Reactive intermediates. Part XVIII. An N-aminopyridone-to-pyridazine rearrangement; a new decarbonylation reaction

Abstract

Oxidation of 1-amino-3,4,5,6-tetraphenyl-2-pyridone with lead tetra-acetate results in loss of carbon monoxide and retention of nitrogen to give 3,4,5,6-tetraphenylpyridazine. This rearrangement is thought to involve ring expansion of the N-nitrene to a diazepinone and valence tautomerism of this to give a bicyclic intermediate which extrudes carbon monoxide. This reaction can be suppressed by competitive intermolecular reaction of the nitrene with sulphoxides or with cyclohexene. This pyridone-to-pyridazine rearrangement is observed to a much smaller extent with di- and tri-phenyl-1-amino-2-pyridones, and not at all with 1-amino-2,3-diphenylquinolin-4-one or 5-aminophenanthridin-6-one.