decarboxylation, followed by intramolecular cycloaddtion of the resultant non-stabilised azomethine ylides. Evidence is produced for syn-anti dipole equilibration and it is found that intramolecularcycloadditions to a terminal alkyne involve only the anti-dipole and proceed via an exotransition state to give a single cycloadduct. In contrast, intramolecularcycloaddition to a terminal alkene involves