| 1. |
Di Wu, Akira Shiozuka, Kyohei Kawashima, Toshifumi Mori, Kohei Sekine, Yoichiro Kuninobu, Bifunctional 1-Hydroxypyrene Photocatalyst for Hydrodesulfurization via Reductive C(Aryl)-S Bond Cleavage, Organic Letters, 10.1021/acs.orglett.3c01061, 25, 18, 3293-3297, 2023.05, We developed the visible-light-induced hydrodesulfurization of alkyl aryl thioethers via the reductive cleavage of the C(aryl)-S bond using 1-hydroxypyrene as a Brønsted acid-reductant bifunctional photocatalyst. The hydrodesulfurization reaction proceeded under simple reaction conditions (1-hydroxypyrene and Et3N in THF under purple LED illumination); this reaction did not require chemicals commonly used for hydrodesulfurization, such as hydrosilanes, transition metal catalysts, and/or stoichiometric amounts of metal reagents. Detailed mechanistic studies based on control experiments, spectroscopic measurements, and computational studies revealed that the cleavage of the C(aryl)-S bond and the formation of the C(aryl)-H bond proceeded via the formation of the ion pair between the radical anion of alkyl aryl thioether and Et3N+H, resulting in the generation of a sulfur radical. In addition, the 1-hydroxypyrene catalyst was regenerated via hydrogen atom transfer (HAT) from Et3N.. |
| 2. |
Shiozuka, Akira; Sekine, Kohei; Kuninobu, Yoichiro, Photoinduced Organic Reactions by Employing Pyrene Catalysts, SYNTHESIS-STUTTGART, 10.1055/a-1739-4793, 54, 10, 2330-2339, 2022.05. |
| 3. |
Mori, Toshiaki; Sekine, Kohei; Kawashima, Kyohei; Mori, Toshifumi; Kuninobu, Yoichiro, Near-Infrared and Dual Emissions of Diphenylamino Group-Substituted Malachite Green Derivatives, EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, 10.1002/ejoc.202200873, 2022, 31, 2022.08. |
| 4. |
Shiozuka, Akira; Sekine, Kohei; Toki, Takumi; Kawashima, Kyohei; Mori, Toshifumi; Kuninobu, Yoichiro, Photoinduced Divergent Deaminative Borylation and Hydrodeamination of Primary Aromatic Amines, ORGANIC LETTERS, 10.1021/acs.orglett.2c01663, 24, 23, 4281-4285, 2022.06. |
| 5. |
Jiang, Zhiyan; Sekine, Kohei; Kuninobu, Yoichiro, Synthesis of fluorenes and their related compounds from biaryls and Meldrum's acid derivatives, CHEMICAL COMMUNICATIONS, 10.1039/d1cc06212c, 58, 6, 843-846, 2022.01. |
| 6. |
Yafang Dong, Kohei Sekine, Yoichiro Kuninobu, Facile synthesis of tribenzosilepins from terphenyls and dihydrosilanes by electrophilic double silylation., Chemical communications (Cambridge, England), 10.1039/d1cc02326h, 57, 57, 7007-7010, 2021.07, Tribenzosilepins were synthesized from terphenyls and dihydrosilanes via a facile approach using a double sila-Friedel-Crafts reaction. Several silepin derivatives were obtained in moderate to high yield. The reaction system was found to be suitable for synthesizing a bidirectional silepin. Furthermore, the transformation of the amino groups of tribenzosilepin derivatives to aryl groups and the extension of the backbone π-system in tribenzosilepin were demonstrated.. |
| 7. |
Christoph M Hendrich, Kohei Sekine, Takumi Koshikawa, Ken Tanaka, A Stephen K Hashmi, Homogeneous and Heterogeneous Gold Catalysis for Materials Science., Chemical reviews, 10.1021/acs.chemrev.0c00824, 121, 14, 9113-9163, 2021.07, Often stoichiometric amounts of gold find use in materials science; occasionally gold is even used as a support. This review discusses the contributions of gold catalysis, both homogeneous and heterogeneous, to the field of materials science. One topic is the synthesis of polymers, including nanowires and polyesters, the postcyclization of polymers, polymerization by cyclopropanation, and gold-catalyzed radical polymerization reactions. Other topics are dyes, phosphonium salts, and a wide range of extended conjugated π-systems, the latter ranging from acenes, pentalene derivatives, and different heterocyclic π-systems to fascinating applications in the synthesis of helical anellated aromatic molecules. The existing contributions clearly demonstrate the potential of gold catalysis for significant future impulses for the field of materials science.. |
