|Kohei Sekine||Last modified date：2021.06.05|
Assistant Professor / Department of Fundamental Organic Chemistry / Institute for Materials Chemistry and Engineering
|Kohei Sekine||Last modified date：2021.06.05|
|1.||R. Konrath, K. Sekine, I. Jevtovikj, R. Paciello, A. S. K. Hashmi, T. Schaub, Performance Enhancing Additives for Reusable Ruthenium-Triphos Catalysts in the Reduction of CO2 to Dimethoxymethane, Green Chemistry, 22, 6464-6470, 2020.10.|
|2.||S. Tavakkoli Fard, K. Sekine, K. Farshadfar, F. Rominger, M. Rudolph, A. Ariafard, A. S. K. Hashmi, Gold-Catalysed Annulation of 1,8-Dialkynylnaphthalenes: Synthesis and Photoelectric Properties of Indenophenalene-Based Derivatives, Chemistry -A European Journal, 2021.02.|
|3.||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, 18, 3239-3242, 2020.03.|
|4.||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..|
|5.||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, 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..
|6.||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, 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..|
|7.||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, 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..|
|8.||Yufeng Wu, Bing Tian, Chao Hu, Kohei Sekine, Matthias Rudolph, Frank Rominger, A. Stephen K. Hashmi, Chemodivergent reaction of azomethine imines and 2
H -azirines for the synthesis of nitrogen-containing scaffolds, Organic and Biomolecular Chemistry, 10.1039/c9ob00740g, 17, 22, 5505-5508, 2019.05, The metal-free reactions of 2H-azirines with C,N-cyclic azomethine imines were investigated. N-Bridged strained ring-fused triazole derivatives or 1,2,4-triazine derivatives are obtained, and the chemoselectivity is dependent on the protecting group on the azomethine dipole. Although benzoyl-protected starting materials give access to strained polycyclic compounds, a ring-opening occurs in the case of a tosyl protecting group that is cleaved during the process with elimination of sulfinic acid. 1,2,4-Triazine can be prepared on a mmol-scale and concomitantly oxidized with air as an oxidant to form the corresponding ketone, which is an interesting structural motif that can be found in bioactive scaffolds..
|9.||Lumin Zhang, Xiaojia Si, Yangyang Yang, Sina Witzel, Kohei Sekine, Matthias Rudolph, Frank Rominger, A. Stephen K. Hashmi, Reductive C-C Coupling by Desulfurizing Gold-Catalyzed Photoreactions, ACS Catalysis, 10.1021/acscatal.9b01368, 6118-6123, 2019.05, [Au2(μ-dppm)2]Cl2-mediated photocatalysis reactions are usually initiated by ultraviolet A (UVA) light; herein, an unreported system using blue light-emitting diodes (LEDs) as excitation light source was found. The red shift of the absorption wavelength originates from the combination of [Au2(μ-dppm)2]Cl2 and ligand (Ph3P or mercaptan). On the basis of this finding, a gold-catalyzed reductive desulfurizing C-C coupling of electrophilic radicals and styrenes mediated by blue LEDs is presented, a coupling which cannot be efficiently accessed by previously reported methods. This mild and highly efficient C-C bond formation strategy uses mercaptans both as electron-deficient alkyl radical precursor as well as the hydrogen source. Two examples of amino acids have also been modified by using this strategy. Moreover, this methodology could be applied in polymer synthesis. Gram-scale synthesis and mechanistic insights into this transformation are also presented..|
|10.||Yangyang Yang, Patrick Antoni, Marc Zimmer, Kohei Sekine, Florian F. Mulks, Long Hu, Lumin Zhang, Matthias Rudolph, Frank Rominger, A. Stephen K. Hashmi, Dual Gold/Silver Catalysis Involving Alkynylgold(III) Intermediates Formed by Oxidative Addition and Silver-Catalyzed C−H Activation for the Direct Alkynylation of Cyclopropenes, Angewandte Chemie - International Edition, 10.1002/anie.201812577, 58, 15, 5129-5133, 2019.04, While gold-mediated synergistic catalytic processes involving transmetalations with other metals are well understood, Au I /Au III cycles in these reactions are rarely reported. Herein a gold-catalyzed direct alkynylation of cyclopropenes is enabled by two operating catalytic cycles, an oxidative catalytic cycle involving an alkynyl Au III complex formed by oxidative addition and one involving a silver-mediated C−H activation..|
|11.||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(sp 3 )−H Alkylation/Arylation, Angewandte Chemie - International Edition, 10.1002/anie.201810526, 58, 6, 1823-1827, 2019.02, Herein we report a highly selective photoredox C(sp 3 )−H alkylation/arylation of ethers through the combination of a photo-organocatalyst (benzaldehyde) and a transition-metal catalyst (nickel). This method provides a simple and general strategy for the C(sp 3 )−H alkylation/arylation of ethers. A selective late-stage modification of (−)-ambroxide has also been conducted to demonstrate the applicability of the method..|
|12.||Kohei Sekine, Jürgen 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, 25, 1, 216-220, 2019.01, The gold-catalyzed facile synthesis of U-shaped and S-shaped bispentalenes is described from easily available tetra(arylethynyl)-benzenes and -naphthalenes. The optoelectronic and transistor properties were also investigated. The selectivity between the U-shaped and S-shaped bispentalene isomers can be tuned by the bulkiness of the ligand and the substrates. The S-shaped naphthalene-based bispentalene shows a one-dimensional face-to-face packing pattern in solid state and a good hole mobility, indicating that the S-shaped bispentalene core is highly suitable for transistor applications. The gold-catalyzed annulation of tetraynes provides a useful protocol in the synthesis of bispentalenes for organic semiconductors..|
|13.||Jin Xie, Kohei Sekine, Sina Witzel, Petra Krämer, 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, 2018.12, Organoboron compounds are versatile synthetic building blocks. We herein report a new strategy, a photochemical gold-catalyzed chemo-selective Hiyama arylation of B,Si bifunctionalized reagents with diazonium salts, which is orthogonal to common strategies and therefore a unique tool for synthesis of valuable biarylboronates. With this new methodology a wide array of diversely functionalized sp2- and sp3-hybridized biarylboronates were obtained. Notably, the synergism of gold catalysis with copper catalysis or palladium catalysis, allows for one-pot iterative C−X (heteroatom) and C−C couplings for the rapid assembly of several simple fragments to relatively complex molecules. Mechanistic studies indicated that photosensitizer-free conditions were superior to gold/Ru(bpy)3Cl2 dual catalysis..
