Intramolecular aromatic ipso-substitution in the photolysis of 2-iodoazobenzenes

Abstract

Photolysis of 2-iodoazobenzene (2a) and 4′-chloro-2-iodoazobenzene (2b) affords the corresponding 2-arylazophenyl radicals which undergo hydrogen abstraction to give the azobenzenes (5a,b), intramolecular 1,6-cyclization to give the benzo[c]cinnolines (6a,b), and intramolecular ipso-substitution leading ultimately to the biphenyls (7a,b); photolysis of 2-(o-iodophenylazo)biphenyl (2; R¹= Ph, R²= H) affords 2-(phenylazo)bi-phenyl (5; R¹= Ph, R²= H) and triphenylene (8) as the only identifiable products.