Organocatalytic asymmetric Michael addition of 3-substituted oxindoles to α,β-unsaturated acyl phosphonates for the synthesis of 3,3′-disubstituted oxindoles with chiral squaramides

Abstract

A highly enantioselective Michael addition of 3-monosubstituted oxindoles to α,β-unsaturated acyl phosphonates with chiral squaramides as catalysts is investigated for the first time. A wide range of 3,3′-disubstituted oxindole adducts bearing adjacent quaternary and tertiary stereogenic centres could be smoothly obtained in good yields (up to 98%), diastereo- (up to >99 : 1 dr) and enantioselectivities (up to 98% ee) with the developed protocols.