|14.||Kohei Sekine, Fabian Stuck, Jürgen 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, 48, 12515-12518, 2018.08, The gold-catalyzed annulation of diethynyl N-heterocycles for the synthesis of quinoxaline-/phenazine-based pentalenes and the study of their optoelectronic properties are described. The inhibition of the gold catalyst by the nitrogen centers in the substrate and the product could be overcome by increasing the reaction temperature to 130 °C, which usually leads to catalyst decomposition in gold catalysis. At 130 °C, 6,7-di(arylethynyl)quinoxalines in chlorobenzene give the corresponding pentalenes. The annulation of 2,3-di(arylethynyl)quinoxalines requires an even higher temperature under microwave irradiation. The quinoxaline-based pentalenes showed lower LUMO levels compared to the corresponding naphthalene-based pentalenes..|
|15.||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, 2018.06, We describe a novel, short, and flexible approach to diverse N-doped polycyclic aromatic hydrocarbons (PAHs) through gold-catalyzed π-extension of anthranils with o-ethynylbiaryls as reagents. This strategy uses easily accessible starting materials, is simple due to high step and atom economy, and shows good functional-group compatibility as well as scale-up potential. Mechanistically, the tandem reaction is proposed to involve a nucleophilic addition/ring opening/regiospecific C−H annulation/protodeauration sequence terminated by a Friedel–Crafts-type cyclization. Photophysical studies of the products indicated violet-blue fluorescence emission with quantum yields up to 0.45..
|16.||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, In this report, hydroxymethylfurfural (HMF) is used as a bio-based feedstock for homogeneous metal-catalysed hydrogenation. Several ligand classes and metals are employed to reduce the aldehyde and aromatic ring of HMF. The previously unknown homogeneous catalysed hydrogenation of HMF to tetrahydrofuran-dimethanol (THFDM) was investigated using different catalyst systems. NHCs and phosphites give higher trans/cis ratios (between 1:1.25 and 1:3.95) of the product THFDM, but low conversions of only up to 17% accompanied by up to 92% yield of bis(hydroxymethyl)furan at 10 bar H
and 120 °C. Conversely, di-phosphine ligated ruthenium catalysts in up to 87% yield lead to the highest overall conversion but only moderate trans/cis ratios of only 1:3.1-1:5..
|17.||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, The scope of photosensitizer-free visible light-driven gold-catalyzed cross-coupling was evaluated by a wide variety of organoboron and organosilicon species using four equivalents of aryldiazonium salts and (4-CF3-C6H4)3PAuCl in MeOH. In addition, a C(sp or sp2)-C(sp2) cross-coupling of organotrimethylsilanes and aryldiazonium salts was investigated. The reactions can be conducted under very mild reaction conditions, with a reduced amount of aryldiazonium salt (1.2 equiv.) by using a catalytic amount of Ph3PAuNTf2 in MeCN under irradiation with blue LEDs at room temperature..|
|18.||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, 2017.01, 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..|
|19.||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, 2017.01, 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..|
|20.||Kohei Sekine, Yuta Sadamitsu, Tohru Yamada, SilverCatalyzed 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-methylenebut-3-yn-1-yl)silane 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..|
|21.||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, Highly Z-selective syntheses of oxazolidin-2-ones from propargylic alcohols containing internal alkynes and phenyl isocyanate were achieved by using a combination of silver acetate and N,N-dimethylaminopyridine. The catalytic system was applied to propargylic alcohols containing alkyl-substituted alkyne groups. By considering the results in the presence and absence of an electron-withdrawing group on the aromatics, it was shown that the silver catalyst effectively activates the C≡C triple bond by acting as a π-Lewis acid to produce the corresponding oxazolidinones with high Z-selectivities..|
|22.||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, 2015.01, 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 Eisomer 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..|
|23.||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, The silver salt catalyzed the C-C bond forming reaction of o-alkynylacetophenone derivatives and carbon dioxide. In this reaction, a carbonyl group and a furan skeleton were successively constructed to afford the corresponding dihydroisobenzofuran derivatives..
|24.||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, A catalytic amount of silver benzoate with 7-methyl-1,5,7-triazabicyclo[4. 4.0]dec-5-ene (MTBD) was an effective catalytic system for the reaction of carbon dioxide with various ketones containing an alkyne group at an appropriate position (see scheme). These reactions afforded the corresponding γ-lactone derivatives in good to high yields under mild conditions..|
|25.||Satoshi Kikuchi, Shunsuke Yoshida, Yuudai Sugawara, Wataru Yamada, Hau Man Cheng, Kohei Sekine, Izumi Iwakura, Taketo Ikeno, Tohru Yamada, 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 MeyerSchuster- type rearrangement of the propargylic alcohol was mediated by CO2 in DMF to afford the corresponding α,β-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..|