Highly Enantioselective Hydrogenation of Imines Catalyzed by Chiral Macrocyclic Boranes

In this paper, we report a macrocyclic alkene-derived borane catalyst for the asymmetric hydrogenation of imines. A wide range of imines was successfully converted to chiral amines in 80-97% yields and 40-97% ee. The macrocyclic framework is indispensable for excellent catalytic activity and enantioselectivity. A gram-scale reaction with 0.2 mol % catalyst loading achieved a turnover number of 485, the highest reported to date for frustrated Lewis pair-catalyzed asymmetric imine hydrogenation.