Oxadiazoles furazans

Nitro and amino derivatives of the furazan ring (1,2,5-oxadiazole) are nitrogen-rich energetic materials with potential use in both propellant and explosive formulations. Some 

4-Diaminofurazan (DAF) (24) is a starting material for the synthesis of many nitro-substituted furazans and is readily prepared from the cyclization of 1,2-diaminoglyoxime (23) in the presence of aqueous base under pressure at 180 °C the latter prepared from the reaction of glyoxal/ glyoxime/ cyanogen or dithiooxamide with hydroxylamine. 

DAAzF (26) can be oxidized with a mixture of 30% aqueous hydrogen peroxide, sodium tungstate and ammonium persulfate in concentrated sulfuric acid to yield 

4-amino-4 -nitro-3,3 -azofurazan (29). The use of stronger hydrogen peroxide solutions can oxidize both amino groups and yield either DNAzBF (30) or DNABF (31).  

Some energetic compounds have picryl groups (2,4,6-trinitrophenyl-) introduced as substituents in the 3- and 4-positions of the furazan ring. Coburn synthesized a series of picrylamino-substituted furazans, including 4,4 -bis(picrylamino)-3,3 -bifurazan (BPABF) (34) from the reaction of 4,4 -diamino-3,3 -bifurazan (DABF) (32) with two equivalents of picryl fluoride. 

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Ab initio calculations, correlations of molecules geometries, spectroscopic data with chemical properties, and quanta-tive structure-activity relationship have been conducted for both furazans and furoxans. Thus, the structures of 1,2,5-oxadiazole (furazan) and benzo[c][l,2,5]oxadiazole (benzofurazan) have been calculated by ab initio and Becke3-LYP... 

Cycloreversion with nitrile oxide formation is known not only in furoxans but also in isoxazolines, 1,2,4-oxadiazoles, furazans, and some other live-membered heterocycles (76). Such process, eliminating nitrile oxide fragment 3-R CeHiC N+Cr ", was observed mass spectrometrically in 3a,4,5,6-tetrahydro-[ 1,2,4 oxadiazolo[4,5-a J [ 1,5 benzodiazepine derivatives 11 (83). 

Furazane (1,2,5-Oxadiazole), Furazan-2-oxide (Furoxane, 1,2,5-Oxadiazol-2-oxide), Benzofurazane (2,1,3-Benzoxadiazole) und Benzofurazan-1 -oxide (Benzofuroxane,... 

A unique example is found in 2,1-benzisoxazole (40), which undergoes N-methylation 1.9 times faster than isoxazole (37).122 This is the only known example of rate acceleration resulting from benzo-fusion. Other interesting comparisons involve 2,1,3-benzoxadiazole (benzofurazan, 41), and 1,2,5-oxadiazole (furazan, 42),123 and also isothiazole (37), and 2,1-benzisothiazole (40).122 For these two pairs essentially no change in reactivity results when the azole is converted into its benzolog. 

Beckman rearrangements102,103 of a-dioximes sometimes lead to 1,2,4-oxadiazoles, although more often the dehydrating conditions produce 1,2,5-oxadiazoles (furazans). In fact, a-benzildioxime in poly-phosphoric acid gives diphenyl-1,2,4-oxadiazole in 99% yield104 [Eq. (26)]. 

A series of 3-amino (or 3-N-substituted amino)-l,2,4-oxadiazoles 108 can be obtained in moderate to high yields by the photoinduced rearrangement of 3-acylamino-l,2,5-oxadiazoles (furazans) 106 irradiated in the presence of an excess of ammonia or aliphatic amines [64—66]. The reaction follows a fragmentation-cycloaddition route, with the initial formation of a nitrile and a nitrile-oxide the latter is attacked by a nitrogen nucleophilic reagent (ZH in Scheme 12.29), and the open-chain interme-... 

Buscemi, S., Vivona, N. and Caronna, T. (1995) Photoinduced molecular rearrangements. Some investigations of the photochemical behaviour of 3-acylamino-l,2,5-oxadiazoles (furazans). Journal of Organic Chemistry, 60 (13), 4096—4101. 

Furan-2-carboxaldehyde see furfural Furan-2-carboxylic acid 78 Furan-2-methanthiol 78 Furazan see 1,2,5-oxadiazole Furazan oxide see furoxane Furfural 77 Furocumarin 325 Furoxan 253... 

There are not many examples regarding the synthesis of fluorinated 1,2,5-oxadiazole (furazan) systems in the literature. Furazans bearing fluoro atoms were easily obtained by nucleophilic displacement of a nitro group at the furazan ring by using... 

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