Furoxans amino

An attempt at Hofmann degradation of 4-carboxamidobenzo-furoxan failed to give any 4-amino compound. - Nitro groups appear to stabilize aminobenzofuroxans. however 4-amino-5-nitro, 5-anilino-6-nitro- and several substituted 4-ammo-7-nitro- and 5-amino-4-mtrobenzofuroxans have been isolated. 

It should be noted that the oxidation of 3-amino-4-phenylfuroxan by CF3CO3H gives a mixture of the furoxan 23 (R = Ph) with 3-nitro-4-phenylfurazan and 3-nitro-4-phenylfuroxan (82BAU573, 82IZV646). 

Diaroylfuroxans react with an excess of diazomethane in diethyl ether at 20°C to form oxiranes 131 (Scheme 76). These compounds were reduced with LiAllTj (diethyl ether, reflux) to 1 -amino-2-arylpropan-2-ols in moderate yields (67JOC4050). Treatment of diacylfuroxans with LiAlH4 under similar conditions resulted in degradative reduction of the furoxan ring to arylethanolamines (67JOC1255). 

Other examples of nucleophilic attack on a furoxan ring leading to ring opening/recyclization are the formation of 1,2,3-triazole 1-oxides 198 from 4-alkylamino-3-nitrofuroxans 197 and alkylamines (Scheme 129). 3-Amino-4-nitrofurazan was observed as by-product (95MC194, 96CHE580, 96KGS675). 

Azidofurazans and -furoxans undergo dipolar cycloaddition reactions with unsaturated compounds, in some cases regiospecifically. Thus, reaction of 3-amino-4-azidofurazan with l-morpholinyl-2-nitroethene (toluene, reflux, 70 hours) gives 4-nitro-l,2,3-triazole 204 in 87% yield (99MI1, 000KGS406). Cycloaddition of the same azide to alkynes was accomplished by formation of a mixture of position isomers 205 and 206. Regiospecific addition was observed only in singular cases... 

The thermally induced rearrangements in the furoxan series have also been found. In particular, the transformation of 3-R-substituted 4-(3-ethoxycarbonylthioureido)-l,2,5-oxadiazole 2-oxides into derivatives of 5-amino-3-(a-nitroalkyl)-l,2,4-thiadiazole and into (5-amino-l,2,4-thiadiazol-3-yl)nitroformaldehyde arylhydrazones has been reported (Equation 8) <2003MC188>. 

Arylazo-4-(3-ethoxycarbonylureido)furoxans 62, which were synthesized by the reactions of 4-amino-3-arylazo-furoxans with ethoxycarbonyl isocyanate, were subjected to cascade rearrangements under the action of potassium r/-butoxidc in dimethylformamide or by heating in dimethyl sulfoxide to form 4-amino-2-aryl-5-nitro-2//-l,2,3-triazoles 63 (Scheme 13) <2001MC230, 2003RCB1829>. 

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. 

Dimerization of nitrile oxides derived from 4-amino- and 4-R-substituted l,2,5-oxadiazole-3-carbohydroximoyl chlorides 201 leads to the formation of tricyclic furoxans 200 or compound 202 (Scheme 45) <2001RJ01355>. 

A convenient method was developed for the synthesis of 4-amino-3-furoxancarboxylic acid azide, which is a universal synthon for the preparation of furoxan derivatives 320 (Scheme 81). This method was used for the synthesis of new azo-, azoxy-, azido-, cyano-, nitro-, carbonylamino-, and hydroxylamino-substituted furoxan derivatives that are difficult to prepare using alternative procedures <2003RCB1822>. 

Furoxans are very feeble bases, even when an amino group is attached to the ring. 4-Amino-3-methylfuroxan behaves as a Hammett base [15], as does benzofuroxan (2, R=H) [7]. By contrast, the two methylfuroxan carboxylic acid isomers show equal high dissociation constants [9]. 

A. N. Binnikov, A. S. Kulikov, N. N. Makhov, 1. V. Orchinnikov and T. S. Pivina, 4-Amino-3-azidocarbonyl Furoxan as an Universal Synthon for the Synthesis of Energetic Compounds of the Furoxan Series , 30th International Annual Conference of ICT, Karlsruhe, Germany, 1999, 58/1-58/10. 

Dioximes of a-diketones such as benzil on oxidation with IBTA are converted into 1,2,5-oxadiazole-A-oxides (furoxans) in high yields (75S445) (Eq. 35). Benzo- (Scheme 46) and pyrido-oxadiazoles (Eq. 36) are formed when o-nitroaniline and 3-amino-2-nitropyridine are subjected to similar oxidation. 

This route is compatible with various functionality and by choosing the appropriate reagents amino-, halo-, and nitro-substituted furoxans can be prepared illustrative examples include the conversion of cyclopentan-l,2-dione dioxime to the thermally labile trimethylenefuroxan using aqueous sodium hypochlorite <79JCR(S)314>, and of the parent glyoxime to 3,4-dinitrofuroxan by... 

Das aus 3,4-Dibcnzoyl-furoxan mit Ammoniak zugangliehe 4-Amino-3-benzoyl-furazan lie-fert bei der Behandlung mit Kalium-ethanolat 3-Aminocarbonyl-5-phenyl-l, 2,4-oxadiazol376 ... 

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