Enantioselective amine-catalyzed [4+2] annulations of allenoates and oxo-dienes: An asymmetric synthesis of dihydropyrans

Article abstract of DOI:10.1002/anie.201100945

Biologically significant polysubstituted dihydropyrans have been prepared in high to excellent yields and enantioselectivities (see scheme). The interaction between functional groups in the zwitterionic intermediate, which is generated by addition of the amine catalyst to the allenoate substrate, is thought to play a crucial role in the stereochemical outcome. Bn=benzyl, DMAP=4-dimethylaminopyridine.