The cycloaddition of nitrones with homochiral cyclopropanes.

The cycloaddition of nitrones and enantiomerically pure cyclopropane-1,1-dicarboxylates is examined. Transfer of optical activity to the adduct is dictated by thermal reaction conditions and nature of cyclopropane substitution. Optically active 2-substituted cyclopropane-1,1-dicarboxylates are shown to racemize under typical reaction conditions, providing evidence for a zwitterionic ring-opened intermediate.