| 8. |
Akira Shiozuka, Kohei Sekine, Yoichiro Kuninobu, Photoinduced Deaminative Borylation of Unreactive Aromatic Amines Enhanced by CO2., Organic letters, 10.1021/acs.orglett.1c01503, 23, 12, 4774-4778, 2021.06, Herein, direct unreactive C-N borylation of aromatic amines by a photocatalyst was achieved. The C-N borylation of aromatic amines with bis(pinacolato)diboron (B2pin2) proceeded using a pyrene catalyst under light irradiation to afford desired borylated products and aminoborane as a byproduct. The yield of the borylated product improved under a CO2 atmosphere which probably reduced the inhibitory effect of aminoborane. Mechanistic studies suggested that the C-N bond cleavage and C-B bond formation proceeded via a concerted pathway.. |
| 9. |
Sara Tavakkoli Fard, Kohei Sekine, Kaveh Farshadfar, Frank Rominger, Matthias Rudolph, Alireza Ariafard, A Stephen K Hashmi, Gold-Catalyzed Annulation of 1,8-Dialkynylnaphthalenes: Synthesis and Photoelectric Properties of Indenophenalene-Based Derivatives., Chemistry (Weinheim an der Bergstrasse, Germany), 10.1002/chem.202004846, 27, 10, 3552-3559, 2021.02, A simple gold-catalyzed annulation of 1,8-dialkynylnaphthalenes utilizing a cationic gold catalyst was developed. Such a peri-position of two alkynyl substituents has not been studied in gold catalysis before. Dependent on the substrate, the reactions either follow a mechanism involving vinyl cation intermediates or involve a dual gold catalysis mechanism which in an initial 6-endo-dig-cyclization generates gold(I) vinylidene intermediates that are able to insert into C-H bonds. Indenophenalene derivatives were obtained in moderate to high yields. In addition, the bidirectional gold-catalyzed annulation of tetraynes provided even larger conjugated π-systems. The optoelectronic properties of the products were also investigated.. |
| 10. |
Robert Konrath, Kohei Sekine, Ivana Jevtovikj, Rocco A. Paciello, A. Stephen K. Hashmi, Thomas Schaub, Performance enhancing additives for reusable ruthenium-triphos catalysts in the reduction of CO2 to dimethoxymethane, Green Chemistry, 10.1039/d0gc02528c, 22, 19, 6464-6470, 2020.09, Additives enhance the performance of a recyclable ruthenium-triphos catalyst system in the hydrogenation of carbon dioxide to dimethoxymethane. . |
| 11. |
Shohei Furuta, Toshiaki Mori, Yusuke Yoshigoe, Kohei Sekine, Yoichiro Kuninobu, Synthesis, structures and photophysical properties of hexacoordinated organosilicon compounds with 2-(2-pyridyl)phenyl groups, ORGANIC & BIOMOLECULAR CHEMISTRY, 10.1039/d0ob00484g, 18, 17, 3239-3242, 2020.05, We synthesised novel hexacoordinated organosilicon compounds with two 2-(2-pyridyl)phenyl groups. Single-crystal X-ray structure analyses indicated that Lewis acid-base interactions exist between the silicon atom and two nitrogen atoms of the pyridine rings, and that hexacoordinated organosilicon compounds have slightly distorted octahedral structures in the solid state. The hexacoordinated organosilicon compounds are stable in air, water, heat, acids, and bases. The fluorescent quantum yield increased dramatically and a significant red-shift of the maximum fluorescence wavelength was observed with the introduction of amino groups on the 2-(2-pyridyl)phenyl aromatic rings. The fluorescence colours of a hexacoordinated organosilicon compound with two amino groups can be switched by protonation and deprotonation (neutralisation) of the amino groups.. |
