Flash vacuum pyrolysis of N-phenylbenzamide oxime and related compounds

Flash vacuum pyrolysis (FVP) of the benzamide oxime 1 at 650 °C leads to the imino-oxadiazole 10 as the major product. It is probably formed by intermolecular cycloaddition of benzonitrile oxide 11 and the diphenylcarbodiimide 12, an unexpected process to take place under FVP conditions. Intermediates 11 and 12 are themselves obtained by competitive dehydration and elimination of aniline from 1. Mixed products were obtained from FVP of the C- and N-p-tolyl analogues of 1 (5 and 6, respectively) probably owing to equilibration of the carbodiimide intermediate.