Furazan Ring Research Articles

Synthesis of 1,2,4-oxadiazole-, pyrrole- and 1,2,3-triazole-substituted (1,2,3-triazol-1-yl)furazans

The synthesis of tricyclic compounds with hitherto unknown combinations of heterocycles (1,2,3-triazol-1-yl)-1,2,5-oxadiazoles with 1,2,4-oxadiazol-3-yl, pyrrol-1-yl or 1,2,3-triazol-1-yl substituents at the furazan ring, was developed by interaction of corresponding substituted azidofurazans with 1,3-dicarbonyl compounds, and pyrrolyl derivatives were also synthesised by condensation of amino(1,2,3-triazol-1-yl)furazans with 2,5-dimethoxytetrahydrofuran.

Study on thermal decomposition and combustion of insensitive explosive 3,3′-diamino-4,4′-azofurazan (DAAzF)

Thermal decomposition of an explosive with low sensitivity, 3,3′-diamino-4,4′-azofurazan (DAAzF), has been investigated under isothermal conditions at 200–320 °C using the thin-walled glass manometer of the compensation type. Changing the ratio of the sample weight to the vessel volume allowed us to measure the kinetic parameters of DAAzF decomposition predominantly in the solid state ( k = 5.0 × 10 11 exp(−21,320/ T), s −1) and the gas phase ( k = 3.3 × 10 12 exp(−21,020/ T), s −1). The kinetics of decomposition in solution ( k = 3.5 × 10 6 exp(−14,070/ T), s −1) have also been measured. Based on the burning rate and thermocouple measurement data, rate constants of DAAzF decomposition in the molten layer at 600–800 °C have been derived from a condensed-phase combustion model ( k = 4.6 × 10 8 exp(−16,680/ T), s −1), which is in a good agreement with kinetic data obtained in the solution at 235–260 °C. The mechanism of DAAzF thermolysis and combustion includes initial rupture of C–N bond between the azo-group and furazan ring with subsequent nitrogen evolution and decomposition of the heterocyclic ring. In the combustion wave, the heat release from decomposition of the stable furazan ring follows the heat release from azo-group decomposition, resulting in a distinct two-stage flame structure.

Excited electronic state decomposition of furazan based energetic materials: 3,3′-diamino-4,4′-azoxyfurazan and its model systems, diaminofurazan and furazan

We report the first experimental and theoretical study of gas phase excited electronic state decomposition of a furazan based, high nitrogen content energetic material, 3,3'-diamino-4,4'-azoxyfurazan (DAAF), and its model systems, diaminofurazan (DAF) and furazan (C2H2N2O). DAAF has received major attention as an insensitive high energy explosive; however, the mechanism and dynamics of the decomposition of this material are not clear yet. In order to understand the initial decomposition mechanism of DAAF and those of its model systems, nanosecond energy resolved and femtosecond time resolved spectroscopies and complete active space self-consistent field (CASSCF) calculations have been employed to investigate the excited electronic state decomposition of these materials. The NO molecule is observed as an initial decomposition product from DAAF and its model systems at three UV excitation wavelengths (226, 236, and 248 nm) with a pulse duration of 8 ns. Energies of the three excitation wavelengths coincide with the (0-0), (0-1), and (0-2) vibronic bands of the NO A 2Sigma+<--X 2Pi electronic transition, respectively. A unique excitation wavelength independent dissociation channel is observed for DAAF, which generates the NO product with a rotationally cold (20 K) and a vibrationally hot (1265 K) distribution. On the contrary, excitation wavelength dependent dissociation channels are observed for the model systems, which generate the NO product with both rotationally cold and hot distributions depending on the excitation wavelengths. Potential energy surface calculations at the CASSCF level of theory illustrates that two conical intersections between the excited and ground electronic states are involved in two different excitation wavelength dependent dissociation channels for the model systems. Femtosecond pump-probe experiments at 226 nm reveal that the NO molecule is still the main observed decomposition product from the materials of interest and that the formation dynamics of the NO product is faster than 180 fs. Two additional fragments are observed from furazan with mass of 40 amu (C2H2N) and 28 amu (CH2N) employing femtosecond laser ionization. This observation suggests a five-membered heterocyclic furazan ring opening mechanism with rupture of a CN and a NO bond, yielding NO as a major decomposition product. NH2 is not observed as a secondary decomposition product of DAAF and DAF.

Furazan ring opening upon treatment of benzofurazan with ethanolamine to yield quinoxalines

Heating of benzofurazans with ethanolamine in the presence of catalytic amount of p-toluenesulfonic acid leads to quinoxalines.

Reactions of (pyrrol-1-yl)furazans with electrophilic reagents

The behavior of (pyrrol-1-yl)furazans in electrophilic substitution reactions (halogenation, nitration, and acylation) was studied. The presence of the furazan ring substantially did not affect the regioselectivity of the reactions but it prevented replacement of all the hydrogen atoms in the pyrrole ring by electrophiles.

Synthesis of Fluorofurazans

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Synthesis of fluorofurazans

Furazans bearing fluoro atoms are easily obtained by nucleophilic displacement of a nitro group at the furazan ring upon treatment with TEAHF in a solution of [BMIM][BF 4 ].

Nucleophilic substitution in the series of (1,2,3-triazol-1-yl)-1,2,5-oxadiazoles. Reactions with N-, O-, and S-nucleophiles

Methods for the synthesis of amino(1,2,3-triazol-1-yl)-1,2,5-oxadiazoles (amino-triazolylfurazans) with CH2Cl and COCH2Br substituents in the triazole ring were developed and nucleophilic substitution for their halogen atom in reactions with N-, O-, and S-nucleophiles were studied. The possibility of displacing the NO2 group from the furazan and triazole rings in triazolylfurazans by an azido group was investigated. Novel compounds of this series were synthesized; the reaction rate and pathway were found to depend on the nature of the substrate and the reagent and the position of the substituent in isomers.

