herein, we report a reversible ratiometric photoacoustic (PA) imaging nanoprobe (1-PAIN) for the real-time imaging of (OH)-O-center dot/H2S redox cycle in vivo. 1-PAIN displays a low PA ratio between 690 and 825 nm (PA(690)/PA(825)), which significantly increases by approximate to 5-fold upon oxidation by (OH)-O-center dot, and is switched back to the initially low PA(690)/PA(825) value upon reduction by H2S. 1-PAIN could dynamically report on the hepatic (OH)-O-center dot production in mice during the lipopolysaccharide (LPS)-induced liver inflammation process, and visualize hepatic H2S generation during the N-acetyl cysteine (NAC)-induced anti-inflammation process. 1-PAIN can act as a useful tool to probe the redox state in living biology, beneficial for the study of redox imbalance-related diseases.
  • Yusuke Ishigaki, Kota Asai, Henri‐Pierre Jacquot de Rouville, Takuya Shimajiri, Johnny Hu, Valérie Heitz, Takanori Suzuki
    ChemPlusChem 87 (4) e202200075  2192-6506 2022/04 
    In contrast to p-quinodimethane tetraesters, which undergo facile polymerization due to their diradical character, newly synthesized 1 and 2 consisting of a chalcogenadiazole fused to a p-naphthoquinodimethane tetraester are thermodynamically stable due to butterfly-shaped deformation. Such a folded molecular structure is also favorable for chalcogen bond (ChB) formation through intermolecular close contacts between a chalcogen atom (E: Se or S) and the oxygen atoms of ester groups in a crystal. The less-explored chelating-ChB through a C=O⋅⋅⋅E⋅⋅⋅O=C contact [Se⋅⋅⋅O: 2.94–3.37 Å] is the key supramolecular synthon for the formation of a one-dimensional rod-like assembly in a crystal, which is commonly observed in selenadiazole-tetraesters (1) with OMe, OEt, and OiPr groups. The formation of inclusion cavities between the rods shows that 1 could serve as solid-state host molecules for clathrate formation, as found in a hexane-solvated crystal. In contrast, thiadiazole-tetraesters (2) are less suitable for the formation of a rod-like assembly since the ChB involving S is less effective, and thus is overwhelmed by weak hydrogen bonds through C−H⋅⋅⋅O contacts.
  • Wenhui Zeng, Luyan Wu, Yusuke Ishigaki, Takashi Harimoto, Yuxuan Hu, Yidan Sun, Yuqi Wang, Takanori Suzuki, Hong Yuan Chen, Deju Ye
    Angewandte Chemie - International Edition 61 (4) e202111759  1433-7851 2022/01/21 
    Accurate detection of hepatic hydrogen sulfide (H2S) to monitor H2S-related enzymes’ activity is critical for acute hepatitis diagnosis, but remains a challenge due to the dynamic and transient nature of H2S. Here, we report a H2S-activatable near-infrared afterglow/MRI bimodal probe F1-GdNP, which shows an “always-on” MRI signal and “off-on” afterglow signal toward H2S. F1-GdNP shows fast response, high sensitivity and specificity toward H2S, permitting afterglow imaging of H2S and evaluation of cystathionine γ-lyase (CSE)’s activity in living mice. We further employ the high spatial-resolution MRI signal of F1-GdNP to track its delivery and accumulation in liver. Importantly, F1-GdNP offers a high signal-to-background ratio (SBR=86.2±12.0) to sensitively report on the increased hepatic H2S level in the acute hepatitis mice via afterglow imaging, which correlated well with the upregulated CSE activity in the liver, showcasing the good potential of F1-GdNP for monitoring of acute hepatitis process in vivo.
  • Shigeki Kawai, Kazuma Sugawara, Yujing Ma, Kewei Sun, Oscar Custance, Yusuke Ishigaki, Takanori Suzuki
    Physical Chemistry Chemical Physics 24 (36) 22191 - 22197 1463-9076 2022 
    Multiple intermolecular interactions offer a high-degree of controllability of on-surface molecular assemblies. Here, two kinds of molecular networks were formed by depositing 11,11,12,12-tetrabromo-1,4,5,8-tetraaza-9,10-anthraquinodimethane derivatives with two different alkyl groups in...
  • Yusuke Ishigaki, Tomoki Tadokoro, Yu Harabuchi, Yuki Hayashi, Satoshi Maeda, Takanori Suzuki
    Bulletin of the Chemical Society of Japan 95 (1) 38 - 46 0009-2673 2022 
    From the viewpoint of the development of molecular response systems, stimulus-induced switching of multiconformational/multi-configurational overcrowded ethylenes are interesting, whose properties could be manipulated by understanding the detailed isomerization paths. Anthraquinodimethane (AQD) ring-flip is usually a very fast process, and thus less studied experimentally. Herein, we studied AQDs with dibenzo- and tribenzocycloheptatrienylidene units, which have large enough steric hindrance to retard the AQD ring-flip to allow determination of the ¦Gºvalue experimentally. Their thermal isomerization was also scrutinized using the artificial force induced reaction method to elucidate the intermediates. Based on the structural unsymmetry in a newly prepared AQD, one of the isomers that undergoes a reversible conformational change via AQD ring-flip was isolated and analyzed by X-ray for the first time.
  • Yusuke Ishigaki, Kai Shimomura, Kota Asai, Takuya Shimajiri, Tomoyuki Akutagawa, Takanori Fukushima, Takanori Suzuki
    Bulletin of the Chemical Society of Japan 95 (3) 522 - 531 0009-2673 2022 
    In the crystals of 4,7-dihalobenzo[c][1,2,5]chalcogenadiazoles, the molecules are connected by two competing secondary bonding interactions: chalcogen bond (ChB) and halogen bond (HaB). Because the strengths of ChB and HaB change according to the kind of chalcogen (E: S, Se, Te) and halogen (X: Cl, Br, I), their relative contributions in determining the crystal packing can also change. Six newly determined crystal structures as well as 3 previously reported structures can be categorized into two groups: ChB-dominant and HaB-dominant structures. HaB in which X = I is strong enough to dictate the crystal packing of compounds with E = S and Se, but not where E = Te, whereas HaB in which X = Cl or Br has little effect on ChB-dominant molecular networks in crystals. The observed changing contributions of ChB and HaB may be useful for designing new supramolecular synthons for crystal engineering.
  • Luyan Wu, Yusuke Ishigaki, Wenhui Zeng, Takashi Harimoto, Baoli Yin, Yinghan Chen, Shiyi Liao, Yongchun Liu, Yidan Sun, Xiaobo Zhang, Ying Liu, Yong Liang, Pengfei Sun, Takanori Suzuki, Guosheng Song, Quli Fan, Deju Ye
    Nature Communications 12 (1) 2021/12 [Refereed]
     
    AbstractTumor response to radiotherapy or ferroptosis is closely related to hydroxyl radical (•OH) production. Noninvasive imaging of •OH fluctuation in tumors can allow early monitoring of response to therapy, but is challenging. Here, we report the optimization of a diene electrochromic material (1-Br-Et) as a •OH-responsive chromophore, and use it to develop a near-infrared ratiometric fluorescent and photoacoustic (FL/PA) bimodal probe for in vivo imaging of •OH. The probe displays a large FL ratio between 780 and 1113 nm (FL780/FL1113), but a small PA ratio between 755 and 905 nm (PA755/PA905). Oxidation of 1-Br-Et by •OH decreases the FL780/FL1113 while concurrently increasing the PA755/PA905, allowing the reliable monitoring of •OH production in tumors undergoing erastin-induced ferroptosis or radiotherapy.
  • Hiroshi Ikeda, Takashi Hirano, Kan Wakamatsu, Takanori Suzuki, Eietsu Hasegawa
    JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY C-PHOTOCHEMISTRY REVIEWS 48 1389-5567 2021/09
  • Kewei Sun, Kazuma Sugawara, Andrey Lyalin, Yusuke Ishigaki, Kohei Uosaki, Tetsuya Taketsugu, Takanori Suzuki, Shigeki Kawai
    Angewandte Chemie 133 (17) 9513 - 9518 2021/04/19
  • Sun, K., Sugawara, K., Lyalin, A., Ishigaki, Y., Uosaki, K., Taketsugu, T., Suzuki, T., Kawai, S.
    Angewandte Chemie - International Edition 60 (17) 9427 - 9432 1521-3773 2021/04/19 
    Cyclo-dehydrogenation is of importance to induce the planarization of molecules on noble surfaces upon annealing. In contrast to a number of successful syntheses of polycyclic aromatic hydrocarbons by forming carbon–carbon bonds, it is still rare to conduct conjugation and cleavage of carbon–nitrogen bonds in molecules. Here, we present a systematic transformation of the C−N bonds in11,11,12,12-tetraphenyl-1,4,5,8-tetraazaanthraquinodimethane as well as three other derivatives on Au(111). With bond-resolved scanning tunneling microscopy, we discovered novel the “heterocyclic segregation” reaction of one pyrazine ring with two nitrogen atoms to form two quinoline rings with one nitrogen each. Density functional theory calculations showed that the intramolecular ring-forming and -opening of N-heterocycles are strongly affected by the initial hydrogen–substrate interaction.
  • Yusuke Ishigaki, Kota Asai, Takuya Shimajiri, Tomoyuki Akutagawa, Takanori Fukushima, Takanori Suzuki
    Organic Materials 03 (02) 090 - 096 2021/04 
    The crystal structures of a series of tetracyanonaphthoquinodimethanes fused with a selenadiazole or thiadiazole ring revealed that their molecular packing is determined mainly by two intermolecular interactions: chalcogen bond (ChB) and weak hydrogen bond (WHB). ChB between Se and a cyano group dictates the packing of selenadiazole derivatives, whereas the S-based ChB is much weaker and competes with WHB in thiadiazole analogues. This difference can be explained by different electrostatic potentials as revealed by density functional theory calculations. A proper molecular design that weakens WHB can change the contribution of ChB in determining the crystal packing of thiadiazole derivatives.
  • Yusuke Ishigaki, Takashi Harimoto, Kazuma Sugawara, Takanori Suzuki
    Journal of the American Chemical Society 143 (9) 3306 - 3311 1520-5126 2021/03/10 
    Octaaryl-substituted bisquinodimethanes (BQDs) with a zigzag structure were designed as redox-switchable molecules that undergo four-electron oxidation to produce tetracationic pentacenes with a doubly twisted structure. In contrast to one-stage four-electron oxidation of BQDs, stepwise two-electron reduction of tetracationic pentacenes occurs to give dicationic anthracenes and then the original BQDs, step-by-step. Since both tetracations and dications exhibit near-infrared (NIR) absorptions (-1400 nm) based on an intramolecular charge-transfer interaction, changes in not only their structures but also their UV-vis-NIR spectra can be controlled by redox stimuli. In this Communication, we present an unprecedented one-step π-extension to pentacene from non-fused benzene rings by oxidation, and subsequent two-stage deannulation to benzene rings via anthracene upon reduction. All structures were determined by single-crystal X-ray analyses, and their properties were characterized by spectroscopic and theoretical studies.
  • Ishigaki, Y., Asai, K., de Rouville, H.-P.J., Shimajiri, T., Heitz, V., Fujii-Shinomiya, H., Suzuki, T.
    European Journal of Organic Chemistry 2021 (6) 990 - 997 1099-0690 2021/02/12 
    The title nonplanar electron acceptor (1) fused with a selenadiazole ring selectively forms a crystalline charge-transfer complex (CT crystal) with 2,6-dimethylnaphthalene (2,6-DMN). On the other hand, the sulfur analogue (2) has less recognition ability and forms CT crystals with both 2,6- and 2,7-DMN. X-ray analyses of 1, 2, and their CT crystals revealed that the Se⋅⋅⋅N chalcogen bond (ChB) in 1 is strong enough to determine the crystal packing with the formation of a cavity suitable for 2,6-DMN. On the contrary, ChB through S⋅⋅⋅N contact in 2 competes with other weak interactions such as a C−H⋅⋅⋅N hydrogen bond. The stronger ChB involving Se is the key for 1 to separate 2,6-DMN (>97 wt %) from a complex isomer mixture containing ca. 10 wt % each of 2,6- and 2,7-DMN by a simple, efficient and straightforward mixing-filtration-heating process.
  • Suzuki, T., Ishigaki, Y., Takata, M., Nishida, J.-I., Fukushima, T.
    Heterocycles 102 (3) 419 - 450 1881-0942 2021 
    9-Phenylxanthenyl radical can undergo facile C-C bond formation at C9-position when the two units of the radical are connected at C2'-positions to give stable intramolecular dimer (1), which is a clamped hexaphenylethane derivative with an elongated C-C bond. The newly formed bond in 1 can be cleaved easily upon two-electron oxidation to give bis(9-xanthenylium)-type dication (22+), from which the diradical is generated upon two-electron reduction. This review account describes the dynamic redox ("dyrex") pair of colorless 1 and yellow-orange 22+, which provides a versatile scaffold to develop multi-functional electrochromic systems. Both of 1 and 22+ are sterically challenged molecules and thus adopt characteristic skewed geometries. Electrochiroptical response was realized by suppressing the chiral inversion of helicity in 1 and axial chirality in 22+ whereas redox-induced fluorescence switching was attained by attaching the fluorophore whose emission is quenched by xanthenylium in 22+ but not by spiro(xanthene) unit in 1. By the molecular design that allows intramolecular chiral transmission, the spectral changes were also induced by the external stimuli (e.g. heat, pH) other than redox input, which made it possible to construct less well-explored multi-input-multi-output response systems. More advanced functions could be endowed, such as chiral redox memory or reversible O2-storage, by further modification of the prototype.
  • Ishigaki, Y., Uchimura, Y., Shimajiri, T., Suzuki, T.
    Bulletin of the Chemical Society of Japan 94 (4) 1385 - 1393 1348-0634 2021 
    Molecules with an extreme structural parameter, such as an elongated C-C bond, have attracted much attention due to their special properties, which ordinary molecules do not have. Stabilized hexaphenylethanes are suitable compounds for seeking for the longest C-C bond. In addition to steric repulsion among the aryl groups (“front strain”) found in 1,1,2,2-tetra-arylacenaphthenes (1), “scissor effects” cause expansion of the C1-C2 bond in 1,1,2,2-tetraarylpyracenes (2). A series of crystallographic analyses of 2 revealed that the substituent on the aryl group also affects the C1-C2 bond length. The “front strain” over the weakened bond is enhanced by the ring-fused structure in di(spiroacridan)pyracene (2A). The bond length of 1.771(3) ¡ determined by X-ray analysis at 93 K is one of the largest values for a Csp3-Csp3 bond, and increases to 1.791(3) ¡ when the single crystal is heated to 413 K. Further expansion over 1.80 ¡ was achieved by maximizing the front strain by fixing the spirodibenzocycloheptatriene units in an eclipsed manner in the core-shell-type dihydropyracylene (3B) [1.795(2) ¡ at 100 K, 1.806(2) ¡ at 400 K]. Several studies show that “bond expandability” is a newly discovered feature of an elongated covalent bond, which could be used for the future design of novel materials with a mechanical/thermal response.
  • Ishigaki, Y., Sugawara, K., Tadokoro, T., Hayashi, Y., Harimoto, T., Suzuki, T.
    Chemical Communications 57 (59) 7201 - 7214 1364-548X 2021 

    In this Feature Article, we focus on our research history for constructing functional response systems based on redox-active quinodimethanes with electron-donating aryl groups, which undergo reversible interconversion with twisted cations.

  • Ishigaki, Y., Asai, K., Shimajiri, T., Suzuki, T.
    Chemistry Letters 50 (6) 1184 - 1187 1348-0715 2021 
    The title electron acceptors are planar molecules undergoing reversible two-stage one-electron reduction processes. In the crystal of selenadiazole derivative (1), tetrameric structure is formed by two kinds of chalcogen bond (ChB), which is further connected by ChB and weak hydrogen bond (WHB). Although sulfur analogue (2) has only weaker ChB, it crystallizes isomorphously to 1 forming ChB-Tetramer, thus contribution from ChB is more dominant than WHB in determining the crystal packing, which is different from the corresponding tetracyanoquinodimethane analogues.
  • Hayashi, Y., Ishigaki, Y., Merad, J., Suzuki, T., Médebielle, M.
    Heterocycles 103 (1) 165 - 171 1881-0942 2021 
    Bis[4-methoxy-5-methylenefuran-2(5H)-one]-type electron acceptors with anthracene-9,10-diyl and thiophene-2,5-diyl spacer were prepared by one-pot condensation of methyl tetronate with the corresponding dialdehydes. They undergo reversible electrochemical reduction, thus showing the potential utility of 5-arylidenetetronate as an electrophore for developing novel electron acceptors.
  • Shimajiri, T., Suzuki, T., Ishigaki, Y.
    Angewandte Chemie - International Edition 59 (49) 22252 - 22257 1521-3773 2020/12/30 
    Since carbon-carbon (C-C) covalent bonds are rigid and robust, the bond length is, in general, nearly constant and depends only on the bond order and hybrid orbitals. We report herein direct visualization of the reversible expansion and contraction of a C(sp(3))-C(sp(3)) single bond by light and heat. This flexibility of a C-C bond was demonstrated by X-ray analysis and Raman spectroscopy of hexaphenylethane (HPE)-type hydrocarbons with two spiro-dibenzocycloheptatriene units, the intramolecular [2+2] photocyclization of which and thermal cleavage of the resulting cyclobutane ring both occur in a single-crystalline phase. The force constant of the contracted C-C bond is 1.6 times greater than that of the expanded bond. Since formation of the cyclobutane ring and contraction of the C-C bond lower the HOMO level by approximately 1 eV, the oxidative properties of these HPEs with a flexible C-C bond can be deactivated/activated by light/heat.
  • Takuya Shimajiri, Takanori Suzuki, Yusuke Ishigaki
    Angewandte Chemie 132 (49) 22436 - 22441 2020/12/30
  • Luyan Wu, Yusuke Ishigaki, Yuxuan Hu, Keisuke Sugimoto, Wenhui Zeng, Takashi Harimoto, Yidan Sun, Jian He, Takanori Suzuki, Xiqun Jiang, Hong-Yuan Chen, Deju Ye
    Nature Communications 11 (1) 2020/12 [Refereed]
     
    AbstractAfterglow luminescent probes with high signal-to-background ratio show promise for in vivo imaging; however, such probes that can be selectively delivered into target sites and switch on afterglow luminescence remain limited. We optimize an organic electrochromic material and integrate it into near-infrared (NIR) photosensitizer (silicon 2,3-naphthalocyanine bis(trihexylsilyloxide) and (poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]) containing nanoparticles, developing an H2S-activatable NIR afterglow probe (F12+-ANP). F12+-ANP displays a fast reaction rate (1563 ± 141 M−1 s−1) and large afterglow turn-on ratio (~122-fold) toward H2S, enabling high-sensitivity and -specificity measurement of H2S concentration in bloods from healthy persons, hepatic or colorectal cancer patients. We further construct a hepatic-tumor-targeting and H2S-activatable afterglow probe (F12+-ANP-Gal) for noninvasive, real-time imaging of tiny subcutaneous HepG2 tumors (<3 mm in diameter) and orthotopic liver tumors in mice. Strikingly, F12+-ANP-Gal accurately delineates tumor margins in excised hepatic cancer specimens, which may facilitate intraoperative guidance of hepatic cancer surgery.
  • Yusuke Ishigaki, Takumi Hashimoto, Kazuma Sugawara, Shuichi Suzuki, Takanori Suzuki
    Angewandte Chemie 132 (16) 6643 - 6646 2020/04/16
  • Ishigaki, Y., Hashimoto, T., Sugawara, K., Suzuki, S., Suzuki, T.
    Angewandte Chemie - International Edition 59 (16) 6581 - 6584 1521-3773 2020/04/16 [Refereed][Not invited]
     
    Thermally switchable redox properties have been reported to be due to a change in the spin state of newly designed overcrowded ethylenes, which can adopt closed-shell folded and open-shell twisted forms. In this study, tetrathienylanthraquinodimethane derivatives were designed to be in thermal equilibrium between a more stable folded form and less stable but more donating twisted diradical in solution, so that the oxidation potential can be controlled by heating/cooling. This is the first example of a switching of redox properties based on a thermally equilibrated twisted diradical, which can be more readily oxidized to the twisted dication.
  • Yusuke Ishigaki, Takashi Harimoto, Keisuke Sugimoto, Luyan Wu, Wenhui Zeng, Deju Ye, Takanori Suzuki
    Chemistry – An Asian Journal 15 (7) 1147 - 1155 1861-4728 2020/04 
    When the 1,1,4,4-tetraanilinobutadiene skeleton is attached with two halogenated aryl units at the 2,3-positions, they undergo facile two-electron oxidation to give stable dicationic dyes which exhibit a near-infrared (NIR) absorption whereas the neutral dienes show only pale color. Therefore, a distinct electrochromic response with an absorption change in the NIR region is achieved, which is attracting considerable recent attention from the viewpoint of bioimaging. Herein, we demonstrate that the redox potentials of the 1,1,4,4-tetraanilinobutadiene can be precisely controlled by the donating properties of the amino group on the aniline unit as well as the number of halogen atoms on the aryl units at 2,3-positions on the butadiene. In contrast, the NIR absorption bands mainly depend on the number of halogen atoms irrespective to the donating properties of aniline unit. Thus, the hexaarylbutadiene skeleton is proven to be a versatile scaffold to develop less-explored organic NIR electrochromic materials, whose redox and spectroscopic properties can be finely tuned by modifying/attaching the proper substituents.
  • Yusuke Hosoya, Wataru Nojo, Isao Kii, Takanori Suzuki, Miki Imanishi, Junko Ohkanda
    Chemical Communications 56 (76) 11203 - 11206 2020 
    Essential components of the human circadian clock, BMAL1 and CLOCK, which are intrinsically disordered transcription factors, were expressed and subjected to a fluorescent in vitro binding assay using an E-box DNA fragment. Screening of a chemical library identified 5,8-quinoxalinedione (1), which was found to inhibit binding of the heterodimer BMAL1/CLOCK to E-box at low micromolar concentrations.
  • Shintaro Fujii, Masato Koike, Tomoaki Nishino, Yoshiaki Shoji, Takanori Suzuki, Takanori Fukushima, Manabu Kiguchi
    Journal of the American Chemical Society 141 (46) 18544 - 18550 0002-7863 2019/11/20 
    Molecular isomerism has been discussed from the viewpoint of the tiniest switch and memory elements in electronics. Here, we report an overcrowded ethylene-based molecular conductance switch, which fulfills all the essential requirements for implementation into electronic devices, namely, electric-field-controllable reversible conductance change with a molecular-level spatial resolution, robust conformational bistability under ambient conditions, and ordered monolayer formation on electrode surfaces. The conformational state of this overcrowded ethylene, represented by a folded or twisted conformer, is susceptible to external environments. Nanoscopic measurements using scanning tunneling microscopy techniques, together with theoretical simulations, revealed the electronic properties of each conformer adsorbed on Au(111). While the twisted conformer prevails in the molecularly dispersed state, upon self-assembly into a monolayer, a two-dimensional network structure of the folded conformer is preferentially formed due to particular intermolecular interaction. In the monolayer state, folded-to-twisted and its reverse isomerization can be controlled by the modulation of electric fields.
  • Yusuke Ishigaki, Yuki Hayashi, Takanori Suzuki
    Journal of the American Chemical Society 141 (45) 18293 - 18300 0002-7863 2019/11/13 [Refereed][Not invited]
     
    Highly strained hydrocarbons with two di/tribenzocycloheptatriene units were designed as electrochromic overcrowded ethylenes that undergo reversible interconversion with stable dicationic dyes. Due to severe steric repulsion, two configurational isomers (anti,anti-folded and syn,anti-folded forms) were isolated as stable entities. Photo- and thermal interconversion of these isomers proceeded cleanly: one-way photo-isomerization occurred from anti,anti- to syn,anti-form and one-way thermal isomerization was observed from syn,anti- to anti,anti-form. Even though both isomers undergo two-electron oxidation into the same twisted dications, quite different oxidation potentials enable completely selective oxidation of syn,anti-isomers. Thus, the present multiconfigurational strained hydrocarbons are capable of switching of activation/deactivation of their electrochromic properties by light/heat.
  • Wataru Nojo, Hitomi Tamaoki, Yusuke Ishigaki, Ryo Katoono, Kenshu Fujiwara, Takanori Fukushima, Takanori Suzuki
    ChemPlusChem Wiley 84 (6) 634 - 642 2192-6506 2019/06/24 [Refereed][Not invited]
     
    © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim A perfluorobiphenyl-2,2′-diyl dication and its corresponding dihydrophenanthrene-type electron donor are interconvertible upon two-electron transfer. Redox-triggered C−C bond-formation/cleavage caused a drastic change in the torsion angle of the biphenyl unit. Thus, π-delocalization ON/OFF switching was observed as a change in the UV absorption upon electrolysis of the linearly extended analogue with two phenylethynyl groups. A further extended π-system with a molecular length of ca. 3.5 nm, which has two switching units, was synthesized. Spectroelectrograms as well as voltammetric analyses showed that the two units act nearly simultaneously because of the very small inter-unit electrostatic repulsion in the tetracationic state. Thus, the present pair is a promising candidate as a switching unit for “molecular wires” with controllable π-delocalization, in which a higher ON/OFF ratio of delocalization could be realized by incorporating multiple switching units.
  • Wataru Nojo, Yusuke Ishigaki, Takashi Takeda, Tomoyuki Akutagawa, Takanori Suzuki
    Chemistry – A European Journal Wiley 25 (32) 7759 - 7765 0947-6539 2019/06/07 [Refereed][Not invited]
     
    A method to obtain an organic mixed-valence state with long-range delocalization is proposed, which enables the selective generation of half-filled (n/2-charged) polycations from linearly bridged oligomers with n electron-donating units. When pi-extended phenylenediamine units are connected by meta-xylylene-type spacers, the resulting oligomers adopt non-folded structures in the neutral state owing to the non-conjugating and flexible nature of the spacer, whereas the structure shows a drastic change into a one-dimensional columnar stack upon oxidation to the corresponding half-filled polycations. Although they are nano-sized discrete molecules, they can mimic the electronic structure of crystalline organic conductors in a mixed-valence state. The key for the oligomer design is adoption of the best-matched spacer that facilitates formation of the singly charged pimer in the dichromophoric system whereas the corresponding doubly charged pi-dimer is disfavored.
  • Kenshu Fujiwara, Ryosuke Motousu, Daisuke Sato, Yoshihiko Kondo, Uichi Akiba, Takanori Suzuki, Tetsuo Tokiwano
    Tetrahedron Letters 60 (18) 1299 - 1301 0040-4039 2019/05/02 
    © 2019 Elsevier Ltd The total synthesis of a dibenzofuran rhamnoside, kehokorin A, and its aglycone, kehokorin B, was achieved via a route including Suzuki-Miyaura cross-coupling followed by Ullmann ether synthesis to form a dibenzofuran, stepwise bromination at C7 of the dibenzofuran, a second Suzuki-Miyaura cross-coupling to install a 4-methoxyphenyl group at C7, and rhamnosylation.
  • Takafumi Saito, Kenshu Fujiwara, Yoshihiko Kondo, Uichi Akiba, Takanori Suzuki
    Tetrahedron Letters 60 (4) 386 - 389 0040-4039 2019/01/24 
    © 2018 Elsevier Ltd The synthesis of the cyclohexene segment of portimine, a marine cytotoxin from the dinoflagellate Vulcanodinium rugosum, was achieved. The route includes an acylation/aldol reaction from 3-ethoxycyclohex-2-enone to create the C3 center, the 1,4-addition of a vinyl group at C16, the diastereoselective dihydroxylation of the vinyl group to generate the C15 center, a vinylation/dehydration sequence to set up the diene moiety, and stepwise installation of the amino-group-substituted C1 unit.
  • Kazuma Sugawara, Wataru Nojo, Yusuke Ishigaki, Junko Ohkanda, Takanori Suzuki
    Heterocycles published online. (1) 99 - 103 0385-5414 2019 [Not refereed][Not invited]
     
    Upon oxidation of hydroquinone fused with 1,2,5-thiadiazole by using FeCl3, a novel dibenzofurano[1,2-c:6,7-c]bis[1,2,5]thiadiazole-type quinone was obtained whereas the similar dimerization-condensation process did not occur for the pyrazine-fused hydroquinone under the similar conditions.
  • Ishigaki Y, Sugawara K, Yoshida M, Kato M, Suzuki T
    Bulletin of the Chemical Society of Japan 92 (7) 1211 - 1217 0009-2673 2019 [Refereed][Not invited]
     
    Tetraarylanthraquinodimethane derivatives 1 with butterfly-shaped folded structures and the corresponding dications 1(2+) with twisted conformations can undergo interconversion upon two-electron transfer, which is accompanied by a drastic color change. While reversible electrochromic behavior occurs in solution, electron donors 1 exhibit fluorescence only in the solid state. The emission color changed upon grinding assynthesized samples of 1, and the original emission color was recovered by a dissolving-drying process. Such mechanofluoro-chromic behavior can be accounted for by the results of powder X-ray diffraction (PXRD), for which as-synthesized crystalline sample was transformed into an amorphous state after grinding. Thus, the title electron donors 1 provided two-way chromic systems exhibiting electrochromism in solution as well as mechanofluorochromism in a solid state.
  • Ryo Katoono, Kazuki Sakamoto, Takanori Suzuki
    Chemical Communications 55 (38) 5503 - 5506 1359-7345 2019 [Refereed][Not invited]
     
    We demonstrated dynamic chirality based on assemblies of three achiral rods with a twisted macrocycle. The three-fold twisting of a macrocycle can lead to two different chiral forms with C-2- or D-3-symmetry. Through a transmission of chirality to each dynamic chiral form, a helical-sense preference was successfully induced.
  • Ryo Katoono, Keiichi Kusaka, Yuki Saito, Kazuki Sakamoto, Takanori Suzuki
    Chemical Science 10 (18) 4782 - 4791 2041-6520 2019 [Refereed][Not invited]
     

    Multiple chiral molecules were generated through the assembly and double-bridging of achiral phenylacetylene macrocycles.

  • Luyan Wu, Yidan Sun, Keisuke Sugimoto, Zhiliang Luo, Yusuke Ishigaki, Kanyi Pu, Takanori Suzuki, Hong-Yuan Chen, Deju Ye
    Journal of the American Chemical Society 140 (47) 16340 - 16352 0002-7863 2018/11/28 [Refereed][Not invited]
     
    Electrochromic materials (EMs) are widely used color-switchable materials, but their applications as stimuli-responsive biomaterials to monitor and control biological processes remain unexplored. This study reports the engineering of an organic pi-electron structure-based EM (dicationic 1,1,4,4-tetraarylbutadiene, 1(2+)) as a unique hydrogen sulfide (H2S)-responsive chromophore amenable to build H2S-activatable fluorescent probes (1(2+)-semiconducting polymer nanoparticles, 1(2+)-SNPs) for in vivo H2S detection. We demonstrate that EM 1(2+), with a strong absorption (500-850 nm), efficiently quenches the fluorescence (580, 700, or 830 nm) of different fluorophores within 1(2+)-SNPs, while the selective conversion into colorless diene 2 via H2S-mediated two-electron reduction significantly recovers fluorescence, allowing for non-invasive imaging of hepatic and tumor H2S in mice in real time. Strikingly, EM 1(2+) is further applied to design a near-infrared photosensitizer with tumor-targeting and H2S-activatable ability for effective photodynamic therapy (PDT) of H2S-related tumors in mice. This study demonstrates promise for applying EMs to build activatable probes for molecular imaging of H2S and selective PDT of tumors, which may lead to the development of new EMs capable of detecting and regulating essential biological processes in vivo.
  • Takanori Suzuki, Yusuke Ishigaki, Tomohiro Iwai, Yuki Hayashi, Aiichiro Nagaki, Ryo Katoono, Kenshu Fujiwara, Jun-ichi Yoshida
    Synlett 29 (16) 2147 - 2154 0936-5214 2018/10/25 [Refereed][Not invited]
     
    Triarylmethylium-o,o-dimers adopt a twisted geometry so that two diarylmethyliums are stacked in a slipped manner. Thus, chiral auxiliaries on the aryl groups induce a preference in the axial chirality of the central biphenyl unit. Strong circular dichroism is attained through exciton coupling, which can be used for additional spectral output in their electrochromic behavior. Diastereoselectivity based on - stacking exhibits unique solvent effects, thus endowing multifunctional response properties.
  • Takayuki Tsunoda, Kenshu Fujiwara, Satoshi Okamoto, Yoshihiko Kondo, Uichi Akiba, Yusuke Ishigaki, Ryo Katoono, Takanori Suzuki
    Tetrahedron Letters 59 (19) 1846 - 1850 0040-4039 2018/05 [Refereed][Not invited]
     
    © 2018 Elsevier Ltd During the course of our studies toward the total synthesis of nigricanoside A dimethyl ester, a prototype method for the connection of the left- and right-half segments at the C9′–C10′ double bond was developed using a model system. The method was based on a simple three-step process including: (i) a nitroaldol reaction, (ii) chlorination or thionocarbonylation, and (iii) radical elimination.
  • Yusuke Ishigaki, Takuya Shimajiri, Takashi Takeda, Ryo Katoono, Takanori Suzuki
    Chem 4 (4) 795 - 806 2451-9294 2018/04/12 [Refereed][Not invited]
     
    On the basis of the intramolecular “core-shell strategy,” we designed dihydropyracylene with two spiro(dibenzocycloheptatriene) units, for which theoretical calculations predicted a very weak C–C bond with a bond length around 1.8 Å. This bond is expanded by the forced adoption of an eclipsed conformation and by angle strain through a “scissor effect.” The highly strained hydrocarbon was isolated as a thermally stable compound with no signs of diradical contribution because the weak C–C bond (core) is protected by the shape-persistent fused-ring structure (shell). A Raman shift corresponding to the C–C stretching vibration (587 cm−1) was very different from that for ethane (993 cm−1). The bond length determined by X-ray (1.806(2) Å) was greater than the shortest non-bonded intramolecular C…C contact (1.80(2) Å). The assumed limit for a C–C bond (1.803 Å) by supposing linear correlation between bond length and bond-dissociation energy for covalent bonding was proven to be invalid. The nature of chemical bonds is of fundamental importance in chemistry. Clarifying the new facets of covalent bonds is also helpful to promote green chemistry by allowing chemists to design novel chemical products and new processes to advance sustainability. We have successfully synthesized highly strained “core-shell”-type hydrocarbons and demonstrated that the C–C covalent bond can be expanded beyond 1.80 Å, which is 1.17 times greater than the standard length (1.54 Å). By the discovery of such a “hyper covalent bond,” the covalently bonded state and non-bonded state are seamlessly connected in terms of the interatomic distance. Compounds with the hyper covalent bond are potential candidates for making a novel class of materials whose crystals, films, or polymers can respond to external mechanical stimuli with anisotropic contraction or expansion of the matter, accompanied by reversible compression, extension, or fission of the “bond” in the molecule. Compounds with an ultralong C–C single bond have been successfully constructed in three steps from commercially available dihalo aromatics. The intramolecular “core-shell strategy” is a key tactic for stabilizing compounds with an ultralong C–C bond. Using this concept could lead to an even longer C–C bond (“hyper covalent bonds” with a bond length of 1.8–2.0 Å) because the covalently bonded state and non-bonded state are seamlessly connected in terms of the interatomic distance.
  • Takafumi Saito, Kenshu Fujiwara, Yusuke Sano, Takuto Sato, Yoshihiko Kondo, Uichi Akiba, Yusuke Ishigaki, Ryo Katoono, Takanori Suzuki
    Tetrahedron Letters 59 (14) 1372 - 1376 0040-4039 2018/04 [Refereed][Not invited]
     
    © 2018 Elsevier Ltd In our previously reported method for the construction of the IJKLM-ring of ciguatoxin 3C (CTX3C), the lengthy synthetic process for the intermediate C42–C52 (L-ring) segment was problematic. Therefore, a new and improved procedure for the C42–C52 segment, having modified protecting groups, was developed. The new route includes a chirality transferring Ireland-Claisen rearrangement for the construction of the vicinal dimethyl branching at C47–48, a one-pot cyclization process for the establishment of the stereocenters at C45 and C46 as well as the γ-hydroxy δ-lactone framework corresponding to the L-ring, and Brown's asymmetric crotylboration for the installation of the stereocenters at C43 and C44. The new C42–C52 segment was successfully coupled with the previously reported C32–C41 (I-ring) segment to produce the IJKLM-ring.
  • Suzuki, T, Ishigaki, Y, Sugawara, K, Umezawa, Y, Katoono, R, Shimoyama, A, Manabe, Y, Fukase, K, Fukushima, T
    Tetrahedron 74 (18) 2239 - 2244 0040-4020 2018/04 [Refereed][Not invited]
     
    2,3,6,7,11,11,12,12-Octaphenyl-1,4,5,8-tetraaza-9,10-anthraquinodimethane was prepared as a sterically hindered molecule from 2,3,6,7-tetraphenyl-1,4,5,8-tetraaza-9,10-anthraquinone via bis(dibromomethylene) derivative through the quadruple Suzuki-Miyaura coupling reaction. An X-ray analysis revealed that steric repulsion is relieved mainly by twisting the exomethylene bonds, which is less common deformation for hindered quinodimethanes. According to the OFT calculations, the folded geometry with bent exomethylene bonds is the metastable conformer, and thus the nitrogen atoms at peri-positons and polyaryl substituents induce novel switching for the preferred geometry of 9,10-anthraquinodimethane skeleton from the common bent form to the twisted form, which causes a decrease in the HOMO-LUMO-gap energy by ca. 1 eV. (C) 2018 Elsevier Ltd. All rights reserved.
  • Yasuto Uchimura, Takuya Shimajiri, Yusuke Ishigaki, Ryo Katoono, Takanori Suzuki
    Chemical Communications Royal Society of Chemistry ({RSC}) 54 (73) 10300 - 10303 1359-7345 2018 [Refereed][Not invited]
     
    The angle strain induced by ring annulation on a spiro-type naphthofuran weakens its C(sp(3))-O bond at the opposite peri-position and endows expandability, so that quite different bond lengths [1.493(3)-1.526(6) angstrom] are determined for the elongated C(sp(3))-O bond of the corresponding spiro-acenaphthofuran derivative upon X-ray analyses of its pseudopolymorphs.
  • Ryo Katoono, Yudai Obara, Keiichi Kusaka, Takanori Suzuki
    Chemical Communications 54 (7) 735 - 738 1364-548X 2018 [Refereed][Not invited]
     
    We synthesized molecular assemblies of a ring and rod that were covalently bound in a molecule. The bridged components were helically arranged in a threaded or unthreaded form to show unique chiroptical properties based on shape-persistent m-phenylacetylene rings with six, five and four units and phenylene-ethynylene rods.
  • Ryo Katoono, Keiichi Kusaka, Yuki Tanaka, Kenshu Fujiwara, Takanori Suzuki
    Organic and Biomolecular Chemistry 16 (7) 1167 - 1171 1477-0520 2018 [Refereed][Not invited]
     
    We demonstrate a chiroptical switching system with a simple molecule. The molecule contains a pair of chromophores of diphenylacetylene that are linked with a diyne bond and arranged to exert exciton coupling in helically folded forms with (M)- or (P)-helicity. A tertiary amide group is attached to each end of the looped molecule. The amide carbonyls were used to capture a ditopic hydrogen-bonding guest. A chiral auxiliary group on the amide nitrogen acted as a chiral handle to control the helical-sense preference of dynamic helical forms of the loop. The helical-sense preference is brought about by an intramolecular transmission of point chirality associated with the loop. The preferred sense was switched upon complexation with an achiral additive through the formation of hydrogen bonds. In both states, before and after complexation, the helical-sense preferences were controlled through two-way transmission of the single chiral source.
  • Ryo Katoono, Yudai Obara, Kenshu Fujiwara, Takanori Suzuki
    Chemical Science 9 (8) 2222 - 2229 2041-6539 2018 [Refereed][Not invited]
     
    When two planes stacked one above the other are twisted, they provide a dynamic pair of helical conformations with (M)- or (P)-helicity. We designed a three-layer cyclophane that consists of two such dynamic pairs: the top and middle planes, and the middle and bottom planes. Hence, several global conformations could be created for the overall molecule, e.g., double-helical forms with a pair with the same helicity [(M,M) or (P,P)], and a meso-like form with a pair with a different helicity (M,P). These conformations dynamically interconvert to each other in solution. Chiroptical properties were given by the helical-sense preference of the double-helical forms, which was brought about through complexation with a chiral hydrogen-bonding guest. In terms of the conformational energy in a complexed state, when a desirable relationship between double-helical and meso-like forms was attained, complexation-induced circular dichroism was enhanced at elevated temperatures and decreased at lowered temperatures.
  • Yuiki Kawada, Shunsuke Ohmura, Misaki Kobayashi, Wataru Nojo, Masaki Kondo, Yuka Matsuda, Junpei Matsuoka, Shinsuke Inuki, Shinya Oishi, Chao Wang, Tatsuo Saito, Masanobu Uchiyama, Takanori Suzuki, Hiroaki Ohno
    Chemical Science 9 (44) 8416 - 8425 2041-6520 2018 [Refereed][Not invited]
     

    The gold-catalysed annulation of conjugated alkynes bearing an azido group with arenes gave annulated [c]carbazoles.

