Furazan compounds

DFT was used to calculate the heats of formation and infrared active vibrational frequencies of 12 furazan compounds (Figure 1). The absolute values of the heats of formation are unreliable but the trends with systematic variations of the bridge and terminal groups are reasonable. The assignments of the vibrational motions to IR frequencies based on a force field analysis are given to clarify the complex coupling in these molecules <2000MI247>. 

Figure 1 Furazan compounds investigated by DFT computational methods.

Furazan compound 278 was obtained as a by-product from cholestan-3-one oxime 277 by prolonged heating in an acetic anhydride-pyridine mixture followed by treating with acetyl nitrate prepared from acetic anhydride and nitric acid (Equation 53) <1997T16161>. 

Only one furazan compound, DNFP, has been investigated in detail to date [52]. DNFP contains both a furazan ring and nitramine groups. The nitramine groups appear to trigger the thermal decomposition of the molecule. Further work on furazans and metal complexes of furazans is under way at the present time [84]. 

Furazano[3,4-/]quinoxaline, 7,8-diphenyl-synthesis, 6, 412 Furazanothiophene synthesis, 6, 417 Furazans, 6, 393-426 biological activity, 6, 425 bond angles, 6, 396 bond lengths, 6, 396 coordination compounds, 6, 403 diamagnetic susceptibilities, 6, 395 dipole moments, 6, 395, 400 heats of combustion, 6, 400 heterocyclic ring reactions, 6, 400-403 IR spectra, 6, 398 isoxazoles from, 6, 81 mass spectra, 6, 399 microwave spectroscopy, 6, 395, 396 MO calculations, 6, 395 monosubstituted... 

The action of hydroxylamine and sodium acetate in ethanol upon picryl chloride was stated to give 4,6-dinitrobenzofuroxan, and probably some of this compound was formed, although it was later shownthat much of the original work was faulty. A report that hydroxylamine and 2,4,5-trinitrotoluene give 5-methyl-6-nitro-benzofuroxan has been found to be incorrect. Benzofuroxan has not been prepared by V-oxidation of benzofurazan, and it seems unlikely that this could be achieved, since benzofuroxan itself is oxidizable by powerful reagents to o-dinitrobenzene (Section VI, B). A report of the oxidation by nitric acid of anthraceno[l,2-c]furazan to the furoxan is incorrectlv abstracted. 

Attempts to prepare 6-hydroxybenzofuroxan by demethylation of 5-methoxybenzofuroxan, by pyrolysis of 4-azido-3-nitrophenol, and by hypochlorite oxidation of 4-amino-3-nitrophenoD failed. This rather unstable compound was finally prepared by hydrolysis of 5-acetoxybenzofuroxan its tautomeric possibilities are numerous, but from the similarity of its ultraviolet spectrum to that of 5-methoxybenzofuroxan it was considered to be largely in the hydroxy form. It is a fairly strong acid, of pK 6.76 (cf. 5-hydroxybenzo-furazan, pK 7.28). 7-Hydroxy-4,6-dinitrobenzofuroxan has been reported as arising from oxidation and nitration of dinitrosoresorcinol monooxime (tetraoxocyclohexene trioxime). ... 

The furazan ring is stable under the conditions used to reduce the nitro group to the amine (Scheme 6). Thus, on treatment of compound 19 with SnC in HCl, the nitro group was reduced and the cyano group underwent hydrolysis and decarboxylation yielding salt 20 (30G721). 

Elimination of the hydroxyaminomethyl moiety from nitro oxime 15 by treatment with a diazonium salt gave hydrazone 43 (75LA1029) (Scheme 15). The same product was obtained by coupling the diazonium salt with the compound 16. On heating in aniline, oxime 15 was transformed into Schiff base 42. Acylation of the oxime 15 with benzoyl chloride in pyridine led to a mixture of furazan 44 and dinitrile 45. 

Vinyl azides 50 (73CJC2406) and vicinal vinyl nitro compounds of type 51 (57JOC456, 75MI1) can be precursors for furoxans and furazans (Scheme 20). 

Because of the difficulties encountered in preparing starting materials, further data on the synthesis of these compounds are rare. Exceptionally, 3,4-dimethyl-furazan [630S(1V)342] and 3,4-dimethylfuroxan (1890CB3490, 80URP721430) were synthesized in a straightforward manner from commercially available dimethylgly oxime. 

Sheremetev and co-workers employed diazo compounds of type 60, prepared from the corresponding amines in moderate yields as alternative excellent precursors for the preparation of side-chain-functionalized derivatives (Scheme 29). Several furazans bearing reactive groups or cyclopropyl or five-membered heterocyclic substituents have been prepared by standard procedures (99MI6). 

Aldehydes and ketones of furazans and furoxans have many properties resembling those of the aryl derivatives. Reduction of the carbonyl compounds with... 

Ylidene-substituted furazans, which may be used in some cases without purification, are excellent building blocks for the construction of heteroaryl substituted derivatives. Simple variations in the substituents on the furazan ring, the active methylene compounds, and reagents can lead to a variety of products (99MI7) (Scheme 68). 

Active methylene compounds also displace the nitro group at the furazan ring. Thus, 3,4-dinitrofurazan reacted with the sodium salt of ethyl (3-oxo propionate or related compounds in the presence of a crown ether to give the corresponding ester, which was readily hydrolyzed and decarboxylated (92UP1) (Scheme 146). 

The hydroxy group undergoes 0-acylation and deacylation (79JHC689). These reactions of functionalized hydroxyfurazans are valuable methods for modification of these compounds. Thus, hydroxybifurazan 248 was aroylated with benzoyl chloride in the presence of pyridine with concomitant cleavage of the unsubstituted furazan ring to give nitrile 262 (Scheme 170) (75LA1029). 

Heating 3,4-bis(phenylsulfonyl)furoxan with a solution of sodium butoxide in butanol followed by reduction with trimethyl phosphite gives furazan 281 (Scheme 183). Compound 281 was converted into dialkoxy derivative 282 with the lithium salt of ( )-l-azabicyclo[2.2.2]octan-3-ol in 33% overall yield (96W012711, 97EUP773021, 98JMC379). 

This oxygen rich explosive is claimed to be the first pemitro heterocycle known. See other furazan /v-oxidks, c-nitro compounds... 

See Other CYANO COMPOUNDS, endothermic compounds, FURAZAN a-oxides... 

See Other CYANO COMPOUNDS, ENDOTHERMIC COMPOUNDS, FURAZAN /V-OXIDES... 

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