Asymmetric Hydrogenation of Hydrazones with Chiral Boranes.

An enantioselective metal-free hydrogenation of hydrazones has been realized successfully using chiral boranes as catalysts, producing a range of optically active hydrazines in 87-99% yields with 75-93% ee's. The bulky 2,2,6,6-tetramethylpiperidinyl moiety was found to be essential for achieving the high enantioselectivities.