  • Yusuke Ishigaki, Yuki Hayashi, Kazuma Sugawara, Takuya Shimajiri, Wataru Nojo, Ryo Katoono, Takanori Suzuki
    MOLECULES 22 (11) 1420-3049 2017/11 [Refereed][Not invited]
     
    The title dispiro hydrocarbon 1 was designed as a new electrochromic material. This multiply clamped hexaphenylethane-type electron donor was prepared from 2,2'-diiodobiphenyl via biphenyl-2,2'-diylbis(dibenzotropylium) 2(2+) salt. X-ray analysis of 1 revealed a highly strained structure as reflected by an elongated ethane bond [bond length: 1.6665(17) angstrom] and nearly eclipsed conformation. The weakened bond was cleaved upon two-electron oxidation to regenerate the deeply colored dication 2(2+). The reversible interconversion between 1 and 2(2+) is accompanied not only by a drastic color change but also by C-C bond formation/cleavage. Thus, the voltammogram showed a pair of well-separated redox waves, which is characteristic of "dynamic redox (dyrex)" behavior. The tetrahydro derivative of 1 with two units of spiro(dibenzocycloheptadiene), which suffers from more severe steric congestion, was also prepared. The crystallographically determined bond length for the central C-C bond [1.705(4) angstrom] is greatest among the values reported for 9,9,10,10-tetraaryl-9,10-dihydrophenanthrene derivatives.
  • Eisuke Ohta, Hiromitsu Uehara, Ying Han, Kazuhisa Wada, Hidenori Noguchi, Ryo Katoono, Yusuke Ishigaki, Hiroshi Ikeda, Kohei Uosaki, Takanori Suzuki
    ChemPlusChem 82 (7) 1043 - 1047 2192-6506 2017/07/14 [Refereed][Not invited]
     
    Biphenyl-2,2'-diylbis(10-methyl-9-methyleneacridan)-type electron donor 1, which has two tethered cyclic disulfide units at the 6,6'-positions, was designed and synthesized as the first member of a dynamic redox (dyrex) system that can form molecular layers on a Au(111) electrode. Upon the two-electron (2 e) oxidation of 1, the persistent dicationic dye 22+ was generated with the formation of a new C = C bond, which is reversibly cleaved upon 2e reduction to regenerate 1 (dyrex behavior). Similar dyrex interconversion occurs in the molecular layer of 1 on gold. The chemical identities of 1/Au and electrochemically generated 2(2+)/Au were unambiguously determined by in situ IR spectroscopy in the attenuated total reflection mode. In situ scanning tunneling microscopy (STM) was conducted under electrochemical conditions to examine the surface structure of 1 adsorbed on a Au(111) electrode. Although no longrange- ordered morphology was found in the STM image of 1, an in situ STM study of the potential-induced dyrex reaction of 1 to 2(2+) showed that the grained spots in the image became slightly brighter.
  • Eisuke Ohta, Hiromitsu Uehara, Ying Han, Kazuhisa Wada, Hidenori Noguchi, Ryo Katoono, Yusuke Ishigaki, Hiroshi Ikeda, Kohei Uosaki, Takanori Suzuki
    CHEMPLUSCHEM 82 (7) 1043 - 1047 2192-6506 2017/07 [Refereed][Not invited]
     
    Biphenyl-2,2'-diylbis(10-methyl-9-methyleneacridan)-type electron donor 1, which has two tethered cyclic disulfide units at the 6,6'-positions, was designed and synthesized as the first member of a dynamic redox (dyrex) system that can form molecular layers on a Au(111) electrode. Upon the two-electron (2 e) oxidation of 1, the persistent dicationic dye 22+ was generated with the formation of a new C = C bond, which is reversibly cleaved upon 2e reduction to regenerate 1 (dyrex behavior). Similar dyrex interconversion occurs in the molecular layer of 1 on gold. The chemical identities of 1/Au and electrochemically generated 2(2+)/Au were unambiguously determined by in situ IR spectroscopy in the attenuated total reflection mode. In situ scanning tunneling microscopy (STM) was conducted under electrochemical conditions to examine the surface structure of 1 adsorbed on a Au(111) electrode. Although no longrange- ordered morphology was found in the STM image of 1, an in situ STM study of the potential-induced dyrex reaction of 1 to 2(2+) showed that the grained spots in the image became slightly brighter.
  • Yusuke Ishigaki, Hidetoshi Kawai, Ryo Katoono, Kenshu Fujiwara, Hiroki Higuchi, Hirotsugu Kikuchi, Takanori Suzuki
    CANADIAN JOURNAL OF CHEMISTRY 95 (3) 243 - 252 0008-4042 2017/03 [Refereed][Not invited]
     
    2,5-Bis(diarylethenyl)thiophenes (1) and their bithiophene (2) and terthiophene (3) homologues were designed as a new series of violene/cyanine-hybrid-type electrochromic materials. Alkoxyphenyl and dialkylaminophenyl groups are used as the aryl group in the cyanine parts of 1/2/3O and 1/2/3N, respectively, which emit fluorescence in the neutral state but not in the oxidized state. Voltammetric analyses of 18 newly prepared electron donors show that they all undergo two reversible one-electron oxidations. Redox potentials, UV-vis spectral features, and fluorescence quantum yields are important parameters for characterizing the present electrochromic behavior with a fluorescence response, and can be finely tuned by changing aryl groups in the cyanine part, the number of thiophene rings in the violene part, and the alkyl-chain length of the alkoxyphenyl or diaklylaminophenyl groups (R = CH3, C8H17, C16H33), which makes this a versatile platform for the design of novel electrochromic materials.
  • Takuto Sato, Kenshu Fujiwara, Keisuke Nogoshi, Akiyoshi Goto, Daisuke Domon, Natsumi Kawamura, Yoshitaka Nomura, Daisuke Sato, Hideki Tanaka, Akio Murai, Yoshihiko Kondo, Uichi Akiba, Ryo Katoono, Hidetoshi Kawai, Takanori Suzuki
    TETRAHEDRON 73 (6) 703 - 726 0040-4020 2017/02 [Refereed][Not invited]
     
    The synthesis of the ABCDEF-ring of ciguatoxin 3C was achieved via a route that included anion coupling of a dimethyldithioacetal mono-S-oxide derivative corresponding to the AB-ring and an aldehyde corresponding to the EF-ring, followed by cyclization using reductive etherification. The AB-ring was synthesized from a known D-glucose derivative based, on ring-closing olefin metathesis, and the EF-ring was prepared by a process employing chirality-transferring Ireland-Claisen rearrangement and ring-closing olefin metathesis. (C) 2016 Elsevier Ltd. All rights reserved.
  • Suzuki, Takanori, Kuroda, Takuma, Tamaoki, Hitomi, Higasa, Sho, Nehira, Tatsuo, Katoono, Ryo, Ishigaki, Yusuke, Fujiwara, Kenshu, Fukushima, Takanori, Yamada, Hidetoshi
    Heterocycles 95 (2) 816 - 829 0385-5414 2017 [Refereed][Not invited]
     
    Upon oxidation of the title heterocycle (1A) with dimethylamino groups, elemental sulfur is extruded to form dicationic dye (1B(2+)), from which the starting dibenzothiepin derivative was generated by the reaction with Na2S. The bay-region substituents enhance configurational stability, so that, the optically pure heterocycles [(M)-2A, (M)-3A)] can be obtained in terms of helicity of one-handedness by starting with the corresponding optically pure dicationic dyes [(R)-2B(2+), (R)-3B(2+))]. Similar oxidative desulfurization occurs in dibenzo-1,5-oxathiocin 4A, a structurally related 8-membered heterocycle.
  • Suzuki, Takanori, Suzuki, Takanori, Ceron-Carrasco, Jose P., Ceron-Carrasco, Jose P., Tamaoki, Hitomi, Tamaoki, Hitomi, Ishigaki, Yusuke, Ishigaki, Yusuke, Katoono, Ryo, Katoono, Ryo, Fukushima, Takanori, Fukushima, Takanori, Perez-Sanchez, Horacio, Perez-Sanchez, Horacio
    Heterocycles 94 (6) 1123 - 1132 0385-5414 2017 [Refereed][Not invited]
     
    Upon 1:1 complexation with gamma-cyclodextrin (CyD) in water, easily interconverting rotational isomers of biphenyl-2,2'-diylbis[bis(4-dimethylaminophenyl)methylium] (R)/(S)-1a(2+) were biased to prefer an R configuration (75:25 at 25 degrees C). Docking and quantum chemical calculations revealed two modes (on-top and botton-side) of encapsulation of gamma-CyD, which shed a light on the origin of the first chiral recognition of axially chiral dicationic dyes by using natural CyDs.
  • Takanori Suzuki, Wataru Nojo, Yuto Sakano, Ryo Katoono, Yusuke Ishigaki, Hiroaki Ohno, Kenshu Fujiwara
    CHEMISTRY LETTERS 45 (7) 720 - 722 0366-7022 2016/07 [Refereed][Not invited]
     
    The title electron-donors with two units of a disk-shaped heterocyclic diamine undergo two-stage stepwise one-electron oxidation to the corresponding cation radicals and dication diradicals. They adopt a stacked geometry as in pimers and pi-dimers, respectively. In contrast, the third and fourth oxidation processes occur nearly at the same potential, indicating that tricationic/tetracationic species prefer the extended geometry. The similar redox-induced conformational changes were not observed in 1,5-pentylene or o-xylylene derivatives, which prefer the extended geometry irrespective of the oxidation states.
  • Hitomi Tamaoki, Ryo Katoono, Kenshu Fujiwara, Takanori Suzuki
    Angewandte Chemie 128 (7) 2628  2016/02/12 [Refereed][Not invited]
  • Hitomi Tamaoki, Ryo Katoono, Kenshu Fujiwara, Takanori Suzuki
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 55 (7) 2582 - 2586 1433-7851 2016/02 [Refereed][Not invited]
     
    The incorporation of F atoms endows a diethenylbiphenyl-based electron donor with configurational stability and SNAr reactivity. The former enables the dynamic redox pair of (R-ax)-1/(R-ax,R,R)-1(2+) to exhibit drastic UV/Vis and CD spectral changes upon electrolysis, whereas the latter makes it possible for (R-ax)-1 to serve as a useful chiral synthon for the production of larger assemblies [(R-ax,R-ax)-2d,p,m and (R-ax,R-ax,R-ax)-3] containing two or three dyrex units. These dyads and triad also exhibit a clean electrochiroptical response with isosbestic points owing to one-wave multi-electron transfer.
  • Ryo Katoono, Shunsuke Kawai, Takanori Suzuki
    CHEMICAL SCIENCE 7 (5) 3240 - 3247 2041-6520 2016 [Refereed][Not invited]
     
    We describe the design of two types of cyclophanes that generate dynamic helicity through the twisting of two planes in a clockwise or counterclockwise direction to give (M)- or (P)-helicity. We used a rectangular and anisotropic plane of 1,2,4,5-tetrakis(phenylethynyl) benzene (TPEB), since it can be stacked in pairs in two ways, in parallel or orthogonally, to be identified as distinct cyclophane molecules. We adopted a synthetic strategy for obtaining these two cyclophanes as a mixture using a macrocyclic intermediate that possessed two rotatable phenyl rings. We introduced necessary parts into the rotators to give a mixture of rotational isomers leading to a parallel or orthogonal arrangement of TPEBs, and then doubly bridged two planes of TPEB to form quadruply-bridged cyclophanes. We consider that such two planes in each cyclophane are in an "obverse and/or reverse" relation. In each cyclophane, we found unique dynamic helical forms with (M)- or (P)-helicity as well as an inherently non-chiral form. Normally, the screw-sense preference of dynamic helicity would be controlled through the intramolecular or supramolecular transmission of central chirality, when a chiral auxiliary is attached to the cyclophanes or a chiral guest is allowed to form a complex with the cyclophanes. In a case where two different substitution groups were used on bridging units to generate planar chirality in each cyclophane, the screw-sense preference was controlled through the arrangement of these substitution groups, and did not depend on the transmission of central chirality. Two different substitution groups desymmetrize the enantiomeric forms with (M)- or (P)-helicity generated in each dynamic helical cyclophane so that two dynamic helical forms with (M)- or (P)-helicity can be in a diastereomeric relation. Thus, a particular screw sense of dynamic helicity can be preferred, regardless of whether or not the two substitution groups possess some chiral element.
  • Suzuki, Takanori, Tamaoki, Hitomi, Nishida, Jun-ichi, Higuchi, Hiroki, Iwai, Tomohiro, Ishigaki, Yusuke, Hanada, Keisuke, Katoono, Ryo, Kawai, Hidetoshi, Fujiwara, Kenshu, Fukushima, Takanori, Nishinaga, T
    Organic Redox Systems: Synthesis, Properties, and Applications 2016 [Refereed][Not invited]
  • Ryo Katoono, Takanori Suzuki
    CHEMICAL COMMUNICATIONS 52 (5) 1029 - 1031 1359-7345 2016 [Refereed][Not invited]
     
    We designed a planar chiral two-layered cyclophane, which is inherently achiral but desymmetrized by the arrangement of two nonstereogenic centers. We demonstrate the control of dynamic helicity that is generated by the helical twisting of two-layered planes in the cyclophane, where methyl and cyclohexylmethyl groups act as directing groups.
  • Fujiwara K, Kushibe K, Sato T, Norikura T, Matsue H, Iwai K, Katoono R, Suzuki T
    Eur. J. Org. Chem. 26 (26) 5798 - 5809 1434-193X 2015/09 [Refereed][Not invited]
     
    The syntheses of ganbajunins D and E and of the structure proposed for thelephantin D, as well as its regioisomer, were achieved in a divergent manner via a common monoester intermediate. The proposed structure of thelephantin D had NMR chemical shifts different from those of natural thelephantin D. This supported Takahashi's suggestion that the true structure of natural thelephantin D should be the same as that of terrestrin C, as was deduced from the similarities in their NMR spectra. The presence of isomerization equilibria between 2′,5′- and 2′,6′-diacyloxy-p-terphenyl derivatives in solution, which are the cause of the inseparability of these derivatives, was also demonstrated by monitoring the dynamic transition from a 2′,6′-diacyloxy-p-terphenyl-rich mixture of the derivatives to an equilibrium mixture. The results of biological and chemical property tests - such as cytotoxicity against cancer cells, affinity towards Fe2+ ion, and antioxidative activity - with the synthesized compounds are also described.
  • Takanori Suzuki, Yuto Sakano, Tomohiro Iwai, Shinichi Iwashita, Youhei Miura, Ryo Katoono, Hidetoshi Kawai, Kenshu Fujiwara, Yasushi Tsuji, Takanori Fukushima
    ChemInform 46 (38) no - no 2015/09 [Refereed][Not invited]
  • Ryo Katoono, Yuki Tanaka, Keiichi Kusaka, Kenshu Fujiwara, Takanori Suzuki
    JOURNAL OF ORGANIC CHEMISTRY 80 (15) 7613 - 7625 0022-3263 2015/08 [Refereed][Not invited]
     
    We demonstrate two types of inversion of a helical preference upon the 1:1 complexation of a dynamic figure eight molecule with a guest molecule through the controlled transmission of point chirality. We designed a series of macrocycles that prefer a nonplanar conformation with figure eight chirality. These macrocycles are composed of a chirality-transferring unit (terephthalamide) and a structure-modifying unit (two o-phenylene rings spaced with a varying number of triple bonds). The former unit provides a binding site for capturing a guest molecule through the formation of hydrogen bonds. The attachment of chiral auxiliaries to the former unit induces a helical preference for a particular sense through the intramolecular transmission of point chirality. For relatively small-sized macrocycles, the preferred sense was reversed upon complexation with an achiral guest. Contrary preferences before and after complexation were both seen for chiral auxiliaries associated with a figure eight host through two-way intramolecular transmission of the single chiral source. Alternatively, the helical preference induced in relatively large-sized macrocycles was reversed only when a figure eight host formed a 1:1 complex with a particular enantiomeric guest through the supramolecular transmission of point chirality in the guest. This stereospecific inversion of a helical preference is rare.
  • Takanori Suzuki, Yu Umezawa, Yuto Sakano, Hitomi Tamaoki, Ryo Katoono, Kenshu Fujiwara
    CHEMISTRY LETTERS 44 (7) 905 - 907 0366-7022 2015/07 [Refereed][Not invited]
     
    11,11,12,12-Tetrakis (4-methoxyphenyl)-1,4-diaza-2,3-diphenyl- and -1,4,5,8-tetraaza-2,3,6,7-tetraphenylanthraquinodimethanes (1 and 2) adopt a bent geometry. They undergo reversible redox interconversion with twisted dications 1(2+) and 2(2+), exhibiting a vivid change in color (electrochromism). Treatment with acid also induced drastic color change due to the formation of protonated species H-1(+) and H-2(+) (halochromism), thus demonstrating their two-way-input chromic behavior.
  • Takanori Suzuki, Takashi Takeda, Eisuke Ohta, Kazuhisa Wada, Ryo Katoono, Hidetoshi Kawai, Kenshu Fujiwara
    ChemInform 46 (18) no - no 2015/04 [Refereed][Not invited]
  • Yasuto Uchimura, Takashi Takeda, Ryo Katoono, Kenshu Fujiwara, Takanori Suzuki
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 54 (13) 4010 - 4013 1433-7851 2015/03 [Not refereed][Not invited]
     
    Upon reduction of a 1H-cyclobuta[de] naphthalene-4,5-diylbis(diarylmethylium) species, a new C-C bond is formed between the C-alpha and C-ortho atoms of the two chromophores, which presents an unprecedented coupling pattern for the dimerization of two trityl units. By attaching an annulated cyclobutane ring at the opposite peri position of the naphthalene core, the distance between the C-alpha carbon atoms was elongated beyond the limit of sigma-bond formation through "scissor effects". The suppression of C-alpha-C-alpha bond formation, which would lead to hexaphenylethane-type compounds, is key to the first successful isolation of the alpha,o-adducts. The 5-diarylmethylene-6-triarylmethyl-1,3-cyclohexadiene unit in the alpha,o-adducts is stable, and isomerization of the cyclohexadiene unit into an aromatic system was not observed. The newly formed C-alpha-C-ortho bond was cleaved upon two-electron oxidation to regenerate the dicationic dye.
  • Yasuto Uchimura, Takashi Takeda, Ryo Katoono, Kenshu Fujiwara, Takanori Suzuki
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Wiley-Blackwell 54 (13) 4010 - 4013 1433-7851 2015/03 [Refereed][Not invited]
     
    Upon reduction of a 1H-cyclobuta[de] naphthalene-4,5-diylbis(diarylmethylium) species, a new C-C bond is formed between the C-alpha and C-ortho atoms of the two chromophores, which presents an unprecedented coupling pattern for the dimerization of two trityl units. By attaching an annulated cyclobutane ring at the opposite peri position of the naphthalene core, the distance between the C-alpha carbon atoms was elongated beyond the limit of sigma-bond formation through "scissor effects". The suppression of C-alpha-C-alpha bond formation, which would lead to hexaphenylethane-type compounds, is key to the first successful isolation of the alpha,o-adducts. The 5-diarylmethylene-6-triarylmethyl-1,3-cyclohexadiene unit in the alpha,o-adducts is stable, and isomerization of the cyclohexadiene unit into an aromatic system was not observed. The newly formed C-alpha-C-ortho bond was cleaved upon two-electron oxidation to regenerate the dicationic dye.
  • Takanori Suzuki, Takashi Takeda, Eisuke Ohta, Kazuhisa Wada, Ryo Katoono, Hidetoshi Kawai, Kenshu Fujiwara
    CHEMICAL RECORD 15 (1) 280 - 294 1527-8999 2015/02 [Refereed][Not invited]
     
    10-Methylacridinium is a stable aromatic cation exhibiting yellow-orange color and strong green fluorescence (FL), and can be used as a versatile building block in constructing a wide variety of novel -electron systems. The dications with the two chromophores connected by a proper spacer undergo reversible dyrex (dynamic redox) behavior, and C-C bond formation/cleavage is accompanied by their redox reactions. The prototype is biphenyl-2,2-diylbis(10-methylacridinium), which exhibits electrochromic response with ON/OFF switching of FL during the reversible interconversion with the di(spiroacridan)-type electron donor. Slight structural alteration under the concept of MFMS (maximum function on the minimum skeleton) endowed the dyrex system with metal-binding or chiroptical properties, which could be modified by the redox reactions. Some of the di(spiroacridan) derivatives generated from bis(10-methylacridinium)s have extreme structural parameters, such as the greatest C-C bond length ever reported.
  • Yasuto Uchimura, Takashi Takeda, Ryo Katoono, Kenshu Fujiwara, Takanori Suzuki
    Angew. Chem. Wiley-Blackwell 127 (13) 4082 - 4085 2015/02 [Refereed][Not invited]
  • Yasuto Uchimura, Takashi Takeda, Ryo Katoono, Kenshu Fujiwara, Takanori Suzuki
    Angew. Chem. Int. Ed. Wiley-Blackwell 54 (13) 4125 - 4125 2015/02 [Refereed][Not invited]
  • Yuto Sakano, Ryo Katoono, Kenshu Fujiwara, Takanori Suzuki
    CHEMICAL COMMUNICATIONS 51 (76) 14303 - 14305 1359-7345 2015 [Not refereed][Not invited]
     
    Two-proton or two-electron transfer of the title biphenolic dication proceeds nearly simultaneously to induce 2,6'/2',6- or 6,6'-bond formation to give dioxapyrene or dihydrophenanthrene derivatives, respectively, with vivid changes in color (halochromism and electrochromism).
  • Yuta Hirose, Kenshu Fujiwara, Takafumi Saito, Ryo Katoono, Takanori Suzuki
    HETEROCYCLES 91 (1) 76 - 103 0385-5414 2015/01 [Refereed][Not invited]
     
    The stereoselective synthesis of the A-ring of armatol A, a natural polycyclic ether triterpene from the red alga Chondria armata, was achieved in a non-biomimetic way. The synthesis employed Ireland-Claisen rearrangement of an ester, prepared from a bromo-substituted chiral building block, for the construction of C6 and C7 stereocenters and a relay ring-closing olefin metathesis for the seven-membered ring formation.
  • Yusuke Ishigaki, Satoshige Yoshida, Hidetoshi Kawai, Ryo Katoono, Kenshu Fujiwara, Takanori Fukushima, Takanori Suzuki
    HETEROCYCLES 90 (1) 126 - 135 0385-5414 2015/01 [Refereed][Not invited]
     
    Starting from (S)-dimethyl 1,1'-binaphthyl-2,2'-dicarboxylate, optically pure (P)-3,3,4,4-tetrakis(3,4-dialkoxyphenyl)-3,4-dihydro[5]helicenes (P)-1 were prepared via bis(diarylhyclroxymethyl)binaphthyl and/or tetraaryldinaphthodihydroxepin as key intermediates. Upon electrochemical oxidation to the corresponding (S)-1,1'-binaphthyl-2,2'-diylbis(diarylcarbenium)s (S)-2(2+), three kinds of spectral changes (UV-Vis, circular dichroism, fluorescence) were successfully observed. Compared to the methoxy compound, the octyloxy and hexadecyloxy derivatives exhibit a redshifted emission maxima in the dihydro[5]helicenes. The long alkyl chains induce step-by-step two-electron reduction of the binaphthyldiyl(dicarbenium)s whereas the dication with methoxy groups exhibits one-wave two-electron process.
  • Ryo Katoono, Shunsuke Kawai, Kenshu Fujiwara, Takanori Suzuki
    CHEMICAL SCIENCE 6 (11) 6592 - 6600 2041-6520 2015 [Refereed][Not invited]
     
    We describe a quantitative analysis of the complexation-induced inversion of a screw-sense preference based on a conformationally dynamic double-helix structure in a macrocycle. The macrocycle is composed of two twisting units (terephthalamide), which are spaced by two strands (1,3-bis(phenylethynyl)benzene), and is designed to generate a double-helix structure through twisting about a C-2 axis in a conrotatory manner. The attachment of chiral auxiliaries to the twisting units induces a helical preference for a particular sense of (M)- or (P)-helicity through the intramolecular transmission of chirality to dynamic double helices. The twisting unit can also act as a binding site for capturing a guest molecule, and, in a complexed state, the preferred screw sense of the dynamic double-helix structure is reversed to exhibit the contrary preference. We quantitatively monitored the complexation-induced inversion of the screw-sense preference using H-1 NMR spectroscopy, which enabled us to observe independently two species with (M)- or (P)-helicity in both the absence and presence of a guest molecule. Inversion of the screw-sense preference was induced upon complexation with an achiral guest as well as a chiral guest.
  • Yusuke Ishigaki, Hidetoshi Kawai, Ryo Katoono, Kenshu Fujiwara, Takanori Suzuki
    HETEROCYCLES 90 (1) 136 - 143 0385-5414 2015/01 [Refereed][Not invited]
     
    The title fluorescent (oligo)thiophenes 1-3 were designed as new violene/cyanine-hybrid-type electron donors, which have two 4-methoxyphenyl groups each on the two cyanine parts. Voltammetric analyses showed that they all undergo reversible two-stage one-electron oxidation. The intramolecular short S(thiophene) -- C-ipso(Ar) contacts were commonly present in their X-ray structures, and the coplanarily extended geometries are suitable for pi-delocalization. Electrochemical oxidation of 1-3 caused continuous changes in their UV-Vis-NIR and fluorescence spectra although the oxidized species are too labile to be isolated.
  • Yusuke Ishigaki, Satoshige Yoshida, Hidetoshi Kawai, Ryo Katoono, Kenshu Fujiwara, Takanori Fukushima, Takanori Suzuki
    HETEROCYCLES 90 (1) 126 - 135 0385-5414 2015/01 [Refereed][Not invited]
     
    Starting from (S)-dimethyl 1,1'-binaphthyl-2,2'-dicarboxylate, optically pure (P)-3,3,4,4-tetrakis(3,4-dialkoxyphenyl)-3,4-dihydro[5]helicenes (P)-1 were prepared via bis(diarylhyclroxymethyl)binaphthyl and/or tetraaryldinaphthodihydroxepin as key intermediates. Upon electrochemical oxidation to the corresponding (S)-1,1'-binaphthyl-2,2'-diylbis(diarylcarbenium)s (S)-2(2+), three kinds of spectral changes (UV-Vis, circular dichroism, fluorescence) were successfully observed. Compared to the methoxy compound, the octyloxy and hexadecyloxy derivatives exhibit a redshifted emission maxima in the dihydro[5]helicenes. The long alkyl chains induce step-by-step two-electron reduction of the binaphthyldiyl(dicarbenium)s whereas the dication with methoxy groups exhibits one-wave two-electron process.
  • Yuta Hirose, Kenshu Fujiwara, Takafumi Saito, Ryo Katoono, Takanori Suzuki
    HETEROCYCLES 91 (1) 76 - 103 0385-5414 2015/01 [Refereed][Not invited]
     
    The stereoselective synthesis of the A-ring of armatol A, a natural polycyclic ether triterpene from the red alga Chondria armata, was achieved in a non-biomimetic way. The synthesis employed Ireland-Claisen rearrangement of an ester, prepared from a bromo-substituted chiral building block, for the construction of C6 and C7 stereocenters and a relay ring-closing olefin metathesis for the seven-membered ring formation.
  • Ryo Katoono, Shunsuke Kawai, Kenshu Fujiwara, Takanori Suzuki
    CHEMICAL SCIENCE 6 (11) 6592 - 6600 2041-6520 2015 [Refereed][Not invited]
     
    We describe a quantitative analysis of the complexation-induced inversion of a screw-sense preference based on a conformationally dynamic double-helix structure in a macrocycle. The macrocycle is composed of two twisting units (terephthalamide), which are spaced by two strands (1,3-bis(phenylethynyl)benzene), and is designed to generate a double-helix structure through twisting about a C-2 axis in a conrotatory manner. The attachment of chiral auxiliaries to the twisting units induces a helical preference for a particular sense of (M)- or (P)-helicity through the intramolecular transmission of chirality to dynamic double helices. The twisting unit can also act as a binding site for capturing a guest molecule, and, in a complexed state, the preferred screw sense of the dynamic double-helix structure is reversed to exhibit the contrary preference. We quantitatively monitored the complexation-induced inversion of the screw-sense preference using H-1 NMR spectroscopy, which enabled us to observe independently two species with (M)- or (P)-helicity in both the absence and presence of a guest molecule. Inversion of the screw-sense preference was induced upon complexation with an achiral guest as well as a chiral guest.
  • Yusuke Ishigaki, Hidetoshi Kawai, Ryo Katoono, Kenshu Fujiwara, Takanori Suzuki
    HETEROCYCLES 90 (1) 136 - 143 0385-5414 2015/01 [Refereed][Not invited]
     
    The title fluorescent (oligo)thiophenes 1-3 were designed as new violene/cyanine-hybrid-type electron donors, which have two 4-methoxyphenyl groups each on the two cyanine parts. Voltammetric analyses showed that they all undergo reversible two-stage one-electron oxidation. The intramolecular short S(thiophene) -- C-ipso(Ar) contacts were commonly present in their X-ray structures, and the coplanarily extended geometries are suitable for pi-delocalization. Electrochemical oxidation of 1-3 caused continuous changes in their UV-Vis-NIR and fluorescence spectra although the oxidized species are too labile to be isolated.
  • Ryo Katoono, Keiichi Kusaka, Kenshu Fujiwara, Takanori Suzuki
    CHEMISTRY-AN ASIAN JOURNAL 9 (11) 3182 - 3187 1861-4728 2014/11 [Not refereed][Not invited]
     
    Dynamic helicity in a folded macrocycle and control of the helical preference are described. We designed macrocycle 1 with a dual mode of folding through the integration of two flexible units that are arranged twice to form a cyclic structure. As a folding unit, we used a terephthalamide skeleton and a Z-shaped hydrocarbon: the former acted as a control unit to induce a preference of a particular sense of dynamic helicity and the latter was just a spacer. A terephthalamide unit provided a binding site for capturing a ditopic hydrogen-bonding guest when it adopted helically folded syn forms (M/P). Thus, only the terephthalamide unit controlled the helical sense of dynamic helicity in a folded macrocycle through the supramolecular transmission of chirality upon complexation with a chiral ditopic guest. In addition, chirality on a host could also contribute to the control of the helical preference in a folded macrocycle, which led to exceptionally enhanced chiroptical signals.
  • Ryo Katoono, Yuki Tanaka, Kenshu Fujiwara, Takanori Suzuki
    JOURNAL OF ORGANIC CHEMISTRY 79 (21) 10218 - 10225 0022-3263 2014/11 [Refereed][Not invited]
     
