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Energetic compounds 1-6, consisting of one or two furazan rings linked by azo or azoxy bridges and one or two nitro-NNOazoxy substituents, were synthesized by nitration of the corresponding tert-butyl-NNO-azoxy precursors with NO 2 BF 4. Novel methods for the synthesis of 3,4-bis(tert-butyl-NNOazoxy)furazan (7) and bis-4,4'-(tert-butyl-NNO-azoxy)-3,3'-azoxyfurazan (21) were elaborated. The nitro-NNO-azoxy compounds obtained display high calculated detonation performance (v D = 8.07-9.40 km s À 1 and P C-J = 27.4-43.4 GPa) that is superior to the corresponding nitrofurazans (DNF, DNAzF, DNAF). The replacement of nitrofurazans with the corresponding (nitro-NNO-azoxy)furazans increases the specific impulse of the model solid composite propellant formulations by 2-10 s, which is due to high calculated heats of formation (600-892 kcal kg À 1) and positive oxygen balance (0-20 %) of the latter compounds.

Two approaches to the synthesis of bis-3,3'-(nitro-NNO-azoxy)difurazanyl ether 2 have been tested, that is, varying the sequence of the introduction of the nitro-NNO-azoxy group and ether bridge. Difurazanyl ether formation through basepromoted transformation of nitrofurazans has been studied in which the nitro groups were activated by ortho electron-withdrawing substituents such as nitro-NNO-azoxy and tert-butyl-NNO-azoxy groups. The nitro-NNO-azoxy group was formed by destructive N-nitration of the tert-butyl-NNO-azoxy group. The X-ray crystal structure of 2 is reported.