Furoxans structure

Khmelnitskii, L. I., Novikov, S. S., Godovikova, T. I., Chemistry of Furoxans Structure and Synthesis, Nauka, Moscow 1996 (in Russian)... 

Khmelnitckii LI, Novikov SS, Godovikova TI (1981) Chemistry of Furoxanes, Structure and Synthesis (in Russian) Nauka, Moscow... 

B-81MI 405-01 L. I. Khmelnitskii, S. S. Novikov and T. I. Godorova Chemistry of Furoxans Structure... 

L. I. Khmel nitskii u. S. S. Novikov, Chemistry of Furoxans, Structure and Synthesis (Russ.), Nauka, Moskau 1981. 

The product obtained melted at 116°C. However, the results have not been confirmed by the investigations of other workers. For example, Will [61] boiled l,2-dinitroso-4,6-dinitrobenzene with nitric acid for 3 hr, but failed to observe any change in the compound. This is probably due to furoxane structure of o- dinitroso groups (p. 603). 

The benzofuroxans and naphthofuroxans presented an apparently different problem, because the isomerism that might have been expected by analogy with the monocyclic series was not found. Although by the time of Beilstein s Second Supplement (1929) the furoxan structure (5) was considered the most likely, another symmetrical formula, i /- pseudo-) o-dinitrosoben-... 

Many furoxan structures have been determined by crystallographic methods, and as a result the dimensions of the heterocyclic ring are known in a wide variety of fused and substituted examples. The earliest to be studied were the benzofuroxans, for which the rather rough results that were obtained confirmed their bicyclic structures.35 Of the many subsequent determinations, a considerable number have been of pairs of isomers with a methyl group as one of the substituents. Table I lists the compounds which have been studied.4163... 

Since the earlier reviewers, and Mallory and Wood, and, for the earlier literature, Hammick el al. have summarized the history of the structure problem fairly fully, and since it cannot in any case be treated properly in isolation from that of the monocyclic furoxans, we shall present only a brief outline here. The earliest formulas to be suggested (3 and 4), in connection with 1,2-naphthofuroxan, discovered by Koreff and von Ilinski in 1886, were open to the objections that the first is a peroxide structure, whereas the benzofuroxans... 

The tautomeric structure leads to ambiguities in the nomenclature of compounds in this series. Thus, 5-methyl- and 6-methylbenzo-furoxan denote two different molecules which, because of their interconversion, cannot be isolated separately at normal temperatures. Throughout this review, when we intend to refer to the ambiguous mixture, we shall use the system employing the lowest numbers. The above methyl derivative, for example, will be described as 6-methyl-benzofuroxan regardless of the form adopted in the crystal. When a... 

Linnett and Rosenberg have discussed the electronic structure of a number of nitroso and potential nitroso systems, including benzo-furoxans, using the non pairing approach. ... 

Further benzofuroxan spectra are reported by Gaughran, Picard, and Kaufman, who compare them with benzofurazans, by Boyer et al., who find similarities with furoxans and nitroso compounds, and by others. Hexanitrosobenzene was shown by IR and Raman spectroscopy to exist in the benzotrifuroxan structure. ... 

The first evidence for an unsymmetrical structure for the benzo-furoxan molecule and for the tautomerism of Eq. (3) was provided in 1961 by several groups of workers," using proton resonance... 

H. Dinitronaphtho[l,2 cjfuroxan is also reported to form a mildly explosive salt. An anilide of 4,6-dinitrobenzofuroxan, of uncertain structure, is also known.Naphtho[I,2-c]furoxan does not form an... 

The 1-oxide 3-oxide tautomerism [Eq. (3), p. 4] has been discussed earlier (Sections II and III,C) in connection with the problem of the structure of benzofuroxan. A second type of rearrangement involves the furoxan ring and an adjacent substituent group, and arose out of a suggestion of Bailey and Case that 4-nitro-benzofuroxan might be a resonance hybrid of type (57)-(-> (58), rather than 57. NMR ruled out this possibility the three protons present in... 

Intermediates involved in the tautomerization of furoxans gave rise to speculations about their structure. Systematic calculations on possible intermediates being involved in the reaction of furoxan [92JCC177] and benzofuroxan 79 showed that dinitrosoethylene and dinitrosobenzene 81 are the most likely ones (Scheme 50) [94JOC6431, 94JPC12933]. 

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... 

The reaction of 3,4-bis(benzenesulfonyl)furoxan with alcohols and thiols in basic media affords a variety of alkoxy-and alkylthio-substituted (benzenesulfonyl)furoxans. For these derivatives a paramount problem is to determine the position (3- or 4-) of the substitution in the furoxan ring. The structures of these derivatives were assigned on the basis of both chemical and NMR evidence. In particular, 13C NMR substituent constants were obtained by NMR study of suitable furoxan models. By assuming a complete additivity of the substituent effects at the furoxan ring, these values were used for structural determination <1997FES405>. 

The reactions of 4-nitrobenzodifuroxan 242 with a series of common dienes, such as cyclopentadiene, cyclohexa-diene, isoprene, 2,3-dimethylbutadiene, and 1-acetoxybutadiene, with ethoxymethyleneacetylacetone were found to proceed very readily to afford stable cycloadducts, which are the result of highly stereoselective normal electron-demand (NED) Diels-Alder reactions. Due to the additional activation provided by the two adjacent furoxan rings, the nitroalkene double bond of compound 242 is also prone to undergo NED reactions with less reactive dienic structures, such as the enol form of ethoxymethyleneacetylacetone and the in situ generated 2-ethoxy-4-(2-furfur-yl)buta-l,3-diene <2004TL1037, 2005T8167>. 

---