A Highly cis-Selective and Enantioselective Metal-Free Hydrogenation of 2,3-Disubstituted Quinoxalines

摘要

A wide range of 2,3-disubstituted quinoxalines have been successfully hydrogenated with H-2 using borane catalysts to produce the desired tetrahydroquinoxalines in 80-99% yields with excellent cisselectivity. Significantly, the asymmetric reaction employing chiral borane catalysts generated by the insitu hydroboration of chiral dienes with HB(C6F5)(2) under mild reaction conditions has also been achieved with up to 96% ee, and represents the first catalytic asymmetric system to furnish optically active cis-2,3-disubstituted 1,2,3,4-tetrahydroquinoxalines.