Enantioselective Synthesis of Highly Substituted Chromans via the Oxa-Michael-Michael Cascade Reaction with a Bifunctional Organocatalyst

A highly enantioselective synthesis of chiral chroman derivatives via an oxa-Michael-Michael cascade reaction has been developed using a bifunctional thiourea organocatalyst. The products were obtained with excellent enantioselectivities (up to >99%), good yields (up to 95%), and diastereoselectivities (up to 5:1).