Enantioselective Syntheses of 3,4‐Dihydropyrans Employing Isochalcogenourea‐Catalyzed Formal (4+2)‐Cycloadditions of Allenoates

Abstract

AbstractWe herein successfully demonstrate the use of chiral isochalcogenoureas as Lewis Base catalysts for a variety of (4+2)‐cycloaddition reactions of allenoates and different Michael acceptors. In all cases the same structural key‐motive, a dihydropyran with a (Z)‐configurated exocyclic double bond could be accessed as the major regio‐ and diastereoisomer in an enantioselective manner. Furthermore, these chiral dihydropyrans were successfully engaged in different follow‐up transformations.