Manganese-catalyzed asymmetric transfer hydrogenation of hydrazones

Abstract

The enantioselective reduction of CN bonds constitutes an effective strategy for the production of chiral amines. Herein, we report the first example of manganese-catalyzed asymmetric transfer hydrogenation of hydrazones by employing a readily available chiral aminobenzimidazole manganese(I) complex under mild conditions. The present protocol allows for the enantioselective transfer hydrogenation of a wide range of arylalkyl, dialkyl and diaryl hydrazones, providing the desired chiral hydrazines in excellent yields and enantioselectivities (65 examples, up to 99.9% ee). Of note, the current method is compatible with the challenging diaryl hydrazones without the requirement of an ortho-substitution on the phenyl ring. A preliminary study of the mechanism suggests that a manganese-hydride pathway is involved, and the high enantiocontrol of the reaction is attributed to a π-π stacking interaction between substrate and catalyst.