Reactive intermediates. Part XVI. Dihydrobenz[cd]indazoles and attempted routes to benz[cd]indazole

Attempted synthesis of 1,2-dihydrobenz[cd]indazole from dimethyl 1,2-dihydrobenz[cd]indazole-1,2-dicarboxylate yielded only the more stable 1,3- and 1,5-dihydro-forms, (7) and (8), with the indazole rather than the naphthalene nucleus aromatic. These indazoles can be reconverted into NN-disubstituted dihydrobenzindazole derivatives but cannot be oxidised to benz[cd]indazole. Several other unsuccessful attempts to obtain the elusive benz[cd]indazole system are described.