Highly enantioselective direct vinylogous Michael addition of γ-substituted deconjugated butenolides to maleimides catalyzed by chiral squaramides

Abstract

Highly enantioselective direct vinylogous Michael reactions of γ-aryl-substituted deconjugated butenolides with maleimides, catalyzed by only 1 mol% bifunctional squaramides derived from cinchona alkaloids, were achieved with excellent yields (up to 96%) and enantioselectivities (up to 97% ee). This protocol features a very low catalyst loading, mild reaction conditions and provides a potential and effective method for the construction of optically active chiral butenolides with adjacent quaternary and tertiary stereocenters.