Squaramide-Tertiary Amine Catalyzed Asymmetric Cascade Sulfa-Michael/Michael Addition via Dynamic Kinetic Resolution: Access to Highly Functionalized Chromans with Three Contiguous Stereocenters

An efficient asymmetric cascade sulfa-Michael/Michael addition reaction catalyzed by a chiral bifunctional squaramide-tertiary amine catalyst has been developed. This organocatalytic cascade reaction provides easy access to highly functionalized chromans with three contiguous stereocenters, including one quaternary center. In addition, a novel cascade sulfa Michael/retro-sulfa-Michael/sulfa-Michael/Michael reaction process, Involving dynamic kinetic resolution, is described.