Preparation of ring-fused pyridazines by reduction of 3,3′-dinitro-4,4′-bipyridyl and 3,3′-dinitro-4,4′-biquinolyl

Ullmann coupling of 4-chloro-3-nitropyridine and of 4-chloro-3-nitroquinoline in amide solvents gives the dinitrobipyridyl (2) and -biquinolyl (9), which on reductive ring closure give dipyrido- and diquinolino-pyridazines and their mono- and di-N-oxides; further reduction easily opens the pyridazine rings giving the diamines (6) and (12). The pyridazine ring can be reformed by oxidation of the diamine (12) with perdisulphuric acid. Hydrazine with sodium hydroxide converts the dinitro-biquinolyl (but not the bipyridyl) into an N-hydroxypyrrole (11), probably by nucleophilic displacement of a nitro-group, and further reduction gives the diquinolinopyrrole (14).