Lewis Acid-catalysed Aza-Diels–Alder versus Mannich Reactions of N-Diethyl Phosphoryl Imino Dienophiles with Oxygenated Dienes and Application of a Chiral Lewis Acid

N-Phosphoryl imines react with oxygenated dienes in the presence of Lewis acids to provide either the formal aza-Diels-Alder adduct. or the acyclic Mannich-type addition product, depending upon the catalyst and work up used, which is in agreement with the hypothesis that these reactions are mediated by zwitterionic Lewis acid-complex intermediates, rather than a concerted cycloaddition transition-state followed by hydrolytic ring opening. Stoichiometric asymmetric induction can he achieved using a zinc(II)-binol complex, producing up 77% ee.