A New Chiral P,N-Ligand Derived from 1-Phenylphospholane-2-carboxylic Acid (Phenyl-P-proline) for Palladium-Catalyzed Asymmetric Allylic Substitution Reactions

New types of P,N-ligands, cis- and trans-3, containing a tetrahydroisoquinoline skeleton as an N-donor were synthesized from (1R,2S)-1-phenylphospholane-2-carboxylic acid (phenyl-P-proline, 1). The cis isomer, cis-3, was found to act as an excellent ligand in palladium-catalyzed asymmetric allylic substitution reactions. The reactions of 1,3-diphenyl-2-propenyl acetate (5) with several nucleophiles in the presence of [Pd(π-allyl)Cl]2, cis-3 (Pd : ligand=1 : 2), and a base afforded the desired products in high yields with high enantioselectivity. It was suggested that these ligands did not serve as P,N-bidentate ligands but as P-monodentate ligands in these reactions.