Electron transfer in the cathodic reduction of α-dicarbonyl compounds

Electron transfer processes take place during the cathodic reduction, under an argon atmosphere, of different α-dicarbonyl substrates. Carboxylic acids or methylene diesters are obtained from benzil or furil after electron transfer to the oxygen in the air, during the workup, or after electron transfer to the solvent. Involving an electron transfer to dichloromethane, 2-hydroxy-2-hydroxymethyl-2H-acenaphtylen-1-one or benzo[1,3]dioxin-8-one are formed when acenaphthenequinone or 1,2-cyclohexanedione are, respectively, reduced.     

Oxidation of β-dicarbonyl compounds with tert-butyl hydroperoxide in the presence of vanadyl acetylacetonate

Oxidation of β-dicarbonyl compounds with tert-butyl hydroperoxide in the presence of vanadyl acetylacetonate (benzene, 20°C) involves the activated methylene group with intermediate formation of trioxo derivatives and is accompanied by decomposition of carbon skeleton. The oxidation products are carbon dioxide, carboxylic acids, and tert-butyl and peroxy esters derived from the latter.     

Selective reduction of the acyl group in cyclic α-acyl-β-dicarbonyl compounds with sodium cyanoborohydride. Efficient synthesis of cyclic α-alkyl-β-dicarbonyl compounds

Efficient synthesis of cyclic -alkyl--dicarbonyl compounds of the cyclopentane, cyclohexane, tetronic acid, and -pyrone series from the corresponding cyclic -acyl--dicarbonyl compounds under the action of NaBH₃(CN) in a THF--HCl system is described.     

Reactions of aminoguanidine with α-dicarbonyl compounds studied by electrospray ionization mass spectrometry

Aminoguanidine possesses extensive pharmacological properties. This drug is recognized as a powerful α-dicarbonyl scavenger. In order to better elucidate the reactivity of aminoguanidine with α-dicarbonyls, aminoguanidine was reacted with several aldehydic and diketonic α-dicarbonyls. Electrospray ionization mass spectrometry is a suitable technique to study chemical and biochemical processes, and was selected for the purpose. In aminoguanidine reactions, triazines were detected and, other compounds that have never been reported before were identified. Triazine precursor forms were detected, namely tetrahydrotriazines and singly dehydrated tetrahydrotriazines. Moreover, species with bicyclic ring structures, and dehydrated forms, were also identified in aminoguanidine reactions. These species appear to result from tetrahydrotriazines and triazines reactions with one dicarbonyl molecule. Experiments revealed that these bicyclic species, in particular the ones resulting from triazines reactivity, could exist in solution, since they were both identified in the reactions of aminoguanidine and of a selected triazine with the dicarbonyls studied. The results obtained, regarding aminoguanidine/triazines reactivities, appear to support the capability of triazines to condensate and form polycyclic ring structures, and also to support literature mechanistic data for dihydroimidazotriazines formation via dihydroxyimidazolidine-triazines. The data obtained in this study may prove to be valuable to complement solution information, concerning the reactivity of amines with α-dicarbonyls, in particular.     

A new facile synthesis of α-dicarbonyl compounds by oxidation of alkynes with Mo(VI) peroxocomplex promoted by mercuric acetate

Mercuric acetate promoted oxidation of diaryl-, dialkyl-, and aralkyl alkynes with (HMPA)MoO(O₂)₂ in 1,2-dichloroethane affords the corresponding α-diketones in good yields. Likewise, terminal alkynes can be converted into α-ketoaldehydes in excellent yields by using the same oxidizing system.     

Nucleophilic addition reaction of aromatic compounds with α-chloroglycidates in the presence of Lewis acid

The epoxide 1 obtained by the Darzens condensation reaction of aldehydes with methyl dichloroacetate, reacted with aromatic compounds in the presence of aluminium chloride to afford α-aryl-β-chloro-α-hydroxyalkanoate 3. The intra-molecular nucleophilic addition of epoxide 1′ gave cyclisation compound 4. The scope and limitation of these reaction were studied for various aldehydes and aromatic compounds. The reaction was also studied in the presence of aluminium chloride supported on alumina or silica gel, which is thought to be a mild Lewis acid and harmless for environment.     

Synthesis of fullerene Γ-lactones by free radical reaction of C60 with ketones promoted by compounds of transition metals Cr(VI), Ce(IV)

One-step synthesis was developed for fullerene Γ-lactones by the reaction of C₆₀ with aromatic and aliphatic ketones in the presence of transition metal compounds CrO₃, K₂Cr₂O₇, (NH₄)₂Ce(NO₃)₆ ·6H₂O.     

Formation of five- and six-membered nitrogen-containing heterocycles on the basis of hydrazones derived from α-dicarbonyl compounds (microreview)

Chemistry of Heterocyclic Compounds - In this microreview we provide a broad coverage of methods used over the previous 20 years for the synthesis of nitrogen-containing heterocyclic structures on...     