    A foldable cyclic oligomer 1 consisting of three terephthalamide units spaced with a 3-fold o-phenylene unit presented a dynamic pair of enantiomeric forms through molecular folding, to which the external chirality on a ditopic guest [(S,S)-2 or (R,R)-2] was supramolecularly transferred to prefer a particular sense of dynamic helicity [(M,M)-/(P,P)-1 and (M,M,P)-/(P,P,M)-1]. In the macrocycle, the terephthalamide units acted as exotopic binding sites to fold into helical forms upon complexation. The internal chirality associated with a host [(R,R,R,R,R,R)-1b] had no preference in a helical sense in the absence of a guest. Instead, the internal chirality was responsible for the signal modulation that it was cooperatively or competitively transferred in response to the external chirality on a guest (S,S)-2 or (R,R)-2. During the diastereomeric complexation, a particular sense of dynamic helicity was favored due to cooperative transmission of chirality when the helical preference was matched between the host and guest. Alternatively, the host complexed with an antipodal guest underwent a drastic change in conformation upon a change in temperature.
  • Takashi Takeda, Yasuto Uchimura, Hidetoshi Kawai, Ryo Katoono, Kenshu Fujiwara, Takanori Suzuki
    ChemInform 45 (30) no - no 2014/07/10 [Refereed][Not invited]
  • Takanori Suzuki, Yuto Sakano, Yusuke Tokimizu, Youhei Miura, Ryo Katoono, Kenshu Fujiwara, Naoki Yoshioka, Nobutaka Fujii, Hiroaki Ohno
    CHEMISTRY-AN ASIAN JOURNAL 9 (7) 1841 - 1846 1861-4728 2014/07 [Refereed][Not invited]
     
    Electron-donating dihydrobenzindolocarbazoles (BICs) 1a-c, which adopt planar disk-shaped geometries, were prepared by gold(I)-catalyzed cyclization as a key step. Due to the presence of a 1,4-phenylenediamine (PD) moiety in the framework, they undergo reversible one-electron oxidation to the corresponding Wurster's Blue (WB)-type species that exhibits NIR absorptions up to lambda=1200 nm. In the case of the N,N'-dimethyl derivative, cation radical 1c(+center dot) is stable enough to be isolated as a salt and Xray analysis indicated paraquinoid-type bond alternation in the WB core unit, whereas the bond lengths in the peripheral benzene rings are identical to those in the neutral donor. Upon electrochemical interconversion, the redox pairs of 1a-c and 1a-c(+center dot) exhibited an electrochromic response in the UV/Vis/NIR region, which was accompanied by a drastic change in the fluorescence spectrum because only neutral donors 1a-c are highly emissive (Phi(F): 0.7-0.8).
  • Yuto Sakano, Ryo Katoono, Kenshu Fujiwara, Takanori Suzuki
    CHEMISTRY LETTERS 43 (7) 1143 - 1145 0366-7022 2014/07 [Refereed][Not invited]
     
    Tetrakis(4-methoxyphenyl)anthraquinodimethane 1(b) with a bent geometry undergoes reversible redox interconversion with twisted dication 1(t)(2+) exhibiting a vivid change in color (electrochromism) accompanied by a drastic structural change. Electrochemical oxidation of bianthraquinodimethane 2(b) with a doubly bent structure to bianthrylidene-type twisted dication 2(t)(2+) proceeded smoothly, whereas the reverse conversion was less effective because 2(t)(2 center dot) generated upon reduction of 2(t)(2+) is a long-lived species to undergo side reactions.
  • Takanori Suzuki, Keisuke Hanada, Ryo Katoono, Yusuke Ishigaki, Sho Higasa, Hiroki Higuchi, Hirotsugu Kikuchi, Kenshu Fujiwara, Hidetoshi Yamada, Takanori Fukushima
    CHEMISTRY LETTERS 43 (7) 982 - 984 0366-7022 2014/07 [Refereed][Not invited]
     
    Upon electrochemical oxidation of configurationally stable biphenyl-based electron donors (R-ax)-1a and -1b to butane-1,4-diyl dications (M)-2a(2+) and -2b(2+), drastic changes were induced not only in UV-vis but also in CD spectra. Because of the hydrophilic oligoethylene glycol units on the amino nitrogens, (R-ax)-1b and (M)-2b(2+) are soluble in water, thus realizing the electrochiroptical behavior not only in organic solvents but also in aqueous media.
  • Takanori Suzuki, Yusuke Kuroda, Kazuhisa Wada, Yuto Sakano, Ryo Katoono, Kenshu Fujiwara, Fumitoshi Kakiuchi, Takanori Fukushima
    CHEMISTRY LETTERS 43 (6) 887 - 889 0366-7022 2014/06 [Refereed][Not invited]
     
    Upon electrochemical oxidation of configurationally stable (M)-4,5-dimethyl-9,10-dihydrophenanthrene attached with two spiroacridan units at the C9 and C10 positions [(M)-1c], a three-way-output response by UV vis, FL, and CD spectra was realized via clean conversion to the corresponding bond-dissociated dication (R-ax)-2c(2+). Similar gradual changes were induced upon standing of an aerated MeCN solution of (M)-1c after the addition of CF3CO2H because the elongated C9 C10 bond was also cleaved by oxidative protonolysis to give (R-ax)-2c(2+).
  • Takanori Suzuki, Yuto Sakano, Yusuke Tokimizu, Youhei Miura, Ryo Katoono, Kenshu Fujiwara, Naoki Yoshioka, Nobutaka Fujii, Hiroaki Ohno
    Chem. Asian J. Wiley-Blackwell 9 (7) 1967 - 1967 2014/06 [Refereed][Not invited]
  • Keiji Tanino, Takumasa Yamada, Fumihiko Yoshimura, Takanori Suzuki
    CHEMISTRY LETTERS 43 (5) 607 - 609 0366-7022 2014/05 [Refereed][Not invited]
     
    A series of 4-cyanoazulene derivatives 1-5 were synthesized from 4-cyanohexahydroazulen-l-one, which was efficiently obtained by the annulation of the seven-membered ring on the cyclopentenone skeleton via the divinylcyclopropane rearrangement. This synthetic protocol is also effective in preparing 1,1'-bi(4-cyanoazulene) (6) and its p-phenylene-extended derivative 7, which undergo multistage redox reactions exhibiting electrochemical amphotericity.
  • Takanori Suzuki, Yuto Sakano, Tomohiro Iwai, Shinichi Iwashita, Youhei Miura, Ryo Katoono, Hidetoshi Kawai, Kenshu Fujiwara, Yasushi Tsuji, Takanori Fukushima
    PURE AND APPLIED CHEMISTRY 86 (4) 507 - 516 0033-4545 2014/04 [Refereed][Not invited]
     
    Electron-donating 1,1,4,4-tetraarylbutadiene is a representative electrochromic dye, and the same chromophore can be found in 9,10-bis(diarylmethylene)-9,10-dihydrophenanthrene (dibenzo-oQD) albeit in a fixed s-cis geometry. Unlike thermodynamically unstable 7,7,8,8-tetraaryl-o-quinodimethane, spontaneous electrocyclization is prohibited by dibenzo-annulation. Several derivatives of dibenzo-oQD were successfully generated despite highly strained geometry caused by steric hindrance between the bulky diarylmethylene units. Their precursors are phenanthrene-9,10-diyl bis(diarylmethylium) dyes (PDM2+) stabilized by four electron-donating alkoxy groups. The redox pairs of dibenzo-oQD/PDM2+ exhibit vivid change in color upon redox interconversion (electrochromism). Both dibenzo-oQD and PDM2+ adopt a helical conformation, whose configuration is unstable. When a chiral alkoxy substituent is attached on each of the aryl groups, the point chirality is successfully transmitted to helicity of PDM2+. Resulting diastereomeric biasing is the key for dibenzo-oQD/PDM2+ to exhibit the two-way-output response (e.g., UV-vis and CD). In addition, much more strained quinodimethane derivatives, 1,2-bis(diarylmethylene) acenaphthene and 1,16-diaryldibenzo[b, n] perylene, were also generated from the dicationic precursors, demonstrating that the reductive transformation can serve as a useful protocol to generate severely deformed pi-conjugated systems.
  • Kenshu Fujiwara, Yuki Suzuki, Nao Koseki, Yu-ichi Aki, Yuta Kikuchi, Shun-ichi Murata, Fuyuki Yamamoto, Mariko Kawamura, Toshio Norikura, Hajime Matsue, Akio Murai, Ryo Katoono, Hidetoshi Kawai, Takanori Suzuki
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 53 (3) 780 - 784 1433-7851 2014/01 [Refereed][Not invited]
     
    Pectenotoxin-2 (PTX2) is a shellfish toxin and has a non-anomeric spiroacetal, which is not stabilized by an anomeric effect. The selective construction of the non-anomeric spiroacetal has been a major problem in the synthesis of PTX2. Described herein is the stereoselective total synthesis of PTX2 via the isomerization of anomeric spiroacetal pectenotoxin-2b (PTX2b). The synthesis of PTX2b was achieved by a simple process including sulfone-mediated assembly of spirocyclic and bicyclic acetals and subsequent macrocyclization by ring-closing olefin metathesis. Finally, the selective construction of PTX2 was accomplished by the early termination of a dynamic transition process to equilibrium in the acid-catalyzed isomerization of anomeric PTX2b. [6,6]-Spiroacetal pectenotoxin-2c (PTX2c) was also synthesized from PTX2b. The cytotoxicity assay of the synthetic compounds against HepG2 and Caco2 cancer cells showed a potency of the order: PTX2 >> PTX2b > PTX2c.
  • Ryo Katoono, Kenshu Fujiwara, Takanori Suzuki
    CHEMICAL COMMUNICATIONS 50 (41) 5438 - 5440 1359-7345 2014 [Refereed][Not invited]
     
    A tristerephthalamide host exhibited two helical geometries with (M)- and (P)- helicity, respectively, in terms of the twisting direction of a two-layer structure, and the helical preference switched upon complexation with a ditopic guest. In both uncomplexed and complexed states, the intramolecular transmission of chirality was responsible for the control of helicity.
  • Takanori Suzuki, Yasuto Uchimura, Fumika Nagasawa, Takashi Takeda, Hidetoshi Kawai, Ryo Katoono, Kenshu Fujiwara, Kei Murakoshi, Takanori Fukushima, Aiichiro Nagaki, Jun-ichi Yoshida
    CHEMISTRY LETTERS 43 (1) 86 - 88 0366-7022 2014/01 [Refereed][Not invited]
     
    Low-temperature X-ray analyses on several pseudopolymorphs (solvate crystals) revealed that the C-1-C-2 bond length of the highly congested title molecule can adopt quite different values [1.700(6)-1.739(6)angstrom]. Such an unusual observation indicates that the ultralong covalent bond is endowed with "expandability," thus the prestrained bond can be elongated or shortened very easily accompanied by only a minute change in energy, which can be compensated by intermolecular perturbation in the crystal.
  • Ryo Katoono, Keiichi Kusaka, Shunsuke Kawai, Yuki Tanaka, Keisuke Hanada, Tatsuo Nehira, Kenshu Fujiwara, Takanori Suzuki
    ORGANIC & BIOMOLECULAR CHEMISTRY 12 (47) 9532 - 9538 1477-0520 2014 [Not refereed][Not invited]
     
    We designed hexakis(phenylethynyl) benzene derivatives with a tertiary amide group on each blade to achieve a helically biased propeller arrangement through the complexation-induced intramolecular transmission of point chirality. A hydrogen-bonding ditopic guest was captured at two amide groups, and thus could pair two neighboring blades to form a supramolecular cyclic structure, in which an auxiliary chiral group associated with a blade acted as a chiral handle to control the helical bias, while the chiral auxiliary did not exert any helical influence on the dynamic helicity in the absence of a guest due to the high flexibility of each blade.
  • Takashi Takeda, Yasuto Uchimura, Hidetoshi Kawai, Ryo Katoono, Kenshu Fujiwara, Takanori Suzuki
    CHEMICAL COMMUNICATIONS 50 (30) 3924 - 3927 1359-7345 2014 [Refereed][Not invited]
     
    Due to purely steric effects of acridine units, acenaphthylene-1,2-diyldi(9-acridine) has a long C=C bond [1.3789(19) angstrom] while maintaining its sp(2) hybridized nature and bond order.
  • Kazuhisa Wada, Yuna Chiba, Takashi Takeda, Hidetoshi Kawai, Ryo Katoono, Kenshu Fujiwara, Takanori Suzuki
    HETEROCYCLES 88 (2) 945 - 952 0385-5414 2014/01 [Refereed][Not invited]
     
    The configuration of helical dicationic dyes 2(2+) with a dihydrodibenzoxepinone unit is stable, whereas the corresponding neutral electron donors 1 with a tetrahydrophenanthroxepinone skeleton easily undergo ring-flip. Thanks to their electrochemical bistability, electron exchange between 1 and 2(2+) is prohibited. Thus, the above electrochromic pairs 1/2(2+) can serve as new members of less well-explored redox-based chiral-memory units.
  • Ryo Katoono, Hidetoshi Kawai, Masakazu Ohkita, Kenshu Fujiwara, Takanori Suzuki
    Chemical Communications 49 (88) 10352 - 10354 1359-7345 2013/11/14 [Refereed][Not invited]
     
    Propeller-shaped dynamic helicity was generated in a hexakis(phenylethynyl) benzene framework that preferred a particular sense to afford a strong CD signal, which was realized by the cooperative transmission of point chiralities upon complexation with a chiral guest through a threefold binding site presented by a syn-formed terephthalamide. © 2013 The Royal Society of Chemistry.
  • Kenshu Fujiwara, Yuki Suzuki, Nao Koseki, Yu-ichi Aki, Yuta Kikuchi, Shun-ichi Murata, Fuyuki Yamamoto, Mariko Kawamura, Toshio Norikura, Hajime Matsue, Akio Murai, Ryo Katoono, Hidetoshi Kawai, Takanori Suzuki
    Angew. Chem. 126 (3) 799 - 803 2013/11 [Refereed][Not invited]
  • Toshiyuki Hamura, Ryosuke Nakayama, Keisuke Hanada, Yuto Sakano, Ryo Katoono, Kenshu Fujiwara, Takanori Suzuki
    CHEMISTRY LETTERS 42 (10) 1244 - 1246 0366-7022 2013/10 [Refereed][Not invited]
     
    1,3-Bis[4-(dimethylamino)phenyl]isobenzofuran (1a) and a derivative were efficiently prepared through a sequence of reactions in a single batch reactor (time integration). The o-quinodimethane-type pi-conjugation in 1a was confirmed by bond alternation determined by a low-temperature X-ray analysis. Brightly colored heterocycle 1a undergoes reversible two-stage one-electron oxidation, and electrolysis of 1a induces a vivid change in UV-vis-NIR. absorptions exhibiting several isosbestic points (electrochromism).
  • Kazuhisa Wada, Takashi Takeda, Hidetoshi Kawai, Ryo Katoono, Kenshu Fujiwara, Takanori Suzuki
    CHEMISTRY LETTERS 42 (10) 1194 - 1196 0366-7022 2013/10 [Refereed][Not invited]
     
    By attaching bulky substituents at the bay region of di(spiroacridan)-substituted dihydrophenanthrene la, the prestrained C-9-C-10 bond in the dihydrophenanthrene (DHP) skeleton of le le is expanded from 1.634(2) to 1.649(3)-1.652(6)angstrom, which demonstrates the bond expansion through remote steric effects. Twisting deformation of the DHP skeleton is the key to transfer the steric bulkiness from the C-4/C-5 positions to cause the additional strain in the C-9-C-10 bond.
  • Takanori Suzuki, Yuulci Hoshiyama, Kazuhisa Wada, Yusuke Ishigaki, Youhei Miura, Hidetoshi Kawai, Ryo Katoono, Kenshu Fujiwara, Takanori Fukushima
    CHEMISTRY LETTERS 42 (9) 1004 - 1006 0366-7022 2013/09 [Refereed][Not invited]
     
    The newly designed title dyes 1-3 have a thiophene-type pi-skeleton, to which two methyleneacridan subunits are attached as electron-donating end groups. They undergo reversible one-wave 2e-oxidation to the corresponding dications containing a thienoquinoid moiety. The redox and spectral properties can be modified by changing the pi-skeleton, and bithiophene 2 and terthiophene 3 can serve as new entries of UV-vis-NIR. electrochromic materials.
  • Takanori Suzuki, Yusuke Toldmizu, Yuto Sakano, Ryo Katoono, Kenshu Fujiwara, Saori Naoe, Nobutaka Fujii, Hiroaki Ohno
    CHEMISTRY LETTERS 42 (9) 1001 - 1003 0366-7022 2013/09 [Refereed][Not invited]
     
    Through gold(I)-catalyzed cascade cyclization as a key step, the title electron donor was prepared, which adopts a planar geometry, as confirmed by an X-ray analysis. Due to 1,4-phenylenediamine moiety incorporated in the framework, it undergoes reversible one-electron oxidation. Upon electrolysis, it exhibited an electrochromic response in the UV-vis-NIR region, which was accompanied by a drastic change in the fluorescence spectrum since only the neutral donor is highly fluorescent.
  • Takashi Takeda, Yasuto Uchimura, Hidetoshi Kawai, Ryo Katoono, Kenshu Fujiwara, Takanori Suzuki
    CHEMISTRY LETTERS 42 (9) 954 - 962 0366-7022 2013/09 [Refereed][Not invited]
     
    Over the past few decades, many studies have been conducted on ultralong C-C bonds (bond length greater than 1.7 angstrom). This highlight review discusses the molecular design of ultralong C-C bonds and their bonding properties, especially their "expandability." In particular, the ultralong C-C bonds in tetraarylpyracene derivatives can change in length by adopting a slightly different conformation in the crystalline state. This expandability of ultralong C-C bonds could be due to the smaller decrease in bond energy at a longer interatomic distance (>1.7 angstrom). This interesting property can be applied to stimulus-responsive materials, as illustrated in the thermochromism of a bis(methylacridan)-substituted pyracene crystal, since the thermally induced change in bond-length modifies the HOMO-LUMO gap.
  • Naoto Kinashi, Kenshu Fujiwara, Takayuki Tsunoda, Ryo Katoono, Hidetoshi Kawai, Takanori Suzuki
    TETRAHEDRON LETTERS Elsevier {BV} 54 (34) 4564 - 4567 0040-4039 2013/08 [Refereed][Not invited]
     
    A method for the stereoselective construction of the C8'-O-C6" ether of nigricanoside-A, an antimitotic natural product from the green alga Avrainvillea nigricans, has been developed based on chirality-transferring Ireland-Claisen rearrangement. The method was successfully applied to the synthesis of simple models for the C20 lipid chain/galactosyl glycerol segment of the natural product. (C) 2013 Elsevier Ltd. All rights reserved.
  • Takanori Suzuki, Hitomi Tamaoki, Ryo Katoono, Kenshu Fujiwara, Junji Ichikawa, Takanori Fukushima
    CHEMISTRY LETTERS Chemical Society of Japan 42 (7) 703 - 705 0366-7022 2013/07 [Refereed][Not invited]
     
    Octafluorobiphenyl-2,2'-diylbis(diarylmethylium) dye 2a(2+) prepared from 1,2-dibromotetrafluorobenzene is interconvertible with colorless dihydrophenanthrene donor la. By the SNAr reactions of la with acetylides, pi-extended analogues 1b and 1c were obtained. Their electrochromic behavior is accompanied by a drastic absorption change not only in the visible but also UV region, because the torsion angle of the biaryl unit is modified upon redox reactions.
  • Takanori Suzuki, Takuma Kuroda, Hitomi Tamaoki, Sho Higasa, Ryo Katoono, Kenshu Fujiwara, Takanori Fukushima, Hidetoshi Yamada
    CHEMISTRY LETTERS 42 (7) 706 - 708 0366-7022 2013/07 [Refereed][Not invited]
     
    Upon oxidation of the title heterocycles with dimethylamino groups, elemental sulfur is extruded to form dicationic dyes, which regenerate the heterocycles by the reaction with Na2S. The electrolysis of the heterocycles induces a drastic change in UV-vis spectrum exhibiting several isosbestic points. The bay-region substituents enhance configurational stability, so the optically pure heterocycle can be obtained in terms of helicity of one-handedness, and its chromism is accompanied by a large chiroptical response as detected by CD spectroscopy.
  • Hidetoshi Kawai, Tatsuya Utamura, Erina Motoi, Tomoko Takahashi, Hiroyoshi Sugino, Manabu Tamura, Masakazu Ohkita, Kenshu Fujiwara, Takao Saito, Takashi Tsuji, Takanori Suzuki
    Chemistry - A European Journal 19 (14) 4513 - 4524 0947-6539 2013/04/02 [Not refereed][Not invited]
     
    The macrocyclization of 2,6-diethynyl hydrindacenes (1) with functional groups at mutually perpendicular positions results in the formation of novel macrocycles which, as a result of the hindered rotation of the hydrindacene units, possess directionally persistent peripheral functionalities. The two hydrindacene units in the dimer macrocycle (2) have been shown to interact electronically through their respective butadiyne moieties, whereas the trimer macrocycle (3) demonstrates a moderate degree of geometrical flexibility as a result of the five-membered hydrindacene rings. In addition, these trimer macrocycles contain a central cavity suitably sized for the inclusion of various solvent molecules. These new macrocycles can be further modified by introducing π-conjugated side groups, such as styryl and thienyl groups, as well as by attaching a variety of peripheral ester groups. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
  • Keisuke Nogoshi, Daisuke Domon, Kenshu Fujiwara, Natsumi Kawamura, Ryo Katoono, Hidetoshi Kawai, Takanori Suzuki
    TETRAHEDRON LETTERS Elsevier {BV} 54 (7) 676 - 680 0040-4039 2013/02 [Refereed][Not invited]
     
    The EF-ring of ciguatoxin 3C, a marine toxin from the dinoflagellate Gambierdiscus toxicus, was stereoselectively synthesized by iterative use of a cyclic ether formation process based on chirality-transferring Ireland-Claisen rearrangement and ring-closing olefin metathesis. (c) 2012 Elsevier Ltd. All rights reserved.
  • Takanori Suzuki, Yuto Sakano, Tomohiro Iwai, Shinichi Iwashita, Youhei Miura, Ryo Katoono, Hidetoshi Kawai, Kenshu Fujiwara, Yasushi Tsuji, Takanori Fukushima
    CHEMISTRY-A EUROPEAN JOURNAL Wiley-Blackwell 19 (1) 117 - 123 0947-6539 2013/01 [Refereed][Not invited]
     
    When two benzene rings are fused to a tetraaryl-o-quinodimethane skeleton, sterically hindered helical molecules 1 acquire a high thermo-dynamic stability. Because the tetraarylbutadiene subunit contains electrondonating alkoxy groups, 1 undergo reversible two-electron oxidation to 2(2+), which can be isolated as deeply colored stable salts. Intramolecular transfer of the point chirality (e. g., sec-butyl) on the aryl groups to helicity induces a diastereomeric preference in dications 2b(2+) and 2c(2+), which represents an efficient method for enhancing circular-dichroism signals. Thus, those redox pairs can serve as new electrochiroptical response systems. X-ray analysis of dication 2(2+) revealed pi-pi stacking interaction of the diarylmethylium moities, which is also present in solution. The stacking geometry is the key contributor to the chirosolvatochromic response.
  • Daisuke Domon, Kenshu Fujiwara, Natsumi Kawamura, Ryo Katoono, Hidetoshi Kawai, Takanori Suzuki
    Natural Product Communications 8 (7) 929 - 934 1934-578X 2013 [Not refereed][Not invited]
     
    A new variant of fused cyclic ether synthesis based on Ireland-Claisen rearrangement and ring-closing olefin metathesis (RCM) was developed. The Ireland- Claisen rearrangement of a (Z)-3-alkoxyprop-2-en-1-yl glycolate ester having a cyclic ether on the oxygen at C3 of the (Z)-prop-2-en-1-yl group stereoselectively produced an anti-α,β-dialkoxyester, which was successfully transformed to a fused bicyclic ether via a reaction sequence including RCM.
  • Youhei Miura, Hiroshi Chiba, Ryo Katoono, Hidetoshi Kawai, Kenshu Fujiwara, Shuichi Suzuki, Keiji Okada, Takanori Suzuki
    TETRAHEDRON LETTERS 53 (48) 6561 - 6564 0040-4039 2012/11 [Refereed][Not invited]
     
    Upon the one-electron reduction of N-methylquinoxalino[2,3-b]quinoxaliniums 2, neutral radicals 1 without any bulky protecting groups were generated and isolated as stable solids, which exhibit electric conductivity (sigma = 10(-7) 10(-9) S cm(-1)) as a single-component organic material due to high electrochemical amphotericity (Delta E = ca. 0.9 V). (C) 2012 Elsevier Ltd. All rights reserved.
  • Hiroyoshi Sugino, Hidetoshi Kawai, Takeshi Umehara, Kenshu Fujiwara, Takanori Suzuki
    CHEMISTRY-A EUROPEAN JOURNAL 18 (43) 13722 - 13732 0947-6539 2012/10 [Refereed][Not invited]
     
    Imine-bridged rotaxanes are a new type of rotaxane in which the axle and macrocyclic ring are connected by imine bonds. We have previously reported that in imine-bridged rotaxane 5, the shuttling motion of the macrocycle could be controlled by changing the temperature. In this study, we investigated how the axle and macrocycle structures affect the construction of the imine-bridged rotaxane as well as the dynamic equilibrium between imine-bridged rotaxane 5 and [2]rotaxane 7 by using various combinations of axles (1?A,B), macrocycles (2?ae), and side-stations (XYL and TEG). In the threading process, the flexibility of the macrocycle and the substituent groups at the para position of the aniline moieties affect the preparation of the threaded imines. The size of the imine-bridging station and the macrocyclic tether affects the hydrolysis of the imine bonds under acidic conditions.
  • Kinashi Naoto, Fujiwara Kenshu, Katoono Ryo, Kawai Hidetoshi, Suzuki Takanori
    Symposium on the Chemistry of Natural Products, symposium papers 天然有機化合物討論会 (54) 345 - 350 2012/09/01 
    Nigricanocide A dimethyl ester (1), which originated from the green alga Avrainvillea nigricans, is an antimitotic galactoglycerolipid. It is structurally characterized by two ether linkages between a galactosyl glycerol and a C20 oxylipin and between C16 and C20 oxylipins. While the planar structure of the lipid chains and the partial relative configuration of the galactosyl glycerol moiety have been determined, the full absolute stereochemistry is unclear. Therefore, we started a program for determining the full absolute stereostructure of nigricanoside A dimethyl ester by total synthesis. As a part of the program, stereoselective methods for constructing the ether linkages between the galactosyl glycerol and the C20 lipid chain and between the C20 and C16 lipid chains have been developed. Model compounds ((8'R)-4 and (8'S)-4) corresponding to the bottom half of 1, including the C20 lipid chain and the galactosyl glycerol, has also been synthesized. The ether linkage between the galactose and the C20 lipid chain was constructed stereoselectively by the chirality-transferring Ireland-Claisen rearrangement of a 1-substituted-2-bromoallyl alkoxyacetate, which consisted of an optically active 2-bromo-1-alken-3-ol and a 6-(carboxymethoxy)galactose derivative. The rearrangement products were converted to model conpounds (8'R)-4 and (8'S)-4 via a process including Julia olefination with sulfone 5, Mori's alkyne formation, and Lindlar hydrogenation. The ether linkage between lipid chains was stereoselectively synthesized by an Evans type aldol reaction under lithium enolate conditions. Details will be presented in the poster session.
  • Kenshu Fujiwara, Takuto Sato, Yusuke Sano, Toshio Norikura, Ryo Katoono, Takanori Suzuki, Hajime Matsue
    JOURNAL OF ORGANIC CHEMISTRY American Chemical Society ({ACS}) 77 (11) 5161 - 5166 0022-3263 2012/06 [Refereed][Not invited]
     
    The first total synthesis of natural, unsymmetrical 2',3'-diacyloxy-p-terphenyls, thelephantin O (1) and terrestrins C and D (2 and 3, respectively), was achieved via a practical route which was also applicable to the synthesis of the symmetrical diesters vialinin A/terrestrin A. (4) and terrestrin B (5). Compounds 1-5 exhibited cytotoxicity against cancer cells (HepG2 and Caco2) with IC50 values of 13.6-26.7 mu mol/L.
  • Takanori Suzuki, Yasuto Uchimura, Yusuke Ishigaki, Takashi Takeda, Ryo Katoono, Hidetoshi Kawai, Kenshu Fujiwara, Aiichiro Nagaki, Jun-ichi Yoshida
    CHEMISTRY LETTERS 41 (5) 541 - 543 0366-7022 2012/05 [Refereed][Not invited]
     
    Based on space integration using a flow microreactor system, the title unsymmetrically substituted pyracenes with an extremely long C C bond [1.714(2)-1.739(4)angstrom] are readily accessible, whose structures demonstrate nonadditive substituent effects on expanding the polyarylated C-1-C-2 bond in crystal. The bond lengths rather exhibit correlation with the eclipsing degree of the C-sp3-C-sp3 bond, which is more affected by the intermolecular factors such as crystal packing.
  • Hiroyoshi Sugino, Hidetoshi Kawai, Kenshu Fujiwara, Takanori Suzuki
    CHEMISTRY LETTERS 41 (1) 79 - 81 0366-7022 2012/01 [Refereed][Not invited]
     
    Condensation reactions of macrocyclic diamines 1 and cyclohexane-1,4-dicarbaldehydes 2 with the substituents at 1,4-positions gave a series of macrocage molecules that can be considered molecular gyroscopes. The gyro-rotational behavior of the cyclohexane rotor is largely affected by the degree of steric requirement of the substituents, and isolation of syn-isomer suggests stepwise motion in the macrocages attached with bulky substituents on the rotor.
  • Takanori Suzuki, Hitomi Tamaoki, Kazuhisa Wada, Ryo Katoono, Tatsuo Nehira, Hidetoshi Kawai, Kenshu Fujiwara
    CHEMICAL COMMUNICATIONS Royal Society of Chemistry ({RSC}) 48 (22) 2812 - 2814 1359-7345 2012 [Refereed][Not invited]
     
    The ratio of the easily interconverting rotational isomers of biphenyl-2,2'-diylbis[bis(4-dimethylaminophenyl)methylium] (R)/(S)-1a(2+) can be biased to prefer an R configuration upon 1 : 1 complexation with gamma-cyclodextrin in water. Through the reaction with Na2S, the preference of 1a(2+) @gamma-CyD for an axial chirality of R can be fixed as the M-helicity of dihydrothiepin 2.
  • Ryo Katoono, Hidetoshi Kawai, Kenshu Fujiwara, Takanori Suzuki
    Yuki Gosei Kagaku Kyokaishi/Journal of Synthetic Organic Chemistry 70 (6) 640 - 650 0037-9980 2012 [Not refereed][Not invited]
     
    This article describes the chirality sensing systems based on changes in conformation of dynamic terephthalamide hosts from a nonhelical form to a helical form with biasing to prefer one handedness upon complexation with a chiral guest through supramolecular transmission of chirality. The syn form is endowed with the ability to capture a ditopic guest through hydrogen bonds at the amide carbonyls thus in a complexed state, a strong CD signal is produced thanks to a helical conformation induced by the conformational change and a biased handedness. Attachment of chirality to the terephthalamide host itself leads to an intrinsic preference in the sense of dynamic helicity in a helical syn form. Cooperative transmission of chiralities within the host and from the guest enables to further design an advanced sensing system with stereospecific chiroptical modulation, based on a stereospecific change in conformation of the chiral dynamic host upon complexation with a pair of enantiomeric guests.
  • Yusuke Ishigaki, Takanori Suzuki, Jun-ichi Nishida, Aiichiro Nagaki, Naofumi Takabayashi, Hidetoshi Kawai, Kenshu Fujiwara, Jun-ichi Yoshida
    MATERIALS 4 (11) 1906 - 1926 1996-1944 2011/11 [Refereed][Not invited]
     
    A series of biphenyl-2,2'-diylbis(diarylmethanol) s 3, which have two kinds of aryl groups at the bay region, were efficiently obtained by integrated flow microreactor synthesis. The diols 3NO/NX are the precursors of unsymmetric biphenylic dications 2NO/NX2+, which are transformed into the corresponding dihydrophenanthrenes 1NO/NX via 2NO/NX+center dot upon reduction, when they exhibit two-stage color changes. On the other hand, the steady-state concentration of the intermediate 2NO/NX+center dot is negligible during the oxidation of 1NO/NX to 2NO/NX2+, which reflects unique tricolor electrochromicity with a hysteretic pattern of color change [color 1 -> color 2 -> color 3 -> color 1].
  • Kenshu Fujiwara, Yuki Suzuki, Nao Koseki, Shun-ichi Murata, Akio Murai, Hidetoshi Kawai, Takanori Suzuki
    TETRAHEDRON LETTERS Elsevier {BV} 52 (43) 5589 - 5592 0040-4039 2011/10 [Refereed][Not invited]
     
    The C8-C20 segment of pectenotoxin-2 was efficiently synthesized in 16% overall yield in 22 steps from L-malic acid via an improved route. (C) 2011 Elsevier Ltd. All rights reserved.
  • Youhei Miura, Hidetoshi Kawai, Kenshu Fujiwara, Takanori Suzuki
    CHEMISTRY LETTERS 40 (9) 975 - 977 0366-7022 2011/09 [Refereed][Not invited]
     
    Due to the high-lying HOMO of the substituents and the low-lying LUMO inherited by the heterocyclic skeleton, the title quinoxalinoquinoxalines 1 exhibit absorption bands which extend to the NIR region, whereas the dihydro derivatives 2 are less colored but emit strong green fluorescence. Thus, the present pairs can serve as novel redox dyes for drastic spectral changes.
  • Masakazu Ohkita, Ayataka Endo, Kimihiro Sumiya, Hajime Nakanotani, Takanori Suzuki, Chihaya Adachi
    JOURNAL OF LUMINESCENCE Elsevier {BV} 131 (7) 1520 - 1524 0022-2313 2011/07 [Refereed][Not invited]
     
    4,4'-bis(N-carbazolyl)tolan (BCT) and 4,4'-bis[N-(3,6-di-t-butyl)carbazolyl]tolan (BCT-t-Bu) were synthesized as pi-expanded analogs of 4,4'-bis(N-carbazolyl)biphenyl. Their photophysical characteristics both in solution and films were thoroughly investigated. Interestingly, the phosphorescence spectrum of BCT was significantly medium-dependent, and the emission maximum was red-shifted by 131 nm from 489 nm in solution at 77 K to 620 nm in a deposited film at 5 K. suggesting the presence of strong intermolecular interactions in the film. BCT and BCT-t-Bu were found to be useful as host materials for fluorescence-based organic light emitting diodes (OLEDs). However, their low triplet energy levels in films negated their potential to act as hosts in phosphorescence-based OLEDs. (C) 2011 Elsevier B.V. All rights reserved.
  • Atsushi Takemura, Yasushi Katagiri, Kenshu Fujiwara, Hidetoshi Kawai, Takanori Suzuki
    TETRAHEDRON LETTERS Elsevier {BV} 52 (11) 1222 - 1224 0040-4039 2011/03 [Refereed][Not invited]
     
    The synthesis of the C22-C37 segment of prorocentin, isolated from the dinoflagellate Prorocentrum lima, was achieved. Because the relative stereochemical relationship between C26 and other stereocenters (C28/C31/C32 established as R*/R*/R*) in the C22-C37 region of natural prorocentin has not yet been determined, both epimers at C26 of the C22-C37 segment were selectively constructed. The synthesis was based on a 5-exo epoxide ring opening reaction to form an oxolane (E-ring). Brown asymmetric methallylation to install the C26-stereocenter, acryloylation of the resulting alcohol, and ring-closing olefin metathesis to establish the Z-olefin at C23/C24. (C) 2011 Elsevier Ltd. All rights reserved.
  • Sugino, H, Kawai, H, Fujiwara, K, Suzuki, T
    Kobunshi Ronbunshu The Society of Polymer Science, Japan 68 (12) 795 - 803 0386-2186 2011 [Refereed][Not invited]
     
