Synthesis of pyridazine derivatives. XXI. Tetrazolo-azido transformations in some fused azolopyridazines

6-Azidotetrazolo[1,5-b]pyridazine (III) has been prepared by two different routes and is easily transformed into the 6-amino derivative (IV). The attempted cyclization of 6-hydrazinotetrazolo[1,5-b] pyridazine (II) into the postulated tricycle has been shown to result in the formation of 6-azido-s-triazolo [4,3-b]pyridazine (VI), obtained also in a separate experiment from VII. The azido structure of VI has been confirmed from spectroscopic data and from its conversion into 6-amino-s-triazolo [4,3-b]pyridazine (VIII), obtained in another experiment from VII. Similarly, cyclization of II with cyanogen bromide resulted in the simultaneous formation of the s-triazolo ring and ring opening of the fused tetrazolo ring, giving IX. For 6-azido-2-phenylimidazo[1,2-b]pyridazine (XII) the expected azide structure proved to be correct.