Transformations of anthra[1,9-cd]isoxazol-6-ones in hydrohalic acids

4-Halo-1-aminoanthraquinones are formed when anthra [1,9-cd]isoxazol-6-ones are refluxed in hydrohalic acids. The 3 position undergoes halogenation when 5-substituted isoxazoles are used. The process takes place via a one-proton mechanism with the participation of halide ion in the rate-determining step, possibly with the intermediate formation of N-haloaminoanthraquinones.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1471–1473, November, 1980.     

4-Alkoxycarbonyl- and aminocarbonyl-substituted isoxazoles as masked acrylates and acrylamides in the asymmetric synthesis of delta2-isoxazolines

4-Alkoxycarbonyl and aminocarbonyl-substituted isoxazoles undergo conjugate reduction to give delta2-isoxazolines on treatment with sodium borohydride and sodium trifluoroacetoxyborohydride, respectively. They are also alkylated at C5 through sonication with secondary and tertiary alkyl iodides in the presence of zinc dust and copper(I) iodide. These reactions are analogous to those observed with acrylates and acrylamides. The behavior is characteristic of the 4-substituted isoxazoles but not the 5-substituted regioisomers. The reductions of 4,5-disubstituted isoxazoles and the C5 alkylations of 4-substituted isoxazoles generally afford trans-4,5-disubstituted isoxazolines. Incorporating chiral auxiliaries into the alkoxycarbonyl group maintains this relative stereoselectivity. It does not provide significant levels of asymmetric induction in the reductions, but the alkylations occur with good levels of stereocontrol at both C4 and C5. Because both enantiomers of the auxiliaries are available, this provides access to either enantiomer of the products, in 93 to > or = 98% de. The methodology, therefore, provides a complementary approach to nitrile oxide cycloadditions to alkenes for the asymmetric synthesis of delta2-isoxazolines.     

Electroreduction of molecular oxygen on carbon electrode modified by dispersed silver

Silver particles are formed by electrochemical deposition on the carbon electrode surface. It is found that the deposition process occurs according to the progressive nucleation mechanism, which results in formation of silver particles with the size of 95 to 190 nm as dependent on the electrodeposition time. The values of silver particle size and support surface coverage by metal obtained on the basis of microphotographs indicate that cathodic polarization in the presence of dissolved oxygen results in particle size redistribution due to the reaction of silver particle dissolution with further deposition simultaneously with oxygen electroreduction. The reaction of molecular oxygen electroreduction on a carbon electrode with deposited dispersed silver occurs via a mixed two- and four-electron mechanism. The observed limiting reaction current is of diffusion nature.     

Electroreduction of oxygen on carbon black with adsorbed peroxidase or a peroxidase—nafion composite

The oxygen electroreduction on electrodes with adsorbed peroxidase (POD) or a POD-Nafion composite is studied. In the conditions of direct bioelectrocatalysis, the process occurs on both POD and POD in the composite. The higher the electrode coverage by POD, the higher the measured current. The composite electrodes have a higher activity and stability. A mechanism of the cathodic reduction of oxygen by immobilized POD is discussed     

Etude de l'équilibre azido ⇌ tétrazole dans la séric du thiazolo[2,3-e]-tétrazole. III. Effects des substituants

The substituent effects on azido/tetrazole equilibrium on a series of 2-substituted thiazoles, benzothiazoles, thiadiazoles, benzoxazoles and isoxazoles has been studied by proton magnetic resonance in two solvents (DMSO-d₆ and deuteriochloroform). For thiazole an excellent Hammett relationship was found, both for the 4 and 5 positions.     

Facile one-pot synthesis of 5-substituted isoxazoles and pyrazoles through microwave-promoted intramolecular cyclization of γ-hydroxyalkynal oximes and hydrazones

Simple and efficient one-pot synthesis of 5-substituted isoxazoles and pyrazoles has been developed. The formation of the target isoxazoles and pyrazoles is initiated by 1,2-nucleophilic addition of generated in situ hydroxylamine or hydrazine to α-acetylenic γ-hydroxyaldehydes with further intramolecular cyclization of the adducts. The protocols are associated with readily available substrates, simple procedure, short reaction time, and moderate to high yields.     

