Rh-Catalyzed Asymmetric Hydrogenation of γ-Phthalimido-Substituted α,β-Unsaturated Carboxylic Acid Esters:  An Efficient Enantioselective Synthesis of β-Aryl-γ-amino Acids

A series of chiral beta-aryl-gamma-amino acid ester derivatives were synthesized in high enantioselectivities (93-97% ee) via the Rh-catalyzed asymmetric hydrogenation of gamma-phthalimido-alpha,beta-unsaturated carboxylic acid esters using highly modular chiral BoPhoz-type phosphine-aminophosphine ligands. The method has been applied successfully to the synthesis of several chiral pharmaceuticals including (R)-baclofen and (R)-rolipram with high enantioselectivities.