The flash vacuum pyrolysis products of 2-(benzotriazol-1-ylmethyl)benzonitrile, methyl 2-(benzotriazol-1-ylmethyl)benzoate and the corresponding benzisoxazolones have been characterized. The benzotriazoles lose nitrogen to give diradicals which undergo intramolecular hydrogen-atom transfer or cyclization, while the benzisoxazolones rearrange initially to the corresponding benzaldehyde N-(2-carboxyphenyl)imines which undergo subsequent intramolecular addition reactions.