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

Abstract

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 cyclo-addition transition-state followed by hydrolytic ring opening. Stoichiometric asymmetric induction can be achieved using a zinc(II)binol complex, producing up 77% ee