Synthesis of 1‐substituted [1,2,3]triazolo[4,5‐ d ]pyridazines as precursors for novel tetraazapentalene derivatives

A series of 1‐substituted 4,5‐diformyl‐[1,2,3]triazole derivatives were prepared by 1,3‐dipolar cyclo‐addition of aryl azides with acetylene dicarboxaldehyde mono‐diethylacetal. The triazoles were readily converted into 1‐substituted [1,2,3]triazolo[4,5‐ d ]pyridazines in good yields. The 1‐(2‐nitrophenyl)‐[1,2,3]triazolo[4,5‐ d ]pyridazine was found to be a useful intermediate for the generation of the novel 5 H ‐benzo[1,2,3]triazolo[1′,2′:1,2]triazolo[4,5‐ d ]pyridazin‐6‐ium inner salt ring system.