Synthesis of macrocycles incorporating azo‐bis(azofurazan) framework

AbstractA series of macrocycles containing four furazan rings bonded by three azo bonds 2, 5 and 7 have been synthesized from the common precursor, 3‐amino‐3′‐nitro(azofurazan) 3. The macrocycles closure is a result of NN bond formation at oxidative cyclization of corresponding bis(3‐aminofurazan‐4‐yl) precursors. X‐Ray crystal structures of macrocycles 2, 2•AcOH, 11 and 13 are reported.

Synthesis and Cytotoxic Evaluation of Combretafurazans

Combretastatin A-4 is an antitumoral and antitubulin agent that is active only in its cis configuration. In the present manuscript, we have synthesized cis-locked combretastatins embodying a furazan ring (combretafurazans). To achieve this, we have developed a new strategy that exploits the dehydration of vicinal dioximes using the Mitsunobu reaction. Among the advantages of following such a strategy are the mild conditions used for the construction of the diarylfurazan derivatives, allowing for the presence of highly functionalized substrates and deactivated aromatic rings. Combretafurazans are more potent in vitro cytotoxic compounds compared to combretastatins in neuroblastoma cells, yet maintaining similar structure-activity relationship and pharmacodynamic profiles.

Unusual Reaction of Iodofurazans with Nucleophilic Reagents.

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Synthesis of Secondary and Tertiary Aminofurazans.

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Difurazano[3,4-b:3',4'-f]-4,5-diaza-1,8-dioxacyclododecine and an acyclic analogue.

The novel title furazan-containing macrocycle (systematic name: 6,9,14,17-tetraoxa-2,3,5,7,16,18-hexaazatricyclo[13.3.0.0(4,8)]octadeca-4,7,15,18-tetraene), C8H10N6O4, (I), is the first macrocycle where the furazan rings are connected via a hydrazine group. In spite of the strain in the 12-membered macrocycle of (I), the geometry of the furazan fragment is the same in (I) and in its acyclic analogue 1,8-bis(5-aminofurazan-4-yloxy)-3,6-dioxaoctane, C10H16N6O6, (II). In both compounds, the participation of the furazan rings in intermolecular hydrogen bonding equalizes the N-O bonds within the furazan rings, in contrast with rings which do not participate in such interactions.

Unusual reaction of iodofurazans with nucleophilic reagents

Nucleophilic reagents cause detachment of the iodine atom from 3-iodo-4-R-furazans and opening of the furazan ring to give salts of the corresponding α-hydroxyiminoacetonitriles.

Synthesis of secondary and tertiary aminofurazans

Reactions of nitrofurazans with primary and secondary amines were studied. Conditions were found which allow the efficient replacement of the nitro group with these nucleophiles. Transformations of the amidoxime fragment, which is bound to the furazan ring and contains an amino substituent, enable one to substantially expand the spectrum of polyfunctional derivatives. The structures of the amines synthesized were studied by X-ray diffraction analysis.

Nucleophilic Substitution in the Furazan Series. Reactions of Nitrofurazans with Ammonia.

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Nucleophilic substitution in the furazan series. Reactions of nitrofurazans with ammonia

The reactions of 3-nitro-4-R-furazans with ammonia were studied. The effect of the substituent R on the specific features of the nucleophilic substitution reaction observed was considered. The nitro group attached to the furazan ring can act as both the leaving group and the activating group facilitating the displacement of the second substituent (for example, OR" or N(NO2)R").

Fluorinated heterocyclic compounds. A photochemical synthesis of 3-amino-5-perfluoroaryl-1,2,4-oxadiazoles

A photochemical methodology for the synthesis of 3-amino- (or 3- N-substituted amino) 5-pentafluorophenyl-1,2,4-oxadiazoles is reported. Irradiation of 3-pentafluorobenzoylamino-4-methyl-1,2,5-oxadiazole (Furazan) at 254 nm in methanol and in the presence of ammonia, primary or secondary aliphatic amines produces 3-amino-, 3-( N-alkylamino)-, 3-( N, N-dialkylamino)-5-pentafluorophenyl-1,2,4-oxadiazoles. The photoreaction follows the fragmentation pattern of the furazan ring with the extrusion of acetonitrile and the formation of a counterpart fragment which the nitrogen nucleophile will capture. Depending on the nature of the reagent, displacement of a fluoride anion at the C(5)-pentafluorophenyl moiety of the first-formed oxadiazoles by the nitrogen nucleophile and/or the solvent also takes place. By the same photochemical approach, the synthesis of the 3-methoxy-5-pentafluorophenyl-1,2,4-oxadiazole is also described.

Synthesis and properties of furazanyl-substituted acetylenes and diacetylenes

Compounds of the acetylene and diacetylene series, containing a furazan ring, were synthesized by alkylation of 3,4-diaminofurazan and nucleophilic substitution of the nitro group in 3-amino-4-nitrofurazan under conditions of phase-transfer catalysis.

Synthesis of (1,2,3-triazol-1-yl)furazans. 2. Reaction of azidofurazans with morpholinonitroethene

We have studied the 1,3-dipolar cycloaddition of azidofurazans to morpholinonitroethene and prepared 1,2,3-triazoles with furazan ring in position 1 and NO2 group at position 4.