| 12. |
Yafang Dong, Masahiko Sakai, Kazuto Fuji, Kohei Sekine, Yoichiro Kuninobu, Synthesis of six-membered silacycles by borane-catalyzed double sila-Friedel-Crafts reaction, BEILSTEIN JOURNAL OF ORGANIC CHEMISTRY, 10.3762/bjoc.16.39, 16, 409-414, 2020.03, We have developed a catalytic synthetic method to prepare phenoxasilins. A borane-catalyzed double sila-Friedel-Crafts reaction between amino group-containing diaryl ethers and dihydrosilanes can be used to prepare a variety of phenoxasilin derivatives in good to excellent yields. The optimized reaction conditions were also applicable for diaryl thioethers to afford their corresponding six-membered silacyclic products. The gram-scale synthesis of a representative bis(dimethylamino)phenoxasilin and the transformation of its amino groups have also been demonstrated.. |
| 13. |
Yafang Dong, Yuta Takata, Yusuke Yoshigoe, Kohei Sekine, Yoichiro Kuninobu, Lewis acid-catalyzed synthesis of silafluorene derivatives from biphenyls and dihydrosilanes: Via a double sila-Friedel-Crafts reaction, Chemical Communications, 10.1039/c9cc07692a, 55, 88, 13303-13306, 2019.10, This journal is © The Royal Society of Chemistry. The synthesis of silafluorene derivatives from aminobiphenyl compounds and dihydrosilanes via a double sila-Friedel-Crafts reaction using a borane catalyst has been achieved. This method is applicable to the synthesis of a variety of silafluorene derivatives, such as multisubstituted silafluorenes, spirosilabifluorenes, and silicon-bridged terphenyl compounds, which are not readily obtained using conventional synthetic methods. In addition, we have demonstrated the transformation of the amino groups in these silafluorene derivatives into other substituents.. |
| 14. |
Katelyn P. Goetz, Kohei Sekine, Fabian Paulus, Yu Zhong, Daniel Roth, David Becker-Koch, Yvonne J. Hofstetter, Elena Michel, Lisa Reichert, Frank Rominger, Matthias Rudolph, Sven Huettner, Yana Vaynzof, Eva M. Herzig, A. Stephen K. Hashmi, Jana Zaumseil, The effect of side-chain length on the microstructure and processing window of zone-cast naphthalene-based bispentalenes, Journal of Materials Chemistry C, 10.1039/c9tc04470a, 7, 43, 13493-13501, 2019.10, © 2019 The Royal Society of Chemistry. The solubilizing side-groups of solution-processable π-conjugated organic semiconductors affect both the crystal structure and microstructure of the respective thin films and thus charge-carrier mobility in devices. In this work, we explore how the alkyl side-chain length influences thin-film structure and charge transport in field-effect transistors of zone-cast, naphthalene-based bispentalenes. By tuning the alkyl-chain length and the casting speed, we alter the microstructure from highly aligned ribbons, to feathered ribbons, to disordered grains. Concurrently, the hole mobility changes over two orders of magnitude, from 0.001 cm2 V-1 s-1 at the fastest speeds to roughly 0.1 cm2 V-1 s-1 at slower speeds. The highest mobilities correspond to the presence of an aligned ribbon morphology. While optical measurements indicate negligible electronic differences between the molecules, grazing incidence X-ray diffraction measurements show that the films display different degrees of order and alignment. The compound with pentyl side-chains exhibits the largest tolerance to different processing conditions, yielding an aligned ribbon microstructure and high mobility over a wide range of casting speeds. Our results highlight the impact that even small changes to the molecular structure can have on the processing window and transport properties of thin-film devices.. |
| 15. |
