Thermolysis of furoxans annulated with five-membered carbocycles in the presence of dipolarophiles

The conditions for the thermolysis of furoxans annulated with differently strained five-membered carbocycles (cyclopentafuroxan 1, norbornenofuroxan 2, and acenaphthofuroxan 3) to bis(nitrile oxides) in the presence of various dipolarophiles (diethyl acetylenedicarboxylate, benzoylformonitrile, and ethoxycarbonylformonitrile) were optimized. It was found that the reactivities of the above furoxans as sources of bis(nitrile oxides) decrease in the order 2 > 1 > 3. Among the furoxans studied, only norbornenofuroxan 2 can be recommended as a possible cross-linking reagent for polymers. The formation of di-N-oxides of 3,4-bis(cyanopropyl)-, 3,4-bis(cyanocyclopentyl)-, and 3,4-bis(cyanonaphthyl)furoxans was detected. They resulted from intermolecular cyclodimerization of bis(nitrile oxides) initially formed in the thermolysis of furoxans 1–3. Dedicated to Academician V. A. Tartakovsky on the occasion of his 75th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1521–1528, August, 2007.     

Unsymmetrically substituted furoxans. Part 16 . Reaction of benzenesulfonyl substituted furoxans with ethanol and ethanethiol in basic medium

The use of benzenesulfonyl substituted furoxans as flexible intermediates for the synthesis of new functionalized furoxans interesting for their potential biological properties is discussed. Reaction of benzenesul-fonylphenylsulfonylfuroxan isomers 7a and 7b with ethanol and ethanethiol in basic medium affords the expected ethers and sulphides respectively. Reaction of bis(benzenesulfonyl)furoxan ( 1 ) with ethanol in basic medium gives 3-benzenesulfonyl-4-ethoxyfuroxan ( 2 ) or diethoxyfuroxan (3), according to the experimental procedure. In contrast the reaction of 1 with ethanethiol gives a mixture of substitution compounds and the 4-benzenesulfonyl-3-ethylthiofurazan ( 11 ). The structure of the compounds has been assigned by nmr spectroscopy and, in the case of 3-benzenesulfonyl-4-ethylthiofuroxan ( 9b ), confirmed by X-ray analysis.     

Unsymmetrically substituted furoxans. IIII. Methylnitrofuroxan: Its structure and behavior toward nucleophilie substitution

A series of unsymmetrically substituted furoxans have been prepared from methyinitro-furoxan and a variety of nucleophilic reagents. The nmr study of these compounds and of their parent furazans suggested the structure of 3-methyl derivatives for all the furoxans synthesized: on this ground the 3-methyl structure for methylnitrofuroxan was proposed. On heating some 3-methylfuroxan derivatives, a partial isomerization into the corresponding 4-methyl isomers occurred.     

Reduction of the furoxan ring to the furazan ring in some carbonyl-substituted furoxans

It was shown that the furoxan ring is efficiently reduced to the furazan ring in carbonylsubstituted furoxans with other functional groups by the action of the SnCl₂-HC1-AcOH system.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 679–680, April, 1994.     

Synthesis of (2-bromo-2-hydroxyiminoacetyl)furazans(or furoxans) and 3,4-bis[furazanoyl(or furoxanoyl)]furoxans

(2-Bromo-2-hydroxyiminoacetyl)furazans and -furoxans were synthesized by nitrosation of bromoacetylfurazans and -furoxans with nitrosylsulfuric acid in conc. H₂SO₄ An efficient method for preparing the previously unknown 3,4-bis[furazanoyl(or furoxanoyl)]furoxans has been proposed; it consists of the reaction of acetylfurazans and acetylfuroxans with a mixture of a nitrating reagent and a catalytic amount of a nitrosating reagent in conc. H₂SO₄.     