    Imine-bridged pseudorotaxanes can be prepared by forming imine bonds between the diformyl hydrindacene axle and diamino-substituted macrocycles. Such pseudorotaxanes can be used as intermediates for a series of interlocked molecules with multiple rotaxane substructures, since they do not dethread under neutral or basic reaction conditions. Such imine-bridged oligorotaxanes were prepared by connecting the imine-bridged pseudorotaxane using a triethylene glycol spacer followed by introducing end-caps under basic conditions. The resulting oligorotaxanes with different subunit numbers were separated by GPC.
       The imine-bridged oligorotaxanes are interconvertible with the hydrogen-bonded oligorotaxanes under acidic hydrolyzing conditions by using trifluoroacetic acid. Upon heating the hydrolyzed solution of the oligorotaxane, the imine-bridged oligorotaxane was regenerated since the bridged forms are the thermodynamically favored species.
  • Takanori Suzuki, Takashi Takeda, Yasuyo Yoshimoto, Takayuki Nagasu, Hidetoshi Kawai, Kenshu Fujiwara
    ChemInform 41 (39) no - no 2010/09/02 [Refereed][Not invited]
  • Katagiri Yasushi, Fujiwara Kenshu, Takemura Atsushi, Kawai Hidetoshi, Suzuki Takanori
    Symposium on the Chemistry of Natural Products, symposium papers 天然有機化合物討論会 (52) 187 - 192 2010/09/01 
    Prorocentin, isolated from dinoflagellate Prorocentrum lima by Lu et al., exhibits inhibitory activity against some human cancer cell lines [IC_<50>: 16.7μg/mL (DLD-1); 83.67μg/mL (RPM17951)] and possesses an unique polyether structure, characterized by a [6,6]-spirocyclic acetal fused with an oxane ring (BCD-ring), an epoxide (A-ring), a five membered ether (E-ring) and a side chain including a conjugated triene group. Although the absolute configuration of prorocentin has not yet been determined, its biological and structural features make it an attractive synthetic target. Thus,a project toward the total synthesis of prorocentin aiming at determination of the absolute stereochemistry has been commenced. The partial relative structure of prorocentin was proposed by Lu et al. from their intensive NMR experiments, and a possible stereostructure was also shown as 1 in their report. Therefore, we first performed the total symthesis of 1. First, the C8-C20 segment (6) was synthesized from alkyne 7 and 8 via a process including Pd-catalyzed 6-endo cyclization. Aldehyde 6 was then connected with the C21-C35 segment(5), and the resulting alcohol was transformed to 27. The intramolecular double conjugate addition reaction of 27 produced the CD-ring spiroacetal (28), which was transformed to E-iodoalkene 4. The Suzuki-Miyaura coupling of 4 with dienylborane 3 followed by the removal of TBS groups and the concomitant epoxide fromation completed the total synthesis of 1. However, the ^1H and ^<13>C NMR spectra of 1 disagreed with those of natural prorocentin. Since the large deviations of chemical shifts between them were observed in the B-ring, we conferred with Lu on the deviations and deduced structure 2, having a hydroxy group at C17 of the B-ring, as a plausible structure of prorocentin. Thus, we next achieved the total synthesis of 2. The synthetic process was almost similar to that of 1, except the preparation of the B-ring (36), which was carried out by a process involving the aldol reaction of ketone 37 and 38. Finally, compound 2 showed the same spectral properties as natural prorocentin, except the opposite sign of optical rotation, thereby concluding that natural prorocentin is the enantiomer of 2.
  • Rui Kamada, Wataru Yoshino, Takao Nomura, Yoshiro Chuman, Toshiaki Imagawa, Takanori Suzuki, Kazuyasu Sakaguchi
    BIOORGANIC & MEDICINAL CHEMISTRY LETTERS 20 (15) 4412 - 4415 0960-894X 2010/08 
    Li-Fraumeni syndrome, a hereditary disorder characterized by familial clusters of early-onset multiple tumors, is caused by mutation of the TP53 gene, which encodes the p53 tumor suppressor protein. Mutation of Arg337 to histidine in the tetramerization domain of p53 is most frequently observed in Li-Fraumeni syndrome. This mutation is reported to destabilize the tetrameric structure of p53. We designed and synthesized calix[6] arene derivatives, which have six imidazole or pyrazole groups at the upper rim. In this study, we report, for the first time, the enhancement of the in vivo transcriptional activity of the most common Li-Fraumeni p53 mutant by imidazole-calix[6] arene through stabilization of the oligomer formation. (C) 2010 Elsevier Ltd. All rights reserved.
  • Kenshu Fujiwara, Yuta Hirose, Daisuke Sato, Hidetoshi Kawai, Takanori Suzuki
    TETRAHEDRON LETTERS 51 (32) 4263 - 4266 0040-4039 2010/08 [Refereed][Not invited]
     
    Armatol F, isolated from the red alga Chondria armata as a polyether triterpene, has a solitary oxepane (A-ring) and a fused tricyclic ether moiety (BCD-ring). The A-ring features a rare cis-relationship between the hydroxy group at the quaternary carbon C6 and the carbon chain at C7. As part of our program toward the total synthesis of armatol F, a new stereoselective method for the construction of the C6 and C7 stereocenters has been developed based on chirality-transferring Ireland-Claisen rearrangement. The A-ring skeleton has also been synthesized from the rearrangement product by a process including ring-closing olefin metathesis. (C) 2010 Elsevier Ltd. All rights reserved.
  • Kenshu Fujiwara, Keita Tanaka, Yasushi Katagiri, Hidetoshi Kawai, Takanori Suzuki
    TETRAHEDRON LETTERS 51 (34) 4543 - 4546 0040-4039 2010/08 [Refereed][Not invited]
     
    Armatol F, isolated from the red alga Chondria armata as a polyether triterpene, has a fused tricyclic ether moiety (BCD-ring) with an unusual cis ring junction at C18-C19 between the C- and D-rings. En route to the total synthesis of armatol F, the stereoselective construction of the C18 and C19 stereocenters by Ireland-Claisen rearrangement and the formation of the C-ring by relay ring-closing olefin metathesis were established through the synthesis of monocyclic (C-ring) and bicyclic (BC-ring) model compounds. (C) 2010 Elsevier Ltd. All rights reserved.
  • Takanori Suzuki, Youhei Miura, Tatsuo Nehira, Hidetoshi Kawai, Kenshu Fujiwara
    CHEMISTRY LETTERS 39 (7) 695 - 697 0366-7022 2010/07 [Refereed][Not invited]
     
    Not only the configuration at the C5 and C6 stereocenters but also the intra/intermoleculer hydrogen-bonding mode are determinant for the sense of mobile helicity of the dihydrophenanthroline unit in the title diols in solution. Thus, drastic changes in chiroptical signals are induced through conformational switching of 1 upon addition of protic solvent and/or acid.
  • Takanori Suzuki, Takashi Takeda, Yasuyo Yoshimoto, Takayuki Nagasu, Hidetoshi Kawai, Kenshu Fujiwara
    PURE AND APPLIED CHEMISTRY Walter de Gruyter {GmbH} 82 (4) 1033 - 1044 0033-4545 2010/04 [Refereed][Not invited]
     
    A series of title carbocations was generated and isolated as stable salts. X-ray analyses revealed a preference for an unsymmetric structure in which the bridging hydrogen is localized on one of the two triarylmethane units. NMR spectroscopy showed a similar preference in solution. The bridging hydrogen fluctuates between the two chromophores in solution, and the energy barrier for the H shift is linearly correlated with the C center dot center dot center dot C(+) separation determined by X-ray. According to an extrapolation, the energy barrier should decrease when the C center dot center dot center dot C(+) separation is less than 2.7 angstrom, which suggests a new model for isolable pure organic species with a three-center two-electron bond.
  • Takanori Suzuki, Takashi Takeda, Yasuyo Yoshimoto, Takayuki Nagasu, Hidetoshi Kawai, Kenshu Fujiwara
    PURE AND APPLIED CHEMISTRY Walter de Gruyter {GmbH} 82 (4) 1033 - 1044 0033-4545 2010/04 [Refereed][Not invited]
     
    A series of title carbocations was generated and isolated as stable salts. X-ray analyses revealed a preference for an unsymmetric structure in which the bridging hydrogen is localized on one of the two triarylmethane units. NMR spectroscopy showed a similar preference in solution. The bridging hydrogen fluctuates between the two chromophores in solution, and the energy barrier for the H shift is linearly correlated with the C center dot center dot center dot C(+) separation determined by X-ray. According to an extrapolation, the energy barrier should decrease when the C center dot center dot center dot C(+) separation is less than 2.7 angstrom, which suggests a new model for isolable pure organic species with a three-center two-electron bond.
  • Tatsuo Nehira, Yasuyo Yoshimoto, Kazuhisa Wada, Hidetoshi Kawai, Kenshu Fujiwara, Takanori Suzuki
    CHEMISTRY LETTERS 39 (3) 165 - 167 0366-7022 2010/03 [Not refereed][Not invited]
     
    Acridine-based novel fluorophores 1/2 with a helical dihydrodibenzoxepin/azepine skeleton exhibit halochromic response upon addition of Bronsted acid in CH2Cl2, thus giving UV-vis and fluorescence spectral changes. By using the optically resolved species [(M)-1/2], circular dichroism (CD) and fluorescence detected-CD (FDCD) signals were also changed drastically, thus demonstrating four-way-output response thanks to configurational stability of helicity and efficient exciton coupling.
  • Takanori Suzuki, Yasuyo Yoshimoto, Kazuhisa Wada, Takashi Takeda, Hidetoshi Kawai, Kenshu Fujiware
    HETEROCYCLES 80 (1) 149 - 155 0385-5414 2010/01 [Not refereed][Not invited]
     
    The title dication (1(2+)) was generated by oxidative bond cleavage of a 4,5-dihydoropyrene derivative (2) with two spiro(10-methylacridan) units. Despite the skewed deformation of the arylene spacer, two cationic chromophores in 1(2+) are forced to face in a proximity with a very short interatomic separation of 2.98(1) angstrom between carbenium centers (X-ray), which makes the LUMO level of 1 much lower than that of biphenyl-2,2'-diyl-type dication (3(2+)).
  • Takanori Suzuki, Kazuhisa Wada, Yusuke Ishigaki, Yasuyo Yoshimoto, Eisuke Ohta, Hidetoshi Kawai, Kenshu Fujiwara
    CHEMICAL COMMUNICATIONS 46 (23) 4100 - 4102 1359-7345 2010 [Refereed][Not invited]
     
    The helical configuration of dication dyes 2(2+) with a dihydro-dibenzoxepin unit remained unchanged even at high temperature, whereas the corresponding neutral electron donors 1 with a tetrahydrophenanthroxepin skeleton easily underwent racemization. Due to their electrochemical bistability, electron exchange between 1 and 2(2+) is prohibited. Thus, the above electrochromic pairs can serve as novel chiral-memory units where redox reactions trigger switching between an "erasable/writable''-state (1) and a "memorizing''-state (2(2+)).
  • Takanori Suzuki, Yasuyo Yoshimoto, Kazuhisa Wada, Takashi Takeda, Hidetoshi Kawai, Kenshu Fujiware
    HETEROCYCLES 80 (1) 149 - 155 0385-5414 2010/01 [Refereed][Not invited]
     
    The title dication (1(2+)) was generated by oxidative bond cleavage of a 4,5-dihydoropyrene derivative (2) with two spiro(10-methylacridan) units. Despite the skewed deformation of the arylene spacer, two cationic chromophores in 1(2+) are forced to face in a proximity with a very short interatomic separation of 2.98(1) angstrom between carbenium centers (X-ray), which makes the LUMO level of 1 much lower than that of biphenyl-2,2'-diyl-type dication (3(2+)).
  • Takanori Suzuki, Shintaro Mikuni, Yusuke Ishigaki, Hiroki Higuchi, Hidetoshi Kawai, Kenshu Fujiwara
    ChemInform 40 (44) 2009/11/03 [Refereed][Not invited]
  • Ryo Katoono, Hidetoshi Kawai, Kenshu Fujiwara, Takanori Suzuki
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 131 (46) 16896 - 16904 0002-7863 2009/11 [Refereed][Not invited]
     
    The secondary terephthalamide host la-H attached to four aryl blades was prepared from tetrabromide 2a by Suzuki-Miyaura coupling and undergoes a conformational change from a nonpropeller anti-form to a propeller-shaped syn-form upon complexation with ditopic guests such as p-xylylenediammonium derivatives (RR)/(SS)-3 (chirality generation). Through transmission of the point chiralities attached on the nitrogens in the chiral guests to the mobile helicity in 1a-H, the propeller-shaped host in the complex is biased to prefer a particular handedness (chirality biasing). While chiral guests with simple point chiralities such as (R,R)/(S,S)-3 exhibit only very weak CD activity, complexation with the dynamic propeller host 1 a-H results in much stronger chiroptical signals (chiroptical enhancement). The chirality generation-chirality biasing protocol was successfully applied to a neurotransmitter, (-)-phenylephrine 4, acting as a chiral ditopic guest. When the chiral auxiliaries are attached to the host as in (R,R)-1b-H, complexation with (S,S)-3 causes CD enhancement but not with (R,R)-3, due to chiral recognition.
  • Fujiwara Kenshu, Hirose Yuta, Tanaka Keita, Katagiri Yasushi, Sato Daisuke, Kawai Hidetoshi, Suzuki Takanori
    Symposium on the Chemistry of Natural Products, symposium papers 天然有機化合物討論会 (51) 347 - 352 2009/09/01 
    Armatol F (1), isolated from the red alga Chondria armata by Ciavatta et al., is an unusual triterpene compound characterized by the presence of an oxepane (A-ring), a 6/7/7 fusea-tricyclic ether (BCD-ring), six quaternary carbons, and two bromine atoms in its structure. It is also notable that 1 has a cis ring-fusion between C- and D-rings, which is a rare mode of ring-fusion in polycyclic ether natural procudts. The absolte configuraton of the A-ring and relative stereostructure of the BCD-ring have been elucidated by NMR and degradation studies, but the full absolute stereochemistry of 1 remains unclear. Although the bioactivity of 1 has not been reported, it is strongly expected that 1 would have some biological properties because of its striking structural similarity to bioactive thyrsiferol and the congeners. Since we have been interested in the structural complexity and the potential bioactivity of 1, we have been engaged in studies toward the total synthesis of 1 and the determination of its full absolute configuration. As a part of the studies, the model syntheses of the A and BCD-ring skeletons were performed. In the synthesis of A-ring model 16, a chirality transferring Ireland-Claisen rearrangement and a ring-closing olefin metathesis (RCM) were employed as key reactions for the construction of the oxepane skeleton, and the final bromination at C3 is now under investigation. BCD-ring model 18 was designed to be constructed from B-ring model 36 via a chirality transferring Ireland-Claisen rearrangement, an RCM, and Morimoto's intramolecular bromoetherification. At present, BC-ring 50, possessing a carbon chain corresponding to the D-ring, has been synthesized. The details of the model syntheses will be presented in the poster session.
  • Takashi Takeda, Hidetoshi Kawai, Rainer Herges, Eva Mucke, Yoshitaka Sawai, Kei Murakoshi, Kenshu Fujiwara, Takanori Suzuki
    TETRAHEDRON LETTERS 50 (26) 3693 - 3697 0040-4039 2009/07 [Refereed][Not invited]
     
    There is evidence that the crystalline-state thermochromic behavior of dispiropyracene acr-1 with an ultralong C-C bond [1.791(3) angstrom at 413 K, 1.771(3) angstrom at 93K] might be due to thermal generation of a bond-dissociated triplet diradical. The C(1)-C(2) bond lengths (d) in the newly prepared 1,1,2,2-tetraarylpyracenes 1a-e [1.717(4)-1.761(4) angstrom at 113/123/153 K] are also much larger than the standard value for C(sp(3))-C(sp(3)) (1.54 angstrom). The fact that there is no correlation between d and the radical-stabilizing parameter (sigma(center dot)) provides evidence that there is no contribution from a crystallographic artifact caused by contamination of the diradical in the crystal of 1 at room temperature or below. Further indication for the covalent nature of the ultralong C-C bond in tetraphenylpyracene 1c was attained by Raman spectroscopy, showing the far Fed-shifted C(1)-C(2) Stretching vibration (638 cm(-1)) and by the theoretical prediction of very large vertical singlet-triplet energy gap (58.3 kcal mol(-1) at the UB3LYP/6-31G* level). However, at elevated temperatures bond dissociation might occur forming a triplet diradical. (C) 2009 Elsevier Ltd. All rights reserved.
  • Takanori Suzuki, Youhei Miura, Ryuuichi Tamaki, Hidetoshi Kawai, Kenshu Fujiwara
    CHEMISTRY LETTERS 38 (7) 670 - 671 0366-7022 2009/07 [Refereed][Not invited]
     
    A series of X-ray analyses on the newly prepared title molecules have revealed that the one-dimensional rod-like structures are commonly present in the crystals of trans-dihydrophenan-throlinediols. The architecture is of interest from the viewpoint of supramolecular chirality because homochiral diol molecules with the same sense of helicity are connected in a head-to-tail fashion by a pair of N center dot center dot center dot H-O hydrogen bonds.
  • Takanori Suzuki, Shintaro Mikuni, Yusuke Ishigaki, Hiroki Higuchi, Hidetoshi Kawai, Kenshu Fujiwara
    CHEMISTRY LETTERS 38 (7) 748 - 749 0366-7022 2009/07 [Refereed][Not invited]
     
    Vivid color change from intense yellow to deep purple was observed upon electrochemcal oxidation of the title donor 1 to bis(Michler's hydrol blue)-type dication 1(2+). Since the interconversion was also accompanied by drastic geometric changes, configurational stability of the helical pi-arrangement is modified upon redox reactions.
  • Kata Mlinarić-Majerski, Helena Dodziuk, Tatyana N. Gribanova, Vladimir I. Minkin, Ruslan M. Minyaev, Takanori Suzuki, Takashi Takeda, Hidetoshi Kawai, Kenshu Fujiwara, Vladimir Y. Lee, Akira Sekiguchi
    Strained Hydrocarbons: Beyond the van-t Hoff and Le Bel Hypothesis 33 - 102 2009/05/08 [Refereed][Not invited]
  • Kenshu Fujiwara, Natsumi Kawamura, Hidetoshi Kawai, Takanori Suzuki
    TETRAHEDRON LETTERS Elsevier {BV} 50 (11) 1236 - 1239 0040-4039 2009/03 [Refereed][Not invited]
     
    The asymmetric synthesis of an acyclic anti-beta-alkoxy ether was achieved by the Ireland-Claisen rearrangement of Z-3-aikoxy-2-propenyl glycolate ester, prepared from Garner's aldehyde, a glycolic acid derivative, and ethynyl N,N-diisopropylcarbamate. The resulting acyclic ether was facilely converted to seven- and eight-membered cyclic ethers via processes involving ring-closing olefin metatheses. (C) 2009 Elsevier Ltd. All rights reserved.
  • Strained Hydrocarbon (Chap 2.5 Ultralong C-C Bond)
    Wiley-VCH 2009 [Not refereed][Not invited]
  • Takanori Suzuki, Yasuyo Yoshimoto, Takashi Takeda, Hidetoshi Kawai, Kenshu Fujiwara
    CHEMISTRY-A EUROPEAN JOURNAL 15 (9) 2210 - 2216 0947-6539 2009 [Refereed][Not invited]
     
    The isolation and low-temperature X-ray analyses of a series of intramolecular methylacridan-methylacridinium complexes have been achieved. The two chromophores are in close proximity due to an arylene spacer, such as a phenanthrene-4,5-diyl or biphenyl-2.2'-diyl unit. These bridged carbocations prefer the C-H localized structure both in solution and in the solid state. The bridging hydrogen atom undergoes a facile intramolecular hydride shift from one carbon atom to another in solution, and the energy barrier is linearly correlated with the intramolecular C center dot center dot center dot C(+) distance in the solid state geometry, as determined by single-crystal X-ray analyses. By extrapolation from the data, the delocalized three-center bond of [C-H-C](+) would be formed when the C center dot center dot center dot C(+) distance is less than 2.7 angstrom.
  • Takanori Suzuki, Yusuke Ishigaki, Tomohiro Iwai, Hidetoshi Kawai, Kenshu Fujiwara, Hiroshi Ikeda, Yusuke Kano, Kazuhiko Mizuno
    CHEMISTRY-A EUROPEAN JOURNAL 15 (37) 9434 - 9441 0947-6539 2009 [Refereed][Not invited]
     
    3,3,4,4-Tetaaryldihydro[5]helicenes (1) and 1,1'-binaphthyl-2,2'-diyl-bis(diarylcarbenium)s (2(2+)) can be reversibly interconverted upon electron transfer, which is accompanied by a vivid color change (electrochromism) as well as by the formation/cleavage of a C-C bond ("dynamic redox behavior"). Because only the neutral donor 1 exhibits strong fluorescence, electrochemical input can further modify the fluorescent properties of the pair. Due to the configurational stability of the helicity in 1 and axial chirality in 2(2+), the redox reaction of optically pure material proceeds stereospecifically, which induces a chiroptical change such as circular dichroism (CD) as an additional output. The CD spectra of dications 2(2+) exhibit solvent dependency (chiro-solvatochromism), which is accompanied by solvatochromic behavior based on the pi-pi interaction of the two cationic chromophores as well as coordinative interaction of the Lewis basic solvent to the Lewis acidic triarylcarbenium moieties. Thus, the present system is endowed with multi-input functionality for modifying multiple output signals.
  • Takeshi Umehara, Hidetoshi Kawai, Kenshu Fujiwara, Takanori Suzuki
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 130 (42) 13981 - 13988 0002-7863 2008/10 [Refereed][Not invited]
     
    The construction and switching properties of a novel class of molecular shuttles 1 with imine-bonding stations for macrocyclic diamine parts are reported. Studies on dithioacetalized [2]rotaxane 4 with two hydrogen-bonding stations and a masked imine-bonding station showed that protonation of a macrocycle increases the shuttling barrier due to hydrogen-bond formation between NH(3)(+) groups and the TEG-stations. Hydrolysis of the imine-bonds of the imine-bridged molecular shuttles 1b,c with TEG-stations could exclusively give the [2]rotaxane 2b,c center dot 2H(2+), With the macrocycle hydrogen-bonded with the TEG-station. In contrast, la without TEG-stations gave an equilibrated mixture of la, monoimine 3a center dot H(+), and 2a center dot 2H(2+) under similar acidic hydrolytic conditions. The equilibrium between 1b,c and 2b,c center dot 2H(2+) to control the position of the macrocycle could be successfully switched to either side by applying acidic hydrolytic or dehydrating conditions. Furthermore, the equilibrium was largely biased to [2]rotaxane 2b,c center dot 2H(2+) under acidic hydrolytic conditions and could be reversed in favor of bis-imine 1b,c just by heating. This is a successful example of a molecular shuttle exhibiting entropy-driven translational isomerism with remarkable positional discrimination. An examination of thermodynamic parameters showed that imine-bond hydrolyses and the formation of hydrogen bonds between the macrocycle and the station are thermodynamically matched processes, because both processes are enthalpically favored and accompanied by a loss of entropy. The combination of imine-bonding and hydrogen-bonding station in a rotaxane system is the key to realizing the clear entropy-driven positional switching of the macrocycle observed.
  • Fujiwara Kenshu, Katagiri Yasushi, Takemura Atsushi, Kawai Hidetoshi, Suzuki Takanori
    Symposium on the Chemistry of Natural Products, symposium papers 天然有機化合物討論会 (50) 783 - 787 2008/09/01 
    Prorocentin, isolated from dinoflagellate Prorocentrum lima by Lu et al., exhibits inhibitory activity against some human cancer cell lines [IC_<50>: 16.7μg/mL (DLD-1); 83.6μg/mL (RPMI7951)] and possesses an unique polyether structure, featured by a [6,6]-spirocyclic acetal fused with an oxane ring (BCD-ring), an epoxide (A-ring), a five membered ether (E-ring), and a side chain including a conjugated triene group. Although the absolute configuration of prorocentin has not yet been determined, its biological and structural features make it an attractive synthetic target. Thus, a project toward the total synthesis of prorocentin aiming at determination of the absolute stereochemistry has been commenced. The partial relative stereochemistry of prorocentin was proposed by Lu et al. from their intensive NMR experiments, and a possible stereostructure was also shown as 1 in their report. Therefore, we first elucidated a synthetic plan for prorocentin based on the stereochemistry of 1. At the final stage in the synthesis, assembly of 1 from dienyl boran 2 and iodoalkene 3 via a Suzuki-Miyaura coupling followed by removal of TBS group and the simultaneous epoxide formation is intended. Iodoalkene 3 would be derived from C8-C35 segment 4 in a few steps including Takai olefination and protective group manipulation. So far, we have synthesized segments 2 and 4, and examined the above transformation processes (4→3 and 3+2→1) in a model system. Details of the synthesis of 4, based on 6-endo Utimoto cyclization to create the B-ring and intramolecular double conjugate addition to produce the CD-ring, and the model experiments will be described in the poster session.
  • Takahiro Katagiri, Kenshu Fujiwara, Hidetoshi Kawai, Takanori Suzuki
    TETRAHEDRON LETTERS 49 (20) 3242 - 3247 0040-4039 2008/05 [Refereed][Not invited]
     
    To confirm the natural relative stereochemistry of the ABC-ring of goniodomin A (1), the corresponding three stereoisomeric compounds, (2R,5S,6S,7S,9S,11R,15S)-, (2R,5S,6S,7R,9R,11S,15R)-, and (2R,5S,6S,7R,9R,11R,15S)-isomers (2, 3, and 5, respectively), were stereoselectively synthesized using a Nozaki-Hiyama-Kishi reaction as a key step. It was also found that a (2R,5S,6S,7R,9R,11S,15S)-isomer (4), corresponding to the absolute configuration of I recently proposed by Sasaki, was not detected during the formation of 5 from a common ketodiol substrate under acid-catalyzed spiroacetalization conditions. This would be attributable to the absence of a macrocyclic framework. (c) 2008 Elsevier Ltd. All rights reserved.
  • Takanori Suzuki, Takashi Takeda, Hidetoshi Kawai, Kenshu Fujiwara
    PURE AND APPLIED CHEMISTRY 80 (3) 547 - 553 0033-4545 2008/03 [Refereed][Not invited]
     
    The longer C-C bond than the standard (1.54 angstrom) is so weakened that it is cleaved easily, as found in the parent hexaphenylethane (HPE). However, the compounds with an ultralong C-C bond (1.75 angstrom) can be isolated as stable solids when the bond-dissociated species does not undergo any reactions other than bond reformation. This is the central point in designing the highly strained HPEs, which were obtained by two-electron reduction of the corresponding dications. Steric repulsion of "front strain" is the major factor to expand the central C-C bond of HPEs. During the detailed examination of the ultralong C-C bond, the authors discovered the intriguing phenomenon of "expandability": the C-C bond length can be altered over a wide range by applying only a small amount of energy (1 kcal mol(-1)) supplied by crystal packing force. This observation indicates that the much longer C-C bond than the shortest nonbonded contact (1.80 angstrom) will be realized under the rational molecular design concept.
  • Daisuke Sato, Kenshu Fujiwara, Hidetoshi Kawai, Takanorl Suzuki
    TETRAHEDRON LETTERS 49 (9) 1514 - 1517 0040-4039 2008/02 [Not refereed][Not invited]
     
    A concise process for the stereoselective synthesis of chiral cis-3-alkoxy-2-carbomethoxy medium-ring oxacycles from (R)-3-(3-butenyl)-4-propynoyloxazolidin-2-one (1) was developed. The process includes five major steps: (i) hetero-Michael reaction between an alcohol and 1, (ii) stereoselective reduction of the resulting ketone, featuring stereochemical assistance of the neighboring oxazolidin-2-one group, (iii) esterification with an alkoxy acetic acid, (iv) chirality-transferring Ireland-Claisen rearrangement of the resulting 3-alkoxyallyl glycolate ester to provide a syn-2,3-dialkoxy carboxylate ester, and (v) relay ring-closing olefin metathesis to form a medium-ring ether along with the simultaneous removal of the oxazolidin-2-one moiety. (c) 2007 Elsevier Ltd. All rights reserved.
  • Takahiro Katagiri, Kenshu Fujiwara, Hidetoshi Kawai, Takanori Suzuki
    TETRAHEDRON LETTERS 49 (2) 233 - 237 0040-4039 2008/01 [Not refereed][Not invited]
     
    Goniodomin A (1) was first isolated from Alexandrium hiranoi as a stereochemically unidentified antifungal agent in 1987 by Murakami. In this study, two stereoisomeric series of non-macrocyclic and macrocyclic DE-ring model compounds of I were synthesized, and the natural relative stereochemistry of the DE-ring was predicted by NMR comparison of I with these model compounds. (c) 2007 Elsevier Ltd. All rights reserved.
  • Hidetoshi Kawai, Takashi Takeda, Kenshu Fujiwara, Makoto Wakeshima, Yukio Hinatsu, Takanori Suzuki
    CHEMISTRY-A EUROPEAN JOURNAL 14 (19) 5780 - 5793 0947-6539 2008 [Refereed][Not invited]
     
    Acenapthalene, pyracene, and dihydropyracylene attached to two units of spiroacridan are a novel class of hexaphenylethane (HPE) derivatives that have an ultralong C-sp3-C-sp3 bond (1.77-1.70 angstrom). These sterically challenged molecules were cleanly prepared by C-C bond formation through two-electron reduction from the less-hindered dications. These ultralong bonds were realized based on several molecular-design concepts including enhanced "front strain" through "multiclamping" by means of fusing or bridging aryl groups in the HPE molecule. The lengths of these ultralong bonds and their relation to the conformation (torsional angle) were also validated by means of theoretical calculations. Bond-fission experiments revealed that the bonds are more easily cleaved than standard covalent bonds to produce the corresponding dication upon oxidation with an increase in the length of the C-C bond.
  • Ryo Katoono, Hidetoshi Kawai, Kenshu Fujiwara, Takanori Suzuki
    CHEMICAL COMMUNICATIONS (40) 4906 - 4908 1359-7345 2008 [Refereed][Not invited]
     
    The syn-atropisomers of the title bis(tertiary amide)s were designed as six-bladed molecular propellers based on the ''directing effects'' of amide dipoles; the helicity of the propeller is biased to prefer one handedness upon the attachment of point chirality to the amide nitrogens to attain stronger circular-dichroism activity than for the non-propeller-shaped anti-isomers.
  • Takanorl Suzuki, Kenji Ohta, Tatsuo Nehira, Hiroki Higuchi, Eisuke Ohta, Hidetoshi Kawai, Kenshu Fujiwara
    TETRAHEDRON LETTERS 49 (5) 772 - 776 0040-4039 2008/01 [Refereed][Not invited]
     
    Upon the attachment of N-(R)-2-phenylethylamide moieties to the acridinium units of the title dication, intramolecular hydrogen bonds induce a diastereomeric preference in terms of axial chirality (70% de at -40 degrees C in CH(2)Cl(2)). Thus, external stimuli induce not only UV-vis and fluorescence spectra changes but also changes in the CD and fluorescence-detected CD (FDCD) spectra, realizing unprecedented four-way-output molecular response systems. (C) 2007 Elsevier Ltd. All rights reserved.
  • Eisuke Ohta, Tatsuo Nehira, Hidetoshi Kawai, Kenshu Fujiwara, Takanori Suzuki
    TETRAHEDRON LETTERS 49 (5) 777 - 781 0040-4039 2008/01 [Refereed][Not invited]
     
    Presence or absence of electron-accepting dye chromophores is the key function for ON/OFF switching of fluorescence from the dihydrodibenzo[c,g]phenanthrene skeleton in 2(2+)/3. The helical fluorophore in 2(2+) could be generated stereoselectively upon electrolysis of binaphthylic donor 1 through intramolecular chirality transmission. Huge chiroptical signals are easily detected by circular dichroism, (CD) and fluorescence-detected CD (FDCD) techniques to realize novel four-way-output response. (C) 2007 Elsevier Ltd. All rights reserved.
  • Akiyoshi Goto, Kenshu Fujiwara, Ayako Kawai, Hidetoshi Kawai, Takanori Suzuki
    ORGANIC LETTERS 9 (26) 5373 - 5376 1523-7060 2007/12 [Refereed][Not invited]
     
    The EF-ring segment of ciguatoxin 3C, a causative toxin of ciguatera fish poisoning, was synthesized in three major steps: 1,4-addition for the C20O-C27 bond connection, chirality transferring anti selective [2,3]-Wittig rearrangement for the construction of the anti-2-hydroxyalkyl ether part, and ring-closing olefin metathesis for the F-ring formation.
  • Goto Akiyoshi, Fujiwara Kenshu, Kawai Ayako, Kawai Hidetoshi, Suzuki Takanori
    Symposium on the Chemistry of Natural Products, symposium papers 天然有機化合物討論会 (49) 703 - 708 2007/08/24 
    Stereoselective construction of medium-sized cyclic ethers is one of the major problems in the synthesis of fused-polycyclic ether natural compounds, represented by ciguatoxin CTX3C. We have explored efficient solutions for the problem, and examined an application of a ring-closing olefin metathesis reaction (RCM), one of the most reliable methods for the formation of medium-ring structure, to cyclic ether synthesis. Although preparation of the precursors for RCM involved a serious difficulty in the stereoselective construction of their acyclic di-sec-alkyl ether part, we found its effective answers, namely, the [2,3]-Wittig rearrangement of a 3-alkoxyallyloxyacetic acid ester and the Ireland-Claisen rearrangement of a 3-alkoxyallyl glycolate. These rearrangement reactions stereoselectively produced 1,2-dialkoxy structures, which were easily transformed to medium cyclic ethers through a process including RCM. Details of the rearrangement reactions and the preparation method for the substrates using a hetero-conjugate addition reaction will be discussed at the presentation. The applications of these rearrangement reactions to the synthesis of the EF-ring of CTX3C will also be described.
  • Kenshu Fujiwara, Jota Naka, Takahiro Katagiri, Daisuke Sato, Hidetoshi Kawai, Takanori Suzuki
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 80 (6) 1173 - 1186 0009-2673 2007/06 [Not refereed][Not invited]
     
    The synthesis of the A- and F-rings of goniodomin A (1), which is a stereochemically unidentified antifungal agent isolated from dinoflagellate Alexandrium hiranoi, was performed to determine of the relative stereochemistry of these parts. The relative stereochemistry of the A- and F-rings was first deduced from Murakami's NMR data, and model compounds corresponding to these parts were then synthesized. The synthetic A-ring model, of which the structure was established by X-ray crystallographic analysis, showed good agreement with the natural A-ring on the basis of J and NOE behavior in the H-1 NMR spectroscopy. The chemical shifts in H-1 and C-13 NMR specta and J(32-OH-H33) of the synthetic F-ring model having a 33S,34R configuration also agreed with those of the F-ring of 1. Thus, the relative stereochemistry of the A- and F-rings of 1 was elucidated.
  • Kenshu Fujiwara, Yu-ichi Aki, Fuyuki Yamamoto, Mariko Kawamura, Masanori Kobayashi, Azusa Okano, Daisuke Awakura, Shunsuke Shiga, Akio Murai, Hidetoshi Kawai, Takanori Suzuki
    TETRAHEDRON LETTERS 48 (26) 4523 - 4527 0040-4039 2007/06 [Refereed][Not invited]
     
    In this study, we synthesized the C8-C20 and C21-C30 segments of the diarrhetic shellfish toxin pectenotoxin 2. The C8C20 segment was assembled from a phosphonate corresponding to the C8-C15 segment (prepared from L-malic acid in 19 steps) and an aldehyde corresponding to the C16-C20 segment (synthesized from 3-methyl-3-butenol in nine steps) by a twelve-step process including the Homer-Wadsworth-Emmons reaction, regio- and stereoselective reduction of the resulting enone, diastereoselective epoxidation, and 5-exo epoxide cleavage forming the C-ring. The C21-C30 segment was constructed in 13 steps from (S)-glycidol via a route involving E-ring formation by 5-exo epoxide cleavage and stereoselective methylation at C27 by the Evans method. (c) 2007 Elsevier Ltd. All rights reserved.
  • Takanori Suzuki, Tomohiro Iwai, Eisuke Ohta, Hidetoshi Kawai, Kenshu Fujiwara
    TETRAHEDRON LETTERS 48 (20) 3599 - 3603 0040-4039 2007/05 [Refereed][Not invited]
     
