A Domino Ring‐Closure Followed by Retro‐Diels–Alder Reaction for the Preparation of Pyrimido[2,1‐ a ]isoindole Enantiomers

A simple method was developed to prepare pyrimido[2,1‐ a ]isoindole derivatives by using di‐ endo ‐ and di‐ exo ‐ethyl 3‐aminobicyclo[2.2.1]hept‐5‐ene‐2‐carboxylate enantiomers as chiral sources. The method is based on a domino ring‐closure reaction of norbornene 2‐aminohydroxamic acid followed by microwave‐induced retro‐Diels–Alder reaction. In the case of enantiomeric starting substances, the chirality is transferred from norbornene derivatives to pyrimido[2,1‐ a ]isoindoles. The configurations of the synthesized compounds were determined by 1D and 2D NMR spectroscopy [based on 2D NOE cross‐peaks and 3 J H,H coupling constants] and X‐ray crystallography.