3.8-Disubstituted benzo cinnolines

In the synthesis of symmetrically 3,8-disubstituted benzo[c]cinnolines 52 from the corresponding 4,4-disubstituted 2,2-dinitrobiphenyls 51, acetophenone has been used as reductant in a basic solution (Scheme 26) 2-nitroso-2-hydroxylaminobiphenyls are assumed to be intermediates in this reaction <2004JOC7720, CHEC-III(8.01.9.1)73>. 

Benzo[c]cinnoline derivatives of different oxidation levels are prepared by N-N bond formations from suitable 2,2 -disubstituted biphenyls as outlined in Scheme 5. 

Benzo[c]cinnolines have been conveniently prepared by the cyclization of symmetrically disubstituted 2,2-diami-nobiphenyls using iodobenzene diacetate as the oxidant <1996J(P1)83, CHEC-III(8.01.9.1)72>. A similar oxidation of 2,2,6-triamino-6-propylthiobiphenyl 49 afforded a new tetracyclic ring system 50 (Scheme 25) <2000JOC6388>. 

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