Enantioselective Michael addition of N-substituted 3-chlorooxindoles with 1,1-bis(arylsulfonyl)ethylenes: access to 3,3-disubstituted and spirocyclopropane-fused oxindoles.

Abstract

We report a highly enantioselective organocatalyzed Michael addition of N-substituted 3-chlorooxindoles to 1,1-bis(arylsulfonyl)ethylenes. With a readily available quinine-derived catalyst under mild conditions, this reaction delivers chiral 3,3-disubstituted oxindoles in high yields (up to 93%) and enantioselectivities (up to 92% ee). The protocol features broad substrate scope, tolerating a variety of substituents at the 4- to 6-positions of the oxindole ring, as well as diverse N-aryl or N-alkyl groups. Furthermore, the resulting adducts undergo facile intramolecular SN2-type cyclization to give spirocyclopropane-fused oxindoles with full retention of enantiomeric purity. A one-pot cascade variant is also demonstrated; notably, 3-bromooxindole delivers the spirocyclopropane product with 98% ee.