Enantio- and diastereo-selective synthesis of pipecolic acid derivatives using the aza-Diels–Alder reaction of imines with dienes

Optically active pipecolic acid derivatives can be prepared by the aza- Diels–Alder reaction of simple dienes with the imine derived from ethyl glyoxylate and chiral 1-phenylethylamine; the cycloadditions are regiospecific, highly diastereoselective within the heterocyclic ring (>92%exo with cyclic dienes, and 100%endo with acyclic dienes), and lead to high asymmetric induction in most cases (average d.e. = 72%).