A brief review of the dediazoniation of benzenediazonium salts and cyclisation reactions through 2,2'-positions of biphenyls is presented in order to understand and investigate the scope and mechanism of the Mascarelli reaction. It has been shown that 2-alkylbiphenyl-2'-yldiazonium salts cyclise under protic and aprotic conditions to give fluorene derivatives and, in the case where a nucleophilic counter-ion is present, products in which cyclisation has not occurred. A number of mechanistic schemes have been considered and investigated. The reactions carried out in the presence and absence of oxygen and also in the presence of bromotrichloromethane exclude pathways involving free radicals.