Sara Tavakkolifard, Kohei Sekine, Lisa Reichert, Mina Ebrahimi, Ketevan Museridz, Elena Michel, Frank Rominger, Rasool Babaahmadi, Alireza Ariafard, Brian F. Yates, Matthias Rudolph, A. Stephen K. Hashmi, Gold-Catalyzed Regiospecific Annulation of Unsymmetrically Substituted 1,5-Diynes for the Precise Synthesis of Bispentalenes, Chemistry - A European Journal, 10.1002/chem.201902381, 25, 52, 12180-12186, 2019.09, © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Precise control of the selectivity in organic synthesis is important to access the desired molecules. We demonstrate a regiospecific annulation of unsymmetrically substituted 1,2-di(arylethynyl)benzene derivatives for a geometry-controlled synthesis of linear bispentalenes, which is one of the promising structures for material science. A gold-catalyzed annulation of unsymmetrically substituted 1,2-di(arylethynyl)benzene could produce two isomeric pentalenes, but both electronic and steric effects on the aromatics at the terminal position of the alkyne prove to be crucial for the selectivity; especially a regiospecific annulation was achieved with sterically blocked substituents; namely, 2,4,6-trimetyl benzene or 2,4-dimethyl benzene. This approach enables the geometrically controlled synthesis of linear bispentalenes from 1,2,4,5-tetraethynylbenzene or 2,3,6,7-tetraethynylnaphthalene. Moreover, the annulation of a series of tetraynes with a different substitution pattern regioselectively provided the bispentalene scaffolds. A computational study revealed that this is the result of a kinetic control induced by the bulky NHC ligands.. |
| 16. |
Wu Y, Tian B, Hu C, Sekine K, Rudolph M, Rominger F, Hashmi ASK, Chemodivergent reaction of azomethine imines and 2H-azirines for the synthesis of nitrogen-containing scaffolds., Organic & biomolecular chemistry, 10.1039/c9ob00740g, 17, 22, 5505-5508, 2019.06. |
| 17. |
Y. Yang, P. Antoni, M. Zimmer, K. Sekine, F. Mulks, L. Hu, L. Zhang, M. Rudolph, F. Rominger, A. S. K. Hashmi, Dual Gold/Silver Catalysis Involving Alkynylgold(III) Intermediates Formed by Oxidative Addition and C,H-Activation for the Direct Alkynylation of Cyclopropenes, Angewandte Chemie International Edition, 58, 5129-5133, 2019.01. |
| 18. |
Kohei Sekine, Juergen Schulmeister, Fabian Paulus, Katelyn P. Goetz, Frank Rominger, Matthias Rudolph, Jana Zaumseil, A. Stephen, K. Hashmi, Gold-Catalyzed Facile Synthesis and Crystal Structures of Benzene-/Naphthalene-Based Bispentalenes as Organic Semiconductors, Chemistry - A European Journal, 10.1002/chem.201805637, 26, 1, 216-220, 2019.01. |
| 19. |
Lumin Zhang, Xiaojia Si, Yangyang Yang, Marc Zimmer, Sina Witzel, Kohei Sekine, Matthias Rudolph, A. Stephen, K. Hashmi, The Combination of Benzaldehyde and Nickel-Catalyzed Photoredox C(sp3)−H Alkylation/Arylation, Angewandte Chemie International Edition, 10.1002/anie.201810526, 58, 6, 1823-1827, 2019.01. |
| 20. |
Jin Xie, Kohei Sekine, Sina Witzel, Petra Kraemer, Matthias Rudolph, Frank Rominger, A. Stephen, K. Hashmi, Light-Induced Gold-Catalyzed Hiyama Arylation: A Coupling Access to Biarylboronates, Angewandte Chemie International Edition, 10.1002/anie.201806427, 57, 51, 16648-16653, 2018.11. |
| 21. |
Tohru Yamada, Kohei Sekine, Yuta Sadamitsu, Kodai Saito, Silver-Catalyzed CO2 Incorporation, Silver Catalysis in Organic Synthesis, 10.1002/9783527342822.ch7, 407, 2018.08. |
| 22. |
Kohei Sekine, Fabian Stuck, Juergen Schulmeister, Thomas Wurm, Dominik Zetschok, Frank Rominger, Matthias Rudolph, A. Stephen, K. Hashmi, N-Heterocycle-Fused Pentalenes by a Gold-Catalyzed Annulation of Diethynyl-Quinoxalines and -Phenazines, Chemistry - A European Journal, 10.1002/chem.201803096, 24, 12515-12518, 2018.07. |
| 23. |
