Chiral Amine Thiourea-Promoted Enantioselective Michael Addition Reactions of 3-Substituted Benzofuran-2(3<i>H</i>)-ones to Maleimides

A highly diastereo- and enantioselective Michael addition reaction with respect to prochiral 3-substituted benzofuran-2(3H)-ones and maleimides by a chiral bifunctional thiourea−tertiary amine catalyst was investigated. The corresponding adducts, containing a quaternary center at the C3-position of the benzofuran-2(3H)-one as well as a vicinal tertiary center, were generally obtained in high yields (up to 99%) with very good diastereo- (up to >20:1 dr) and enantioselectivities (up to 97% ee).