Electrolysis carbonyl compounds

Furthermore, 2,2-difluoro-3-hydroxyesters are readily obtained from ClCF2COOMe and carbonyl compounds by electrolysis in a one-compartment cell using a sacrificial zinc anode and a nickel-complex catalyst [26], The catalytic cycle is shown in Scheme 3.11 and nickel zinc exchange is a key step. 

Anodic regioselective acetamidosulfeny-lation of alkenes is similarly achieved by oxidation of diphenyldisulfide in acetonitrile [81]. Cyclic enamines, which are intermediates in the oxidation of cyclic N-methoxycarbonyl amines, react in aqueous acetonitrile that contains chloride ions to a-hydroxy- 8-chloro compounds via intermediate chloronium ions [82]. Enolethers undergo a regioselective azidomethoxyla-tion to yield acetals of a-azido carbonyl compounds upon electrolysis in methanol containing sodium azide [83]. The reaction proceeds possibly via addition of an anodicaUy generated azide radical. 

Intermolecular coupling Many papers on hydrodimerization of aromatic carbonyl compounds have appeared indicating the importance of this reaction. The rac/meso ratio for the pinacolization of acetophenone in aqueous ethanol ranges between 0.9 and 1.4 in acidic medium and between 2.5 and 3.2 in basic medium. The diastereoselectivity is independent of the cathode material mercury, tin, or copper. Electrolysis conditions such as current density, potential, or current-controlled electrolysis also do not influence the diastereoselectivity. The same holds for propiophenone. For benzaldehyde, the rac/meso ratio is 1.1 to 1.2 in acidic as well as in basic media [283]. In the presence... 

Historically, the concept of EG Bs was developed in relation to electrochemically induced Wittig reactions [45], Co-electrolysis of the phosphonium salt and the carbonyl compound was carried out using the carbonyl compound as the solvent and gave reasonable yields of the alkene [45]. Most of these reactions can be rationalized within Scheme 19, in which the phosphonium ion participates both as the probase (PB) and as the acidic substrate [46]. 

The Barhier-type reaction of aldehydes and ketones with allyl halides (485) in the presence of Sml2, leading to homoallyl alcohols (486), has received recent interest as a one-step alternative to the Grignard reaction. However, the reactions require the use of stoichiometric amounts of the reducing Sm(III) species. Recently, the electroreductive Barhier-type allylation of carbonyl compounds in an SmH-mediated reaction has been developed [569]. The electrolysis of (485) is carried out in a DMF-SmCl3-(Mg/Ni) system in an undivided cell to give the adduct (486) in 50 85% yields (Scheme 168) [569]. Electrosynthesis of y-butyrolactones has been achieved by the reductive coupling of ethyl 3-chloropropionate with carbonyl compounds in the presence of a catalytic amount of SmCfi [570]. 

Iodine may be employed as a mediator to achieve a-hydroxylation of carbonyl compounds. In basic methanolic solution containing iodide, oxidation was reported to lead to a-iodo ketones, which further reacted to give a-hydroxy ketals [171]. The electrolysis of alkylidenemalonates in the presence of iodide as a mediator has been shown to yield cyclopropane derivatives [172]. 

SiWiiO39Mn(H2O) - Alcohols carbonyl compounds Electrolysis, phosphate buffer (lUlpH 6) 1.25 V vs. Ag/AgCl, divided cell, room temperature, C anode, Pt cathode 153g-hh... 

Synthetically especially valuable is the oxidation of carbonyl compounds and nitroalkanes by manganese(III) salts to form carboxymethyl and nitromethyl radicals, respectively. These radicals can be trapped by olefins like 1,3-butadiene or aromatic compounds to yield synthetically interesting products. In this case it is very advantageous to generate and regenerate the oxidizing species in situ by indirect electrolysis. This was the basis for the development of a process for the synthesis of sorbic acid viay-vinyl-y-butyrolactone Equations (31)—(35) summarize the im-... 

This reaction has been applied both to synthesis and as a mechanistic criterion for the intermediacy of anions, e.g., in the reduction of carbonyl compounds in aprotic solvents. Electrolysis of benzophenone in the presence of ethyl bromide yields diphenylethylcarbinol (41, Eq. (106) ) 2511. When anthraquinone... 

The use of the above methods does not generally result in the coupling reaction of aromatic compounds, ArX, because of the strong bond of C(sp2)-X in ArX. However, the coupling reaction of a cation radical formed from the single-electron oxidation of aromatics readily occurs. For example, 4-methylquinoline coupled to give bis[2-(4-methylquinolyl)] in 90% yield, by electrolysis [14-19]. Direct irradiation (300 nm) of carbonyl compound (13) in dimethylaniline without a solvent gives rise to ethanolamine (14) as the major product as shown in eq. 2.7 [20]. 