Photochemistry of enolizable β-dicarbonyl compounds: study on the photoketonization of some esters of aroylacetic acids

A detailed experimental study of the reversible photochemistry of some esters of aroylacetic acids indicates the photoformation of the respective ketonic forms as a result of the shift of the keto-enol equilibrium. The rate constants and quantum yields of the process under consideration have been determined. Important differences in the photosensitivity of β-ketoesters depending on the structural features have been established.     

Electrochemiluminescence from tris(2,2′-bipyridyl) ruthenium (Ⅱ) in the presence of aminocarboxylic acid co-reactants

Due to the highly sensitive electrochemiluminescence (ECL), tris(2,2′-bipyridyl) ruthenium(II) (Ru(bpy)32+) is often used in the field of bioarrays with the help of co-reactants. However, the generally used co-reactant, tripropylamine (TPA), is toxic, corrosive and volatile. Therefore, the search for safe, sensitive and economical co-reactants is critical. Herein, three aminocarboxylic acids, ethylenediamine-tetraacetic acid (EDTA), nitrilotriacetic acid (NTA), and 2-hydroxyethylethylene diaminetriacetic ac...     

Synthesis of α-functional nitro compounds by the nitration of activated carbonyl compounds in a two-phase system

2-Nitro-1,3-dicarbonyl and -nitromonocarbonyl compounds were synthesized in the yields varying from moderate (30 %) to nearly quantitative by the nitration of -dicarbonyl compounds in a two-phase system: sulfuric/nitric acid mixture-chloroform at - 10÷10 °C. The use of phase transfer conditions made it possible to avoid the formation of furoxans as by-products and to simplify the isolation of products. This method is quite common for preparing various -functional nitro compounds including those containing a CF₃-group. Key words: nitration, -functional nitro compounds.Translated fromIzvestiya Akademn Nauk. Seriya Khimicheskaya, No. 1, pp. 76–79, January, 1994.     

Enhanced solubility of fullerene (C60) in water by inclusion complexation with cyclomaltononaose (δ-CD) using a cogrinding method

The solubilizing effects of cyclomaltononaose (δ-CD), a cyclic oligosaccharide composed of nine α-1,4-linked d-glucose units, on C₆₀ were investigated by using a ball-milling method based on a solid–solid mechanochemical reaction. The complex between C₆₀ and δ-CD was characterized by UV–VIS spectrometry, ¹³C-NMR, and fast atom bombardment mass spectrometry (FAB-MS). Coloration of the C₆₀/δ-CD system was yellowish-brown in aqueous solution, and the UV–VIS spectrum was in agreement with that of C₆₀ in hexane solution. The ¹³C-NMR spectrum of C₆₀/δ-CD system in aqueous solution revealed the presence of free δ-CD and dissolved C₆₀ giving one sharp peak at 144.4 ppm, which was close to that reported for C₆₀ in organic solvents. The FAB-MS spectrum of the C₆₀/δ-CD system showed a negative ion peak corresponding to the molecular weight of a complex between two δ-CDs and one C₆₀. Moreover, the phase solubility diagram of C₆₀ with δ-CD at 10 °C was classified as the Bs-type, resulting in a stoichiometric ratio of 1:2 (C₆₀:δ-CD), in agreement with the stoichiometry obtained from FAB-MS. These findings suggest that the solubilization of C₆₀ in water was due to complex formation of C₆₀ with δ-CD and that the stoichiometric ratio of the complex was 1:2 (C₆₀:δ-CD).     

Room temperature phosphorescence of α-bromonaphthalene induced by β-cyclodextrin in the presence of cyclohexane

β-Cyclodextrin (β-CD) can induce a-bromonaphthalene (BrN) to emit strong room temperature phosphorescence (RTP) in the presence of micro amounts of cyclohexane (c-hexane). Experiments of luminescence spectra, phosphorescence lifetime and fluorescence polarization prove the formation of c-hexane/β-CD/BrN ternary inclusion complex. The apparent formation constant of the ternary inclusion complex was determined and the effect mechanism of c-hexane on the RTP of BrN induced by β-CD is discussed.     

Synthesis of α,β-disubstituted aldehydes involving metallated 1-aza-1,3-butadienes in the presence of phosphine complexes of palladium

A novel catalytic method was developed for the synthesis of,-disubstituted aldehydes by the reaction of N-, O-, and S–containing allyl electrophiles with magnesium azaenolates obtained by metallation of,-unsaturated imines by Grignard reagents. The reaction is carried out with high regio- and stereoselectivity in the presence of phosphine complexes of palladium.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2339–2348, October, 1991.     

