Dinitromethyl-3(5)-1,2,4-oxadiazole Derivatives from Controllable Cyclization Strategies.

N-Cyanoimidate (1) with hydroxylamine hydrochloride in the presence of triethylamine gives different products (2 a or 2 b) as a function of the sequence of reactant addition. Further oxidation/nitration/decarboxylation/acidification reactions of 2 a/2 b generate dinitromethyl-3(5)-1,2,4-oxadiazole derivatives, including a surprising energetic compound with high oxygen balance, 3-(dinitromethyl)-1,2,4-oxadiazol-5-one (5) as well as 5,5'-dinitromethyl-3,3'-azo-1,2,4-oxadiazole (9). Some salts of 5 and 9 as precursors were also prepared. All were fully characterized using multinuclear NMR and IR spectroscopy, and elemental analyses as well as low-temperature single-crystal X-ray diffraction for 4, 5, 7 and 8. In addition, their properties (thermal stability, detonation performance and sensitivity to impact and friction) were investigated. Among them, 5 and 8 show promising detonation performance as energetic materials.