Acid-catalysed decomposition of (4′-azidophenyl)propanoic and butyric acids leads to ipso-attack by the carboxy group para to the nitrenium ion and the formation of imines of cyclohexadienone spiro-lactones, which can rearrange to the benz-fused lactones; 4′-azido-2-carboxydiphenyl ether behaves the same way to give spiro-lactone (9). 4283284