Furazanes

The stability of various heterocycles can be also compared using oxidation procedures. Thus, the oxidation of the heterocycles in Scheme 29 with potassium permanganate showed that under these reaction conditions the isoxazole ring is more stable than the furan ring but less stable than the pyrazole and furazan rings. 

Heterocycles which provide the NOC or CNO component synthon Isoxazoles can be prepared by the thermal or photolytic cleavage of a number of heterocycles, such as 1,3,5-dioxazolidone, furazans, furoxans and 1,3,2,4-dioxathiazole 2-oxides, in the presence of a reactive alkene or alkyne. 

The thermal or photolytic fragmentation of furazans to nitriles and nitrile Af-oxides has been reported (73JOC1054, 75JOC2880). The irradiation of dimethylfurazan (419) in the presence of cyclopentene, and benzofurazan (420) in the presence of dimethyl acety-lenedicarboxylate, gave isoxazoline (421) and isoxazole (422), respectively, in good yields. The thermolysis of acenaphtho[l,2-c]furazan (423) in the presence of phenylacetylene gave isoxazole (424) in 55% yield. 

The treatment of 3-acylisoxazoles (438) with hydroxylamine hydrochloride gives furazan ketones (439). On the other hand, furazan ketones (439) rearrange to 3-acylisoxazoles (438) with a loss of hydroxylamine under the influence of a mineral acid. Thus, by refluxing phenacylphenylfurazan with concentrated alcoholic hydrogen chloride, 3-benzoyl-5-phenyl-isoxazole is formed similarly, phenyl(phenacylphenyl)furazan gives 3-benzoyl-3,5-diphenyl-isoxazole (62HC(17)1, p. 35). 

Acetaldoxime, 2-(furazan-3-yl)-2-nitro-synthesis, 6, 409 Acetals vinyl... 

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... 

Furazans, hydroxyquinol-2-yl-synthesis, 6, 414 Furazans, mercapto-reactions, 6, 414 Furazans, methylphenyl-pX , 6. 401... 

Furazans, methylvinyl-synthesis, 6, 412 Furazans, nitro-reactions, 6, 413-414 Furazans, phenyl-halogenation, 6, 412 nitration, 6, 412 NMR, 6, 397 Furazol, 7, 401 Furazolidone, 6, 233 as antibacterial agent, 1, 180 growth permittant veterinary use, 1, 220 veterinary use, 1, 208... 

S-group removal from, 5, 446 oxidation, 5, 446 Imidazole, 5-aryl-4-nitroso-furazans from, 6, 417... 

Isoxazole, 3-acetyl-4-chloro-5-methyl-oxidation, 6, 27, 53 Isoxazole, 3-acetyl-4,5-dimethyl-oxidation, 6, 27, 53 Isoxazole, 5-acetyl-3-methoxy-reactions, 6, 53 Isoxazole, 3-acyl-furazans from, 6, 417 nucleophilic attack, S, 93 reactions with bases, 6, 30... 

Isoxazole, 3-benzohydroximoyl-4-benzoyI-5-phenyl-furazans from, 6, 417 Isoxazole, 4-benzoyI-synthesis, 6, 69 Isoxazole, 5-benzoyl-synthesis, 6, 69... 

Naphtho[l, 2-c]furazans electrophilic reactions, 6, 410 synthesis, 6, 418 Naphtho[l, 2-c]furoxans eleetrophilic reactions, 6, 410 3-Naphthoic acid, 2-hydroxy-l-(2-thiazolylazo)-analytical uses, 6, 328 Naphtho[ 1,2-h]imidazoles oxidation, 5, 405... 

Oxadiazoles — see also Furazans electrochemical reduction, 5, 73 mass spectra, 6, 522... 

Pyrimido[4,5-6][l,4]diazepine, 6-aeetyl-2-amino-4-oxo-3,4,7,8,9-tetrahydro-biosynthesis, 3, 320 Pyrimido[4,5-c]furazan, 4-amino-reactions... 

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). ... 

Furazan 1 was first prepared and characterized in 1964 by melting glyoxime 2 with succinic anhydride in 57% yield (64JA1863, 65JOC1854). Its A-oxide, furoxan 3, has been in a focus of attention for chemists for more than a century, but was synthesized only in 1994 by oxidation of 2 with dinitrogen tetroxide in dichloromethane in 45% yield (94MC7) (Scheme 1). The A-oxide cannot be prepared by direct oxidation of furazan. 

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