Zhongyi Zeng, Hongming Jin, Kohei Sekine, Matthias Rudolph, Frank Rominger, A. Stephen, K. Hashmi, Gold-Catalyzed Regiospecific C−H Annulation of o-Ethynylbiaryls with Anthranils: π-Extension by Ring-Expansion En Route to N-Doped PAHs, Angewandte Chemie International Edition, 10.1002/anie.201802445, 57, 23, 6935-6939, 2018.05. |
| 24. |
Alban Cadu, Kohei Sekine, Jaroslaw Mormul, Dominik M. Ohlmann, Thomas Schaub, A. Stephen, K. Hashmi, Homogeneous catalysed hydrogenation of HMF, Green Chemistry, 10.1039/c8gc01025k, 20, 14, 3386-3393, 2018.01. |
| 25. |
Sina Witzel, Kohei Sekine, Matthias Rudolph, A. Stephen, K. Hashmi, New transmetalation reagents for the gold-catalyzed visible light-enabled C(sp or sp2)–C(sp2) cross-coupling with aryldiazonium salts in the absence of a photosensitizer, Chemical Communications, 10.1039/c8cc08227h, 54, 98, 13802-13804, 2018.01. |
| 26. |
Nao Sugiyama, Masatoshi Ohseki, Ryo Kobayashi, Kohei Sekine, Kodai Saito, Tohru Yamada, Silver-catalyzed Three-component Reaction of Propargylic Amines, Carbon Dioxide, and N-Bromosuccinimide for Stereoselective Preparation of (E)-Bromovinyloxazolidinones, CHEMISTRY LETTERS, 10.1246/cl.170541, 46, 9, 1323-1326, 2017.09, The stereoselective synthesis of (E)-bromovinyloxazolidinones was developed by the three-component reaction of propargylic amines, carbon dioxide, and N-bromosuccinimide in the presence of a silver catalyst with a base. Among the bases, a guanidine derivative has a significant effect on this bromination reaction. This catalytic reaction could be applied to various propargylic amines to produce the corresponding bromovinyloxazolidinones in good yields.. |
| 27. |
Keiichi Komatsuki, Yuta Sadamitsu, Kohei Sekine, Kodai Saito, Tohru Yamada, Stereospecific Decarboxylative Nazarov Cyclization Mediated by Carbon Dioxide for the Preparation of Highly Substituted 2-Cyclopentenones, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 10.1002/anie.201705909, 56, 38, 11594-11598, 2017.09, Highly substituted 2-cyclopentenones were stereospecifically and regioselectively constructed with high catalytic efficiency through Lewis-acid catalyzed decarboxylative Nazarov cyclization of the cyclic carbonate derivative, which is prepared by reacting the propargyl alcohol with carbon dioxide in the presence of a silver catalyst. The stereochemistry of the 2-cyclopentenone is strictly controlled by the geometry of the alkene in the starting material. This method is applicable for various substrates.. |
| 28. |
Kohei Sekine, Gold and carbon dioxide: quo vadis, Gold Bulletin, 10.1007/s13404-017-0207-y, 50, 2, 203, 2017.04. |
| 29. |
K. Sekine, T. Yamada, Silver-catalyzed carboxylation, CHEMICAL SOCIETY REVIEWS, 10.1039/c5cs00895f, 45, 16, 4524-4532, 2016.08, Silver-catalyzed reactions are some of the important methodologies in organic chemistry. Since 2007, a new application of silver catalysts has been emerging. For the sequential carboxylation and cyclization of alkyne derivatives, such as propargyl alcohols and amines, using carbon dioxide, silver catalysts show significant reactivity under mild conditions unlike other transition metals. These developments have received much attention for the effective utilization of carbon dioxide in organic chemistry to synthesize heterocyclic compounds. Related silver-catalyzed C-C bond forming reactions with carbon dioxide have also provided the synthetic methods of the corresponding carboxylic acid derivatives. In this review, the recent studies of the silver-catalyzed carboxylation reactions using carbon dioxide are described.. |
| 30. |
