Rhodium-Catalyzed Highly Enantioselective Hydrogenation of a Tetrasubstituted Enamine

Abstract

A highly efficient rhodium-catalyzed asymmetric hydrogenation of a sterically hindered tetrasubstituted enamine (5) is disclosed, which facilitated quick and efficient access to a key synthetic chiral intermediate in the route to an active pharmaceutical ingredient. The new rhodium catalyst, prepared by combination of the cationic rhodium chiral diphosphine complex [Rh(cod){(2S,4S)-ptbp-skewphos}]OTf and potassium carbonate under pressurized hydrogen gas, gave full conversion and high enantioselectivity (>95% ee) in the asymmetric hydrogenation of 5. A 31P NMR study of the new catalyst was performed.