Chiral-Squaramide-Catalyzed Sulfa-Michael/Aldol Cascade Reactions for Asymmetric Synthesis of Spirothiochromanones

An efficient, asymmetric sulfa-Michael/aldol cascade reaction catalyzed by a chiral squaramide catalyst has been developed. This organocatalytic cascade reaction provides easy access to highly functionalized spirothiochromanones with three contiguous stereocenters, including one quaternary center, in excellent yields of up to 99% with excellent diastereoselectivity up to >99:1 d.r. and enantioselectivity up to 98% ee. In addition, the key to the present method is introducing indenones that are readily accessible as hydrogen-bond acceptors with very low catalyst loading of 0.5mol%.