    Huge CD amplitude (A = +538) was attained by diastereomeric preference (50% de) for the title dication with two bis[4(R)-sec-butoxyphenyl]methylium units in benzene at 23 degrees C. Intramolecular pi-pi stacking is the origin for effective transmission of point chirality to axial chirality to attain the chiroptical enhancement of 400-times. Thanks to the strong CD signaling, chiroptical changes upon electrolysis could be readily detected, thus realizing a new class of clectrochiroptical response systems. Chiroptical properties could also be modified by solvent polarity. (C) 2007 Elsevier Ltd. All rights reserved.
  • Takanori Suzuki, Ryuuichi Tamaki, Eisuke Ohta, Takashi Takeda, Hidetoshi Kawai, Kenshu Fujiwara, Masako Kato
    TETRAHEDRON LETTERS 48 (22) 3823 - 3827 0040-4039 2007/05 [Refereed][Not invited]
     
    The spiro-acridan/acridinium-based dynamic redox pair (1/2(2+)) transduces the electrochemical input into UV-vis and fluorescence spectra, whereas the 2,2 '-bipyridine units in I works as a bidentate ligand for metal ions. X-ray structural analyses of this redox pair and the corresponding Zn-complexes [1-ZnI2/2(2+)-Zn2+(OTf-)(4)] demonstrate drastic structural changes upon electron-transfer, thus metal binding properties are modified by redox reactions. (C) 2007 Elsevier Ltd. All rights reserved.
  • Takanori Suzuki, Eisuke Ohta, Hidetoshi Kawai, Kenshu Fujiwara, Takanori Fukushima
    SYNLETT 2007 (6) 851 - 869 0936-5214 2007/04 [Refereed][Not invited]
     
    'Dynamic redox systems' is the name given to a certain class of compounds that can be reversibly converted into the corresponding charged species accompanied by C-C bond formation/cleavage upon electron transfer. This account details the two major motifs (hexaphenylethane derivatives and butane-1,4-diyl dications) that have been developed in the principal author's group.
  • Shinichi Iwashita, Takanori Suzuki
    ChemInform 38 (8) 2007/02 [Refereed][Not invited]
  • Takashi Takeda, Hidetoshi Kawai, Kenshu Fujiwara, Takanori Suzuki
    CHEMISTRY-A EUROPEAN JOURNAL 13 (28) 7915 - 7925 0947-6539 2007 [Refereed][Not invited]
     
    Isolation and low-temperature X-ray analyses of intramolecular triarylmethane-triarylmethylium complexes with a naphthalene-1,8-diyl-type skeleton have been achieved. These bridged cations prefer a C-H localized structure both in solution and in the solid state. The bridging hydrogen undergoes a facile intramolecular 1,5-hydride shift from one carbon to another in solution. The C-H delocalized geometry is suggested to be the transition-state structure of the degenerate rearrangement. Charge-transfer interaction from the triarylmethane to the triarylmethylium units is evident in the electronic spectra. This interaction stabilizes the present cations. Low reactivity toward Bronsted acids indicates that these species are not the reaction intermediates in the acid-assisted long-bond cleavage of 1, 1,2,2-tetraarylace-naphthene derivatives.
  • Takanori Suzuki, Shoko Tanaka, Hidetoshi Kawai, Kenshu Fujiwara
    CHEMISTRY-AN ASIAN JOURNAL 2 (1) 171 - 177 1861-4728 2007 [Refereed][Not invited]
     
    The title heterocyclic donors undergo reversible C-C bond formation/cleavage upon electron transfer (dynamic redox behavior). The helical sense in both neutral and cationic states is interconvertible by facile ring flipping. The pi-type asymmetric center on the azepine nitrogen atom induces a significant degree of diasteromeric preference, thus endowing strong CD activity based on exciton coupling. Chi-roptical properties could be modified not only by redox reactions but also by heat and protonation. The present redox pairs can serve as unprecedented three-way-input (e, H+, Delta) and two-way-Output (UV/Vis, CD) response systems.
  • Fujiwara Kenshu, Katagiri Takahiro, Naka Jota, Sato Daisuke, Kawai Hidetoshi, Suzuki Takanori
    Symposium on the Chemistry of Natural Products, symposium papers 天然有機化合物討論会 (48) 421 - 426 2006/09/15 
    Goniodomin A (GDA) was isolated from dinoflagellate Alexandrium hiranoi as an antifungal agent by Murakami in 1988. Later, its particular bioactivities, such as modulation of actomyosin ATPase activities, increasing the filamentous actin content of human astronoma cells, and antiangiogenic activity via inhibition of actin reorganization in endothelial cells, were found. Although its detailed NMR data and unique planer structure featured by a 32-membered macrolactone including 5- and 6-membered cyclic ethers (the A-, D- and E-ring parts), a spirocyclic acetal (the BC-ring part), and a 6-membered cyclic hemiacetal (the F-ring part) were reported, the stereochemistry of GDA was unclear. Since the complex structure and the remarkable bioactivities of GDA prompted our synthetic interest, we started the program of its total synthesis aiming at determination of absolute stereochemistry. In this presentation, synthesis and stereochemical-elucidation of the A-, DE-, and F-ring parts of GDA will be disclosed.
  • Katagiri Takahiro, Fujiwara Kenshu, Naka Jota, Kawai Hidetoshi, Suzuki Takanori
    International Symposium on the Chemistry of Natural Products 天然有機化合物討論会 2006 "P - 409" 2006/07/23
  • Fujiwara Kenshu, Okano Azusa, Aki Yu-ichi, Kawamura Mariko, Murai Akio, Kawai Hidetoshi, Suzuki Takanori
    International Symposium on the Chemistry of Natural Products 天然有機化合物討論会 2006 "P - 408" 2006/07/23
  • Ayumi Takizawa, Kenshu Fujiwara, Eriko Doi, Akio Murai, Hidetoshi Kawai, Takanori Suzuki
    TETRAHEDRON 62 (31) 7408 - 7435 0040-4020 2006/07 [Refereed][Not invited]
     
    Convergent synthesis of the common FGHI-ring part (54) of ciguatoxins was achieved via the following key steps: (i) the Nozaki-Hiyama-Kishi reaction connecting the F-ring part (6) with the I-ring part (7); (ii) regio- and stereoselective epoxidation; (iii) the 6-exo-epoxide opening reaction forming simultaneously the H-ring and the quaternary asymmetric center at C30; (iv) inversion of the C29 stereocenter by a two-step oxidation/reduction process, where the successful inversion depended on proper management of the steric environment of the substrate; and (v) final reductive cyclization constructing the G-ring. (c) 2006 Elsevier Ltd. All rights reserved.
  • Hidetoshi Kawai, Takeshi Umehara, Kenshu Fujiwara, Takashi Tsuji, Takanori Suzuki
    Angew. Chem. 118 (26) 4387 - 4392 2006/06 [Refereed][Not invited]
  • R Katoono, H Kawai, K Fujiwara, T Suzuki
    TETRAHEDRON LETTERS 47 (10) 1513 - 1518 0040-4039 2006/03 [Refereed][Not invited]
     
    Conformation of novel terephthalamide hosts 1 changes from anti to syn upon complexation with a bidentate guest (2 or 3). Chiral sense in the helical syn-form of the double-armed host molecules 1 is biased by the asymmetric centers on the chiral guest [(R,R)1(S,S)-2a], which can be detected by the drastic change in circular dichroism (CD) spectrum thanks to the exciton coupling of two chromophores ('arms') linked to the amide nitrogens. Asymmetric centers on the host molecule also exhibit preference for the twisting direction upon change in geometry from the anti- to syn-form. Thus, the achiral guests (2b or 3) can also be detected by modulation of CD spectrum upon complexation with the chiral host [(,R,R)-1a]. (c) 2006 Elsevier Ltd. All rights reserved.
  • Hidetoshi Kawai, Takeshi Umehara, Kenshu Fujiwara, Takashi Tsuji, Takanori Suzuki
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 45 (26) 4281 - 4286 1433-7851 2006 [Refereed][Not invited]
  • A Takizawa, K Fujiwara, E Doi, A Murai, H Kawai, T Suzuki
    TETRAHEDRON LETTERS 47 (5) 747 - 751 0040-4039 2006/01 [Refereed][Not invited]
     
    The common FGHI-ring part (2) of ciguatoxins has been synthesized from the F- and I-ring parts (6 and 5, respectively). The Nozaki-Hiyama-Kishi coupling of 6 with 5 followed by regio- and stereoselective epoxidation at C29 and C30 afforded an epoxide (4), which was transformed into a tricyclic compound (3) corresponding to the F-HI-ring part by 6-exo-epoxide opening and the subsequent inversion of the C29 stereocenter. Reductive cyclization of 3 forming the C31-O26 bond of the G-ring successfully produced 2. (c) 2005 Elsevier Ltd. All rights reserved.
  • T Suzuki, S Iwashita, T Yoshino, H Kawai, K Fujiwara, M Ohkita, T Tsuji, K Ono, M Takenaka
    TETRAHEDRON LETTERS 47 (4) 467 - 471 0040-4039 2006/01 [Refereed][Not invited]
     
    Severely deformed title quinodimethanes [1,2-bis(diarylmethylene)acenaphthenes] 1 have been designed and prepared as novel electrochromic materials, which can be reversibly interconverted with the deeply colored dicationic dyes 1(2+) with acenaphthylene-1,2-diyl skeleton. The X-ray analysis of 1 revealed that the inner two aryl groups are forced to overlap in proximity, which can account for the facile electrocyclization process to the isomer. By combination of reversible electrochemical transformation with irreversible isomerization process, the present system provides a prototype for novel molecular response systems equipped with the 'write-protect' option. (c) 2005 Elsevier Ltd. All rights reserved.
  • Shinichi Iwashita, Takanori Suzuki
    Yuki Gosei Kagaku Kyokaishi/Journal of Synthetic Organic Chemistry The Society of Synthetic Organic Chemistry, Japan 64 (9) 958 - 968 0037-9980 2006 [Refereed][Not invited]
     
    Introduction of four aryl groups on the highly reactive o-quinodimethane (o-QDM) skeleton suppresses the intermolecular reactivities. Thus, the unimolecular isomerization through electro-cyclization is the major decomposition path for title molecules. Rational design can prevent thermal isomerization of Ar4-o-QDMs. A new general procedure to generate Ar4-o-QDM has been established here that includes two-electron reduction of the corresponding dications, whose reaction conditions no longer promote electrocyclization of Ar4-o-QDM. Several derivatives of Ar4-o-QDM with the dihydrophenanthrene, dibenzoperylene, or acenaphthene skeleton were isolated for the first time, and the details on their highly strained molecular structures were investigated by low-temperature X-ray analyses. Based on the reversible interconversion between Ar4-o-QDMs and the precursor dications, they represent a new class of electrochromic redox pairs.
  • Daisuke Domon, Kenshu Fujiwara, Yuko Ohtaniuchi, Akihiro Takezawa, Sayaka Takeda, Hidekazu Kawasaki, Akio Murai, Hidethoshi Kawai, Takanori Suzuki
    ChemInform Wiley-Blackwell 37 (5) 2006/01 [Refereed][Not invited]
  • Kenshu Fujiwara, Saori Yoshimoto, Ayumi Takizawa, Shin-ichiro Souma, Hirofumi Mishima, Akio Murai, Hidetoshi Kawai, Takanori Suzuki
    ChemInform 37 (3) 2006/01 [Refereed][Not invited]
  • Daisuke Domon, Kenshu Fujiwara, Akio Murai, Hidethoshi Kawai, Takanori Suzuki
    ChemInform 37 (5) 2006/01 [Refereed][Not invited]
  • H Kawai, T Takeda, K Fujiwara, T Inabe, T Suzuki
    CRYSTAL GROWTH & DESIGN 5 (6) 2256 - 2260 1528-7483 2005/11 [Not refereed][Not invited]
     
    A large difference of 0.064(3) angstrom for a chemically equivalent C-sp(3) - C-sp(3) bond was observed among crystallographically independent molecules with different conformations (conformational isomorphs) of a hexaphenylethane derivative, dispiro[(10-methylacridan)-9,1'-pyracene-2',9"-(10-methylacridan)I (1): triclinic, P (1) over bar, a = 17.6990 angstrom, b = 18.1110 angstrom, c = 18.844(3) angstrom, alpha = 111.183(2)degrees, beta = 93.828(1)degrees, gamma = 102.130(2)degrees, V = 5438.5(14) angstrom(3), T = - 180 degrees C, Z = 8 (four independent molecules: A, N, B, and B'). While B and B' adopt the skewed conformation to reduce steric repulsion in 1, in other positions of the crystal, molecules A and X adopt the eclipsed conformation, which induces a much longer bond length [1.771(3) and 1.758(3) angstrom versus 1.712(2) and 1.707(2) angstrom].
  • D Domon, K Fujiwara, Y Ohtaniuchi, A Takezawa, S Takeda, H Kawasaki, A Murai, H Kawai, T Suzuki
    TETRAHEDRON LETTERS Elsevier {BV} 46 (48) 8279 - 8283 0040-4039 2005/11 [Refereed][Not invited]
     
    The C42-C52 part of ciguatoxin CTX3C (1) was synthesized from tri-O-acetyl D-glucal. The synthetic segment had a tetrahydropyran ring corresponding to the 'C49-reduced' L-ring of 1, designed to avoid side reactions due to acid-labile C49 acetal carbon during acidic reductive conditions planned in further synthesis toward 1. The vicinal dimethyl part at C47-C48 was constructed by a stepwise conjugate addition/methylation procedure. The C50-C52 unit was installed by Grignard addition of the C-3 unit followed by of the spirocyclic acetal. Stereoselective assembly of the C42-C44 part was achieved by Brown's asymmetric crotylboration. (c) 2005 Elsevier Ltd. All rights reserved.
  • D Domon, K Fujiwara, A Murai, H Kawai, T Suzuki
    TETRAHEDRON LETTERS 46 (48) 8285 - 8288 0040-4039 2005/11 [Refereed][Not invited]
     
    Convergent synthesis of the IJKLM-ring part (2) of ciguatoxin CTX3C has been achieved from the I-ring and the L-ring parts (4 and 5) in total eight steps in 27% overall yield. The carbanion derived from 4, stabilized by a dimethyldithioacetal S-oxide group, was readily reacted with aldehyde 5 to give an adduct, which was facilely transformed into the corresponding alpha,epsilon-dihydroxy ketone 3. The JK-ring formation from 3 under reductive conditions followed by oxidative M-ring cyclization efficiently led to the pentacyclic ether 2. Improved synthesis of 6, a synthetic intermediate for 4, was also established. (c) 2005 Elsevier Ltd. All rights reserved.
  • K Fujiwara, S Yoshimoto, A Takizawa, S Souma, H Mishima, A Murai, H Kawai, T Suzuki
    TETRAHEDRON LETTERS 46 (40) 6819 - 6822 0040-4039 2005/10 [Refereed][Not invited]
     
    Laurencin was efficiently synthesized from a C-glycoside derivative based on ring expansion of the oxane part of the starting compound into an eight-membered cyclic ether via a ring-cleavage/ring-closing olefin metathesis process, stereoselective introduction of a brotno group at C4, and convergent construction of the side-chain part using a lithiated enyne unit. (c) 2005 Elsevier Ltd. All rights reserved.
  • Takemura Atsushi, Fujiwara Kenshu, Murai Akio, Kawai Hidetoshi, Suzuki Takanori
    Symposium on the Chemistry of Natural Products, symposium papers 天然有機化合物討論会 (47) 493 - 498 2005/09/15 
    Since trans-fused polycyclic ethers are often seen in potently bioactive natural products, such as ciguatoxin (1), they attract significant synthetic attention. So far, many approaches have been studied for their efficient construction. Among these approaches, a ring-closing olefin metathesis reaction (RCM) has now become one of the most reliable methods for the construction of medium-sized cyclic ethers. However, preparation of the precursors for RCM involves a serious difficulty of the stereoselective construction of their acyclic branched ether part. Therefore, we explored an efficient branched ether formation reaction. Here, BF_3・OEt_2 promoted site-selective reduction of 4-alkoxy-2-trimethylsilyloxy-3-butenenitrile (5), prepared through a process including intermolecular hetero-Michael reaction of a 2-butynoate ester derivative (3) with an alcohol (2), with R_3SiH or Bu_3SnH is disclosed, along with the efficient application to the synthesis of fused medium-ring ethers involving the EF-ring segment of CTX1B (1).
  • H Kawai, T Takeda, K Fujiwara, T Suzuki
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 127 (35) 12172 - 12173 0002-7863 2005/09 [Refereed][Not invited]
     
    The intramolecular triarylmethane-methylium complex with an averaged C2v-symmetry was successfully generated by N-methylation of the acridine-acridan hybrid. Theoretical calculation and VT-NMR analyses in solution indicate the unsymmetric geometry for the three-center bond, which was finally confirmed crystallographically. Significant degree of CT interaction is induced through the very short C-H⋯C+ contact. Copyright © 2005 American Chemical Society.
  • A Takemura, K Fujiwara, K Shimawaki, A Murai, H Kawai, T Suzuki
    TETRAHEDRON 61 (31) 7392 - 7419 0040-4020 2005/08 [Refereed][Not invited]
     
    Aiming at a convergent total synthesis of ciguatoxin CTX1B, its EF-ring segment has been synthesized. During the synthesis, a novel method for the construction of branched ethers, based on regioselective reduction of gamma-alkoxy beta,gamma-unsaturated alpha-silyloxy nitriles with borontrifluoride etherate and trialkyl silane or tributyltin hydride, has been developed. Combination use of the method and ring-closing olefin metathesis successfully provided medium-sized cyclic ethers. Efficient site-selective reduction of vinyl epoxides into homoallyl alcohols has also been developed. (c) 2005 Elsevier Ltd. All rights reserved.
  • T Suzuki, K Ichioka, H Higuchi, H Kawai, K Fujiwara, M Ohkita, T Tsuji, Y Takahashi
    JOURNAL OF ORGANIC CHEMISTRY 70 (14) 5592 - 5598 0022-3263 2005/07 [Refereed][Not invited]
     
    A series of butterfly-shaped tetracyanoanthraquinodimethanes (TCNAQs) with a chiral amide auxiliary 1a-f were prepared from the corresponding anthraquinones. They are stronger acceptors than the unsubstituted derivative and undergo one-wave two-electron reduction. They form weak electron-donor-acceptor (EDA) complexes with the title pinacol 2. Upon charge-transfer excitation of these complexes, dihydro-TCNAQs 3 and 1,8-dianisoylnaphthalene 4 were efficiently formed, the latter of which is the product of a retropinacol reaction via 2(+.). Partial enantiodifferentiation of rac-2 was realized during the photoreactions with 2-[(R)-1-phenylethylcarbamoyl]-TCNAQ la in CD3CN. Thus, optically active (S,S)-(+)-pinacol 2 (12.3% ee at 54% conversion; 21.5% ee at 70% conversion) was recovered from the photolyzates. This reaction represents a new and rare example of the pseudokinetic resolution of tert-alcohol accompanied by C-C bond fission. Significant differences in the association constants for the diastereomeric EDA complexes are responsible for the observed enantiodifferentiation.
  • K Fujiwara, A Goto, D Sato, H Kawai, T Suzuki
    TETRAHEDRON LETTERS Elsevier {BV} 46 (20) 3465 - 3468 0040-4039 2005/05 [Refereed][Not invited]
     
    A simple stereoselective synthesis of cis- and trans-2,3-disubstituted medium-sized cyclic ethers has been developed based on geometry-selective synthesis of 3-alkoxy-2-propenyl glycolate esters, Ireland-Claisen rearrangement of the glycolate esters, and ring-closing olefin metathesis. (c) 2005 Elsevier Ltd. All rights reserved.
  • R Katoono, H Kawai, K Fujiwara, T Suzuki
    CHEMICAL COMMUNICATIONS (41) 5154 - 5156 1359-7345 2005 [Refereed][Not invited]
     
    Upon complexation of a rectangular-shaped achiral macro-cyclic host with chiral guests, twisting deformation occurs to induce exciton-type bisignated CD, whereas a chiral rectangular host undergoes a similar structural change only with the matching enantiomer of a chiral guest.
  • E Ohta, H Higuchi, H Kawai, K Fujiwara, T Suzuki
    ORGANIC & BIOMOLECULAR CHEMISTRY 3 (16) 3024 - 3031 1477-0520 2005 [Not refereed][Not invited]
     
    Incorporation in the dihydro[ 5] helicene framework prevents deprotonation of the title dications by steric factors, thus allowing their isolation as deeply colored stable salts. Based on the reversible interconversion with the electron-donating binaphthylic diolefins, they constitute a new class of electrochromic systems, in which C-C bond making/breaking is accompanied by two-electron transfer. Optically pure (R)-binaphthylic donors are interconvertible with the 1,4-dications with the R,R-configuration. The very large molar ellipticity makes it possible for them to be used as electrochiroptical response systems, by which the electrochemical input is transduced into two spectral outputs, i.e. UV-Vis and circular dichroism. Structurally related push-pull-type bis(quinonemethide)s also exhibit a similar multi-output electrochemical response.
  • Fujiwara, K., Kobayashi, M., Yamamoto, F., Aki, Y.-I., Kawamura, M., Awakura, D., Amano, S., Okano, A., Murai, A., Kawai, H., Suzuki, T.
    Tetrahedron Letters 46 (30) 5067 - 5069 0040-4039 2005 [Refereed][Not invited]
  • H Kawai, R Katoono, K Fujiwara, T Tsuji, T Suzuki
    CHEMISTRY-A EUROPEAN JOURNAL 11 (3) 815 - 824 0947-6539 2005/01 [Refereed][Not invited]
     
    The molecular recognition of catecholamines by hydrindacene-based receptors 1 and 2, as well as the durene-based receptor 3, and the guest-induced conformational changes are reported. These receptors selectively bind adrenaline and dopamine salts through the guests' ammonium group and 3-hydroxyl group on the aromatic ring. In the case of adrenaline, an additional hydrogen bond with a benzylic hydroxyl group is formed. In 2% CD3CN/CDCl3, the association constants are of the order of 10(4)m(-1), which is much larger than with guests without the 3-hydroxyl groups (10(3)m(-1)). The two amide groups of receptor 1 can rotate freely around the C-aromatic-C-amide bond, whereas the tert-amide in 2 changes between two stable conformations at a slow enough rate to allow detection by H-1 NMR spectroscopy. In the absence of a guest molecule, the syn-conformer is less stable than the anti-conformer. On complex formation with adrenaline, the syn-conformer becomes dominant due to an intramolecular dipole-reversal effect in addition to multipoint hydrogen bonding.
  • H Kawai, T Takeda, K Fujiwara, T Suzuki
    TETRAHEDRON LETTERS 45 (45) 8289 - 8293 0040-4039 2004/11 [Refereed][Not invited]
     
    The extremely long C-C bond [1.696(3) Angstrom] in the colorless dispiroacenaphthene-type hexaphenylethane is cleaved readily upon electrochemical transformation into the orange colored naphthalene-1,8-diylbis(acridinium), in which the two cationic units are forced to overlap in a face-to-face manner exhibiting the shortest C+...C+ interatomic contact of 2.927(7) Angstrom among the values ever reported. (C) 2004 Elsevier Ltd. All rights reserved.
  • T Suzuki, S Tanaka, H Higuchi, H Kawai, K Fujiwara
    TETRAHEDRON LETTERS 45 (46) 8563 - 8567 0040-4039 2004/11 [Refereed][Not invited]
     
    The long C-C bonds (1.614(2)-1.630(2) Angstrom) in newly prepared title donors 2-6 are cleaved upon two-electron oxidation to afford the bond-dissociated dicationic dyes 2(2+)-6(2+), whose electron affinities are stronger than the corresponding biphenyl-2,2'-diyl dications 1(2+) due to the spatial proximity of two xanthenylium units. Not only UV-vis but also fluorescence spectra changed drastically upon electrolysis since only colorless neutral donors are fluorescent. (C) 2004 Elsevier Ltd. All rights reserved.
  • R Katoono, H Kawai, K Fujiwara, T Suzuki
    TETRAHEDRON LETTERS 45 (46) 8455 - 8459 0040-4039 2004/11 [Refereed][Not invited]
     
    2,9-Diaza-1,10-dioxo[10]paracyclophanes were prepared in short steps from the terephthaloyl chlorides via the corresponding 4,6-diyne derivatives, and the amide groups on the bridge endow the skeleton with the guest-binding properties as demonstrated by complexation with adrenaline by hydrogen bonds. The chiral auxiliaries on the bridge induce diastereomeric preference in terms of the planar chirality for the octadehydro derivative with a rigid diyne unit in crystal. (C) 2004 Elsevier Ltd. All rights reserved.
  • Fujiwara Kenshu, Goto Akiyoshi, Sato Daisuke, Ohtaniuchi Yuko, Tanaka Hideki, Murai Akio, Kawai Hidetoshi, Suzuki Takanori
    Symposium on the Chemistry of Natural Products, symposium papers 天然有機化合物討論会 (46) 587 - 591 2004/10/01 
    CTX3C (1) was isolated as congener of ciguatoxin (CTX) from cultured dinoflagellate Gambierdiscus toxicus by the Yasumoto group. Its unique ladder-shaped trans-fused polycyclic structure possessing 13 ether rings is a synthetic challenge and has attracted the attention of synthetic chemists. During the course of our studies directed toward CTXs, we achieved the syntheses of their individual medium ring parts and developed a convergent method for the construction of their X/6/7/X ring systems. Here, we disclose alternative successful convergent construction of the ABCDE ring system 2 of 1 from the AB- and E-ring segments (5 and 6, respectively). Previously, effective convergent method applying coupling reaction of an acyl anion equivalent with an aldehyde followed by reductive cyclization reactions was developed for the synthesis of trans-fused tetracyclic ethers in this laboratory. Therefore, dimethyldithioacetal mono-S-oxide 5 and aldehyde 6 were selected as AB-and E-ring segments, respectively, in our synthetic plan for 1. The segment 5 was prepared in 16 steps from 7 in 12% total yield. The aldehyde 6 was synthesized in 20 steps from 16 in 38% total yield. Coupling reaction of deprotonated 5 with 6 followed by simultaneous removal of TBS and dithioacetal groups afforded ketodiol 4, which was subjected to reductive cyclization and the subsequent oxidation and deprotection to give 3. Hydroxy ketone 3 was efficiently cyclized into pentacyclic ether 35 under the similar reductive conditions as the cyclization of 4. Treatment of 35 with an excess amount of LDBB induced not only benzyl group detachment but also conversion of the PBBO group to a BnO group to produce 2 successfully. Thus, the ABCDE-ring part 2 was efficiently constructed in 10 steps from 6 in 11% total yield.
  • A Takemura, K Fujiwara, A Murai, H Kawai, T Suzuki
    TETRAHEDRON LETTERS 45 (41) 7567 - 7571 0040-4039 2004/10 [Refereed][Not invited]
     
    A synthetic method for a branched ether system was developed. The method was based on Lewis-acid-promoted gamma-position selective reduction of a gamma-alkoxy beta,gamma-unsaturated alpha-silyloxy nitrile, prepared through a process including intermolecular hetero-Michael reaction of a 2-butynoate ester derivative with an alcohol. The method was efficiently applied to the synthesis of fused medium-ring ethers involving the EF-ring segment (2) of ciguatoxin (1). (C) 2004 Elsevier Ltd. All rights reserved.
  • Kenshu Fujiwara, Daisuke Sato, Manabu Watanabe, Hiroshi Morishita, Akio Murai, Hidetoshi Kawai, Takanori Suzuki
    ChemInform 35 (43) 2004/10 [Refereed][Not invited]
  • K Fujiwara, A Goto, D Sato, Y Ohtaniuchi, H Tanaka, A Murai, H Kawai, T Suzuki
    TETRAHEDRON LETTERS 45 (38) 7011 - 7014 0040-4039 2004/09 [Refereed][Not invited]
     
    Convergent synthesis of the ABCDE-ring part (2) of ciguatoxin CTX3C (1) has been achieved. A carbanion stabilized by a dimethyldithioacetal S-oxide group in the AB-ring part (4) readily reacted with an aldehyde group in the E-ring part (5). The resulting adduct was facilely converted to the corresponding beta,gamma-unsaturated alpha,epsilon-dihydroxy ketone (3). The subsequent reductive hydroxy-ketone-cyclization reactions constructed the CD-ring part efficiently. Thus, the ABCDE-ring part (2) was concisely synthesized in 10 steps in 11% overall yield from the AB-ring and the E-ring parts (4 and 5). (C) 2004 Elsevier Ltd. All rights reserved.
  • M Ohkita, C Adachi, M Kawano, T Suzuki
    HETEROCYCLES 63 (7) 1537 - 1540 0385-5414 2004/07 [Refereed][Not invited]
     
    Two new members of snowflake-shaped carbon-rich molecules possessing nitrogen-heterocycles as functional end groups, hexakis(4-pyridylethynyl)benzene (1) and hexakis(5-pyrimidylethynyl)benzene (2), have been prepared by six-fold Sonogashira cross-coupling reaction of hexabromobenzene with 4-ethynylpyridine and 5-ethynylpyrimidine, respectively.
  • K Fujiwara, D Sato, M Watanabe, H Morishita, A Murai, H Kawai, T Suzuki
    TETRAHEDRON LETTERS 45 (27) 5243 - 5246 0040-4039 2004/06 [Refereed][Not invited]
     
    Concise construction of the trans-fused 7/7/6/6 tetracyclic ether part of hemibrevetoxin B (1) was achieved by a convergent strategy based on coupling reaction of an acyl anion equivalent, reductive cyclization of an alpha,epsilon-dihydroxyketone, and introduction of a methyl group at the central ring junction by the Nicolaou method. The resultant tetracyclic ether was transformed into the known intermediate, which was already converted to 1 by the Yamamoto group, thereby completing the formal total synthesis of 1. (C) 2004 Elsevier Ltd. All rights reserved.
  • H Kawai, T Nagasu, T Takeda, K Fujiwara, T Tsuji, M Ohkita, JI Nishida, T Suzuki
    TETRAHEDRON LETTERS 45 (23) 4553 - 4558 0040-4039 2004/05 [Refereed][Not invited]
     
    (8-Diarylmethyl-1-naphthyl)bis(4-dimethylaminophenyl)methyliums (aryl=C6H5, 4-IC6H4, and 4-MeOC6H4) were generated by hydride shift from (4-dimethylaminophenyl)methyl group to the diarylmethylium unit at peri-positions of naphthalene. Successful isolation and low-temperature X-ray analysis indicated that they are novel C-H bridged carbocations, which prefer the localized structure with a short contact of C-H... C+ rather than the delocalized one with a three-centered-two-electron bond of (C... H...C)+. (C) 2004 Elsevier Ltd. All rights reserved.
  • H Higuchi, K Ichioka, H Kawai, K Fujiwara, M Ohkita, T Tsuji, T Suzuki
    TETRAHEDRON LETTERS 45 (15) 3027 - 3030 0040-4039 2004/04 [Refereed][Not invited]
     
    The newly prepared tetracyanoanthraquinodimethane (TCNAQ) derivatives 1a,b with a chiral auxiliary are good electron acceptors and exhibit weak circular dichroism (CD) based on the absorption of TCNAQ. The twin-type electron acceptor 1c with two TCNAQ units shows larger ellipticity by exciton coupling. UV-vis, CD, and fluorescence spectra were changed drastically upon electrochemical reduction of 1c, which demonstrates the unprecedented three-way-output response system. (C) 2004 Elsevier Ltd. All rights reserved.
  • H Kawai, R Katoono, K Nishimura, S Matsuda, K Fujiwara, T Tsuji, T Suzuki
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY American Chemical Society ({ACS}) 126 (16) 5034 - 5035 0002-7863 2004/04 [Refereed][Not invited]
  • T Suzuki, S Miyanari, H Kawai, K Fujiwara, T Fukushima, T Miyashi, Y Yamashita
    TETRAHEDRON 60 (9) 1997 - 2003 0040-4020 2004/02 [Refereed][Not invited]
     
    The X-ray analyses of the title electron acceptors (1) revealed their butterfly-shaped deformed geometry, which is not affected by the pyridyl group attached at 2-position of the pyrazino-TCNNQ skeleton. Small differences between the first and second reduction potentials (ca. 0.1 V) in pyrazino-TCNNQs show that their anion radicals (1(-.)) are prone to disproportionate into the neutral (1) and dianionic (1(2-)) species. The thermodynamically unstable anion radical species based on the pyrazino-TCNNQ skeleton could be isolated as inner salts upon electrochemical reduction of the derivatives having an N-methylpyridinium moiety at 2-position (2(+)). The zwitterionic open-shell species (2) constitute a novel class of radicals that exhibit semiconducting behavior as a single component thanks to the high electrochemical amphotericity. (C) 2004 Elsevier Ltd. All rights reserved.
  • T Suzuki, M Saito, H Kawai, K Fujiwara, T Tsuji
    TETRAHEDRON LETTERS Elsevier {BV} 45 (2) 329 - 333 0040-4039 2004/01 [Refereed][Not invited]
     
    The title electron donors were prepared by the double condensation reactions of 2,2',3,3'-tetraamino-4,4'-bis(l-pyrrolidinyl)biphenyl with 1,2-diketones. They adopt twisted conformations in crystal, yet the reversible two-stage one-electron oxidation process suggests the planar geometries for the oxidized species. Depending on the nature of substituents on the pyrazine ring, this pi-system can be endowed additional features such as chiroptical properties or metal coordination ability. (C) 2003 Elsevier Ltd. All rights reserved.
  • S Iwashita, E Ohta, H Higuchi, H Kawai, K Fujiwara, K Ono, M Takanaka, T Suzuki
    CHEMICAL COMMUNICATIONS 10 (18) 2076 - 2077 1359-7345 2004 [Refereed][Not invited]
     
    Oxidative cyclization of 2,2'-bis(dianisylethenyl) biphenyl yielded the dicationic salt of phenanthrene-9,10-diylbis( dianisylmethylium), which in turn afforded the severely congested title molecule as the first stable tetraaryl-o-quinodimethane derivative upon reduction.
  • M Ohkita, K Sano, K Ono, K Saito, T Suzuki, T Tsuji
    ORGANIC & BIOMOLECULAR CHEMISTRY 2 (17) 2421 - 2425 1477-0520 2004 [Refereed][Not invited]
     
    Kinetic stabilization of the o-quinoidal 3,4-benzotropone system was investigated. The parent 3,4-benzotropone 1 undergoes rapid [pi8+pi10] dimerization in fluid solution even at -78degreesC while triptycene-fused derivative 5 having a tert-butyl group at the C(6) position of the tropone moiety was found to be stable indefinitely under similar conditions. The relative importance of the triptycene moiety and the tert-butyl group in 5 for the kinetic stabilization was evaluated.
  • M Ohkita, K Sano, T Suzuki, T Tsuji, T Sato, H Niino
    ORGANIC & BIOMOLECULAR CHEMISTRY 2 (7) 1044 - 1050 1477-0520 2004 [Refereed][Not invited]
     
    pi-Extended o-quinoidal tropone derivatives, naphtho[2,3-c] tropone (3) and anthro[2,3-c] tropone (4), have been investigated theoretically as well as experimentally. The geometrical optimization of 3, 4, and related compounds at the B3LYP level employing 6-31G* basis set as well as the GIAO calculations at the RHF level employing the 6-31+G* basis set have been performed to evaluate the contributions of the polarized resonance forms to these molecules. The GIAO calculated NICS(1) values indicate that the aromaticities of the tropone rings of o-quinoidal 3 and 4 are significantly increased as compared with that of parent tropone (1) at the expense of the fused benzenoid rings, consistent with the significant electronic polarization of these molecules in the ground state. On the other hand, the fusion of a benzene or naphthalene ring to the 2,3- or 4,5-position of tropone leads to diminution of aromaticity in the resulting tropone moiety. Experimentally, irradiation of 6,7-(2', 3'-naphtho) bicyclo[3.2.0] hepta-3,6-dien-2-one (10) in a rigid glass at - 196 degreesC leads to the formation of 3, which exhibits a characteristic UV-Vis absorption extending to 700 nm and undergoes rapid [pi12 + pi14] dimerization upon thawing the glass. In contrast, 6,7-(2', 3'-anthro) bicyclo[3.2.0] hepta-3,6-dien-2-one (11) showed no sign of isomerization to 4 under the same reaction conditions.
  • S Iwashita, E Ohta, H Higuchi, H Kawai, K Fujiwara, K Ono, M Takanaka, T Suzuki
    CHEMICAL COMMUNICATIONS 36 (18) 2076 - 2077 1359-7345 2004 [Refereed][Not invited]
     
