Pyrazino pyridazine-5,8-diamine

A common access to pyrazino[2,3-c]pyridazines is the condensation of pyridazine-3,4-diamines, e.g. 1 (R1, R2 = H), with 1,2-dicarbonyl compounds 2. 

The pyrazino[2,3-c]pyridazine skeleton is also formed when 3,4-dihalopyridazines are reacted with benzene-1,2-diamine derivatives. The dihydro compound initially formed is oxidized to the fully conjugated pyrazino[2,3-c]pyridazine under the reaction conditions. 9 72,75... 

Pyrazino[2,3-c/]pyridazine-5,8-diamines 6 may be prepared by the reaction of pyrazine-2,3-di-carbonitriles 5 with hydrazine.82... 

Closure of the pyrazine ring with formation of pyrazino[2,3-[Pg.368]

Pyrazino[2,3-reaction with benzoyl chloride in chloroform and triethylamine, leading to 2. 01... 

Formation of annulated five-membered nitrogen-containing heterocycles is also observed in reactions of hydrazino-substituted pyrazino[2,3-d]pyridazines.92 Pyridazine-4,5-diamines 7 are formed when pyrazino[2,3-tf]pyridazines 6 substituted in the 5- and 8-positions are treated with hydrazine hydrate under reflux and a fast stream of air is passed through the reaction mixture. The splitting of the pyrazine ring is supposed to be initiated by the diimide formed under these conditions."... 

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