Kohei Sekine, Yuta Sadamitsu, Tohru Yamada, Silver Catalyzed Cascade Carboxylation and Cyclization of Trimethyl(2-methylenebut-3-yn-1-yl)silane Derivatives, ORGANIC LETTERS, 10.1021/acs.orglett.5b03023, 17, 22, 5706-5709, 2015.11, C-C bond forming carboxylation, and cyclization: of trimethyl(2-rnethylenbut-3,7yl)silaile derivatives and carbon dioxide was developed. Silver catalysts and CsF promoted the reaction to afford the:corresponding 2-furanone and 2-pyrone derivatives in good-to-high yields. The structure of the 2:furanone was confirmed by single-crystal X-ray crystallography, which revealed that the geometry of the exo-olefin was that of a Z-isomer. When an aromatic ring substituted alkyne was used, 2-furanone derivatives were selectively obtained via 5-exo-dig-cyclization, whereas the reaction of alkyl-substituted alkynes produced 2-pyrone derivatives with high selectivity.. |
| 31. |
Kohei Sekine, Ryo Kobayashi, Tohru Yamada, Silver-catalyzed Three-component Reaction of Propargylic Amines, Carbon Dioxide, and N-Iodosuccinimide for Stereoselective Preparation of (E)-Iodovinyloxazolidinones, CHEMISTRY LETTERS, 10.1246/cl.150584, 44, 10, 1407-1409, 2015.10, The silver-catalyzed three-component reaction of propargylic amines, carbon dioxide, and N-iodosuccinimide for the stereoselective synthesis of (E)-iodovinyloxazolidinones was developed. The silver-catalytic system could be applied to various propargylic amines to afford the corresponding iodovinyloxazolidinones in high yields. The structure of the oxazolidinone was confirmed by X-ray structure analysis to be the E-isomer for the geometry of the exo-olefin. The silver-catalyzed cyclization and replacement of silver with the iodine group in the intermediate were thought to be crucial steps.. |
| 32. |
Kohei Sekine, Takanori Mawatari, Tohru Yamada, Synthesis of Oxazolidin-2-ones by Tandem Cyclization of Propargylic Alcohols and Phenyl Isocyanate Promoted by Silver Catalysts as π-Lewis Acids, Synlett, 10.1055/s-0035-1560263, 26, 17, 2447-2450, 2015.10. |
| 33. |
Kohei Sekine, Ayano Takayanagi, Satoshi Kikuchi, Tohru Yamada, Silver-catalyzed C–C bond formation with carbon dioxide: significant synthesis of dihydroisobenzofurans, Chemical Communications, 10.1039/c3cc47221c, 49, 96, 11320-11322, 2013.11. |
| 34. |
Satoshi Kikuchi, Kohei Sekine, Tomonobu Ishida, Tohru Yamada, C-C Bond Formation with Carbon Dioxide Promoted by a Silver Catalyst, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 10.1002/anie.201201399, 51, 28, 6989-6992, 2012.07. |
| 35. |
Kikuchi, Satoshi, Yoshida, Shunsuke, Sugawara, Yuudai, Yamada, Wataru, Cheng, Hau-Man, Fukui, Kosuke, Sekine, Kohei, Iwakura, Izumi, Ikeno, Taketo, Yamada, Tohru, Silver-Catalyzed Carbon Dioxide Incorporation and Rearrangement on Propargylic Derivatives, BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN, 10.1246/bcsj.20110078, 84, 7, 698-717, 2011.07, A silver/DBU catalyst system was developed for the effective synthesis of cyclic carbonate and oxazolidinone from the reaction of CO2 with propargylic alcohols and propargylic amines, respectively, in high yields under mild conditions. It was found that the [3,3]-sigmatropic Meyer Schuster-type rearrangement of the propargylic alcohol was mediated by CO2 in DMF to afford the corresponding alpha,beta-unsaturated carbonyl compounds in high yields. The silver salt combined with the chiral Schiff base ligand could be applied to enantioselective chemical CO2 incorporation into various bispropargylic alcohols to produce the corresponding cyclic carbonate in high yields with high enantioselectivity. The absolute configuration was determined by VCD spectroscopy as well as by X-ray analysis. These products were found to be active for the aminolysis reaction to afford the corresponding carbamate derivatives in high yields without any loss of optical purity.. |
