Enantioselective Synthesis of β2-Amino Acids via Rh-Catalyzed Asymmetric Hydrogenation with BoPhoz-Type Ligands: Important Influence of an N−H Proton in the Ligand on the Enantioselectivity

A series of BoPhoz-type ligands were successfully applied in the rhodium-catalyzed asymmetric hydrogenation of a number of beta-substituted or unsubstituted alpha-(phthalimidomethyl)acrylates, affording good to excellent enantioselectivities. The results suggested that the presence of an N-H proton in the BoPhoz backbone could significantly improve the enantioselectivity, and ligand (Sc,Rp)-1d, bearing two CF3-groups in the 3,5-position of the phenyl ring of aminophosphino moiety, showed the highest enantioselectivity.