Anodic oxidation synthesis

Benzo[b]thiophene, 3-mercapto-2-methyl-synthesis, 4, 931 Benzo[6]thiophene, 2-methoxy-lithiation, 4, 773 synthesis, 4, 929 Benzo[6]thiophene, 3-methoxy-alkylation, 4, 765 synthesis, 4, 929 Benzo[6]thiophene, 4-methoxy-anodic oxidation, 4, 798 Benzo[6]thiophene, 5-methoxy-synthesis, 4, 929 Benzo[6]thiophene, 6-methoxy-synthesis, 4, 929 Benzo[6]thiophene, 7-methoxy-synthesis, 4, 929-930... 

Furfural — see Furan-2-oarbaldehyde, 532 Furfuryl acetate, o -(butoxycarbonyl)-anodic oxidation, 1, 424 Furfuryi acrylate polymerization, 1, 279 Furfuryl alcohol configuration, 4, 544 2-Furfuryl alcohol polyoondensation, 1, 278 reactions, 4, 70-71 Furfuryl alcohol, dihydro-pyran-4-one synthesis from, 3, 815 Furfuryl alcohol, tetrahydro-polymers, 1, 276 rearrangement, 3, 773 Furfuryl chloride reactions... 

The procedure described is essentially that of Belleau and Weinberg and represents the only known way of obtaining the title compound. One other quinone acetal, 1,4,9,12-t6traoxadispiro[4.2.4.2]tetradeea-6,13-diene, has been synthesized by a conventional method (reaction of 1,4-cyclohexanedione with ethylene glycol followed by bromination and dehydrobromination ) as well as by an electrochemical method (anodic oxidation of 2,2-(l,4-phenylenedioxy)diethanol ). Quinone acetals have been used as intermediates in the synthesis of 4,4-dimethoxy-2,5-cyclohexadienone,. syw-bishomoquinone, - and compounds related to natural products. ... 

The anodic oxidation of the carboxylate anion 1 of a carboxylate salt to yield an alkane 3 is known as the Kolbe electrolytic synthesis By decarboxylation alkyl radicals 2 are formed, which subsequently can dimerize to an alkane. The initial step is the transfer of an electron from the carboxylate anion 1 to the anode. The carboxyl radical species 4 thus formed decomposes by loss of carbon dioxide. The resulting alkyl radical 2 dimerizes to give the alkane 3 " ... 

In 1979, Diaz et al. produced the first flexible, stable polypyrrole (PPy) film with high conductivity (1(X) Scm ). The substance was polymerized on a Pt-electrode by anodic oxidation in acetonitrile. The then known chemical methods of synthesis " usually produced low conductivity powders from the monomers. By contrast, electropolymerization in organic solvents formed smooth and manageable films of good conductivity. Thus, this technique soon gained general currency, stimulating further electropolymerization experiments with other monomers. In 1982, Tourillon... 

Faraday, in 1834, was the first to encounter Kolbe-electrolysis, when he studied the electrolysis of an aqueous acetate solution [1], However, it was Kolbe, in 1849, who recognized the reaction and applied it to the synthesis of a number of hydrocarbons [2]. Thereby the name of the reaction originated. Later on Wurtz demonstrated that unsymmetrical coupling products could be prepared by coelectrolysis of two different alkanoates [3]. Difficulties in the coupling of dicarboxylic acids were overcome by Crum-Brown and Walker, when they electrolysed the half esters of the diacids instead [4]. This way a simple route to useful long chain l,n-dicarboxylic acids was developed. In some cases the Kolbe dimerization failed and alkenes, alcohols or esters became the main products. The formation of alcohols by anodic oxidation of carboxylates in water was called the Hofer-Moest reaction [5]. Further applications and limitations were afterwards foimd by Fichter [6]. Weedon extensively applied the Kolbe reaction to the synthesis of rare fatty acids and similar natural products [7]. Later on key features of the mechanism were worked out by Eberson [8] and Utley [9] from the point of view of organic chemists and by Conway [10] from the point of view of a physical chemist. In Germany [11], Russia [12], and Japan [13] Kolbe electrolysis of adipic halfesters has been scaled up to a technical process. 

Carboxylic acids can be converted by anodic oxidation into radicals and/or carbo-cations. The procedure is simple, an undivided beaker-type cell to perform the reaction, current control, and usually methanol as solvent is sufficient. A scale up is fairly easy and the yields are generally good. The pathway towards either radicals or carbocations can be efficiently controlled by the reaction conditions (electrode material, solvent, additives) and the structure of the carboxylic acids. A broad variety of starting compounds is easily and inexpensively available from natural and petrochemical sources, or by highly developed procedures for the synthesis of carboxylic acids. 