Synthesis of sulfonyloxy furoxans via hydroxyfuroxan ammonium salts

Furoxans are distinctive heteroaromatic compounds in that they are potentially capable of releasing nitric oxide under physiological conditions. In order to utilize the furoxan scaffold for the development of functional molecules, synthetically relevant functional groups are required for access to diverse furoxans. In this report, a facile route to furoxans with sulfonyloxy groups, which are halide surrogates, has been developed. The key features of this strategy include the synthesis and utilization of bench-stable hydroxyfuroxan salts, the use of sulfonyl anhydrides in the sulfonylation step instead of sulfonyl chlorides, and the photochemical isomerization of one regioisomer to another in order to gain access to both.     

New methods of preparation of nitrile oxides and the corresponding disubstituted furoxans by interaction of N2O4 with salts of substituted dinitromethanes

A new method of generation of nitrile oxides through interaction of N₂O₄ with salts of substituted dinitromethanes (1) has been worked out. It has been shown by¹H,¹³C,¹⁴N NMR spectroscopy that this reaction proceeds via dinitronitrosomethyl intermediates (one of these has been isolated), and that the reaction is feasible only for substituents capable of conjugation with the nitrile oxide fragment. On the basis of cyclodimerization of the obtained nitrile oxides, preparative methods of synthesis of symmetrically substituted furoxans have been developed.Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 147–151, January, 1993.     

Synthesis of bis(arylsuh'onyl)furoxans from aryl nitromethyl sulfones

The synthesis of some symmetrically substituted bis(arylsulfonyl)furoxans from aryl nitromethyl sulfones is reported.     

Formation of furoxans and 1,2-diazetine 1,2-dioxides by oxidation of α-hydroxylamino oximes

The oxidation of secondary and tertiaryα-hydroxylamino oximes with sodium hypobromite gives, respectively, furoxans and 3-bromo-1,2-diazetine 1,2-dioxides. The intermediate oxidation products, which confirm the proposed reaction mechanism, were isolated. When 3-bromo-1,2-diazetine 1,2-dioxides are heated in benzene, the ring opens with the evolution of nitrogen oxides and the formation of halo olefins.     

The reaction of triphenylphosphine with arylbromonitromethanes. Formation of arylnitriloxides.

Formation of furoxans and δ²-isoxazolines confirms that arylnitriloxides are intermediates in the reaction of arylbromonitromethanes with triphenylphosphine.     

The structures of furazans and furoxans

The IR spectra of furazans and furoxans are characterized by lowered values of frequencies and of integrated absorption band intensities for the C=N bands. The peculiarities of the UV absorption spectra of these compounds are similar to those of pyridine and its benzene analogs in comparison with the corresponding N-oxides. Comparison of the results with those given in the literature regarding chemical properties, delocalization energies, X -ray spectra, and quantum chemistry calculations leads to a conclusion that the 2, 1, 3-oxadiazole ring possesses a definite aromaticity.     

Recyclization of substituted furoxans into 1,2,3-triazol-1-oxide derivatives

The effect of the position and nature of substituents on the recyclization of substituted furoxans has been established.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences (RAN), Moscow 117913, Russia Institute of Chemical Physics in Chernogolovka, Russian Academy of Sciences (RAN), Chernogolovka 142432, Russia. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 202–209, February, 1999.     

New Method for the Synthesis and Reactivity of (5‐R‐1,3,4‐Oxadiazol‐2‐yl)furoxans

A new, simple and general one‐pot method for the preparation of (5‐R‐1,3,4‐oxadiazol‐2‐yl)furoxans has been developed on the basis of the interaction between accessible 3‐methylfuroxan‐4‐carboxylic acid hydrazide and aliphatic, aromatic and heterocyclic carboxylic acids or their chlorides in the presence of POCl₃. The synthesis and study of (5‐R‐1,3,4‐oxadiazol‐2‐yl)furoxans reactivity resulted in new polyheterocyclic ensembles incorporating furoxan, 1,3,4‐oxadiazole, pyrrole, triazole, furan, thiophene, pyrimidine, and other heterocycles in different combinations.     

