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

[GRAPHICS] A series of BoPhoz-type ligands were successfully applied in the rhodium-catalyzed asymmetric hydrogenation of a number of P-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 (S-c,R-p)-1d, bearing two CF3-groups in the 3,5-position of the phenyl ring of aminophosphino moiety, showed the highest enantioselectivity.