Nickel(II)-Catalyzed Asymmetric Propargyl [2,3]Wittig Rearrangement of Oxindole Derivatives: A Chiral Amplification Effect

摘要

A highly enantioselective [2,3]Wittig rearrangement of oxindole derivatives was realized by using a chiral N,N-dioxide/Ni-II complex as the catalyst under mild reaction conditions. A strong chiral amplification effect was observed, and allowed access to chiral 3-hydroxy 3-substituted oxindoles bearing allenyl groups in high yields and enantioselectivities (up to 92% ee) by using a ligand with only 15% ee. A reasonable explanation was given based on the experimental investigations and X-ray crystal structures of enantiomerically pure and racemic catalysts. Moreover, the first catalytic kinetic resolution of racemic oxindole derivatives by a [2,3]Wittig rearrangement was realized with high efficiency and stereoselectivity.