Synthesis of 1-substituted [1,2,3]triazolo[4,5-d]pyridazines as precursorsfor novel tetraazapentalene derivatives

A series of 1-substituted 4,5-diformyl-[1,2,3]triazole derivatives were pre pared by 1,3-dipolar cycloaddition of aryl azides with acetylene dicarboxal dehyde mono-diethylacetal. The triazoles were readily converted into 1-subs tituted [1,2,3]triazolo[4,5-6]pyridazines in good yields. The 1-(2-nitrophe nyl)-[1,2,3]triazolo[4,5-d]pyridazine was found to be a useful intermediate for the generation of the novel SH-benzo[1,2,3]triazolo[1',2':1,2]triazolo [4,5-d]pyridazin-6-ium inner salt ring system.