The characteristics of the electrooxidation of fluorosulfate anions in the electrolysis of a potassium fluorosulfate solution in fluorosulfonic acid have been investigated. The formation of oxide layers on platinum and the modification of glassy carbon with fluorosulfate groups during anodic polarization in fluorosulfonic acid are studied. The reactions of fiuoroolefin fluorosulfation are considered and a mechanism is suggested223. Trifluoromethylation of carbonyl compounds can be achieved using bromo-trifluoromethane and a sacrificial electrode in solvents such as DMF/pyridine, and DMF/TMEDA, as seen in equation 126224. 

Contrary to earlier interpretations of reduction of numerous carbonyl compounds, the role of keto-enol equilibria in electroreductions of carbonyl compounds is rather limited. This is caused by a rapid - acid- or base-catalyzed - conversion of any enol present in the solution or formed in the course of electrolysis into the more... 

Electrolysis of carbonyl compounds provides pinacols, alcohols or hydrocarbons, depending on the conditions, such as pH, the nature of the electrode, and its potential. Fundamental studies have been carried out on the mechanisms of hydrocarbon formation using acetone as a substrate. Although several electrodes, such as Cd, Pt, Pb or Zn, are recommended, carbonyl compounds, including aryl and alkyl derivatives, require strong aqueous acidic media for reduction to the hydrocarbons. The mechanism of the electrolytic reduction is probably similar to that of Clemmensen reduction, which starts from anion radical formation by one-electron transfer, as indicated in Scheme 3. The difference is that electrolytic reduction takes place in an electric double layer, rather than on the surface of the zinc metal. 

Electrolysis of benzothiete sulfone 269 yields the phenylmethanesulfinate anion (major) and the o-toluenesulfinate anion (minor).Thermolysis 618,619 gj. photolysis of thiete 1,1-dioxides proceeds via ring-opening to vinyl sulfines, for example. 288, which have been trapped by reaction with water, phenol,methanol, or norbornenes. These intermediates may recyclize to unsaturated sultines (cyclic sulfinate esters) (e.g., 289) or lose sulfur monoxide to give mainly the trans isomers of a,j3-unsaturated carbonyl compounds (e.g., 290). Mass spectra also indicate the formation of unsaturated sultines. ... 

Furthermore, the addition of chromium salts to electrolysis solutions may give unexpected results. Thus, as first demonstrated by Martinet [64], pinacolization reactions may be carried out successfully by reducing activated carbonyl compounds in DMF in the presence of Since this pioneer and intriguing work, several papers [65,72,73] have... 

Recently Yoshida et al. have employed silyl-stabilized a-alkoxy organolithium reagents for the synthesis of a variety of carbonyl compounds. Methoxy(trimethylsilyl)methane and methoxybis(trimethyl-silyl)methane, when deprotonated with Bu Li and Bu"Li respectively, give anions which can be alkylated with a variety of electrophiles. Electrolysis of a solution of the alkylated product in methanol yields, by virtue of the reduced oxidation potential of ethers a-substituted with silicon, either the dimethyl acetal or in the latter case the orthoester. The mildness of the electrolytic process recommends the method for the preparation of a variety of carbonyl compounds. 

Aromatic hydroxylations of any kind tend to be unsuccessful because the phenol produced is more reactive than the reactant, ArH. In this case, however, only the trifluoroacetate ester, Ar02CCF3, is present in the electrolysis mixture, and it is less reactive than the original ArH. One of the more interesting aspects of this reaction is that aromatic carbonyl compounds can be hydroxylated preferentially ortho, para in contrast to their normal meta directing character. 

An electrochemical-induced Henry reaction has been achieved by Elinson et al. via electrolysis (undivided cell) of solutions of carbonyl compounds and nitromethane in methanol or in methanol-DMF mixture containing alkali metal iodide as supporting electrolyte. p-Nitroalcohols have been isolated in 60-75% yields. The authors suggest that the Henry reaction could be induced by the deprotonation of methanol at the cathode and by the oxidation of the iodide anion at the anode (Scheme 16.27) [165]. 

Furthermore, 2,2-difluoro-3-hydroxyesters are readily obtained from ClCFjCOOMe and carbonyl compounds by electrolysis in a one-compartment cell using a sacrificial zinc anode and a nickel complex as catalyst. The catalytic cycle for this reaction is shown in Scheme 9 with nickel zinc exchange being a key step. In this process, the CHjCyDMF solvent (9 1) system leads to suppression of undesired Claisen condensation and an increase in the yield of 2,2-difluoro-3-hydroxyester formation. It is notable that high yields are obtained even with ketones and enolizable aldehydes, which are not good participants in the Reformatsky reaction alternative for producing these substances. 

Similar polymeric electrolysis conditions are able. In the presence of water, to effect the conversion of olefins Into epoxides (68), In this case, choice of an anion exchange resin was crucial (Amberllte IRA-900 br)). The electrochemical efficiency is substantially lower (due to the competing electrolysis of water) but yields are high. Unsaturated carbonyl compounds do not react. 

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