Highly enantioselective hydrogen-transfer reductive amination: catalytic asymmetric synthesis of primary amines.

Optically active amines are attracting increasing interest in the food, agrochemical, and pharmaceutical industries as building blocks for novel compounds and as templates for asymmetric synthesis. One of the most common methods for preparing amines is the reductive amination of carbonyl compounds. We have successfully explored the rhodiumcatalyzed asymmetric reductive amination with hydrogen as the reducing agent. Recently, we developed a highly active and enantioselective catalytic system for the reductive amination of a-keto acids. In the course of our studies we observed that the reaction of phenylpyruvic acid in methanolic ammonia at 60 8C in the presence of a Rh catalyst smoothly furnished N-(phenylacetyl)phenylalaninamide [Eq. (1)]. The formation of this product from phenylpyruvic acid and ammonium sulfate proceeds in the absence of a catalyst at a higher temperature (105 8C).