Kinetics and mechanism of the oxidation of neutralized α-hydroxy acids by tris(pyridine-2-carboxylato)manganese(III)

The kinetics of oxidation of the neutralized -hydroxy acids: lactic, -hydroxyisobutyric, mandelic, benzilic and atrolactic acids by tris(pyridine-2-carboxylato)manganese(III) have been studied. The reactions were carried out in a Na(pic)-picH [Na(pic) = sodium salt of pyridine-2-carboxylic acid and picH = pyridine-2-carboxylic acid] buffer medium in the 4.89–6.10pH range. The oxidation rate was found to be independent of pH, and rate follows the order: benzilate > mandelate >atrolactate>lactate > -hydroxy isobutyrate. The oxidation products are MeCHO, Me2CO, PhCHO, Ph2CO and PhCOMe for the respective reactions. A mechanism is proposed involving intermediate formation of hepta-coordinated MnIII complexes in a fast step. The complexes then decompose to give free radicals and MnII in the rate determining step. The free radicals subsequently react with another molecule of the MnIII species to give the respective carbonyl compounds in a fast step.     

Cross-linking mechanisms of arginine and lysine with α,β-dicarbonyl compounds in aqueous solution

Cross-linking in proteins by α,β-dicarbonyl compounds is one of the most damaging consequences of reactive carbonyl species in vivo and in foodstuffs. In this article we investigate computationally the cross-linking of glyoxal and methylglyoxal with lysine and arginine residues using density functional theory and the wB97XD dispersion-corrected functional. Five pathways, A-E, have been characterized. In pathways A and B, the reaction proceeds via formation of the Schiff base, aldimine, followed by addition of arginine. In contrast, in pathways C-E, direct addition of arginine to the dicarbonyl compounds occurs first, leading to a dihydroxyimidazolidine intermediate, which then reacts with lysine after dehydration and proton transfer reactions. The results reveal that pathways A, C, and E are competitive whereas reactions via pathways B and D are much less favorable. Inclusion of up to five explicit water molecules in the proton transfer and dehydration steps is found to lower the energy barriers in the feasible pathways by about 5-20 kcal/mol. Comparison of the mechanisms of methylglyoxal-derived imidazolium cross-linking (MODIC) and glyoxal-derived imidazolium cross-linking (GODIC) shows that the activation barriers are lower for GODIC than MODIC, in agreement with experimental observations.     

Cycloaddition of diazoketones to [60]fullerene in the presence of the catalytic system Pd(acac)2—PPh3—Et3Al

A method for the selective and efficient synthesis of methanofullerenes by cycloaddition of diazoketones to [60]fullerene in the presence of a three-component catalytic system Pd(acac)₂—PPh₃—Et₃Al has been developed.     

Selective CC bond hydrogenation in unsaturated nitro compounds in the presence of the RhCl3-aliquat 336 catalyst system

The ion pair formed from aqueous rhodium trichloride and Aliquat 336 catalyzes the selective hydrogenation of olefinic CC bonds of a variety of unsaturated nitro compounds in a two liquid phase system at 30°C. Nitrobenzene gives, under these conditions, a mixture of aniline and nitrocyclohexane.     

Oxidative cleavage of α, β-unsaturated compounds by pentachlorohydroxoplatinate(IV) in alkaline medium

The kinetics of oxidation of α,β-unsaturated compounds by platinum(IV) in the presence of alkali {[OH⁻]= (1–9) × 10⁻³ mol dm⁻³} have been investigated over the 303–318 K temperature range . The rate of the reaction is dependent on the first power of the concentrations of substrates, oxidant, and alkali. The rate constant increases with an increase in ionic strength and also with increasing dielectric constant of the medium. The oxidation rates follow the order: –CN > –CONH₂ > –COO⁻. The values of the third order rate constant (k₃) for the oxidation of acrylonitrile, acrylamide and acrylate are 1.24, 0.826 and 0.628 mol⁻² dm⁶ s⁻¹ respectively, at 303 K. The oxidations of the substrates by PtCl₅(OH)²⁻ take place by an inner-sphere mechanism. Platinum(IV) is reduced to platinum(II) by the substrates in a one-step two-electron transfer process to give reaction products. The major reaction product, HCHO, is identified from the reaction mixture using i.r. spectrometry, n.m.r. and C, H, N analysis. A tentative reaction mechanism, leading to the formation of products, has been suggested. The activation parameters of the reaction have been evaluated.     

An efficient synthesis of α-hydroxyphosphonates and α-aminophosphonates in the presence of chlorotrimethylsilane

Abstract

Solvent free, and quantitative yielding synthesis of α-hydroxyphosphonates (2a–h) from 2-chloroquinolin-3-carbaldehyde (1a–h) and α-aminophosphonates (4a–p) from imines (3a–p), obtained from 2-chloroquinoline-3-carbaldehyde by using triethylphosphite in the presence of chlorotrimethylsilane at room temperature in short time.