Recent Progress in Transition-Metal-Catalyzed Asymmetric Reductive Amination

Asymmetric reductive amination (ARA) of a prochiral carbonyl compound with an amine using a H2/hydrogen surrogate is a concise and operationally simple method for the synthesis of chiral amines. ARA proceeds via condensation of a carbonyl group with an amine/ammonia followed by the enantioselective reduction of the generated intermediate. The activation of reductant and stereoselective transfer of hydrogen to intermediate imine/enamine is often mediated by a chiral transition metal catalyst. Considering the wide applications of enantiopure amines in pharmaceuticals, agrochemicals, and materials, the development of effective catalysts for ARA has been intensively pursued in the last two decades. Since the first report by Blaser in 1999, this key research area has grown significantly in recent years, as reflected by the advances in catalyst design, diversifying substrate scope and better mechanistic understanding. Several highly efficient and general ARA methodologies applicable to challenging carbonyl and amine partners have been demonstrated, providing ready access to a variety of enantiopure amines. In this Review, we present the recent progress in ARA featuring diverse carbonyl and amine partners employing transition metal-catalysts. This Review provides an organized and critical discussion on catalyst engineering and evolution, expanding susbstrate scope and mechanistic insights. To conclude, the remaining challenges and opportunities in ARA are also highlighted.