Radicals, (34), that subsequently dimerise, are also obtained through the anodic oxidation of carboxylate anions, RCO20, in the Kolbe electrolytic synthesis of hydrocarbons ... 

The product, l,4-diacetoxy-2-allyl-3-methyl-2-cyclopentene, obtained (45% current efficiency) from 2-allyl-3-methyl-l,3-cyclopentadiene through anodic oxidation with carbon rod anode in acetic acid is successfully used as a starting compound in the synthesis of allethrolone as shown in equation 23. 

Studies on the electrochemical oxidation of silyl-substituted ethers have uncovered a rich variety of synthetic application in recent years. Since acetals, the products of the anodic oxidation in the presence of alcohols, are readily hydrolyzed to carbonyl compounds, silyl-substituted ethers can be utilized as efficient precursors of carbonyl compounds. If we consider the synthetic application of the electrooxidation of silyl-substituted ethers, the first question which must be solved is how we synthesize ethers having a silyl group at the carbon adjacent to the oxygen. We can consider either the formation of the C-C bond (Scheme 15a) or the formation of the C-O bond (Scheme 15b). The formation of the C Si bond is also effective, but this method does not seem to be useful from a view point of organic synthesis because the required starting materials are carbonyl compounds. 

Nitrogen compounds are also effective as nucleophiles in the anodic oxidation of silyl-substituted ethers. The electrochemical oxidation in the presence of a carbamate or a sulfonamide in dry THF or dichloromethane results in the selective cleavage of the C-Si bond and the introduction of the nitrogen nucleophile at the carbon (Scheme 21) [55]. Since a-methoxycarbamates are useful intermediates in the synthesis of nitrogen-containing compounds [44], this reaction provides useful access to such compounds. Cyclic silyl-substkuted ethers such as 2-silyltetrahydrofurans are also effective for the introduction of nitrogen nucleophiles. The anodic oxidation in the presence of a carbamate or a... 

Various nucleophiles other than methanol can be introduced onto the carbonyl carbon. Anodic oxidation of acylsilanes in the presence of allyl alcohol, 2-methyl-2-propanol, water, and methyl /V-methylcarbamate in dichlorometh-ane affords the corresponding esters, carboxylic acid, and amide derivatives (Scheme 24) [16]. Therefore, anodic oxidation provides a useful method for the synthesis of esters and amides under neutral conditions. 

Recently, acylsilanes have been utilized as useful intermediates in organic synthesis [57], For example, treatment of acylsilanes with the fluoride ion generates the corresponding acyl anions which react with electrophiles. On the other hand, by using the electrochemical method, acylsilanes serve as acyl cation equivalents because nucleophiles are introduced at the carbonyl carbon. Chemical oxidation of acylsilanes with hydrogen peroxide which affords the corresponding carboxylic acids has been reported [58], However, the anodic oxidation provides a versatile method for the introduction of various nucleophiles... 

Over the past few years, a large number of experimental approaches have been successfully used as routes to synthesize nanorods or nanowires based on titania, such as combining sol-gel processing with electrophoretic deposition,152 spin-on process,153 sol-gel template method,154-157 metalorganic chemical vapor deposition,158-159 anodic oxidative hydrolysis,160 sonochemical synthesis,161 inverse microemulsion method,162 molten salt-assisted and pyrolysis routes163 and hydrothermal synthesis.163-171 We will discuss more in detail the latter preparation, because the advantage of this technique is that nanorods can be obtained in relatively large amounts. 

CI2 evolution reaction, 38 56 electrochemical desorption, 38 53-54 electrode kinetics, 38 55-56 factors that determine, 38 55 ketone reduction, 38 56-57 Langmuir adsorption isotherm, 38 52 recombination desorption, 38 53 surface reaction-order factor, 38 52 Temkin and Frumkin isotherm, 38 53 real-area factor, 38 57-58 regular heterogeneous catalysis, 38 10-16 anodic oxidation of ammonia, 38 13 binding energy quantification, 38 15-16 Haber-Bosch atrunonia synthesis, 38 12-13... 

Electroorganic synthesis, 40 151-167 anodic oxidations mediated by ledox coatings, 40 153-157... 

