Stereocontrol in intermolecular nucleophilic addition to N-acyliminium ion directed by a bicyclo(2.2.1)heptene or 7-oxabicyclo(2.2.1)heptene group. A novel route to 5-substituted 3-pyrrolin-2-ones of high optical purity.

Intermolecular nucleophilic additions to the conformationally rigid, tricyclic pyrrolidinium ion (derived from 2 or 6) took place exclusively from the less-hindered face fused with its bicyclo[2.2.1]heptene or 7-oxabicyclo[2.2.1]heptene moiety. Retro-Diels-Alder fragmentation of the resulting chiral 7-oxabicyclo[2.2.1]heptene system furnished a 5-substituted 3-pyrrolin-2-one without a loss of optical purity.