Furazans nitro-substituted

The amino- and nitro-substituted furazans and furoxans have been studied in detail because they are useful precursors for the synthesis of new derivatives and, moreover, they can be used as starting materials for the preparation of new heterocyclic systems. 

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. 

Benzofurazan (benz-1,2,5-oxadiazole) reacted with bromine by addition to give a4,5,6,7-tetrabromo adduct. Bromine in hydrobromic acid solution 4-brominated both 5-methyl- and 5-bromo-benzofurazans (74JHC8I3). When 4,7-dinitrobenzofurazan was treated with ammonium chloride in refluxing acetic acid, nucleophilic displacement gave rise to the 4-chloro-7-nitro derivative (83URP1004375). Naphtho[l, 2-c]furazans (42) are mainly 4-halogenated, but there is minor substitution in the 8-position (73CHE1331). 

One of the nitro groups in furazan (78) can be substituted by chloride and azide, and displacement of sulfonyl groups has also been reported. Nucleophilic reactions in the homocyclic ring of benzofuroxans may be accompanied by deoxygenation of the A-oxide 4-nitrobenzofuroxan with dialkyl-amines affords 4-dialkylamino-7-nitrobenzofurazans as the major product. Substitution reactions... 

The synthesis of furoxans has been discussed in a recent review (81AHC(29)25l), and the material summarized in the following sections is cited therein unless otherwise stated. The principal routes comprise oxidative ring closure of a-dioximes dehydration of a-nitro ketone oximes and dimerization of nitrile oxides. In choosing the method the possibility of equilibration between the 2- and 5-oxides of asymmetrically substituted furoxans, which was described in Section 4.22.3.2.1, must be taken into account. There has been no case of direct oxidation of a furazan to a furoxan. 

H NMR spectroscopy was used for the investigation of 2-(2,4-dinitrophenyl)-4-nitro-l,2,3-triazole [600], 4-amino-3-(4-nitro-l,2,3-triazol-l-yl)furazan [601], 2-aryl(heteryl)-4-acetylamino-5-nitro-l,2,3-triazoles [141, 177, 602-604], nucleophilic substitution in the series of 4,5-dinitro-2-alkyl-l,2,3-triazoles [605] and 4,5-dinitro-2-aryl-l,2,3-triazole-l-oxides [606],... 

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