    Oxidative cyclization of 2,2'-bis(dianisylethenyl) biphenyl yielded the dicationic salt of phenanthrene-9,10-diylbis( dianisylmethylium), which in turn afforded the severely congested title molecule as the first stable tetraaryl-o-quinodimethane derivative upon reduction.
  • J Ishihara, Y Ikuma, S Hatakeyama, T Suzuki, A Murai
    TETRAHEDRON 59 (51) 10287 - 10294 0040-4020 2003/12 [Refereed][Not invited]
     
    Azadirachtin is a C-seco, limonoid, derived from the neem tree. Previously, we reported the synthesis of the right and left segments of azadirachtin, in addition to the coupling reaction of the modeled ester utilizing Claisen rearrangement. Herein we report the transformation of the modeled rearrangement product into a tricyclic dihydrofuran, which would be expected to have bioactivity against insects. (C) 2003 Elsevier Ltd. All rights reserved.
  • T Suzuki, Y Tsubata, Y Obana, T Fukushima, T Miyashi, M Saito, H Kawai, K Fujiwara, K Akiyama
    TETRAHEDRON LETTERS 44 (43) 7881 - 7884 0040-4039 2003/10 [Not refereed][Not invited]
     
    The title electron donors 1 as well as their conjugate bases 2(-) undergo reversible two-stage one-electron oxidation. ESR analysis indicated the important contribution of zwitterionic structure for radicals 2(.). Bis(zwitterionic) but not quinoid structure was suggested for p-4, generated from the twin-type dianionic donor P-4(2-) with a p-phenylene spacer. (C) 2003 Elsevier Ltd. All rights reserved.
  • Fujiwara Kenshu, Watanabe Manabu, Sato Daisuke, Morishita Hiroshi, Murai Akio, Suzuki Takanori
    Symposium on the Chemistry of Natural Products, symposium papers 天然有機化合物討論会 (45) 561 - 566 2003/09/01 
    Hemibrevetoxin B (1), isolated from the red tide dinoflagellate Gymnodinium breve by Shimizu group, is a trans-fused tetracyclic ether. To date, many research groups reported total synthesis of 1. Notably, most of them adopted a linear strategy, though a convergent strategy would have comparable efficiency with linear one even in the synthesis of such small polyether. In this context, we planned to synthesize 1 through a convergent strategy that would allow the large-scale preparation. During our studies, Holton group reported first convergent total synthesis of 1 very recently, where the ABCD ring part was constructed in 15 steps after connection of the cyclic A-ring part with the acyclic C12-C21 (BCD-ring) segment. Here, we disclose alternate successful convergent construction of the ABCD ring system 2 of 1 from the A- and D-ring segments (5 and 6, respectively). Previously, we developed an effective convergent method for the synthesis of trans-fused tetracyclic ethers adopting coupling reaction of an acyl anion equivalent with an aldehyde followed by reductive cyclization reactions. Therefore, dimethyldithioacetal mono-S-oxide 5 and aldehyde 6 were selected as A- and D-ring segments, respectively, in our synthetic plan for 1. The segment 5 was prepared in 14 steps from 2,4,6-tri-O-acetyl-D-glucal 7 in 14% total yield. The aldehyde 6 was synthesized in 19 steps from γ-butyrolactone 14 in 11% total yield. Coupling reaction of deprotonated 5 with 6 followed by simultaneous removal of TBS and dithioacetal groups afforded ketodiol 4, which was subjected to reductive cyclization, oxidation, and deprotection to give 3. Formation of cyclic S,O-acetal 34 from 3 followed by oxidation with mCPBA and in situ treatment with AlMe_3 produced tetracyclic 2. Thus, the ABCD-ring part 2 was successfully constructed in 7 steps from 6 in 12% total yield.
  • T Suzuki, A Migita, H Higuchi, H Kawai, K Fujiwara, T Tsuji
    TETRAHEDRON LETTERS Elsevier {BV} 44 (36) 6837 - 6840 0040-4039 2003/09 [Refereed][Not invited]
     
    The newly prepared title donor 1 has a very long C-C bond [1.635(2) Angstrom], which was readily cleaved upon oxidation to. give dication 2(2+) containing two 10-methylacridinium chromophores. Colorless donor 1 (E-ox +0.18 V) is non-fluorescent whereas orange dication 2(2+) (E-red -0.27 V) emits strong green fluorescence, so that, this pair can be considered as a novel redox switch for fluorescence with high electrochemical bistability. (C) 2003 Elsevier Ltd. All rights reserved.
  • T Suzuki, A Migita, H Higuchi, H Kawai, K Fujiwara, T Tsuji
    TETRAHEDRON LETTERS Elsevier {BV} 44 (36) 6837 - 6840 0040-4039 2003/09 [Refereed][Not invited]
     
    The newly prepared title donor 1 has a very long C-C bond [1.635(2) Angstrom], which was readily cleaved upon oxidation to. give dication 2(2+) containing two 10-methylacridinium chromophores. Colorless donor 1 (E-ox +0.18 V) is non-fluorescent whereas orange dication 2(2+) (E-red -0.27 V) emits strong green fluorescence, so that, this pair can be considered as a novel redox switch for fluorescence with high electrochemical bistability. (C) 2003 Elsevier Ltd. All rights reserved.
  • H Higuchi, E Ohta, H Kawai, K Fujiwara, T Tsuji, T Suzuki
    JOURNAL OF ORGANIC CHEMISTRY American Chemical Society ({ACS}) 68 (17) 6605 - 6610 0022-3263 2003/08 [Refereed][Not invited]
     
    2,2'-[2,2-Bis(4-dimethylaminophenyl)ethenyl]biphenyl (1) is a strong electron donor that undergoes oxidative C-C bond formation to give a stable dication rac-2(2+), the 9,10-dihydrophenanthrene derivative substituted with two bis(4-dimethylaminophenyl)methylium chromophores. This dication salt regenerates the starting diolefin 1 by reductive C-C bond breaking, thus realizing a new electrochronic system with high electrochemical bistability and a vivid change in color from yellow to deep blue. Similarly, the binaphthylic diolefin rac-3 and the helicene-type dication rac-4(2+) are interconvertible upon two-electron transfer. Both the UV-vis and CD spectra changed drastically upon electrochemical transformation between optically pure 3 and 4(2+), which represents a new electrochiroptical system.
  • T Suzuki, T Nagasu, H Kawai, K Fujiwara, T Tsuji
    TETRAHEDRON LETTERS Elsevier {BV} 44 (32) 6095 - 6098 0040-4039 2003/08 [Refereed][Not invited]
     
    Oxidation of 1,2,2-tris(4-dimethylaminophenyl)- and 2,2-bis(4-dimethylaminophenyl)-1-phenylacenaphthen-1-ols 1a,b with I-2 induced the C-1-C-2 bond fission to give 8-aroylnaphthalen-1-yl-bis(4-dimethylaminophenyl)carbenium derivatives 2a,b(+), the intramolecular Lewis acid-base pairs. Treatment of 1 with HBF4 did not induce the expected C-OH bond heterolysis but caused fission of CO-H and C-1-C-2 bonds to give exactly the same carbenium 2(+). (C) 2003 Elsevier Ltd. All rights reserved.
  • T Suzuki, T Nagasu, H Kawai, K Fujiwara, T Tsuji
    TETRAHEDRON LETTERS Elsevier {BV} 44 (32) 6095 - 6098 0040-4039 2003/08 [Refereed][Not invited]
     
    Oxidation of 1,2,2-tris(4-dimethylaminophenyl)- and 2,2-bis(4-dimethylaminophenyl)-1-phenylacenaphthen-1-ols 1a,b with I-2 induced the C-1-C-2 bond fission to give 8-aroylnaphthalen-1-yl-bis(4-dimethylaminophenyl)carbenium derivatives 2a,b(+), the intramolecular Lewis acid-base pairs. Treatment of 1 with HBF4 did not induce the expected C-OH bond heterolysis but caused fission of CO-H and C-1-C-2 bonds to give exactly the same carbenium 2(+). (C) 2003 Elsevier Ltd. All rights reserved.
  • Takanori Suzuki, Hiroki Higuchi, Takashi Tsuji, Jun-ichi Nishida, Yoshiro Yamashita, Tsutomu Miyashi
    ChemInform 34 (23) 2003/06/10 [Refereed][Not invited]
  • T Suzuki, J Nishida, E Hirota, M Ohkita, T Tsuji
    SYNTHETIC METALS 133 357 - 358 0379-6779 2003/03 [Not refereed][Not invited]
     
    The electrochiroptical systems are a new type of transducers that transform the electrochemical input into the UV-Vis as well as chiroptical outputs. Several previous examples are briefly reviewed. The new concept to realize the drastic chiroptical response is proposed. (C) 2002 Elsevier Science B.V. All rights reserved.
  • Suzuki, T., Higuchi, H., Tsuji, T., Nishida, J.-I., Yamashita, Y., Miyashi, T.
    Springer Series in Chemical Physics 70 3 - 24 0172-6218 2003/01/22 [Refereed][Not invited]
     
    "Dynamic redox systems" is the name given to a certain class of compounds that can be reversibly converted into the corresponding charged species upon electron transfer (ET) but accompanied by drastic structural changes and/or covalent bond making/breaking. Although transformation between the neutral and charged species proceeds quantitatively in most cases, their electrochemical processes are irreversible owing to the chemical reactions followed by ET. This situation endows the "dynamic redox pairs" with very high bistability, which is a prerequisite in order to construct the molecular response systems. This chapter first describes the principle of the "dynamic redox properties", and then classifies the compounds into several categories from the viewpoint of the type of structrual changes. After the properties of representative molecules in each category have been described in detail, their expected use as unimolecular devices is commented on in the final part of the chapter.
  • Suzuki, T.; Higuchi, H.; Tsuji, T.; Nishida, J.; Yamashita, Y.; Miyashi, T.: Dynamic Redox Systems: Toward the Realization of Unimolecular Memory, 3-24 (Nakamura, T.; Matsumoto, T.; Tada, H.; Sugiura, K. "Chemistry of Nanomolecular Systems", Springer, ・・・
    2003 [Not refereed][Not invited]
     
    Suzuki, T.; Higuchi, H.; Tsuji, T.; Nishida, J.; Yamashita, Y.; Miyashi, T.: Dynamic Redox Systems: Toward the Realization of Unimolecular Memory, 3-24 (Nakamura, T.; Matsumoto, T.; Tada, H.; Sugiura, K. "Chemistry of Nanomolecular Systems", Springer, Berlin) (2003)
  • T Tsuji, M Okuyama, M Ohkita, H Kawai, T Suzuki
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 125 (4) 951 - 961 0002-7863 2003/01 [Refereed][Not invited]
     
    Kinetic stabilization of the [4]paracyclophane skeleton by the introduction of substituents, which serve to sterically hinder reactions at the reactive bridgehead sites, and properties of the resultant [4]paracyclophanes are investigated in this study. Modification of the property of [4]paracyclophane by functionalization is also intended. [4]Paracyclophanes are designed to be derived from the corresponding Dewar benzene isomers via their photochemical aromatization, and the requisite 1,4-bridged Dewar benzenes bearing sterically demanding functional groups are prepared. Irradiation of these precursors under matrix isolation at 77 K leads to the formation of [4)paracyclophanes, which exhibit characteristic electronic absorption spectra. The half-lives of the generated species vary widely from less than 1 min at -90 degreesC to 0.5 h at -20 degreesC, depending on the type of substituents and the pattern of substitution. One of the derivatives, 24, is stable enough and its content in the irradiated mixture is high enough to permit the measurement of the H-1 NMR spectrum. The recorded spectrum, which is reproduced very well by theoretical calculations using the GIAO method at the hybrid HF-DFT (B3LYP/6-31+G*) level, suggests the sustenance of rather strong diatropicity in its severely bent benzene moiety. Calculations on the bent benzene whose geometry is constrained to that calculated for 24 support that aromaticity is retained to a significant extent as compared to that of planar benzene, as judged by the magnetic criteria of aromaticity, that is, diamagnetic susceptibility exaltation and nucleus-in dependent chemical shift. The reason for the retention of aromaticity despite the severe bending of the benzene ring is discussed. Cyclophane 24 is so strained that it exceeds the corresponding Dewar benzene precursor in energy and thermally reverts to the latter with a half-life of 15 +/- 5 min at -20 degreesC (DeltaG(double dagger) = 18.3 +/- 0.3 kcal mol(-1)).
  • Takanori Suzuki, Rie Yamamoto, Hiroki Higuchi, Erika Hirota, Masakazu Ohkita, Takashi Tsuji
    J. Chem. Soc., Perkin Trans. 2 (11) 1937 - 1942 1470-1820 2002/10/03 [Refereed][Not invited]
     
    Upon two-electron oxidation of the title electron donor 1a, the elongated central C9-C10 bond [1.656(5) Å (X-ray)] is cleaved to give the biphenyl-2,2′-diyl bis(xanthenylium) dye 2a+2, which regenerates the colorless dispiro compound 1a by two-electron reduction. The presence of isosbestic points in the UV-Vis spectra during the electrochemical oxidation of 1a to 2a+2 indicates the negligible steady-state concentration of the intermediate cation radical. Interconversion between optically resolved 1a and 2a+2 is accompanied by drastic changes in the CD spectra again with several isosbestic points, and racemization of (P)- and (M)-1a and (S)- and (R)-2a+2 does not occur at ambient conditions. This redox pair represents a new motif for the multi-output response system, where the electrochemical input is transduced into two independent spectral outputs.
  • Jun-ichi Nishida, Takanori Suzuki, Takashi Tsuji
    ChemInform 33 (26) no - no 2002/07/02 [Refereed][Not invited]
  • T Suzuki, R Yamamoto, H Higuchi, E Hirota, M Ohkita, T Tsuji
    JOURNAL OF THE CHEMICAL SOCIETY-PERKIN TRANSACTIONS 2 (11) 1937 - 1942 1472-779X 2002 [Refereed][Not invited]
     
    Upon two- electron oxidation of the title electron donor 1a, the elongated central C-9-C-10 bond [1.656(5) Angstrom(X-ray)] is cleaved to give the biphenyl-2,2'-diyl bis( xanthenylium) dye 2a(2+), which regenerates the colorless dispiro compound 1a by two- electron reduction. The presence of isosbestic points in the UV- Vis spectra during the electrochemical oxidation of 1a to 2a(2+) indicates the negligible steady- state concentration of the intermediate cation radical. Interconversion between optically resolved 1a and 2a(2+) is accompanied by drastic changes in the CD spectra again with several isosbestic points, and racemization of (P)- and (M)- 1a and (S)- and (R)- 2a(2+) does not occur at ambient conditions. This redox pair represents a new motif for the multi- output response system, where the electrochemical input is transduced into two independent spectral outputs.
  • J Nishida, T Suzuki, T Tsuji
    JOURNAL OF SYNTHETIC ORGANIC CHEMISTRY JAPAN 60 (1) 40 - 51 0037-9980 2002/01 [Refereed][Not invited]
     
    Redox reactions of a series of dicationic dyes (2(2+), 4(2+), 6(2+)) having two triarylmethylenium chromophores were studied, which are interconvertible with colorless hexaarylethane derivatives (1, 3) or 9-membered cyclic peroxides (5), respectively, upon two-electron transfer. They constitute a new class of electrochromic systems endowed with high electrochemical bistability since the reversible bond making/breaking causes the drastic changes in the geometrical and electronic structures of the redox pairs. Bond dissociated cation radical 2(+.) is the stable intermediate for the interconversion between I and 2(2+), and the unprecedented tricolor chromic systems showing a hysteretic color change were constructed based on 1, 2(+.), and 2(2+). Drastic change in CD spectrum was observed during the interconversion between chiral helicenes 3 and binaplithylic dications 4(2+), which is the successful demonstration of electrochiroptical response. Peroxides 5 were readily obtained by two-electron reduction of dications 6(2+) under air. Since 6(2+) were regenerated by the "oxidative deoxygenation" reaction of 5, these pairs can serve as a electrochemically controlled oxygen-storage system.
  • Jun-Ichi Nishida, Takanori Suzuki, Takashi Tsuji
    Yuki Gosei Kagaku Kyokaishi/Journal of Synthetic Organic Chemistry The Society of Synthetic Organic Chemistry, Japan 60 (1) 40 - 51 0037-9980 2002 [Refereed][Not invited]
     
    Redox reactions of a series of dicationic dyes (22+, 42+, 62+) having two triarylmethylenium chromophores were studied, which are interconvertible with colorless hexaarylethane derivatives (1, 3) or 9-membered cyclic peroxides (5), respectively, upon two-electron transfer. They constitute a new class of electrochromic systems endowed with high electrochemical bistability since the reversible bond making/breaking causes the drastic changes in the geometrical and electronic structures of the redox pairs. Bond dissociated cation radical 2+. is the stable intermediate for the interconversion between 1 and 22+, and the unprecedented tricolor chromic systems showing a hysteretic color change were constructed based on 1, 2+., and 22+. Drastic change in CD spectrum was observed during the interconversion between chiral helicenes 3 and binaphthylic dications 42+, which is the successful demonstration of electrochiroptical response. Peroxides 5 were readily obtained by two-electron reduction of dications 62+ under air. Since 62+ were regenerated by the "oxidative deoxygenation" reaction of 5, these pairs can serve as a electrochemically controlled oxygen-storage system.
  • M Ohkita, M Kawano, T Suzuki, T Tsuji
    CHEMICAL COMMUNICATIONS (24) 3054 - 3055 1359-7345 2002 [Refereed][Not invited]
     
    The crystallization of 2,4,6-triethynyl-1,3,5-triazine (2) leads to a pi-stacked layered structure of a C(sp)-H...N hydrogen-bonded unique hexagonal network structure, which may be regarded as a supramolecular analogue of a hitherto unknown graphyne network: in-plane intermolecular interactions are short and linear H...N contacts (2.31 and 2.34 Angstrom) and the interlayer separation is 3.23 Angstrom.
  • T Suzuki, T Tsuji, T Okubo, A Okada, Y Obana, T Fukushima, T Miyashi, Y Yamashita
    JOURNAL OF ORGANIC CHEMISTRY 66 (26) 8954 - 8960 0022-3263 2001/12 [Refereed][Not invited]
     
    4,7-Bis(dialkylamino)benzo[c] [1,2,5]chalcogenadiazoles are a novel class of organic dyes that undergo reversible two-stage one-electron oxidation as well as one-electron reduction. They exhibit absorption maxima in the long-wavelength region, which are assigned as intramolecular charge transfer bands from the phenylenediamine moiety to the electron-accepting heterocycle. Their redox properties as well as molecular and crystal structures are affected by the alkyl substituents on the amino nitrogen and/or by the chalcogen atom (O, S, Se) in the heterocycle.
  • M Ohkita, K Sano, T Suzuki, T Tsuji
    TETRAHEDRON LETTERS 42 (41) 7295 - 7297 0040-4039 2001/10 [Refereed][Not invited]
     
    Irradiation of 6.7-(2',3'-aphtho)bicyclo[3.2.0]hepta-3,6-dien-2-one (10) in a rigid glass at -196 degreesC leads to the formation of hitherto unknown naphtho[2,3-c]tropone (3). which exhibits a characteristic UV-vis absorption extending to 700 nm and undergoes rapid [pi 12+pi 14] dimerization upon thawing the glass. NICS(1) values calculated for a series of benzo- and naphtho-fused tropones suggest that aromatic character of the tropone ring in 3 is significantly increased relative to the parent system. (C) 2001 Elsevier Science Ltd. All rights reserved.
  • M Ohkita, T Suzuki, K Nakatani, T Tsuji
    CHEMISTRY LETTERS (10) 988 - 989 0366-7022 2001/10 [Refereed][Not invited]
     
    The crystallization of 2,6-diethynylpyridine 1 leads to C(sp(2))-H . . .N hydrogen bonded head-to-tail tapes which are held together by C(sp)-H . . . pi hydrogen bridges to form 2D polar sheets; further assembly through pi-pi stacking interaction results in 3D polar crystals which show intense powder SHG response, 5-fold stronger than crystalline urea.
  • Jun-ichi Nishida, Takanori Suzuki, Masakazu Ohkita, Takashi Tsuji
    Angew. Chem. Wiley-Blackwell 113 (17) 3351 - 3354 2001/09/03 [Refereed][Not invited]
  • T Suzuki, K Ono, H Kawai, T Tsuji
    JOURNAL OF THE CHEMICAL SOCIETY-PERKIN TRANSACTIONS 2 Royal Society of Chemistry ({RSC}) (9) 1798 - 1801 1472-779X 2001/09 [Refereed][Not invited]
     
    Push-pull type substitution at C-sp 3-C-sp 3 in the title. compounds does not have special electronic effects on the bond length, and the observed expansion can be best accounted for by steric interaction between substituents.
  • T Suzuki, H Higuchi, M Ohkita, T Tsuji
    CHEMICAL COMMUNICATIONS (17) 1574 - 1575 1359-7345 2001/09 [Refereed][Not invited]
     
    Upon oxidative dimerization of pale yellow Ar2C-CHPh 1 (Ar = 4-Me2NC6H4), deep blue 1,4-dication 2(2+) was obtained as a stable salt, which was transformed into I by reductive C-C bond fission; deprotonation of 22+ gave intense yellow diene 3, which was interconvertible with violet dication 4(2+) by two-electron transfer, thus exhibiting two distinct modes of electrochromism before and after proton transfer.
  • M Ohkita, T Suzuki, K Nakatani, T Tsuji
    CHEMICAL COMMUNICATIONS Royal Society of Chemistry ({RSC}) (16) 1454 - 1455 1359-7345 2001/08 [Refereed][Not invited]
     
    The crystallization of 4-ethynylpyridine (1) and 4-(4-ethynylphenyl)ethynylpyridine (2) leads to C(sp)-H . . .N hydrogen bonded straight tapes that further assemble into polar crystals, in the case of 2, and show intense powder SHG response, 8 times more efficient than crystalline urea.
  • Takanori Suzuki, Tsuyoshi Yoshino, Masakazu Ohkita, Takashi Tsuji
    ChemInform Wiley-Blackwell 32 (7) no - no 2001/02 [Refereed][Not invited]
  • T Suzuki, M Yamada, M Ohkita, T Tsuji
    HETEROCYCLES 54 (1) 387 - 394 0385-5414 2001/01 [Not refereed][Not invited]
     
    One electron oxidation of 4-(2-tetrathiafulvalenyl)phenyl substituted dicyanomethylides (1-) gave black solids of the title radicals (1(.)). They exhibit quite high electrochemical amphotericity, which may be responsible for their good electrical conductivities (sigma = ca. 10(-7) S cm(-1)) as a single component. Isomeric radicals (2(.)) with a m-phenylene spacer could not be obtained under the similar conditions probably due to insufficient delocalization of the unpaired electron.
  • T Suzuki, S Miyanari, Y Tsubata, T Fukushima, T Miyashi, Y Yamashita, K Imaeda, T Ishida, T Nogami
    JOURNAL OF ORGANIC CHEMISTRY American Chemical Society ({ACS}) 66 (1) 216 - 224 0022-3263 2001/01 [Refereed][Not invited]
     
    N,N'-Dicyanonaphthoquinodiimines fused with a pyrazine ring 1 were prepared from the corresponding quinones 4. The new accepters 1 have a planar pi -system and undergo reversible two-stage 1e-reduction. Quaternization of the pyridyl substituent in 1d-f gave pyridinium derivatives 2d(+), 2e(+), and R-3(+), respectively, which are stronger accepters that undergo three-stage le-reduction. Upon electrochemical. reduction of these cations, novel radicals 2d(.) 2e(.), and R-3(.) were generated and isolated as stable solids. The molecular geometries determined by X-ray analysis indicated that these radicals adopt a zwitterionic structure, in which the unpaired electron is located on the quinodiimine unit but not on the pyridyl group. These novel radicals undergo facile and reversible 1e-oxidation as well as two-stage le-reduction. The observed amphotericity endows the radicals with electrical conductivities (10(-5) to 10(-9) S cm(-1)), and these thus represent a new motif for single-component organic semiconductors.
  • J Nishida, T Suzuki, M Ohkita, T Tsuji
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 40 (17) 3251 - + 1433-7851 2001 [Refereed][Not invited]
  • T Suzuki, M Yamada, M Ohkita, T Tsuji
    HETEROCYCLES 54 (1) 387 - 394 0385-5414 2001/01 [Refereed][Not invited]
     
    One electron oxidation of 4-(2-tetrathiafulvalenyl)phenyl substituted dicyanomethylides (1-) gave black solids of the title radicals (1(.)). They exhibit quite high electrochemical amphotericity, which may be responsible for their good electrical conductivities (sigma = ca. 10(-7) S cm(-1)) as a single component. Isomeric radicals (2(.)) with a m-phenylene spacer could not be obtained under the similar conditions probably due to insufficient delocalization of the unpaired electron.
  • H Kawai, T Suzuki, M Ohkita, T Tsuji
    CHEMISTRY-A EUROPEAN JOURNAL 6 (22) 4177 - 4187 0947-6539 2000/11 [Refereed][Not invited]
     
    Intentionally designed kinetic stabilization of the [1.1]paracyclophane skeleton has been achieved by multiple substitution of the aromatic rings with trimethylsilylmethyl and N,N-dimethylcarbamoyl groups, which serve to shield the proximate bridgehead carbon atoms sterically from access by other reagents. The bis(Dewar benzene) precursor (1a) has been prepared in essentially the same manner as previous derivatives-starting from the photocycloaddition of 1,4-bis(trimethylsilyl)-2-butyne to octahydroindacene-1,5-dione-except for a few critical modifications described in the text. Substituted [1.1]paracyclophane (2a), photochemically generated from the precursor, is indefinitely stable at 50 degreesC and suffers decomposition only by 8% after 2 h at 100 degreesC in degassed n-decane, demonstrating its greatly improved kinetic stability compared to previous [1.1]paracyclophanes. Since 2a undergoes efficient photochemical transformation into the transannular addition product 3a, irradiation of 1a tends to produce a mixture of products consisting mainly of 3a. Compound 3a, however, reverts thermally to 2a in a process of half life 40 min at 55 degreesC; the activation parameters for this process are DeltaH(+) = 21.1 +/- 0.8 kcal mol(-1) and DeltaS(+) = - 10.5 +/- 2.6 cal K-1 mol(-1). Thus, on heating 3a in benzene and cooling the resultant solution, 2a is obtained as orange-red crystals. X-ray crystallographic analysis of 2a reveals benzene rings bent to the highest degree ever reported for a paracyclophane, with their face-to-face arrangement in unusually close proximity. The shortest nonbonding interatomic distance is 2.376 Angstrom less than the sum of the van der Waals radii by more than 1.0 Angstrom. The generation of related substituted [1.1]paracyclophanes and their kinetic stabilities are also reported.
  • H Kawai, T Suzuki, M Ohkita, T Tsuji
    CHEMISTRY-A EUROPEAN JOURNAL 6 (22) 4177 - 4187 0947-6539 2000/11 [Refereed][Not invited]
     
    Intentionally designed kinetic stabilization of the [1.1]paracyclophane skeleton has been achieved by multiple substitution of the aromatic rings with trimethylsilylmethyl and N,N-dimethylcarbamoyl groups, which serve to shield the proximate bridgehead carbon atoms sterically from access by other reagents. The bis(Dewar benzene) precursor (1a) has been prepared in essentially the same manner as previous derivatives-starting from the photocycloaddition of 1,4-bis(trimethylsilyl)-2-butyne to octahydroindacene-1,5-dione-except for a few critical modifications described in the text. Substituted [1.1]paracyclophane (2a), photochemically generated from the precursor, is indefinitely stable at 50 degreesC and suffers decomposition only by 8% after 2 h at 100 degreesC in degassed n-decane, demonstrating its greatly improved kinetic stability compared to previous [1.1]paracyclophanes. Since 2a undergoes efficient photochemical transformation into the transannular addition product 3a, irradiation of 1a tends to produce a mixture of products consisting mainly of 3a. Compound 3a, however, reverts thermally to 2a in a process of half life 40 min at 55 degreesC; the activation parameters for this process are DeltaH(+) = 21.1 +/- 0.8 kcal mol(-1) and DeltaS(+) = - 10.5 +/- 2.6 cal K-1 mol(-1). Thus, on heating 3a in benzene and cooling the resultant solution, 2a is obtained as orange-red crystals. X-ray crystallographic analysis of 2a reveals benzene rings bent to the highest degree ever reported for a paracyclophane, with their face-to-face arrangement in unusually close proximity. The shortest nonbonding interatomic distance is 2.376 Angstrom less than the sum of the van der Waals radii by more than 1.0 Angstrom. The generation of related substituted [1.1]paracyclophanes and their kinetic stabilities are also reported.
  • H Kawai, T Suzuki, M Ohkita, T Tsuji
    CHEMISTRY-A EUROPEAN JOURNAL 6 (22) 4177 - 4187 0947-6539 2000/11 [Refereed][Not invited]
     
    Intentionally designed kinetic stabilization of the [1.1]paracyclophane skeleton has been achieved by multiple substitution of the aromatic rings with trimethylsilylmethyl and N,N-dimethylcarbamoyl groups, which serve to shield the proximate bridgehead carbon atoms sterically from access by other reagents. The bis(Dewar benzene) precursor (1a) has been prepared in essentially the same manner as previous derivatives-starting from the photocycloaddition of 1,4-bis(trimethylsilyl)-2-butyne to octahydroindacene-1,5-dione-except for a few critical modifications described in the text. Substituted [1.1]paracyclophane (2a), photochemically generated from the precursor, is indefinitely stable at 50 degreesC and suffers decomposition only by 8% after 2 h at 100 degreesC in degassed n-decane, demonstrating its greatly improved kinetic stability compared to previous [1.1]paracyclophanes. Since 2a undergoes efficient photochemical transformation into the transannular addition product 3a, irradiation of 1a tends to produce a mixture of products consisting mainly of 3a. Compound 3a, however, reverts thermally to 2a in a process of half life 40 min at 55 degreesC; the activation parameters for this process are DeltaH(+) = 21.1 +/- 0.8 kcal mol(-1) and DeltaS(+) = - 10.5 +/- 2.6 cal K-1 mol(-1). Thus, on heating 3a in benzene and cooling the resultant solution, 2a is obtained as orange-red crystals. X-ray crystallographic analysis of 2a reveals benzene rings bent to the highest degree ever reported for a paracyclophane, with their face-to-face arrangement in unusually close proximity. The shortest nonbonding interatomic distance is 2.376 Angstrom less than the sum of the van der Waals radii by more than 1.0 Angstrom. The generation of related substituted [1.1]paracyclophanes and their kinetic stabilities are also reported.
  • Masakazu Ohkita, Kieko Sano, Sotoyuki Dohba, Yuko Fujita, Takanori Suzuki, Takashi Tsuji
    ChemInform 31 (41) no - no 2000/10/10 [Refereed][Not invited]
  • T Suzuki, T Yoshino, J Nishida, M Ohkita, T Tsuji
    JOURNAL OF ORGANIC CHEMISTRY 65 (18) 5514 - 5521 0022-3263 2000/09 [Refereed][Not invited]
     
    A series of 1,3,5-trithianes 1-3 having diarylmethylene units were designed as novel electron donors giving highly colored cationic species upon oxidation. They were prepared along with the dithiane and dithiazine derivatives 4-6 by the reactions of lithiated heterocycles with diaryl ketones followed by dehydration. Voltammetric analyses indicate that a large structural change and/or transannular bonding are induced during their electrochemical oxidation. Mono(diarylmethylene) derivative 1a exhibits electrochromism with vivid change in color from faintly yellow to deep blue with concomitant rotation around the exocyclic bond. Both of the strongly colored salts obtained upon oxidation of 2,4-bis- and 2,4,6-tris(diarylmethylene)-1,3,5-trithianes (2aa and 3) consist of the dications with a 1,2,4-trithiane ring, suggesting the easy skeletal rearrangement of the transannular dications with a trithiabicylo[3. 1.0]hexane ring. Upon reduction of these salts were obtained bright yellow 12 and 13, respectively, with high electron-donating properties due to the tetraarylbutadiene-type conjugation, thus giving another class of electrochromic compounds.
  • T Suzuki, K Ono, J Nishida, H Takahashi, T Tsuji
    JOURNAL OF ORGANIC CHEMISTRY 65 (16) 4944 - 4948 0022-3263 2000/08 [Refereed][Not invited]
     
    9,10-Dihydrophenanthrene derivatives 1-3 with electron-donating and/or -accepting groups at their 9,10-positions were prepared, and their precise molecular structures were determined by X-ray analyses at 203 K. The long C-9-C-10 bond [1.646(4) Angstrom] in the hexaarylethane-type compound 1 with four electron-donating groups is mainly caused by steric interaction. Push-pull type substitution does not induce the elongation of the central bond in the present system; the corresponding distance in 9,9-bis(4-dimethylaminophenyl)-10,10-dicyano derivative 2 [1.599(4) Angstrom] is intermediate between those of 1 and the tetracyano compound 3 [1.587(2) Angstrom].
  • M Ohkita, K Ando, T Suzuki, T Tsuji
    JOURNAL OF ORGANIC CHEMISTRY 65 (14) 4385 - 4390 0022-3263 2000/07 [Refereed][Not invited]
     
    A general synthetic approach to strained p-phenylene-based acetylenic macrocycles is described. A key feature in this approach is exploitation of Dewar benzene as an angular p-phenylene synthon. Thus, 1,4-acetal-bridged 2,5-dichloro(Dewar benzene) 5, prepared in four steps from dimethyl acetylenedicarboxylate and 1,2-dichloroethylene, is applied as such a building block in the syntheses of strained macrocycles 13 and anti-20. For the synthesis of 13, m-phenylene units are used as spacers and modified Eglington-Glaser coupling is applied for the macrocyclization step. For the synthesis of anti-20, on the other hand, o-phenylene units are used as spacers and Sonogashira coupling is applied for the macrocyclization step. Macrocycles 13 and anti-20 are characterized crystallographically? and their strained nature is reflected mainly in the deviation of the acetylene units from linearity; the C=C-C angles range from 168.7(3)degrees to 179.9(3)degrees in 13 and from 168.0(5)degrees to 171.4(4)degrees in anti-20, Macrocycle 13 shows unique conformational property, namely, the p-phenylene units arranged in parallel in the rectangular framework rotate freely about the long axes, as evidenced by the H-1 NMR studies. Macrocycle anti-20 exhibits a Stokes shift of 179 nm, which is exceptionally large for phenylacetylene macrocycles, presumably owing to the characteristic stacking structure.
  • Masakazu Ohkita, Takanori Suzuki, Takashi Tsuji
    ChemInform 31 (2) no - no 2000/01/11 [Refereed][Not invited]
  • Takanori Suzuki, Takashi Tsuji, Takanori Fukushima, Setsuko Miyanari, Tsutomu Miyashi, Yasuyuki Sakata, Tsutomu Kouda, Hiroki Kamiyama
    ChemInform Wiley-Blackwell 31 (2) no - no 2000/01/11 [Refereed][Not invited]
  • T Suzuki, J Nishida, M Ohkita, T Tsuji
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 39 (10) 1804 - + 1433-7851 2000 [Refereed][Not invited]
  • T Suzuki, T Yoshino, M Ohkita, T Tsuji
    JOURNAL OF THE CHEMICAL SOCIETY-PERKIN TRANSACTIONS 1 Royal Society of Chemistry ({RSC}) (20) 3417 - 3420 1470-4358 2000 [Refereed][Not invited]
     
