Nobuyuki Imai

Direct asymmetric aldol reaction with recyclable fluorous organocatalyst.

Direct asymmetric aldol reactions of aldehydes with ketones in the presence of a catalytic amount of fluorous sulfonamide 4 and trifluoroacetic acid result in the corresponding aldol products in high yields with up to 96% ee. The fluorous organocatalyst 4 can be readily recovered from the reaction mixture by fluorous solid-phase extraction and could be reused without a significant loss of the catalytic activity and enantioselectivity.

First catalytic and enantioselective synthesis of silyl and stannyl substituted cyclopropylmethanols

Abstract Optically active silyl and stannyl substituted cyclopropylmethanols were effectively obtained by the catalytic and enantioselective cyclopropanation of γ-silyl and γ-stannyl substituted allylic alcohols with Et 2 Zn and CH 2 I 2 in the presence of chiral N,N′-bis(p-nitrobenzenesulfonyl)-1,2-cyclohexanediamine in good enantioselectivites. The absolute configurations of the resulting metallocyclopropanes were unambiguously established.

Enantioselective synthesis of curacin A. 1. Construction of C1–C7, C8–17, and C18–C22 segments

Abstract Total synthesis of curacin A, a novel antimitotic antiproliferative antibiotic, was achieved by the connection of C1C7, C8C17, and C18C22 segments. Enantioselective preparation of each segments were accomplished by asymmetric allylation, chiral synthon method, and asymmetric hydrolysis by using pig liver esterase, respectively.

Highly efficient asymmetric aldol reaction in brine using a fluorous sulfonamide organocatalyst.

A fluorous organocatalyst promotes direct asymmetric aldol reactions of aromatic aldehydes with ketones in brine to afford the corresponding anti-aldol products in high yield with up to 96% ee. Fluorous organocatalyst can be readily recovered by solid phase extraction using fluorous silica gel and reused without purification.

New generation of thiocarbonyl ylide and its 1,3-cycloaddition leading to tetrahydrothiophene derivatives☆

Abstract Thiocarbonyl ylide was found to be generated by thermolysis of bromo(trimethylsilylmethylthio)methyltrimethylsilane and its 1,3-cyclo-addition provided a new method for synthesis of tetrahydrothiophenes.

Enantioselective synthesis of curacin A. 2. Total synthesis of curacin A by condensation of C1–C7, C8–C17, and C18–C22 segments

Abstract Total synthesis of curacin A, a novel antimitotic antiproliferative antibiotic, was achieved by the connection of C1C7, C8C17, and C18C22 segments by Julia coupling and iminoether condensation.

Pyrrolidine ring formation by a new base-promoted 1,3-dipolar cycloaddition of N-(phenylthiomethyl) amino acid esters

Abstract N-Phenylthiomethyl derivatives of α-amino acid esters are attacked by α,β-unsaturated carboxylates in the presence of sodium hydride, undergoing 1,3-dipolar cycloaddition to give pyrrolidines.

Regiospecific Acetylation of Substituted α,α′‐Benzylidenedimethanols with Vinyl Acetate using Porcine Pancreas Lipase

Abstract Acetylation of substituted α,α′‐benzylidenedimethanols with 10 equivalents of vinyl acetate in the presence of 50 w/w% of porcine pancreas lipase (PPL) type II regiospecifically proceeded to afford only the corresponding E‐monoacetates in excellent yields without Z‐monoacetates, diacetate, or the starting materials.