Dimerizations of nitrile oxides to furoxans are stepwise via dinitrosoalkene diradicals: a density functional theory study

Density functional theory calculations at the B3LYP/6-31G* level on the dimerization reactions of acetonitrile oxide and para-chlorobenzonitrile oxide to form furoxans indicate that these processes are stepwise involving dinitrosoalkene intermediates that have considerable diradical character. The rate-determining steps for these two reactions correspond to C-C bond formation. The retardation of dimerization in aromatic nitrile oxides arises from the interruption of conjugation between the nitrile oxide and aryl groups in the C-C bond formation step. The present study also suggests that the isomerization of single-ring furoxans occurs via a diradical intermediate mechanism.     

Synthesis and cascade rearrangement of 3-arylazo-4-(3-ethoxycarbonylureido)furoxans

3-Arylazo-4-(3-ethoxycarbonylureido)furoxans, which were synthesized by the reactions of 4-amino-3-arylazofuroxans with ethoxycarbonyl isocyanate, were subjected to cascade rearrangements under the action of potassium tert-butoxide in dimethylformamide or by heating in dimethyl sulfoxide to form 4-amino-2-aryl-5-nitro-2H-1,2,3-triazoles. X-ray diffraction study and quantum-chemical calculations (B3LYP/6-31G**) of one of ureidofuroxans demonstrated that the intramolecular contact between the carbonyl group and the nitrogen atom of furoxan corresponds to the charge transfer from the lone electron pair of the oxygen atom to the antibonding orbital of the N—O bond.     

Isolation of nitrile oxides from the thermal fragmentation of furazan N-oxides

Flash vacuum pyrolysis of furoxans generates nitrile oxides, which have been reacted with alkenes to yield 2-isoxazolines, and have been examined by ¹H and ¹³C nmr spectroscopy.     

Unusual transformation of 3-alkylfuroxans into 3-(nitrooxyalkyl)furoxans on treatment with a mixture of nitric and sulfuric acids

A versatile one-pot synthesis of 4-substituted 3-(nitrooxyalkyl)furoxans by the reaction of 3-alkylfuroxans with a mixture of nitric and sulfuric acids was developed. A plausible mechanism of this unusual transformation was explained in terms of a new Grob-type fragmentation.     

Reaction of Aliphatic Diazo Compounds with Dinitrogen Trioxide. A Facile route to 3,4-Disubstituted 1,2,5-Oxadiazole-2-oxides(Furoxans)

As part of our continuing studies¹of the chemistry of diazo compounds, we have investigated the reaction of α-diazosulfones, α-diazoketones and ethyl diazoacetate with dinitrogen trioxide. When a solution of the diazo compound is allowed to react at 0–5° with excess n₂O₃ ² in CH₂Cl₂, and almost instantaneous evolution of a gas (presumably nitrogen) is observed. Work-up afforded 3,4–disubstituted furoxans (I–VII, see Table) in good Yields.     

Relative thermodynamic stabilities of the isomeric dihydrofurans and isomeric dihydropyrans. An experimental and DFT study

The relative thermodynamic stabilities of 2,5-dihydrofuran (1) and 2,3-dihydrofuran (2), and of 3,4-dihydro-6H-pyran (3) and 3,4-dihydro-2H-pyran (4), were determined at several temperatures by base-catalyzed equilibration in DMSO solution. For 1 → 2, = –15.4±0.1 kJ mol⁻¹, =–12.6±0.5 kJ mol⁻¹, and =9.5±1.3 J K⁻¹ mol⁻¹ at 298.15 K. The second-law reaction enthalpy agrees with literature data based on calorimetric enthalpies of hydrogenation of the isomeric forms in hexane. For 3 → 4, =–19.3±0.2 kJ mol⁻¹, = –18.9±1.1 kJ mol⁻¹ and =1.1±3.0 J K⁻¹ mol⁻¹ at 298.15 K: the experimental reaction enthalpy is in marked disagreement with literature data based on estimation. On the other hand, both of the experimental reaction enthalpies of the present study are in good agreement with DFT calculations using the B3LYP functional and 6-311+G(2d,p) basis set.