    The title pi-extended TTF derivatives 1 and 2 were prepared from the corresponding diketones by Wittig-Horner reactions. Donor 1 with a naphthalene-1,8-diyl skeleton adopts a butterfly-shaped geometry; its oxidation caused transannular C-C bonding to give the dicationic cyclopropane derivative 4(2+), from which 1 was regenerated upon 2e-reduction. The 2,3-diyl isomer 2 possesses, on the other hand, an almost planar pi-system and underwent 2-stage 1e-oxidation, thus allowing the isolation of both 2(.+) and 2(2+) as stable salts.
  • M Ohkita, K Ando, K Yamamoto, T Suzuki, T Tsuji
    CHEMICAL COMMUNICATIONS (1) 83 - 84 1359-7345 2000 [Refereed][Not invited]
     
    A novel Dewar benzene approach to the construction of oligophenylene macrocycles has been developed by introducing Dewar benzene 1 as a building block and applied to the synthesis of a molecular rectangle 8, whose structure was characterized crystallographically.
  • Takanori Suzuki, Tsuyoshi Yoshino, Jun-ichi Nishida, Masakazu Ohkita, Takashi Tsuji
    ChemInform 31 (51) no - no 2000 [Refereed][Not invited]
  • M Ohkita, K Sano, S Dohba, Y Fujita, T Suzuki, T Tsuji
    JOURNAL OF THE CHEMICAL SOCIETY-PERKIN TRANSACTIONS 1 Royal Society of Chemistry ({RSC}) (12) 1971 - 1975 1470-4358 2000 [Refereed][Not invited]
     
    A new bisdiene molecule 1, the 1,4-acetal-bridged derivative of the hitherto unknown 2,3,5,6-tetramethylenebicyclo[2.2.0]hexane, is synthesized in four steps from dimethyl acetylenedicarboxylate and (E)-1,4-dichlorobut-2-ene. Reaction of 1 with dimethyl acetylenedicarboxylate or benzyne leads to the formation of the Dewar benzene derivatives 6 and 7, respectively, through two successive Diels-Alder additions of the dienophiles to 1. Dehydrogenation of the adducts 6 and 7 affords the corresponding 9,10-Dewar anthracene derivative 10 and 6,13-Dewar pentacene derivative 11, respectively. Compound 11 is characterized crystallographically. Reactions of 1,4-benzoquinone and N-phenylmaleimide with 1 are also reported.
  • T Suzuki, J Nishida, M Ohkita, T Tsuji
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 39 (10) 1804 - + 1433-7851 2000 [Refereed][Not invited]
     
    The hitherto unknown 1,2,6-tricyclononane derivatives 1 (X = O, S) were readily obtained upon the electrochemical 2 electron reduction of 22+ in air (see scheme). Oxidative deoxygenation of the colorless peroxides 1 regenerates the orange 22+ ions.
  • M Ohkita, T Suzuki, T Tsuji
    CHEMICAL COMMUNICATIONS Royal Society of Chemistry ({RSC}) (19) 1999 - 2000 1359-7345 1999/10 [Refereed][Not invited]
     
    The 1,4-acetal-bridged derivative of hitherto unknown 2,3,5,6-tetramethylidenebicyclo[2.2.0]hexane, which produces the Dewar benzene skeleton through two successive Diels-Alder reactions with dienophiles, has been synthesized in four steps from dimethyl acetylenedicarboxylate and 1,4-dichlorobut-2-ene.
  • T Suzuki, T Tsuji, T Fukushima, S Miyanari, T Miyashi, Y Sakata, T Kouda, H Kamiyama
    JOURNAL OF ORGANIC CHEMISTRY American Chemical Society ({ACS}) 64 (19) 7107 - 7113 0022-3263 1999/09 [Refereed][Not invited]
     
    Charge-transfer complexation of m-nitrobenzoic acid (1) with aromatic hydrocarbons was found to exhibit size and shape selectivity: naphthalene or its 2,7-dimethyl and 2,3,6,7-tetramethyl derivatives failed to afford crystalline complexes with 1 whereas yellow crystals containing a stoichiometric amount of 2,3- or 2,6-dimethylnaphthalene, biphenylene, or anthracene were obtained by the direct method in CH2Cl2. X-ray analyses on these complexes have revealed dimer formation of 1 by O-H ... O hydrogen bonding, yet the important structural motif observed as a common feature is the two-dimensional sheetlike network, in which the dimers of 1 are further connected by C-H ... O hydrogen bonding to form a series of inclusion lattices that incorporate hydrocarbon guests. Such a supramolecular aggregation by C-H ... O bonding was proven to take a significant part in the recognition properties of 1 to differentiate the dimethylnaphthalene isomers in its complexation process.
  • Ikeda, H., Takasaki, T., Takahashi, Y., Konno, A., Matsumoto, M., Hoshi, Y., Aoki, T., Suzuki, T., Goodman, J.L., Miyashi, T.
    Journal of Organic Chemistry 64 (5) 1640 - 1649 0022-3263 1999/03/05 [Not refereed][Not invited]
     
    Under the 9,10-dicyanoanthracene-sensitized photoinduced electron- transfer conditions, (Z,Z)-, (E,E)-, (E,Z)-3,6-diaryl-2,6-octadiene and (d,l),(meso)-2,5-diaryl-3,4-dimethyl-1,5-hexadiene stereospecifically undergo the Cope rearrangement to give a Cope photostationary mixture. Remarkably, the photoinduced electron-transfer Cope rearrangements of the 4-methylphenyl derivatives are concurrent with the formation of trans- or endo,cis-1,4- bis(4-methylphenyl)-2,3-dimethylbicyclo[2.2.0]hexane in a Cope photostationary mixture. Observed stereospecificity of the Cope rearrangement and the formation of the bicyclo[2.2.0]hexane derivatives demonstrate the intermediacies of both the chair and boat 1,4-diaryl-1,2-dimethylcyclohexane- 1,4-diyl and cation radical intermediates in a Cope rearrangement cycle. Photoreactions of trans- and exo,cis-1,4-diaryl-5,6-dimethyl-2,3- diazabicyclo[2.2.2]oct-2-enes further support the interventions of the diyl intermediates in the Cope rearrangement cycle. By photoacoustic analysis, a cation radical cyclization-diradical cleavage mechanism is proposed for the photoinduced electron-transfer Cope rearrangement of the title dienes.
  • Takanori Fukushima, Nobuharu Okazeri, Tsutomu Miyashi, Kazuharu Suzuki, Yoshiro Yamashita, Takanori Suzuki
    Tetrahedron Letters 40 (6) 1175 - 1178 1999/02
  • Nakamura, T., Yumoto, T., Suzuki, T., Akutagawa, T., Hasegawa, T., Tachibana, H., Matsumoto, M., Horiuchi, S., Ikegami, H., Yamochi, H., Saito, G.
    Molecular Crystals and Liquid Crystals Science and Technology Section A: Molecular Crystals and Liquid Crystals 327 1058-725X 1999
  • Fukushima, T., Okazeri, N., Miyashi, T., Suzuki, K., Yamashita, Y., Suzuki, T.
    Tetrahedron Letters 40 (6) 0040-4039 1999
  • T Suzuki, J Nishida, T Tsuji
    CHEMICAL COMMUNICATIONS (20) 2193 - 2194 1359-7345 1998/10 [Refereed][Not invited]
     
    Electrochemical interconversion between 9,9,10,10-tetraaryldihydrophenanthrene 1 and 2,2'-bis(triarylmethylium) 2(2+) has been proven to proceed via open form cation radical 2(+.) as a stable intermediate; using these three species, a novel tricolor electrochromic system that exhibits hysteretic color change (color 1 --> color 2 --> color 3 --> color 1) is formed.
  • T Suzuki, H Takahashi, J Nishida, T Tsuji
    CHEMICAL COMMUNICATIONS Royal Society of Chemistry ({RSC}) (13) 1331 - 1332 1359-7345 1998/07 [Refereed][Not invited]
     
    A novel redox pair undergoing reversible C-C bond making/ breaking has been constructed based on a bis(dicyanovinyl)biphenyl derivative and a dianion with the dihydrophenanthrene skeleton; further cyclization of the latter to an enaminonitrile endows the 'write protect' option to its electrochromic response.
  • H Kawai, T Suzuki, M Ohkita, T Tsuji
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 37 (6) 817 - 819 1433-7851 1998/04 [Refereed][Not invited]
  • H Kawai, T Suzuki, M Ohkita, T Tsuji
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 37 (6) 817 - 819 1433-7851 1998/04 [Refereed][Not invited]
  • Hidetoshi Kawai, Takanori Suzuki, Masakazu Ohkita, Takashi Tsuji
    Angewandte Chemie Wiley-Blackwell 110 (6) 827 - 829 1998/03 [Refereed][Not invited]
  • T Suzuki, T Fukushima, T Miyashi, T Tsuji
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION IN ENGLISH Wiley-Blackwell 36 (22) 2495 - 2497 0570-0833 1997/12 [Refereed][Not invited]
  • T Suzuki, M Kondo, T Nakamura, T Fukushima, T Miyashi
    CHEMICAL COMMUNICATIONS Royal Society of Chemistry ({RSC}) (23) 2325 - 2326 1359-7345 1997/12 [Refereed][Not invited]
     
    The title TTF derivatives and their tricyclic valence isomers afford the same bicyclic dications upon two-electron oxidation, and the resulting dications regenerate either one or the other of the two isomers selectively upon reduction.
  • T Tsuji, M Okuyama, M Ohkita, T Imai, T Suzuki
    CHEMICAL COMMUNICATIONS (22) 2151 - 2152 1359-7345 1997/11 [Refereed][Not invited]
     
    The 3,4-dicyano derivative of hitherto unknown tricycle[4.2.2.2(2,5)]dodeca-1,3,5,7,9,11-hexaene, in which six double bonds are uniquely arranged, is generated and chemically trapped with 1,2-dimethylenecyclopentane and tert-butyl-lithium.
  • T Suzuki, J Nishida, T Tsuji
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION IN ENGLISH 36 (12) 1329 - 1331 0570-0833 1997/07 [Refereed][Not invited]
  • Takanori Suzuki, Jun-Ich Nishida, Takashi Tsuji
    Angew. Chem. 109 (12) 1387 - 1389 1997/06 [Refereed][Not invited]
  • Takanori Suzuki, Yoshiro Yamashita, Takanori Fukushima, Tustomu Miyashi
    Molecular Crystals and Liquid Crystals 296 1997 [Refereed][Not invited]
  • T Kurihara, T Suzuki, H Wakabayashi, S Ishikawa, K Shindo, Y Shimada, H Chiba, T Miyashi, M Yasunami, T Nozoe
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 69 (7) 2003 - 2008 0009-2673 1996/07 [Refereed][Not invited]
     
    The electronic structures of azulene (1) and its alkylated derivatives were investigated on the basis of MO calculations by MNDO and PM3 method. There results were experimentally evaluated by measuring the oxidation potentials (E(ox)) of 1 and its alkylated derivatives, from which the additive property on E(ox) was suggested as shown by E(ox)(Az.subst)=E(ox)(AZ)-0.10n(1,3)+0.06n(2)-0.02n(4,8)-0.11n(5,7)-0.01n(6). Thus, the alkyl groups at the 1,3- and 5,7-positions lower the E(ox) values by ca. 0.1 V, and stronger donating properties were observed for 3-methylguaiazulene (E(ox)=+0.53 V) and 3,3'biguaiazulene (E(ox)=+0.40 V). The redox properties of guaiazulenyl sulfides which were prepared from guaiazulene via a phenylsulfonylthio derivative were also studied. Unlike the alkylated azulenes they underwent reversible one-electron oxidations and exhibited stronger donating properties (E(ox)=+0.40-+0.44).
  • Y Takahashi, H Ohaku, S Morishima, T Suzuki, H Ikeda, T Miyashi
    JOURNAL OF THE CHEMICAL SOCIETY-PERKIN TRANSACTIONS 1 (4) 319 - 325 0300-922X 1996/02 [Refereed][Not invited]
     
    The photochemical reactivities of 1,1-diarylspiropentanes la-c have been investigated under various photolysis conditions. Upon direct photolysis or acetone-sensitized photolysis, 1 underwent skeletal rearrangement to afford methylidenecyclobutanes 2, 3 and 4. A mechanism involving diradical intermediates has been proposed. Also studied were the photochemical and thermal reactions of the electron donor-acceptor (EDA) complexes of 1 with tetracyanoethylene (TCNE). Photoirradiation of the charge-transfer (CT) absorption bands of the EDA complexes resulted in the skeletal rearrangement of 1 to 2 and 3, with concomitant formation of TCNE adducts 11b,c and 12a-c. The X-ray structure of Ile is reported. A mechanism involving ion radical pairs [1'(+), TCNE'(-)] is proposed for the photoreaction. In contrast, no skeletal rearrangement was observed in the thermal reaction of the EDA complexes although 11b and 11c were produced.
  • Suzuki, T.
    Pure and Applied Chemistry 68 (2) 0033-4545 1996
  • M Hirayama, T Terasaka, Y Yamashita, T Susuki, T Miyashi, Y Usui
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 68 (12) 3337 - 3339 0009-2673 1995/12 [Refereed][Not invited]
     
    ESR study of the anion radical produced by the reduction of the title compound (DTB-BDTD) with potassium metal in 1,2-dimethoxyethane is reported. In addition to the satellites of O-17, C-13, and S-33, the second-generation satellite lines of extremely low intensity, arising from both C-13 and S-33 isotopes in natural abundance, have been detected. It was found that these satellites vary markedly in line width among each component of its multiplet. This line width effect was used to determine the sign of hfs constants of these magnetic nuclei, and the resulting signs agreed well with those estimated from the spin densities obtained by the McLachlan procedure and the INDO method.
  • M HIRAYAMA, T TERASAKA, M ITASAKA, T SUZUKI, Y YAMASHITA, T MIYASHI
    CHEMISTRY LETTERS (9) 837 - 838 0366-7022 1995/09 [Refereed][Not invited]
     
    The anion and trianion radicals of title compounds were generated by electrolysis in acetonitrile at room temperature and their ESR spectra were measured, which carl be identified on the basis of pi-MO calculations of hfsc's.
  • Y TAKAHASHI, H OHAKU, S MORISHIMA, T SUZUKI, T MIYASHI
    TETRAHEDRON LETTERS 36 (29) 5207 - 5210 0040-4039 1995/07 [Refereed][Not invited]
     
    Photoreactions of 1,1-diphenylspiropentanes have been investigated under various photochemical conditions. The exploratory studies have provided unprecedented examples of photochemically induced skeletal rearrangement of spiropentanes to methylenecyclobutanes.
  • M HIRAYAMA, M ITASAKA, T SUZUKI, Y YAMASHITA, T MIYASHI
    CHEMISTRY LETTERS (7) 511 - 512 0366-7022 1995/07 [Refereed][Not invited]
     
    The pi-trianion radical of the title compound was formed by electrolysis in acetonitrile and its ESR spectrum with C-13 satellites in natural abundance was observed, which was clearly identified by MO calculation.
  • Y TAKAHASHI, H OHAKU, S MORISHIMA, T SUZUKI, T MIYASHI
    TETRAHEDRON LETTERS 36 (29) 5207 - 5210 0040-4039 1995/07 [Refereed][Not invited]
     
    Photoreactions of 1,1-diphenylspiropentanes have been investigated under various photochemical conditions. The exploratory studies have provided unprecedented examples of photochemically induced skeletal rearrangement of spiropentanes to methylenecyclobutanes.
  • Takanori Suzuki
    Yuki Gosei Kagaku Kyokaishi/Journal of Synthetic Organic Chemistry The Society of Synthetic Organic Chemistry, Japan 53 (5) 403 - 412 0037-9980 1995 [Refereed][Not invited]
     
    The role of weak intermolecular interactions in 'crystal engineering' is briefly reviewed. The selective complexation of TNF (1) and mNBA (2) with 2,6-DMN was studied in detail to test the validity of C-H · · O hydrogen bonding in determining the molecular arrangement in multi-component organic solids. In order to find the new interacting sites in crystal 1,2,5-chalcogenadiazoles substituted with a dicyanomethylene group were designed. Systematic structural analyses of 4-12 indicated the presence of novel chalcogen-cyano interaction. This interaction is one of the sources of the directionality in crystal packing and caused the formation of 'ribbon'-like networks in the anion-radical salts as well as the CT crystals of 7. By the network were formed the inclusion cavities in the latter, which can be used for the isomer recognition or as unique reaction centers for topochemical transformation. The single crystal-to-single crystal reaction occurred in a certain case, and the S · · N ≡ C interaction was suggested to take part in maintaining the crystal matrix during the solid-state reaction.
  • T SUZUKI, T SAKIMURA, S TANAKA, Y YAMASHITA, H SHIOHARA, T MIYASHI
    JOURNAL OF THE CHEMICAL SOCIETY-CHEMICAL COMMUNICATIONS (12) 1431 - 1432 0022-4936 1994/06 [Refereed][Not invited]
     
    The title molecules (1) are strong electron donors like tetrathiafulvalene (TTF) but possess non-planar geometries with short intramolecular contacts between S atoms (av. 3.06 Angstrom in 1b, X-ray); by contrast, their cation radicals are endowed with molecular planarity, and the shorter S...S contacts (av. 2.87 Angstrom in 1b(.+), X-ray) result in the enhanced attractive interaction as well as much smaller Coulombic repulsion in 1(2+) than in TTF2+.
  • T SUZUKI, T FUKUSHIMA, Y YAMASHITA, T MIYASHI
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 116 (7) 2793 - 2803 0002-7863 1994/04 [Refereed][Not invited]
     
    The title electron acceptor, bis[1,2,5]thiadiazolotetracyanoquinodimethane(BTDA,1), formed weak electron-donor-acceptor (EDA) complexes with arylolefins such as styrene (ST) and divinylbenzenes (DVs). Upon charge-transfer (CT) excitation of these complexes in MeCN, the [2 + 2]-type cycloadducts(2) were formed via a single electron transfer. Similar cycloaddition reactions were efficiently induced when the solid-state molecular complexes of 1 and arylolefins were irradiated. In contrast to the close similarities in solution photochemistry, the solid state reactivities of three isomeric divinylbenzenes (oDV, mDV, pDV) were quite dissimilar because of the different molecular overlaps of 1 and DVs in the crystal. The apparent reactivity of the oDV.1 crystal was much higher than that in solution as in the case of the ST.1 crystal, and adduct 2o was formed via the single crystal-to-single crystal transformation. Because of the asymmetric crystal structure in oDV 1, the optically pure product with 95% ee was obtained from the achiral components without any external chiral source. On the other hand, the incomplete conversion of the mDV.1 crystal to 2m is due to the crystal-to-amorphous transformation, and the 1:2 adduct 6 was formed on irradiation of the pDV.1 crystal which could not be obtained on excitation of the EDA complex in MeCN.
  • Y TAKAHASHI, S MORISHIMA, K WAKAMATSU, T SUZUKI, T MIYASHI
    JOURNAL OF THE CHEMICAL SOCIETY-CHEMICAL COMMUNICATIONS (1) 13 - 14 0022-4936 1994/01 [Refereed][Not invited]
     
    Cycloreversion of arene endoperoxides 1-4 can be induced by photoexcitation of their electron donor-acceptor complexes with tetracyanoethylene.
  • T SUZUKI, H FUJII, T MIYASHI, Y YAMASHITA
    JOURNAL OF ORGANIC CHEMISTRY 57 (25) 6744 - 6748 0022-3263 1992/12 [Refereed][Not invited]
     
    Treatment of a dimethylnaphthalene (DMN) isomer mixture with 2,4,7-trinitrofluorenone (TNF) resulted in the predominant formation of 2,6-DMN-TNF (1:1) complex (3) accompanied by a small amount of 2,7-DMN-TNF (1:1) (4). X-ray structural analyses of these charge-transfer crystals showed that coplanar "ribbon"-like networks are formed by C-H...0 hydrogen bonding of TNF and that 3 is thermodynamically more stable than 4 due to the larger interactions through C-H...0 contacts.
  • Y TSUBATA, T SUZUKI, T MIYASHI, Y YAMASHITA
    JOURNAL OF ORGANIC CHEMISTRY 57 (25) 6749 - 6755 0022-3263 1992/12 [Refereed][Not invited]
     
    Pyrazino-TCNQ (1a) prepared from 5,8-diiodoquinoxaline (4a) is, like TCNQ itself, a strong electron acceptor and gives a stable anion radical salt as well as highly conductive charge-transfer crystals with donors. Substituted derivatives 1b-i were similarly prepared from 3,6-diiodo-1,2-phenylenediamine (5) as a common intermediate, and bulky substituents such as the phenyl or pyridyl groups have very little effect on either the redox properties or planar geometry of la. Neutral radicals 3d-g derived from pyridyl-substituted derivatives 1d-g, respectively, are open-shell donor-pi-acceptor systems with high electrical amphotericity designed as a new motif for single-component organic conductors. The powder conductivity of 3f was as high as 3.2 X 10(-5) S cm-1.
  • K IWASAKI, A UGAWA, A KAWAMOTO, Y YAMASHITA, K YAKUSHI, T SUZUKI, T MIYASHI
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 65 (12) 3350 - 3357 0009-2673 1992/12 [Refereed][Not invited]
     
    The charge-transfer complex between naphthaceno[5,6-cd-11,12-c'd']bis[1,2]diselenole (TSeN) and 4,8-bis(dicyanomethylene)-4H,8H-benzo[1,2-c:4,5-c']bis[1,2,5]thiadiazole (BTDA-TCNQ) is found to show at least three different types of crystal modifications; insulating Type-I has a (1 : 1 : 1) ratio containing solvent molecules (chlorobenzene), metallic Type-II has a (1 : 1) stoichiometry, and semiconductive Type-III is conjectured to have a (1 : 2) or (2 : 1) stoichiometry. The crystal structures of Type-I and Type-II were determined by a single-crystal X-ray diffraction method. Type-I comprises mixed-stack molecular columns, and Type-II segregated-stack molecular columns. In both types the neighboring columns are linked along short molecular axes by two Se ... N contacts that are shorter than the corresponding van der Waals contact. In the Type-II crystal, there are other short distances between TSeN and BTDA-TCNQ in the direction of the long molecular axes. From the C=C bond length in the C=C(CN)2 group of BTDA-TCNQ, the degrees of charge transfer of these molecular complexes were estimated as 0.2+/-0.3 in Type-I and 0.9+/-0.2 in Type-II.
  • K KIKUCHI, T KATAGIRI, T NIWA, Y TAKAHASHI, T SUZUKI, H IKEDA, T MIYASHI
    CHEMICAL PHYSICS LETTERS 193 (1-3) 155 - 160 0009-2614 1992/05 [Refereed][Not invited]
     
    The free radical yield of electron-transfer fluorescence quenching and the effective encounter distance are studied to determine the quenching mechanism in very exothermic region. Evidence for electronically excited radical generation as the primary quenching product is given for the first time.
  • K KIKUCHI, T KATAGIRI, T NIWA, Y TAKAHASHI, T SUZUKI, H IKEDA, T MIYASHI
    CHEMICAL PHYSICS LETTERS 193 (1-3) 155 - 160 0009-2614 1992/05 [Refereed][Not invited]
     
    The free radical yield of electron-transfer fluorescence quenching and the effective encounter distance are studied to determine the quenching mechanism in very exothermic region. Evidence for electronically excited radical generation as the primary quenching product is given for the first time.
  • T SUZUKI, H FUJII, Y YAMASHITA, C KABUTO, S TANAKA, M HARASAWA, T MUKAI, T MIYASHI
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 114 (8) 3034 - 3043 0002-7863 1992/04 [Refereed][Not invited]
     
    The intermolecular contacts between chalcogen atoms and cyano lone pairs were found to stabilize the crystalline state by electrostatic interaction. This interaction is one of the sources of the directionality in crystal packing of organic molecules and causes the formation of various types of inclusion lattices in the charge-transfer (CT) crystals of 1-3. By using highly selective formation of CT crystals with substituted aromatic hydrocarbons, particular isomers such as p-xylene or 2,6-dimethylnaphthalene (2,6-DMN) could be separated from the corresponding isomer mixtures. Lattice-related interaction plays a more significant role than molecular orbital interaction in the observed selectivity for para-disubstituted benzenes. However, the latter interaction is important for the recognition of 2,6-DMN from the 2,7 isomer.
  • T SUZUKI, H SHIOHARA, M MONOBE, T SAKIMURA, S TANAKA, Y YAMASHITA, T MIYASHI
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION IN ENGLISH Wiley-Blackwell 31 (4) 455 - 458 0570-0833 1992/04 [Refereed][Not invited]
     
    With a 90-degrees twist between the two halves, dication 1(2+) is the first ethylene dication with the maximum distortion possible. The stabilization of the positive charge is achieved in the separate halves of the dication by delocalization over polymethine units. 1(2+). whose ClO4- salt melts at about 170-degrees-C with decomposition, is obtained from the electrochemical oxidation of 1. The structure of neutral 1 differs substantially from that of its dication.
  • Y TSUBATA, T SUZUKI, Y YAMASHITA, T MUKAI, T MIYASHI
    HETEROCYCLES 33 (1) 337 - 348 0385-5414 1992/01 [Refereed][Not invited]
     
    1,2,5-Thiadiazolopyrazino-TCNQs underwent reversible four-stage one-electron reduction and gave conductive CT complexes with some donors. The X-ray structural analysis of the unsubstituted derivative revealed that the coplanar ''sheet''-like network was formed by interatomic contacts of S--N = C and H--N = C in crystal.
  • A. Ugawa, K. Iwasaki, A. Kawamoto, K. Yakushi, Y. Yamashita, T. Suzuki
    Physical Review B 43 (18) 14718 - 14721 0163-1829 1991 [Refereed][Not invited]
     
    Tetraselenotetracene (TSeT) forms a charge-transfer complex with bis(1,2,5-thiadiazolo)tetracyanoquinodimethane (BTDA-TCNQ), the complex showing a metallic behavior down to 1.5 K without undergoing a Peierls transition. The structure consists of segregated columns of TSeT and BTDA-TCNQ molecules, among which there also exist short intermolecular contacts. The polarized reflectance spectra indicate that the material is a one-dimensional metal in contrast to the structural features. The electronic structure is characterized by a one-dimensional conduction band lying on the two-dimensional lattice, which prevents the system from undergoing a Peierls distortion. © 1991 The American Physical Society.
  • Yoshiro Yamashita, Junko Eguchi, Takanori Suzuki, Chizuko Kabuto, Tsutomu Miyashi, Shoji Tanaka
    Angew. Chem. Wiley-Blackwell 102 (6) 709 - 710 1990/06 [Refereed][Not invited]
  • Y YAMASHITA, J EGUCHI, T SUZUKI, C KABUTO, T MIYASHI, S TANAKA
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION IN ENGLISH Wiley-Blackwell 29 (6) 643 - 645 0570-0833 1990/06 [Refereed][Not invited]
  • Y YAMASHITA, Y TSUBATA, T SUZUKI, T MIYASHI, T MUKAI, S TANAKA
    CHEMISTRY LETTERS (3) 445 - 448 0366-7022 1990/03 [Refereed][Not invited]
  • Kamata, M., Murayama, K., Suzuki, T., Miyashi, T.
    Journal of the Chemical Society, Chemical Communications (11) 0022-4936 1990
  • Y YAMASHITA, T SUZUKI, T MIYASHI
    CHEMISTRY LETTERS (9) 1607 - 1610 0366-7022 1989/09 [Refereed][Not invited]
  • T SUZUKI, Y YAMASHITA, C KABUTO, T MIYASHI
    JOURNAL OF THE CHEMICAL SOCIETY-CHEMICAL COMMUNICATIONS (16) 1102 - 1103 0022-4936 1989/08 [Refereed][Not invited]
  • T MIYASHI, A KONNO, Y TAKAHASHI, A KANEKO, T SUZUKI, T MUKAI, N KOGA, H IWAMURA
    TETRAHEDRON LETTERS 30 (39) 5297 - 5300 0040-4039 1989 [Refereed][Not invited]
  • H YAMOCHI, T TSUJI, G SAITO, T SUZUKI, T MIYASHI, C KABUTO
    SYNTHETIC METALS 27 (1-2) A479 - A484 0379-6779 1988/12 [Refereed][Not invited]
  • T SUZUKI, C KABUTO, Y YAMASHITA, T MUKAI, T MIYASHI
    JOURNAL OF THE CHEMICAL SOCIETY-CHEMICAL COMMUNICATIONS (13) 895 - 896 0022-4936 1988/07 [Refereed][Not invited]
  • M HIRAYAMA, A SEKI, Y YAMASHITA, T SUZUKI, T MIYASHI
    CHEMISTRY LETTERS (5) 769 - 772 0366-7022 1988/05 [Refereed][Not invited]
  • M HIRAYAMA, A SEKI, Y YAMASHITA, T SUZUKI, T MIYASHI
    JOURNAL OF THE CHEMICAL SOCIETY-CHEMICAL COMMUNICATIONS (7) 490 - 491 0022-4936 1988/04 [Refereed][Not invited]
  • Yoshiro Yamashita, Kenichi Saito, Takanori Suzuki, Chizuko Kabuto, Toshio Mukai, Tsutomu Miyashi
    Angew. Chem. Wiley-Blackwell 100 (3) 428 - 429 1988/03 [Refereed][Not invited]
  • Y YAMASHITA, K SAITO, T SUZUKI, C KABUTO, T MUKAI, T MIYASHI
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION IN ENGLISH 27 (3) 434 - 435 0570-0833 1988/03 [Refereed][Not invited]
  • T SUZUKI, C KABUTO, Y YAMASHITA, T MUKAI, T MIYASHI, G SAITO
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 61 (2) 483 - 493 0009-2673 1988/02 [Refereed][Not invited]
  • T SUZUKI, Y YAMASHITA, T MUKAI, T MIYASHI
    TETRAHEDRON LETTERS 29 (12) 1405 - 1408 0040-4039 1988 [Refereed][Not invited]
  • M HIRAYAMA, A SEKI, Y YAMASHITA, T SUZUKI, T MIYASHI
    CHEMISTRY LETTERS (1) 67 - 70 0366-7022 1988/01 [Refereed][Not invited]
  • Masatoshi Hirayama, Akihiko Seki, Yoshiro Yamashita, Takanori Suzuki, Tsutomu Miyashi
    Chem. Lett. (1) 67 - 70 1988 [Refereed][Not invited]
  • T SUZUKI, C KABUTO, Y YAMASHITA, T MIYASHI
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 60 (9) 3459 - 3461 0009-2673 1987/09 [Refereed][Not invited]
  • Y YAMASHITA, T SUZUKI, T MUKAI
    JOURNAL OF THE CHEMICAL SOCIETY-CHEMICAL COMMUNICATIONS (15) 1184 - 1185 0022-4936 1987/08 [Refereed][Not invited]
  • T SUZUKI, C KABUTO, Y YAMASHITA, T MUKAI
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 60 (6) 2111 - 2115 0009-2673 1987/06 [Refereed][Not invited]
  • T SUZUKI, C KABUTO, Y YAMASHITA, T MUKAI
    CHEMISTRY LETTERS (6) 1129 - 1132 0366-7022 1987 [Refereed][Not invited]
  • Y YAMASHITA, T SUZUKI, G SAITO, T MUKAI
    JOURNAL OF THE CHEMICAL SOCIETY-CHEMICAL COMMUNICATIONS (19) 1489 - 1491 0022-4936 1986/10 [Refereed][Not invited]
  • C KABUTO, T SUZUKI, Y YAMASHITA, T MUKAI
    CHEMISTRY LETTERS (9) 1433 - 1436 0366-7022 1986/09 [Refereed][Not invited]
  • Y YAMASHITA, T SUZUKI, G SAITO, T MUKAI
    CHEMISTRY LETTERS (5) 715 - 718 0366-7022 1986/05 [Refereed][Not invited]
  • C KABUTO, Y FUKAZAWA, T SUZUKI, Y YAMASHITA, T MIYASHI, T MUKAI
    TETRAHEDRON LETTERS 27 (8) 925 - 928 0040-4039 1986 [Refereed][Not invited]
  • C KABUTO, Y FUKAZAWA, T SUZUKI, Y YAMASHITA, T MIYASHI, T MUKAI
    TETRAHEDRON LETTERS 27 (8) 925 - 928 0040-4039 1986 [Refereed][Not invited]
  • Y NISHIZAWA, T SUZUKI, Y YAMASHITA, T MIYASHI, T MUKAI
    NIPPON KAGAKU KAISHI (5) 904 - 909 0369-4577 1985 [Refereed][Not invited]
  • Y YAMASHITA, T SUZUKI, T MUKAI, G SAITO
    JOURNAL OF THE CHEMICAL SOCIETY-CHEMICAL COMMUNICATIONS (15) 1044 - 1045 0022-4936 1985 [Refereed][Not invited]
  • Y YAMASHITA, T SUZUKI, G SAITO, T MUKAI
    CHEMISTRY LETTERS (11) 1759 - 1762 0366-7022 1985 [Refereed][Not invited]
  • T MUKAI, T SUZUKI, Y YAMASHITA
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 58 (8) 2433 - 2434 0009-2673 1985 [Refereed][Not invited]

MISC

Presentations

  • 動的酸化還元系の化学 (特別講演)  [Invited]
    鈴木孝紀
    第32回基礎有機化学討論会  2022/09
  • Hexaarylbutadienes Exhibiting NIR-electrochromism for the Development of H2S-Bioimaging and Photodynamic Therapy  [Invited]
    Takanori Suzuki
    19th International Symposnium on Novel Aromatic Compounds  2022/07
  • Studies on Dynamic Redox Systems: Construction of Record-breaking Strained Compounds and Development of Unimolecular Memory  [Not invited]
    鈴木 孝紀
    The 99th CSJ Annual Meeting, Award Lecutre,  2019/03
  • 超結合:共有結合の限界を超えた化学  [Not invited]
    鈴木 孝紀
    日本化学会第99春季年会特別企画  2019/03

Association Memberships

  • 基礎有機化学会   日本化学会   有機合成化学協会   

Research Projects

  • 日本学術振興会:科学研究費助成事業 基盤研究(B)
    Date (from‐to) : 2020/04 -2025/03 
    Author : 鈴木 孝紀, 石垣 侑祐
     
    研究計画に沿った研究実験を実施し、その実績について、”Generation of hydroxyl radical-activatable ratiometric near-infrared bimodal probes for early monitoring of tumor response to therapy.”L. Wu, Y. Ishigaki, W. Zeng, T. Harimoto, B. Yin, Y. Chen, S. Liao, Y. Liu, Y. Sun, X. Zhang, Y. Liu, Y. Liang, P. Sun, T. Suzuki, G. Song, Q. Fan, D. Ye, Nat. Commun. 2021, 12, 6145. [DOI: 10.1038/s41467-021-26380-y (open access)]の論文にて発表した。
    上記論文では、生体内のヒドロキシラジカルを選択的に検知してイメージングを行う方法を開拓したものであり、ヘキサアリールブタジエン骨格に、適切なアルキル基の置換したアミノ基を導入した化合物が有効であった。またNIR蛍光によるイメージングに、NIR吸収に由来する光音響分光スペクトルを併用することで、定量性の高い手法として確立できた点は特筆に値する。
    一方、物質開発については、ヘキサアリールブタジエンの基本骨格を持ちながらも、酸化還元に際して分子内に反芳香族性骨格であるチエピン、オキセピン骨格が生じることで、よりNIRの長波長部分に吸収をもつ化合物群についての検討を中心に進める計画であった。当該物質の合成には成功しており、今後そのスペクトル特性とイメージング法への応用へ進む段階である。
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Challenging Research (Exploratory)
    Date (from‐to) : 2020/07 -2023/03 
    Author : 鈴木 孝紀
     
