Amido-ene(amido) Ni(II)-Catalyzed Highly Enantioselective Transfer Hydrogenations of Ketone: Dual Functions of the Ene(amido) Group

Abstract

Catalytic asymmetric transfer hydrogenation (ATH) reactions of ketones have become an important tool for producing enantiomerically pure alcohols that are widely used in the syntheses of bioactive compounds. However, the high toxicities and low abundances of traditionally employed precious metals serving as catalyst centers have impeded widespread application of precious metal-based catalysts in asymmetric synthesis. Development of catalysts from abundant and less toxic 3d metals is highly desirable but still challenging. We report herein the development of structurally well-defined (R,R)-amido-ene(amido) nickel catalysts for ATH of ketone substrates, facilitating access to a wide range of secondary (S)-configuration alcohols, many of which are synthetic building blocks of biologically relevant molecules, with up to 95% enantiomeric excess (e.e.) and broad scope of functional group tolerance. Catalytic intermediate isolation and density functional theory calculation ascribed the catalytic activity to stabilization of the electron-rich nickel center with the ene(amido) group via a π-backdonation interaction within the catalytic intermediates, while the stereoinduction mainly arises from a catalyst–substrate π–π interaction in the transition state for enantioselective hydride transfer.