Photochemical reactions. Part 20. Photolysis of o-nitrobenzaldehyde N-acylhydrazones leading to benzyne and 5-nitrophthalazines

Abstract

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.