Highly Enantioselective Direct Synthesis of Endocyclic Vicinal Diamines through Chiral Ru(diamine)-Catalyzed Hydrogenation of 2,2'-Bisquinoline Derivatives.

An asymmetric hydrogenation of 2,2'-bisquinoline and bisquinoxaline derivatives, catalyzed by chiral cationic ruthenium diamine complexes, was developed. A broad range of chiral endocyclic vicinal diamines were obtained in high yields with excellent diastereo- and enantioselectivity (up to 93:7 dl/meso and >99 % ee). These chiral diamines could be easily transformed into a new class of chiral N-heterocyclic carbenes (NHCs), which are important but difficult to access.