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]triazolo4,5‐d]pyridazines in good yields. The 1‐(2‐nitrophenyl)‐1,2,3]triazolo4,5‐d]pyridazine was found to be a useful intermediate for the generation of the novel 5H‐benzo1,2,3]triazolo1′,2′:1,2]triazolo4,5‐d]pyridazin‐6‐ium inner salt ring system.