Bi- and Trifunctional Catalysts for Oxindoles with Quaternary Stereocenters

Significance

Zhu and Lu report an efficient conjugate addition of oxindoles to vinyl bis(sulfone) 2 to generate all-carbon quaternary stereocenters. While the known bifunctional catalyst 3 was found to be optimal for the reaction of 3-aryl-substituted oxindoles 1, extension of the scope to 3-alkyl-substituted oxindoles 5 required the synthesis of a novel catalyst class. The trifunctional catalyst 6, which bears a chiral tertiary amine moiety in addition to two (putative) hydrogen bond donors, was developed. It was found to promote the reaction leading to 3-alkyl-3-aryl-disubstituted products 7 with very good enantioselectivities and yields.