Paper | 発表論文

Umpolung-Driven Oxidative β-β Dimerization of Conjugated N-Sulfonylimines Enabled by Fluorinated NHCs

Z. Yang, K. Michigami, M. Ohashi
Chem. Lett. 2025, 54, upaf148.

Abstract:
We herein disclose a unique oxidative β-β dimerization of conjugated N-sulfonylimines via umpolung reactivity mediated by fluorinated N-heterocyclic carbenes. The elusive key aza-Breslow intermediate was successfully isolated and characterized by single-crystal X-ray diffraction studies. This underwent net 1e– oxidation of aza-homoenolate upon treating with a hypervalent iodine reagent, and the successive tail-to-tail radical-coupling afforded the imidzolium-bound dicationic bis-enamide product. The comprehensive studies including single-crystal X-ray analysis elucidated the molecular structure and stereochemistry, revealing the formation of a sole diastereomer.

Intense fluorescence of air-stable sodium diarylformamidinate: effective control with a novel electron-withdrawing 4-cyano-3,5-bis(trifluoromethyl)phenyl group

K. Michigami, D. Kawakami, I. Ueda, S. Ito, T. Ogaki, H. Ikeda, M. Ohashi
J. Mater. Chem. C 2025, 13, 1254-1262.

Abstract:
We developed the 4-cyano-3,5-bis(trifluoromethyl)phenyl group as a novel and potent monoaromatic acceptor unit. The CF₃ and CN substitution effects were evaluated through the absorption and emission properties of readily accessible sodium N,N′-diarylformamidinate salts endowed with electron-withdrawing monoaromatic substituents on the nitrogen atoms. Among the salts examined, the amidinates substituted with 4-cyano-3,5-bis(trifluoromethyl)phenyl were remarkably stable at ambient temperature under air and room light, remaining unchanged for over a year.

Merging Pd(0)-Catalyzed Selective C_acyl−O Bond Activation of Enol Esters with π-Acid Catalysis: Net Hydroxyacylation of Aliphatic Alkynes with Carboxylic Acids

K. Michigami, Y. Otawa, Y. Kanda, D. Kawakami, M. Ohashi
ACS Catal. 2024, 14, 12647-12653.

Abstract:
A catalytic system comprising Pd(0) and N-heterocyclic carbene (NHC) demonstrated remarkable efficiency in the acyl migration of enol carboxylates via the regioselective cleavage of the C_acyl−O bond. Employing NHC ligands with appropriate steric bulkiness and electron-donating ability facilitated the transformation of a diverse array of enol esters containing alkyl-substituted internal and terminal alkenes into unsymmetrical β-diketones.

Isolation of Cationic η³-Allenylnickel(II) Key Intermediate Complexes: Origins of Enantioselectivity and Regioselectivity in Nickel(0)-Catalyzed Asymmetric Propargylic Substitutions

Y. Miyazaki, K. Michigami, M. Ohashi
J. Am. Chem. Soc. 2024, 146, 8757-8767.

Abstract:
We succeeded in isolating the first example of a cationic η³-allenylnickel(II) complex via cleavage of the C−O bond in propargylic tert-butyl carbonate. Further stoichiometric and catalytic reactions employing the (R)-BINAP-coordinated cationic η³-allenylnickel(II) complex unequivocally demonstrated its involvement in the nickel-catalyzed APS reaction.

Asymmetric cyclization catalyzed by a chiral phosphoric acid-gold(I) hybrid complex as a multifunctional catalyst

N. Taniguchi, M. Ueda, K. Michigami, S. Mori, M. Ohashi
Bull. Chem. Soc. Jpn. 2024, 97, uoae026.

Abstract:
We designed and synthesized a novel gold(I) hybrid complex as a multifunctional catalyst that promotes asymmetric catalytic reactions through multipoint nonclassical noncovalent interactions in substrates that lack classical hydrogen-bond donors. We demonstrate its usefulness as a multifunctional catalyst by successfully developing the first catalytic asymmetric synthesis of dihydrocyclohepta[b]indoles.

N-Heterocyclic Carbenes with Polyfluorinated Groups at the 4- and 5-Positions from [3 + 2] Cycloadditions between Formamidinates and cis-1,2-Difluoroalkene Derivatives

M. Ohashi, K. Ando, S. Murakami, K. Michigami, S. Ogoshi
J. Am. Chem. Soc. 2023, 145, 23098-23108.

Abstract:
We developed a unique [3 + 2] cycloaddition reaction between formamidinates and perfluoroalkenes, such as tetrafluoroethylene and octafluorocyclopentene, in the presence of LiBF₄ that affords 4,5-difluorinated imidazolium and perfluorocyclopentene-fused imidazolium salts. This protocol can also be applied to perfluorobenzene to furnish a tetrafluorobenzimidazolium salt.
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Synthesis of Fluoroalkyl Sulfides via Additive-free Hydrothiolation and Sequential Functionalization Reactions

D. E. Sunagawa, N. Ishida, H. Iwamoto, M. Ohashi, C. Fruit, S. Ogoshi
J. Org. Chem. 2021, 86, 6015-6024.

Abstract:
A modular synthetic method, involving a hydrothiolation, silylation, and fluoroalkylation, for the construction of highly functionalized fluoroalkyl sulfides has been developed. The use of the aprotic polar solvent N,N-dimethylacetamide is the key to success in the additive-free chemoselective hydrothiolation of tetrafluoroethylene, trifluorochloroethylene, and hexafluoropropene with various thiols.

Copper(I)-Mediated C–N/C–C Bond-Forming Reaction with Tetrafluoroethylene for the Synthesis of N-Fluoroalkyl Heteroarenes via an Azacupration/Coupling Mechanism

N. Ishida, T. Adachi, H. Iwamoto, M. Ohashi, S. Ogoshi
Chem. Lett. 2021, 50, 442-444.

Abstract:
A novel copper-mediated N-fluoroalkylation of heteroarenes has been developed. Treating an in-situ-generated N–Cu complex with tetrafluoroethylene in the presence of iodoarenes furnished the corresponding N- and aryl-difunctionalized tetrafluoroethanes in up to 98% yield. This method enables the synthesis of tetrafluoroethylene-bridged heteroarenes in a one-pot reaction.

CsF-Catalyzed Fluoroacylation of Tetrafluoroethylene Using Acyl Fluorides for the Synthesis of Pentafluoroethyl Ketones

N. Ishida, H. Iwamoto, D. E. Sunagawa, M. Ohashi, S. Ogoshi
Synthesis 2021, 53, 3137-3143.

Abstract:
A catalytic method for the preparation of pentafluoroethyl ketones has been developed. The cesium fluoride catalyst can be used to convert acyl fluorides into the pentafluoroethyl ketones under tetrafluoroethylene pressure without generating stoichiometric quantities of chemical waste.

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