Isochalcogenourea-catalyzed asymmetric (4 + 2)-heterocycloadditions of allenoates.

Allenoates are versatile reagents that can be used for numerous (formal) cycloaddition reactions under (chiral) Lewis base catalysis. Most commonly, the catalysts of choice are phosphines, amines, and -heterocyclic carbenes. We have recently established the use of readily available chiral isochalcogenoureas as catalysts for asymmetric (4 + 2)-heterocycloadditions of allenoates with various vinylogous acceptors. This represents a complementary approach for allenoate activation and gives access to various highly functionalized chiral dihydropyrans with good to excellent enantioselectivities and diastereoselectivities.