Olefins, see also Alkenes specific compounds added, reactions during Fischer-Tiopsch synthesis, 39 251-253 adsorption of, 20 82-84 anodic oxidation, 40 162-165 autoxidation of, 25 281, 282, 305-308 bicyclic... 

GDE s may be interesting for synthesis cells as depolarized electrodes (e.g. [48]). A hydrogen-consuming anode will work at a low potential that avoids undesired anodic oxidations (e.g. no chlorine evolution in presence of chlorides). In order to reject an excess of the electrolyte from the GDE structure, a proton-conducting membrane (Nafion ) between the GDE and the electrolyte can be used ( Hydrina , De Nora Spa. [49]). 

In the synthesis of an euglobal skeleton, a quinone methide has been generated Y Y in situ by anodic oxidation mediated... 

Because of the efficiency of this process, the anodic oxidation of amino acid precursors can serve as an excellent method for generating chiral building blocks for synthesis. For example (Scheme 17, Eq. 1) [39], the anodic oxidation of (45) was accomplished at a platinum anode using an undivided cell. An acetate nucleophile was used to trap... 

The anodic oxidation utilized in the synthesis of (137) proved equally effective. In this example, the electrochemical step was used to functionalize the amide substrate (141) (Scheme 45) [87, 88]. A... 

A convenient method to affect the oxidation p- to nitrogen in piperidines is based on the anodic oxidation of N-carboalkoxy piperidines (Scheme 35). The electrochemical oxidation of piperidine (152) in the presence of acetic acid and potassium acetate, for example, afforded a mixture of isomeric 2-hydroxy-3-acetoxypiperidines (153) in a combined yield of 93%, following an aqueous workup [61]. Reduction with sodium boro-hydride severed the C-OH bond. Treatment with acid and then base completed a synthesis of pseudoconhydrine (154). 

Heterocycles are of great interest in organic chemistry due to their specific properties. Many of these cycles are widely present in natural and pharmaceutical compounds. Electrochemistry appears as a powerful tool for the preparation and the functionalization of various heterocycles because anodic oxidations and cathodic reductions allow the selective preparation of highly reactive intermediates (radicals, radical ions, cations, anions, and electrophilic and nucleophilic groups). In this way, the electrochemical technique can be used as a key step for the synthesis of complex molecules containing heterocycles. A review of the electrolysis of heterocyclic compounds is summarized in Ref. [1]. 

Diarylamides with arenes activated by electron-donating substituents can be converted to azacycles by anodic oxidation through phenolic oxidative coupling reactions that can be a key step in the synthesis of alkaloids (Schemes 16 and 17). According to the nature of substituents and the experimental conditions, either spiro compounds [22] or non-spiro compounds [23, 24] were obtained. 

Cycloaddition Anodically generated phe-noxy cations, o-quinones, and o-quinone methides react with olefins to bicyclic and tricyclic annelated compounds in stereoselective cycloadditions [250-252]. In the synthesis of a Euglobal skeleton, a quinone methide has been generated in situ by anodic oxidation mediated by DDQ. The cycloaddition was promoted by the use of lithium perchlorate... 

For excellent summaries of recent work see a) Torii S (ed) (1995) Novel trends in electroorganic synthesis. Kodansha, Tokyo b) Nonaka T, Tokuda K (eds) (1994) Denki Kagaku, 62 (12) c) Little RD, Weinberg NL (1991) Electroorganic synthesis Festschrift for Manuel M. Baizer, M Dekker, New York d) Fry A (1993) Aldrichimica Acta 26 3 e) Swenton JS, Morrow GW (eds) (1991) Synthetic applications of anodic oxidations, Tetrahedron 42... 

This article discusses the anodic synthesis of heterocyclic compounds that have appeared during the last decade. The mechanistic aspects involving intramolecular, intermolecular cyclizations and the homogeneous vs heterogeneous anodic oxidations were considered. This review deals with the recent advances in anodic oxidations in which heterocyclic compounds were synthesized through carbon-heteroatom and heteroatom-heteroatom bond formation. 

In 1981 we published the first paper [22] on the synthesis of s-triazolo[4,3-a]pyridinium salts, 4, by the anodic oxidation of hydrazones 3 in the presence of pyridine (Scheme 5). In our working mechanistic scheme we proposed nitrilimine as the possible intermediate and pointed out that this reaction opens the door to a wide range of heterocyclic systems via anodic oxidation of aldehyde hydrazones through 1,3-dipolar cycloaddition reactions of the nitrilimine involved. 

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