Asymmetric Conjugate Addition of Ethylene Sulfonyl Fluorides to 3-Amido-2-oxindoles: Synthesis of Chiral Spirocyclic Oxindole Sultams.

An enantioselective conjugate addition of ethylene sulfonyl fluorides to 3-amido-2-oxindoles has been developed. Quinine-derived squaramides were identified as efficient catalysts. A series of spirocyclic oxindole sultams were prepared with excellent yields and enantioselectivities. A reaction mechanism via bifunctional activation was proposed.