Highly Enantioselective Hydrogenation of Enamides Catalyzed by Chiral Phosphoric Acids

A highly enantioselective hydrogenation of enamides catalyzed by a dual chiral−achiral acid system was developed. By employing a substoichiometric amount of a chiral phosphoric acid and acetic acid, catalyst loadings as low as 1 mol % of the chiral catalyst were sufficient to provide excellent yield and enantioselectivity of the reduction product.