N-Heterocyclic Carbene Catalyzed Asymmetric Synthesis of Pentacyclic Spirooxindoles via [3+3] Annulations of Isatin-Derived Enals and Cyclic N-Sulfonyl Ketimines

A convenient enantioselective route to new types of pentacyclic spirooxindoles via [3+3] annulation reactions of isatin-derived enals and cyclic N-sulfonyl ketimines, using N-heterocyclic carbene (NHC) catalysis has been developed. The new protocol leads to pentacyclic spirooxindoles bearing a quaternary spirostereocenter in good yields and good to high enantiomeric ratios. peerReviewed