A versatile cobalt catalyst for highly enantioselective hydrogenation of carbonyl compounds

Abstract

A general base metal catalytic system for asymmetric hydrogenation of different types of carbonyl compounds has rarely been reported. Here, we describe the development of a versatile Co/BPE system for the asymmetric hydrogenation of both α-ketoamides and aryl alkyl ketones that enable fast access to various chiral α-hydroxy amides and secondary alcohols in excellent yields and enantioselectivities (up to 98% yield and 99:1 enantiomeric ratio [er]) under base- and additive-free conditions. More importantly, cobalt-catalyzed diastereo- and enantioselective hydrogenation of α-substituted β-ketoamides has been achieved for the first time under a dynamic kinetic resolution (DKR) process using the same system. The synthetic potential has been demonstrated through reaction scale-up, product derivatization, and synthesis of various key intermediates for chiral drugs. Mechanistic studies support a new Co(II) instead of a Co(II)/Co(0) catalytic cycle involving hydride transfer and H₂ splitting processes, in which the oxidation state of cobalt remains unchanged.