    「電位入力型ON/OFF機能の付与された双安定性分子ジャンクションの創成」に関する本研究課題では、分子薄膜の両面に電極が接合された分子ジャンクションについて、エレクトロニクスの高速化とダウンサイジングに不可欠な将来的技術であることを鑑み、薄膜を構成する分子の導電性が外部刺激によって変化する設計のもとで、分子ジャンクションにON/OFF機能を付与する挑戦的内容である。国立シンガポール大学C.A.Nijhuis教授との国際共同研究として実施する。電極接合については、Nijhuis教授らが持つ共融ガリウム-インジウム電極の蒸着技術を用い、Au/分子薄膜//GaOx/EGaIn型のデバイスを構築する。 初年度は、中性分子の酸化電位と新たなC-C結合が形成されることによる二価陽イオン種還元電位に1Vもの差を伴う電気化学的双安定性をもった系として、ビフェニル(BP)とジヒドロフェナントレン(DHP)骨格の変換する動的酸化還元対をモチーフとした分子の合成をおこなった。最終的に、酸化還元部位に対して、金表面に結合可能な2つのジスルフィド部位を有する一連の化合物群を合成した。酸化還元骨格上に導入する置換基によって、動作電位が変化させられることをサイクリックポルタンメトリーで確認した。具体的には、同じアミン系置換基であっても、ピロリジノ基、ジメチルアミノ基、モルホリノ基では、0.3Vの変化を観測した。その際、以前に検討したプロトタイプでの問題点であった、遅い結合切断の過程による、変換速度の問題を克服する点を解決できたことも確認した。
  • ドナーアクセプター連結型中分子による生物機能/光機能分子創出
    文部科学省:科学研究費補助金(新学術領域(研究領域提案型))
    Date (from‐to) : 2018/04 -2020/03 
    Author : 鈴木 孝紀
  • 安定な1,4-ジイルジカチオンの発生/消失に伴うモノマー/ポリマースイッチング
    文部科学省:科学研究費補助金(競争的萌芽研究)
    Date (from‐to) : 2016/04 -2019/03 
    Author : 鈴木 孝紀
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 2015 -2019 
    Author : Takanori Suzuki
     
    The dynamic redox (dyrex) systems undergo reversible bond formation/cleavage upon electron transfer. This characteristic feature provides those redox systems with electrochemical bistability, by which oxidation of the donor and reduction of the cationic species occur at difference potentials. Such separation prevents the exchange of electrons between the neutral state and the cationic state, whereas the activation energy for the corresponding process in ordinary redox pairs is negligible. Thus, bistability in dynamic redox pairs can lead to their use in unimolecular memory because one molecule can be considered to be one digit if the two redox states are assigned values of 0 and 1 (e.g., the neutral donor is 0 and the cationic state is 1). We have developed several promising dyrex systems in this work, which would be used as prototypes for developing advanced molecular memory unit.
  • マルチレドックスサイト型オリゴマー中分子による生物機能分子創出
    文部科学省:科学研究費補助金(新学術領域(研究領域提案型))
    Date (from‐to) : 2016/04 -2018/03 
    Author : 鈴木 孝紀
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 2012/04 -2015/03 
    Author : KAWAI Hidetoshi, SUZUKI Takanori
     
    A cooperation of dynamic imine-bon formations and cooperativity of allosteric bindings has been incorporated into various supramolecular motifs and studied to create "dynamic molecular system" with dynamic motion and dynamic equilibrium in this project: The following outstanding results has found: A) Preservation effect of DPs in cooperative supramolecular copolymerization based on allosteric bindings, B) Cooperative hydrogen-bonding in the hydrindacene-geared molecules, C) Opposite thermodynamic selectivity among two formyl-stations in the imine-bridged rotaxane under the hydrolytic conditions and D) Shape-memory effect and template effect by incorporating atropisomerism to imine-based macrocyclic receptors.
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 2013 -2014 
    Author : SUZUKI Takanori
     
    The acronym "MFMS" represents the molecular design concept of "maximum function on the minimum skeleton", which has been increasing in importance, especially for the design of advanced response systems. When a modular design is applied to multi-output-multi-input response systems, the multiple functional moieties have to be connected, resulting in a larger molecular size. On the other hand, under the "MFMS" concept, the potential functions of molecules are educed by slight structural modification of a preexisting moiety to add another functionality. The "MFMS" is an atom-economical approach for the future development of highly functional materials. In this study, two kinds of multi-output molecular response systems were developed based on our electrochromic dyrex (dynamic redox) system.
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 2011 -2013 
    Author : KAWAI Hidetoshi, SUZUKI Takanori
     
    Ring-fused malonamides with two primary amide groups, such as 2,2-indanedicarboxamides, assemble into well-defined 2D-sheet structures based on the formation of 6 to 8 hydrogen bonds per molecule. The fused ring part would be planted above and below the 2D-sheet by supporting with multiple hydrogen-bondings. The stacking manner and the interlayer distances of these sheets in crystal can be manipulated by varying the size of the fused ring, to form either interdigitated or segregated structures. Furthermore, triptycene-fused malonamides for the purpose of formation to tubular structures by rolling 2D-sheet into a cylinder due to their steric hindrance of triptycenes. We revealed their hydrogen-bonding patterns to assemble a tubluar structure by powder X-ray structural analysis. This motif technique allows the ready design of crystalline materials wherein the various functionalities are situated in well-ordered arrays.
  • Ministry of Education, Culture, Sports, Science and Technology:Grants-in-Aid for Scientific Research(新学術領域研究(研究領域提案型))
    Date (from‐to) : 2009 -2013 
    Author : TAKANORI SUZUKI
     
    Electrochromism is a representative function of organic redox systems, by which electrochemical input is reversibly transduced into UV-Vis spectral output. Based on our previous studies on "dynamic redox (dyrex)" systems that undergo reversible C-C bond-formation/-cleavage upon electron transfer, we envisaged that the assembled multiple functions would be endowed under the novel molecular design, and such materials could be prepared exclusively only by using newly developed synthetic methods based on integrated reactions. This work can be divided into two parts: [1] studies on NOVEL MATERIALS exhibiting dynamic redox behavior prepared by integrated reactions; and [2] characterization and exploration of organic redox systems newly prepared by NOVEL INTEGRATED REACTIONS. Most of the research results have been published.
  • Ministry of Education, Culture, Sports, Science and Technology:Grants-in-Aid for Scientific Research(基盤研究(B))
    Date (from‐to) : 2009 -2011 
    Author : Takanori SUZUKI, Kenshu FUJIWARA, Hidetoshi KAWAI
     
    Based on our own results for hexaphenylethane derivative studied so far, it has been proposed that the compound with a ultralong C-C bond would be generated as a stable entity when the two unpaired electron are forced to stay in a proximity in the corresponding diradical without isomerization into the closed-shell species through resonance/peri-cyclic reactions. Based on the above concept have been designed a series of tetraarylpyracenes where the longest C-C bond ever [1.791(3)Å] was determined experimentally. The expandability of such prestrained bonds was also uncovered.
  • 文部科学省:科学研究費補助金(萌芽研究)
    Date (from‐to) : 2005 -2007 
    Author : 鈴木 孝紀, 藤原 憲秀, 河合 英敏
     
    申請者は本課題の中で「動的シクロファン」という概念を提案した。これは、外部刺激によってシクロファンの持つ歪みや骨格構造に摂動を与え、それに付随する渡環相互作用の変化やシクロファンに特徴的な物性値変化を応答出力として取り出すというユニークな試みである。これまでテレフタルアミドの様々誘導体へのp-キシリレンジアンモニウム型ゲストの添加による「超分子シクロファン」の検討を行っている。例えば、応答型レセプター機能を持つシクロファンについての検討を行い、分子内に2つのテレフタルアミド骨格を持ち、,これらが二組の1,4-ビス(フェニルエチニル)ベンゼン発色団で架橋された大環状シクロファンについては、不斉なゲストを錯形成させた時、ゲストのエナンチオマーの一方はねじれ構造への変形を引き起こすが、その鏡像体との錯形成ではホストは長方形の構造のままで変形が誘起されないという興味深い結果が得られている。これらは、円二色性(CD)出力を合わせ持つシグナリングホストとなることものである。上記の成果に基づき今年度は、6置換ベンゼンとなる2,3,5,6-テトラアリールテレフタルアミドをモチーフとして、これらが1)非会合状態ではアミドがアンチ配座となり6つの置換基は非プロペラ配置をとる、2)ジアンモニウムが会合して超分子シクロファンとなると、シン配座になったアミド基のdirecting効果により、プロペラ配座に変化する、3)点不斉の情報がプロペラ構造の動的なヘリシティに効果的に転写されることで動的応答挙動が付与される、という分子プロペラの系を確立に成功した(投稿中)
  • Ministry of Education, Culture, Sports, Science and Technology:Grants-in-Aid for Scientific Research(基盤研究(B))
    Date (from‐to) : 2003 -2005 
    Author : Takanori SUZUKI, Kenshu FUJIWARA
     
    This project has been planned to develop new design concepts on the novel organic responding molecules based on the integration of redox active molecules. The major themes to be tackled with are as follows : (1) Redox response systems with electrochemical bistability and surface modifying properties ; (2) New synthetic strategy for the fused- polyether structures ; (3) Redox active molecules with phase transition properties triggered by external stimuli.We have succeeded in preparing redox systems to meet the requirement in the first theme, and some of them are further endowed with multi-input and multi-output fuctionalities. The disuflide unit or ethynyl groups were selected that act as surface-binding linkers for Au an Si, respectively. Preparation of SAM and examination toward the realization of unimolecular memory are now under way.The fused-polyether skeleton found in some marine natural products should be a suitable motif for studying the aggregation by weak C-H--O hydrogen bonds. In the second theme, facile and general convergent strategy was developed for a variety of polyether skeleton. Based on the newly developed protocol based on the reaction between an aldehyde and an acylanion equivalent, we could synthesize polyetheral natural product (hemibrevetoxin B) and the large segments of ciguatoxins with 4-5 ether units. X-ray analyses on some of them have revealed that several short C-H--O contacts were observed that connect tape-shaped polyethers tol the stacked or dimeric strucures. Not only natural but also non-natural polyethers are shown worth investigated.Reversible oligomerization of bis(diarylethenyl)arenes-type electron donors upon oxidation is the outstanding achievement in terms of the third theme. Deeply-colored polycation oligomers could be isolated as stable salts that regenerated the starting monomeric donors upon reduction. By attaching long alkyl chains on the aryl groups, some of these materials act as organic gelators, thus giving a new desing concept for the dynamic mesophase, whose properties can be modulated by electrochemical input.
  • 文部科学省:科学研究費補助金(萌芽研究)
    Date (from‐to) : 2002 -2004 
    Author : 鈴木 孝紀
     
    本研究課題の目的は、1)不斉要素を有する有機酸化還元系の構築とその応答機能を開発し、2)それらを表面へと固定できる方法論を応用して表面物性としての機能を引き出すことにある。本年度はそれぞれ、1)テトラヒドロフェナントラアゼピン骨格を有する系の開発、2)表面修飾に利用できるアンカー置換基を有する酸化還元系の開発について検討を行った。a)アゼピン骨格を有するキラルな酸化還元系:不斉要素を有する有機酸化還元系は、電気化学的入力に対して電子スペクトル及び円二色性(CD)スペクトルの双方の出力を与える多重出力型分子応答系となる。大きなCD出力を得るためには、エキシトンカップリングの利用できる軸不斉またはらせん状化合物が望ましい。表題骨格のヘリシティは容易に反転するが、N上にキラルなベンジルアミノ基を導入することで一方のジアステレオマーを優先させることに成功した。これにより、煩雑な光学分割を行わずに感度良くエレクトロキロオプティカル出力が得られる系の構築が可能となった。b)末端アセチレンおよびジスルフィド官能基をする酸化還元系:表面での自己組織化膜の形成を行うためには、表面修飾に利用できるアンカー置換基が導入された機能性酸化還元系を合成する必要がある。これまで動的酸化還元活性が確認されたジスピロジヒドロフェナントレン骨格を有する3種の酸化還元対の、a)ベイ領域へのエチニル基に導入、b)スピロ環上へのプロパルギル基の導入、c)ベイ領域へのジスルフィド官能基の導入された化合物の合成に成功した。前2者は水素終端シリコン表面への固定に、後者は金表面への固定に利用できる官能基を有するものであり、現在膜の調製の検討を行っている。
  • Ministry of Education, Culture, Sports, Science and Technology:Grants-in-Aid for Scientific Research(基盤研究(B))
    Date (from‐to) : 2001 -2002 
    Author : Takanori SUZUKI, Takashi TSUJI
     
    This research project is intended to construct the novel molecular response systems that transduce the electrochemical input into two kinds of spectral outputs, they are UV-Vis and CD spectra. These materials are named as "electrochiroptical response systems", and considered as promising candidates for use as chiral redox memories. Compared with the extensively studied electrochromic materials giving the UV-Vis spectral change as a sole output, there have been only a few successful examples reported so far. Based on our previous results on the multi-stage redox systems endowed with high electrochemical bistability, we have designed several chiral electron donors that can be reversibly transformed into the stable dicationic species. They exhibited drastic changes in UV-Vis as well as CD spectra during the interconversion. The high amplitude in CD signals is one of the central points to be considered in the molecular design, and we have realized it by exciton coupling of two identical chromophores located at the proper positions in these molecules. We are now planning to fix these molecules on the metal surface by making SAM, so that these molecules can be used as molecular devices.
  • 日本学術振興会:科学研究費助成事業
    Date (from‐to) : 1998 -2000 
    Author : 小林 啓二, 石黒 勝也, 井上 克己, 岡田 恵次, 阿波賀 邦夫, 鈴木 孝紀, 富岡 秀雄
     
    主な研究実績は以下の三つに大別することができる。 新しい安定スピン共役電子系の開発:立体保護により、半減期が室温で10分近くに及ぶ非常に安定な三重項カルベンを開発した。安定なラジカル種により構成される単一成分分子性金属が見い出された。また、キラルな構造を有する不斉ラジカル種の開発に成功し、不斉分子磁石の構築への指針が提示された。 集合体としてのスピン共役電子系の設計と性質:窒素二座型配位子を中心に、スピン共役電子系を配位子とする自己集積型金属錯体による高スピン種の開発が行われ、配位子におけるスピン伝達の様式が解析できた。また、室温をまたいで磁気的双安定性を示すラジカル集合体結晶が発見され、室温での磁気的性質のスイッチング現象を実現させた。 外部応答を示す動的なスピン共役電子系の研究:プロトン濃度に依存して双極イオン構造とビラジカル構造との平衡が成立する分子開発した。酸性度を磁性をプローブとして計測する方法論の基礎が検討された。電気化学的反応系でも、このようなイオン反応が絡む電子構造スイッチング反応が見い出された。電荷移動を固体摩砕により誘起できることが分かった。固相中に開殻分子種を発生させる手法へと展開が計られ、さらに固相反応の触媒的役割が明らかになった。
  • 日本学術振興会:科学研究費助成事業
    Date (from‐to) : 1999 -1999 
    Author : 辻 孝, 大北 雅一, 鈴木 孝紀
     
    分子認識や自己認識化には、当該分子が分子形状を維持する剛直性と状況に適応し得る柔軟性を併せ備えていることが求められる。本研究では、5員環部が還元されたインダセンがそのような特性を備え、適切に異なる官能基によって構造修飾することにより、三次元的な相互作用を制御できる点に着目した。 1.インダセン骨格を利用した新規ホスト化合物の合成 5員環はenvelop型配座をとっており、(Z)-置換体では嵩高さの小さな基はaxial位をとってπ-πstacking構造の錯体を形成するのに適した約7.0Aの距離をおいてほぼ平行に配列される。(Z)-置換誘導体の結晶構造解析は、計算による予測を裏付けた。また、2分子が歯車のように互いに噛み合った興味深い結晶構造を明らかにした。若干の置換アリールエチニル体を合成し、そのホスト分子としての機能に検討を加えた。その結果、CT吸収強度に(Z)-体と(E)-体では約9倍の差が認められ、(Z)-体とのより強い錯体形成が認められた。 対応する(E)-置換体では、より嵩高い置換基がequatorial配座をとって逆方向に配列される。4-ピリジル/メトキシカルボニル置換体のX線構造解析は、このことを実証した。共有結合あるいは金属への配列を利用して大環状構造を構築すれば、官能基を大環状構造の環内方向に配列させることができる。大環状の構築とその基質の取り組みの選択性と触媒機能を継続課題として解明する計画である。 2.官能基化したパラフェニレン/エチニレン型マクロサイクルの合成 先に合成を報告したジクロロDewarベンゼンが、官能基化したメタおよびパラフェニレン構造をその折れ曲がり構造を利用して大環状構造に組み込むための合成素子として有用であることを見い出した。1, 2-ジエチニルベンセンとの交互(2:2)環化カップリング、および1,3-ジエチニルベンゼン等価体との(2:4)環化カップリング、保護基の交換、光芳香環化によって官能基化したパラフェニレン/エチニレン型マクロサイクルが得られた。それらのキラル性、空孔への基質特異的取り組みと官能基による活性化は今後の検討課題である。
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 1998 -1999 
    Author : TSUJI Takashi, OHKITA Masakazu, IMAI Toshiro, SUZUKI Takanori
     
    [l] Syntheses and Properties of Novel Receptors Possessing Hydrindacene Skeleton Hydrindacene skeleton is consisted of rigid central aromatic ring and flexible peripheral 5-membered rings, and its intermolecular interactions are expected to be adequately regulated by functionalizing those rings with suitable substituents. In this study, the development of title receptors was investigated on the basis of those expectations. The preparation of several substituted derivatives followed by their X-ray structural analyses revealed that the 5-membered rings prefer an envelope conformation and the less bulky substituents (Rs) are disposed nearly parallel to each other at a distance of ca. 7.0 Å, twice the interlayer distance in graphite. Those structural chacteristics were exploited to the design of novel multiply functionalized receptor molecules which preferentially associate with specific stubstrates. Thus, the (Z) Rs = arylethynyl/R_L = alkoxycarbonyl derivatives seem to incorporate aromatic substrates between the arylethynyl groups, facilitated by the π-π stacking interactions. The Rs = alkoxycarbonyl/R_L = aryl derivatives were also prepared and utilized to construct macrocyclic receptors in which the former substituents are oriented to the inside of the cycles. [2] Preparation of Functionalized Phenylene-ethynylene Macrocycles 1,4-Bridged dichloro-Dewar benzenes are accessible in 4 steps from DMAD and dichloroethylene. Functionalized m- and p-phenylene groups are conveniently incorporated into macrocycles by taking advantage of their equivalency to bent benzene derivatives. Thus, their alternating (2 : 2) coupling- cyclization with diethynylbenzenes followed by hydrolysis and aromatization provided functionalized phenylene-ethynylene macrocycles which were otherwise diffiucult to access.
  • 日本学術振興会:科学研究費助成事業
    Date (from‐to) : 1998 -1998 
    Author : 辻 孝, 大北 雅一, 今井 敏郎, 鈴木 孝紀
     
    ベンゼン環の両側に飽和5員環が縮環したヘキサヒドロインダセン骨格では、両末端の5員環上の置換基とベンゼン環上の置換基が直交した配向をとることを特徴とする。その結果、それらの置換基を操作することによりx,y,z3軸方向での分子間相互作用を制御できる。本研究では、5員環およびベンゼン環上に水素結合能や金属配位能を有する置換基を導入したインダセン誘導体と、その骨格を複数個環状に結合したマクロサイクルを設計し、その合成と超分子形成能に検討をくわえた。 1. 官能基化したヘキサヒドロインダセン誘導体の合成に関する報告は少ない。そこで、ベンゼン環上に官能基変換が可能なメトキシ基、また、5員環にカルボニル、カルボキシル基等を導入した誘導体の合成法の開発を行い、それらの誘導体合成への道を開いた。 2. ベンゼン環に縮環した5員環は、カルボニル基や二重結合の導入によりベンゼン環と共平面に固定されるが、飽和の場合には比較的大きな配座自由度をもつ。その特性を利用した超分子形成能を有する基質の設計と官能基による構造修飾の可能性に検討を加えた。 3. ヒドリンダセンの2つの5員環にsyn/anti面選択的に置換基を導入することは困難であるが、環状ケトアミドでの容易なエピマー化能を利用し、基質のsyn/anti立体化学に拘わらず、syn体を経由してアミド基間の水素結合によって大環状構造へと自己組織化三量化する基質の設計と開発を行った。
  • 日本学術振興会:科学研究費助成事業
    Date (from‐to) : 1998 -1998 
    Author : 辻 孝, 大北 雅一, 今井 敏郎, 鈴木 孝紀
     
    適切な官能基の導入によって、x,y,z座標軸方向での相互作用の制御が可能なヘキサヒドロインダセン(ヒドリンダセン)骨格を主要構成単位とする大環状構造の構築と、その多点相互作用による基質特異的ゲスト分子の取り込み、さらに、立体選択的反応場としての機能開発を目指した研究をおこなった。 1.電子供与性基を置換したヒドリンダセン骨格と、環内部への水素結合受容体の取り込みを目指した水素結合供与(アミド)基から成るマクロサイクルの設計と合成をおこなった。π-π stackingの効果と水素結合によってジニトロベンゼン、ジシアノベンゼン等との基質特異的ホスト-ゲスト錯体形成を狙ったものである。錯体形成は吸収スペクトルの変化によって検知できると考えており、上記の化合物に対する特異的センサーとして、また、反応場としての機能をさらに明かにしてゆく予定である。 2.ヒドリンダセン骨格とジエチニルベンゼンを交互に繋ぎ、大きな空孔をもつ環状構造の構築を進めた。ベンゼン環上の置換基は配座間の相互変換によってその位置関係が大きく変化し、置換基との相互作用による基質の取り込みと排出に際して機能すると考えられる。これらの結果に基いてさらに、ヒドリンダセンのベンゼン環上への水素結合能や金属配位能を有する置換基の導入とそれらの基を利用したチャンネル構造の形成、官能基化された開閉機能を備えた側鎖の導入による篭形構造の構築と多点相互作用によって基質を構造特異的に活性化する反応場の形成に検討を加える予定である。
  • 日本学術振興会:科学研究費助成事業
    Date (from‐to) : 1997 -1997 
    Author : 辻 孝, 大北 雅一, 今井 敏郎, 鈴木 孝紀
     
    ベンゼン環の両側に飽和5員環が縮環したヘキサヒドロインダセン骨格は、両末端の5員環上の置換基が環骨格にたいして直交した方向の、一方、ベンゼン環上の置換基は5員環上の置換基に対して垂直方向の配向をとることを特徴とする。5員環およびベンゼン環に水素結合能や金属配位能を有する置換基を導入したインダセン誘導体と、その骨格を複数個環状に結合したマクロサイクルの設計と合成に検討を加えた。 1.官能基化したヘキサヒドロインダセン誘導体の合成に関する報告は少ない。そこで、ベンゼン環上に官能基変換が可能なメトキシ基、また、5員環にカルボニル、カルボキシル基等を導入した誘導体の合成法の開発を行い、それらの誘導体合成への道を開いた。 2.ヘキサヒドロインダセン骨格を5員環末端位で二量化し、二重結合の導入、シクロプロパン化によってシクロプロパン環を介したスピロ結合によってインダセン骨格を結び付けた構造を合成した。2つのインダセン骨格が互いに約120℃の角度をなして折れ曲がった構造をしており、今後のマクロサイクル合成の基本となるものである。 3.ベンゼン環に縮環した飽和5員環の比較的大きな自由度や、環状ケトエステルでの容易なエピマ-化能を利用した分子識別能や自己組織化能をもつヘキサヒドロインダセン誘導体を本研究過程で新たに着想し、その合成研究を進めた。X線構造解析の結果、飽和5員環の両末端位置の置換基がインダセン骨格に対してほぼ垂直の配座を優先することが明らかとなったが、この特徴を今後の分子間会合研究に取り入れ、生かすことを計画している。
  • 日本学術振興会:科学研究費助成事業
    Date (from‐to) : 1996 -1997 
    Author : 辻 孝, 大北 雅一, 今井 敏郎, 鈴木 孝紀
     
    1.速度論的に安定化された[1.1]パラシクロファンの単離とX線構造解析。 我々が1993年にその合成を初めて報告した[1.1]パラシクロファンとその若干の置換体は、いずれも溶液中-20°C以下でのみ安定に存在し得る化合物であった。本研究において、そのベンゼン環上に-CH_2Si(CH_3)_3,-CON(CH_3)_2基を導入することによって著しく安定化されることを見い出し、単結晶として単離することに成功した。そのX線構造解析は、既存化合物中では最高度に変形したベンゼン環の存在を明らかにした。また、著しい変形にもかかわらず、理論計算から予測されたようにベンゼン環に検知し得るほどの結合交替はなく、良好な芳香族性の維持が示唆された。 2.速度論的に安定化された新規[1.1]パラシクロファンおよび[1.1]ナフタレノファンの合成研究。[4]パラシクロファン系における研究成果に基き、新たにメチレン側鎖上にアルキリデンを導入した[1.1]パラシクロファン誘導体、および、ベンゾ縮環を導入して共役系の拡張と速度論的安定化を兼ね備えた[1.1]ナフタレノファン誘導体の合成を進めた。これらの化合物では、[1.1]パラシクロファンの2つのベンゼン環上に電子的性質を異にする置換基の導入が可能であり、[1.1]パラシクロファンの特徴である強制された渡環相互作用による特性の発現が期待される。 3.[1.1]パラシクロファンの酸化還元挙動の解析。 理論計算は、[1.1]パラシクロファンのジカチオン種では2つのベンゼン環の面間隔の著しい減少と2つのベンゼン環に渡る電子の非局在化による新規な芳香族性の発現を示唆した。しかし、Et,CON(CH_3)_2基を置換した誘導体についてのCV測定では、安定なカチオンラジカル、ジカチオン種の生成は見い出せなかった。速度論的安定化が不十分なためと考えられ、上記(2)の化合物の合成を待ってさらに検討を進める。
  • Ministry of Education, Culture, Sports, Science and Technology:Grants-in-Aid for Scientific Research(基盤研究(C))
    Date (from‐to) : 1996 -1997 
    Author : Takanori SUZUKI
     
    The research project is intended to construct the novel redox-type photochromic systems based on the photoinduced electron transfer reactions of electron-donor-acceptor complexes in the crystalline state. In order to realize such an idea it is essential to develop a new type of redox molecules exhibiting bistability. Thus, the redox pairs were designed so as to undergo reversible C-C bond formation and cleavage upon electron transfer. The research started from examining the interconversion hexaphenylethane derivatives 1 and dicationic bis (triarylmethane) dyes 2. It has been found that they constitute the dynamic and reversible redox pair showing vivid change in color and drastic structural change upon electron transfer. They surely are the promising candidate for the present purpose. Unfortunately, however, attempts to obtain the CT crystal of 1 with a variety of electron donors have been unsuccessful, preventing me from realizing my initial proposal. Next, the biphenyl-type electron acceptors having dicyanovinyl moieties were investigated. 2,2'-Disubstituted derivative was found to undergo C-C bond formation upon two-electron reduction. By combining the further isomerization of the reduction product, the latter system constitute a prototype of the novel electrochromic system with "write protect" option.
  • 文部科学省:科学研究費補助金(重点領域研究)
    Date (from‐to) : 1995 -1995 
    Author : 鈴木 孝紀
     
    現在までに良好な電導性を示す数多くの分子性結晶が知らるようになったが、有機超伝導体を含めてそのほとんど全てが二成分以上から形成されている。これは、有機固体での電導性の担い手となる伝導電子を供給するという不可欠な要因によるものであるが、このこと自体が系の複雑さを増大させ、固体物性を司る結晶構造の制御をより困難にしている事も事実である。このような観点からすると単一成分有機電導体の研究はこの分野の新しい展開方向を指し示すものの一つと考えられる。そこで本課題では電気化学的両性度の高い新規な安定ラジカルを合成、単離しその単一成分有機電導体としての有効性を検討する事を目的として研究を行うことにした。実際の研究では四環性窒素複素環化合物であるキノキサロ[2,3-b]キノキサリン骨格(1)をモチーフとして選んだ。これは、ピラジンに代表される窒素複素環が代表的なW eitz型の酸化還元系を為すため電気化学的両性を付与しやすいこと、また極く限られた系ではあるものの中性ラジカルが安定に単離されている例があることを考慮した分子設計による。母体の1aとメチルトリフレートとの反応で5位が4級化されたカチオン種2aとした。このものの電子受容性は非常に高く、塩化メチレン中で還元電位の測定では+0.66及び-0.20Vに可逆な波形を示した。このことは2aの一電子還元で生成するラジカル種3aが0.86Vという小さなEsum値を持つ電気化学的両性の強い分子であることを予想させる。しかし、ヨウ化物イオンを用いた2aの還元では電子スペクトルで748nmの吸収を有する新しい化学種が観測されたものの半減期が10秒程と不安定な為その単離には至らなかった。そこで1aの1,4,7,10位の4箇所に様々な置換基を導入した化合物から出発しラジカル種3を安定に単離した。これらは10^<-7>から10^<-9>Scm^<-1>程度の電導性を示すことが明らかとなった。これらの値は決して高いものではないが、本研究の分子設計の妥当性を示すものである。
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 1994 -1995 
    Author : MIYASHI Tsutomu, MCBRIDE J.Michael, HILINSKI Edwin.F., GOODMAN Joshua.L., WAGNER Peter J., AKIYAMA Kimio, SUZUKI Takanori, TAKAHASHI Yasutake, IKEDA Hiroshi, MARIANO Patrick S., DINNOCENZO Joseph P., BERSON Jerome A.
     
    We have studied the relationship between biradical (BR) and cation radical(CR)intermediates in the photoinduced electron-tranfer(PET)skeletal rearrangement of organic compounds. In general, a nondistonic CR of a donor substrate generated by PET from the excited state of sensitizer (A)can undergo the bond formation or bond cleavage to give a more stable distonic CR intermediates (I^<・+>). Although free distonic CRs have been often observed spectroscopically and/or captured by a trapping reagent such as molecular oxygen or alcohol, reactions of a distonic CR in an ion pair [I^<・+>/A^<・->] have not been well understood yet. There are two possibilities for the decay of a distonic CR intermediate. One is back electron transfer (BET) from A^<・-> to give a singlet or triplet BR intermediate, which give final product (s) by the bond cleavage or formation. The other one is an alternative possible sequence, i.e., bond cleavage or formation in a CR stage followed by BET.In order to know which process is operative, we use two complementary laser techniques, time-resolved absorption spectroscopy for the direct observation of CR and BR intermediates and time-resolved photoacoustic calorimetry for the determination of energy of [I^<・+>/A^<・->]. As result, we found three PET reactions that proceed through both CR and BR intermediates. The first is the PET degenerate Cope rearrangement of 2,5-diaryl-1,5-hexadiene, which proceeds in a CR cyclization-BR cleavage mechanism through 1,4-diarylcyclohexa-1,4-diyl CR and 1,4-diarylcyclohexa-1,4-diyl BR.The second example is the degenerate methylenecyclopropane rearrangement of 2,2-diarylmethylenecyclopropane induced by PET,which involves a trimethlenemethane CR (TMM^<・+>) and corresponding BR (TMM). The last case is the generation of singlet and triplet tetramethyleneethane BRs by cyclization of 5,5-dimethy1-2,3-bis (1-phenylvinyl) cyclopentadiene CR. Those three PET reactions provided an intriguing conclusion that BET in an ion pair is an important key process which connects CR chemistry with BR chemistry. This conclusion is quite noteworthy since, up to the present, BET was usually considered as an energy wasting process.
  • Ministry of Education, Culture, Sports, Science and Technology:Grants-in-Aid for Scientific Research(一般研究(C))
    Date (from‐to) : 1994 -1995 
    Author : Takanori SUZUKI
     
    The research project is intended to construct the organic redox systems which exhibit the electrochemical response such as electrochromism. In order to realize such molecular systems a new way of molecular designing was adopted where (1) the charged species would be stabilized by formation of strong chromophores with large pi-conjugation but not by aromatization and (2) drastic structural changes should be occurred during the electron transfer. These conditions are quite different from what had been used to design the multi-stage redox systems for a long time. The "dynamic redox behavior"is the central concept in this work, thus the redox pairs were designed so as to undergo reversible C-C bond formation andcleavage upon electron transfer. Dibenzo-TTF derivatives inserted with a cycloalkane ring as well as their isomersof the tricyclic skeleton were studiedin detail as prototypes. Some molecules studies here were proven to be thereversible dynamic redox systems . In orderr to construct the electrochromic systems other molecules containing triarylmethane dye skeletons were designed. The reversible interconversion between hexaarylethane derivatives and bis (triarylmethane) dications was demonstrated .
  • 文部科学省:科学研究費補助金(重点領域研究)
    Date (from‐to) : 1994 -1994 
    Author : 鈴木 孝紀
     
    本研究では電気化学的両性度の高い新規な安定ラジカルを合成単離し、その単一成分有機電導体としての有効性を検討する事を目的としている。実際の分子設計に於いては、電子供与性(D)及び受容性(A)双方の部分構造を一分子内に含むA-π-D^・型の中性ラジカルを設計した。平成6年度にはD^・骨格となるピリジル基のN上に、長さの異なるアルキル鎖を有するR-1の研究を行なった。得られたラジカルは高い電気化学的両性度を有し、またRの長さによってその酸化還元挙動は変化しない。しかし、その電導性はRの長さにより系統的に変化することが見いだされた。メチルおよびペンチル体のX線構造解析によれば、これらのラジカルはいずれもA^<-・>-π-D^+型の分極構造を有していることが示され、また結晶中に於ける分子の重なりも非常に良く似ている。しかし、Rが長くなるにつれて結晶構造の二次元性が顕著に低下し、これが電導性の変化につながっていることが明らかとなった。
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research
    Date (from‐to) : 1992 -1993 
    Author : MIYASHI Tsutomu, SUZUKI Takanori, IKEDA Hiroshi, TAKAHASHI Yasutake
     
    The photoinduced CR Cope rearrangements of 2,5-diaryl-1,5-hexadiene derivatives were investigated in terms of the energy surface. Combining chemical evidences with results on Ea for cyclization of diene cation radicals and the energy level of the cyclohexa-1,4-cation radical ion-pair obtained by pulse-radiolysis and photoacoustic calorimetric analysis, a cation radical cyclization-diradical cleavage mechanism was established for the photoinduced CR Cope rearrangement. The PET reaction of 1,4-diaryl-2,3-dimethylbicyclo[2.2.0]hexanes which is related to the CR Cope rearrangement provided the sensitizer and solvent polarity-dependent dual reactivity of 1,4-diaryl-2,3-dimethylbicyclo[2.2.0]hexane cation radicals. The intramolecular [2+2]cycloadditions of 2,6-diaryl-1,6-heptadiene cation radicals to form bicyclo[3.2.0]hexanes occurred efficiently, but the efficiency markedly decreased with an increase in the number of the methylene group between two stirene units for the PET reactions of 2,7-diaryl-1,7-octadienes and 2,8-diaryl-1,8-nonadienes. The PET reactions of the 3,4-bis(styryl)-substituted furan and pyrrole derivatives were investigated by laser flash photolysis, which proved the generation of fused dimethylenefuran and dimethylenepyrrole derivatives and provided rate constants of chemical capture with electron-deficient diylophiles. By combination of these results with stereochemistry of chemical capture and MO calcultations, the ground state singlet states of fused dimethylenefuran and dimethylenepyrrole derivatives was determined. Experimental verification of the inversion of the spin multiplicity of dimethylenepyrroles is currently investigated for pyrrole derivatives with an electron-withdrawing group. Photoexciation reactions of solid state molecular complexes of BTDA and three divinyl benzenes provided intersting [2+2]cycloaddition reactions via electron-transfer. The probable absolute asymmetric synthesis via the single crystal-to-single crystal transformation is currently investigated for the solid state PET reaction of the molecular complex of BTDA and omicron-divinylbenzene.
  • 日本学術振興会:科学研究費助成事業
    Date (from‐to) : 1988 -1988 
    Author : 鈴木 孝紀
  • 機能性多段階酸化還元系の開発とその応答機能
  • Molecular Response System Based on Dynamic Redox Properties

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