On a thermodynamic description of Se(IV) electroreduction and CdSe electrolytic formation on Ni,Ti and Pt cathodes in acidic aqueous solution

A discussion on tetravalent Se electroreduction and CdSe cathodic electrodeposition in terms of thermodynamics, in association with an investigation on the voltammetric behavior of Pt, Ni and Ti working electrodes in a high temperature (85 °C) acidic aqueous bath, is presented. The underpotential co-deposition of Cd with Se is described within the frame of a known electrochemical model of compound formation. The data presented serve as an effective basis for studying the electroreduction of Se(IV) as well as for determining the relevance of theoretical predictions to experimental findings on a binary compound electrodeposition process.     

Radical intermediates in the electrochemical reduction of alizarin

Conclusions In the electroreduction of alizarin in an aprotic medium the stepwise formation of the anion-radical and subsequently of the dianion has been observed; under conditions of the prolonged process the anion-radical disproportionates and through intermediate stages of deprotonation and reduction is converted into the stable dianion-radical.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 983–988, May, 1985.     

Complete Diastereocontrol in Intramolecular 1,3-Dipolar Cycloadditions of 2-Substituted 5-Hexenyl and 5-Heptenyl Nitrones: Application to the Synthesis of the beta-Lactam Antibiotic 1beta-Methylthienamycin

The diastereoselectivity of intramolecular 1,3-dipolar cycloadditions of 2-substituted 5-hexenyl and 5-heptenyl nitrones to give 6-substituted and 3,6-disubstituted perhydrocyclopenta[c]isoxazoles has been investigated. An alkyl or aryl substituent at C2 completely controls the stereochemistry of the ring juncture and, in the case of the 5-heptenyl systems, also the stereochemistry of the 3-methyl group. Thus one stereocenter controls the formation of the other three to give a product with four contiguous stereocenters. The use of an ethylene ketal substituent in these systems allows the reaction to be carried out at much lower temperatures, an example of the gem-dialkoxy effect. This cycloaddition process has been used in an efficient formal total synthesis of the potent beta-lactam antibiotic, 1beta-methylthienamycin.     

氧气在阴极的电还原及其应用研究进展

本文综述了氧阴极电还原的研究进展，着重介绍了阴极表面修饰对该过程的影响以及氧阴极电还原在有机物电合成与废水处理方面的研究进展。     

A novel synthesis of 5-substituted isoxazoles from propargylic amines and N-hydroxyphthalimide

A mild and efficient method for the synthesis of 5-substituted isoxazoles through cyclization of propargylic amines with N-hydroxyphthalimide (NHPI) under metal-free conditions was developed.     

Regioselective conversion of alkynes to 4-substituted and 3,4-disubstituted isoxazoles using titanium-catalyzed multicomponent coupling reactions

Conditions have been developed for the regioselective synthesis of 4-substituted isoxazoles from terminal alkynes and 3,4-disubstituted isoxazoles from internal alkynes. The methodology involves a one-pot titanium-catalyzed multicomponent coupling reaction followed by simple hydroxylamine hydrochloride addition.     

Oxime-based methods for synthesis of stereodefined acyclic polyfunctionalized δ-azido-nitriles and 5-substituted isoxazoles from carbohydrate derivatives

Hydroxylamine-mediated syntheses of stereodefined acyclic polyfunctionalized δ-azido-nitriles and 5-substituted isoxazoles, bearing a differentially protected glycerol moiety, from 2-deoxysugars and glycals are described.     

