Thermal fragmentation and rearrangement of N-arylbenzamidoxime and O-phenylsulfonyloxime derivatives

Thermal fragmentation of N-arylbenzamide oximes I, II (Ar = Ph, p-tolyl) under nitrogen gives rise to benzanilide and 2-phenylbenzoxazole as the major products, in addition to benzonitrile, arylamines, phenols, benzoic acid, o- and p-aminophenols and benzimidazole derivatives. In the presence of naphthalene as radical scavenger, I gave α- and β-naphthols beside the previous products. Also, heating N-arylbenzamide O-phenylsulfonyloximes III under reflux in boiling tetralin lead to the formation of benzonitrile, arylamines, diphenylamine, benzenesulfonic acid, diphenyl sulfone, 1-hydroxytetralin, α-tetralone, and 1,1′-bitetralyl as the major products. Analogous results are obtained on heating III in the presence of isoquinoline as a radical trap which formed 1-phenylisoquinoline. The isolated products have been interpreted in terms of a free radical mechanism involving the homolysis of NO and/or CN bonds.