Abstract: Study has been made of neighboring heteroatom interaction in thermolysis and photolysis of proximally substituted aryldiazomethanes. Thus, (8-bromo-1-naphthyl)- (la), (8-iodo-1-naphthyl )- (lb), and (5,8-dichloro- 1-naphthy1)diazomethane (IC) isomerize at 132 OC to 9-bromo- (Ma), 9-iodo- (18b), and 6,9-dichloro-3H-benz[e]indazoles (18c). Indazoles 18a and 18b are reduced by lithium aluminum hydride to 3H-benz[e]indazole (21), identical with that from ...