An efficient synthesis of heteroring-annulated tetraazapentalenes 1 by a nucleophilic substitution-reductive cyclization of benztriazole and 2-chloro-3-nitropyridine is reported. Thermolysis of product 1 leads to the interesting but known (F. B. Mallory, P. A. S. Smith, J. H. Boyer Org. Synth. Coll. Vol. IV, 1963, 74-78) formation of an oxadiazole 2 which undergoes a further interesting oxadiazole rearrangement-fragmentation to give the complex heterocycle 3. All compounds were fully characterized (including X-ray crystal structure analysis) and show interesting physicochemical properties such as high explosive performance and yet notable thermal stability.