Cinnolines special

The most widely used method for forming the benzo[c]cinnoline nucleus has been the reduction of 2,2 -dinitrobiphenyl (3) and its derivatives under alkaline conditions, analogous to the bimolecular reduction of nitroarenes. As in the latter reaction, the end product is a hydrazo compound (Scheme 1), in this case the cyclic 5,6-dihydrobenzo[c]cinnoline (6), but this is so easily oxidized back to the fully aromatic 1 that it is not isolated unless special precautions are taken (Section IV,D). Tauber originally employed 3% sodium amalgam in methanol or zinc and alkali to reduce 2,2 -dinitro-biphenyl, and these reagents have been used subsequently by other work-ers. ° Reductions using sodium sulfide or hydrosulfide and catalyst/hydrogen or catalyst/hydrazine systems have been used... 

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