Cooperative Heterobimetallic Zinc/Alkaline Earth Metal Catalysis: A Zn/Sr Aminophenol Sulfonamide Complex for Catalytic Asymmetric Michael Addition of 3-Acetoxy-2-oxindoles to β-Ester Enones.

A heterobimetallic zinc/strontium catalyst has been developed for the asymmetric Michael addition of 3-acetoxy-2-oxindoles to β-ester enones in high yields with excellent enantioselectivities and high diastereoselectivities. This process represents that 3-acetoxy-2-oxindoles can be used as a stable air- and base-tolerant precursor for chiral 3-substituted 3-hydroxy-2-oxindoles.