PHOTO-CHEMICAL REACTIONS .20. PHOTOLYSIS OF ORTHO-NITROBENZALDEHYDE N-ACYLHYDRAZONES LEADING TO BENZYNE AND 5-NITROPHTHALAZINES

Irradiation of o-nitrobenzaldehyde N-acetyl-N-alkylhydrazones resulted in the generation of benzyne via decomposition of o-(N-acetyl-N-alkyltriazeno) benzoic acids derived from o-nitrosobenzoyl-N-acetyl-N-alkylhydrazides which are initially formed in an analogous fashion to the o-nitrobenzylideneaniline rearrangement. Photolysis of o-nitrobenzaldehyde N-acylhydrazones, however, resulted in photocyclisation leading to 1-substituted 5-nitrophthalazines, with benzyne generation only as a minor process.