9-Alkoxy and 9-acyloxyanthracenes react with cupric bromide and with cupric chloride to give 9-alkoxy (or acyloxy) 10-halogenoanthracenes and/or bianthron-9-yl. The formation of the former product proceeds by ligand transfer of halogen of the cupric halide whilst bianthron-9-yl results from the dimerization of 9-anthryloxy radicals. These are formed in a 4- centre transition state between the substituted anthracene and the cupric halide. The ratio ...