Enantioselective synthesis of 3,4-dihydropyran derivatives via a Michael addition reaction catalysed by chiral pybox-diph-Zn(II) complex

An enantioselective Michael addition of cyclic 1,3-dicarbonyls to 2-enoylpyridine N-oxides catalyzed by a chiral pybox-diph-Zn(II) complex has been developed. The corresponding Michael adducts have been obtained in high yields with up to >99% ee. The Michael adduct has been transformed to biologically active 2,4-disubstituted hexahydroquinoline. A plausible transition-state model has been proposed to explain the stereochemical outcome of the reaction.