An Efficient Deselenenylation Reaction to the Synthesis of 3, 5-Disubstituted Isoxazoline and Isoxazole

The development of organoselenium chemistry1 has been expanding rapidly during the last decades. Among them, organic selenides are key intermediates, for that they can be efficiently introduced, manipulated, and removed through selenoxide syn-elimination2. Our research group3 has been interested in the application of selenium in organic synthesis for several years. Isoxazolinyl substituted phenyl selenide 13a, although a β-H exists in the molecule, did not undergo selenoxide syn-elimination e…     

Oxygen reduction reaction on polycrystalline gold. Pathways of hydrogen peroxide transformation in the acidic medium

The mechanism of oxygen electroreduction on polycrystalline gold is studied in the acidic medium. Hydrogen peroxide is the main reaction product. However, two potential regions can be singled out in which the oxygen electroreduction reaction proceeds by different pathways. The first region is the potential interval close to the steady-state potential. Here, the oxygen electroreduction virtually completely produces peroxide. The second interval is the potential range of considerable cathodic polarization values. In this case, peroxide can be reduced to water. The low energy of hydrogen peroxide adsorption on gold determines the considerable overpotential of peroxide reduction. It is shown that on the gold electrode surface, the catalytic decomposition of peroxide occurs. The use of the method of electrochemical impedance spectroscopy allows the peculiarities of the oxygen reaction associated with hydrogen peroxide transformations to be revealed. In the acidic medium, the reactions of consecutive reduction of oxygen through the intermediate formation of hydrogen peroxide and the catalytic decomposition of the intermediate product are shown to proceed simultaneously. The ratio of rate constants of electrochemical stages depends on the potential. The chemical decomposition is observed both near the steady-state potential and in the cathodic region where considerable electrochemical reduction of peroxide occurs.     

1,3-Dipolar cycloaddition synthesis of 3-bromo-5-substituted isoxazoles,useful intermediates for the preparation of pharmacologically active compounds

Bromonitrile oxide 2 , generated from easily available dibromoformaldoxime 1 , reacts with monosubstituted acetylenic derivatives 4 to give 3-bromo-5-substituted isoxazoles 5 in high yield. The experimental conditions necessary to overcome difficulties such as the low reactivity of acetylenic dipolarophiles and the high tendency to dimerization of bromonitrile oxide 2 , are discussed; the regioselectivity of this 1,3-dipolar cycloaddition is also studied. The obtained improvements in the synthesis of some pharmacologically active compounds are reported.     

13C nuclear magnetic resonance studies on some substituted isoxazoles

¹³C n.m.r. spectra of some substituted isoxazoles have been examined to ascertain the reactive site in the metallation of 4-substituted 3,5-dimethylisoxazoles. The results obtained indicate that metallation occurred exclusively at the C-5 methyl.     

Synthesis and Antiprotozoal Profile of 3,4,5-Trisubstituted Isoxazoles

A series of 60 4-aminomethyl 5-aryl-3-substituted isoxazoles were synthesized by an efficient method and evaluated in vitro against Leishmania amazonensis and Trypanosoma cruzi, protozoa that cause the neglected tropical diseases leishmaniasis and Chagas disease, respectively. Thirteen compounds exhibited a selective index greater than 10. The series of 3-N-acylhydrazone isoxazole derivatives bearing the bithiophene core exhibited the best antiparasitic effects.     

Reduction of metol on mechanically renewed metal electrodes

The electroreduction of metol on mechanically renewed metallic electrodes is studied by direct voltammetry with linear potential sweep. Reduction peaks of metol are found in a neutral supporting electrolyte (0.02–0.5 M Na₂SO₄) on nickel, silver, and mercury electrodes before the potential of hydrogen liberation from the supporting electrolyte. The shape and parameters of the cathodic peak depend on an electrode material, and also on the composition and pH of the supporting solution. A probable mechanism of the electroreduction of metol is proposed. The regeneration of nickel and silver electrodes by in situ mechanical cutting of a 0.5-μm surface layer provides good reproducibility of the value of peak current; it is proportional to the concentration of metol in the range 2 × 10⁻³–1.8 × 10⁻² M.     

Electrochemical behavior of stainless steel in aerated NaCl solutions by electrochemical impedance and rotating disk electrode methods

Electrochemical behavior of stainless steel in 0.5 M NaCl solutions is studied. It is shown that, for this steel, under a considerable cathodic polarization of electrode, the oxygen electroreduction proceeds via a four-electron mechanism. The corrosion current is estimated. From the impedance spectra, elements of an equivalent circuit that describes the electrode behavior under the ac conditions are calculated. A mechanism of the steel passivation in the electrolyte is proposed.