Carbonyl compounds anodic

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. 

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. 

Radicals are generated at the anode by oxidation of carbanions (Scheme lb), for example, alkoxides and carboxylates (see Chapter 5, 6), and at the cathode by reduction of protonated carbonyl compounds or onium salts (Scheme Ic) (see Chapter 7). Thereby, a wide choice of different radical structures can be mildly and simply... 

The anode is an ideal reagent to oxidize organic substrates such as oxygen-containing compounds (alcohols, carbonyl compounds, and carboxylic acids). Thereby these substrates can be converted avoiding chemical reagents, which simplifies the reaction conditions and the work-up. Additionally, the electron transfer leads selectively to a variety of reactive species, which can find further use in organic synthesis. 

Scheme 5 Mediated anodic oxidation of amine to nitrile and carbonyl compound.

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. 

The mechanism of the Zn chloride-assisted, palladium-catalyzed reaction of allyl acetate (456) with carbonyl compounds (457) has been proposed [434]. The reaction involves electroreduction of a Pd(II) complex to a Pd(0) complex, oxidative addition of the allyl acetate to the Pd(0) complex, and Zn(II)/Pd(II) transmetallation leading to an allylzinc reagent, which would react with (457) to give homoallyl alcohols (458) and (459) (Scheme 157). Substituted -lactones are electrosynthesized by the Reformatsky reaction of ketones and ethyl a-bromobutyrate, using a sacrificial Zn anode in 35 92% yield [542]. The effect of cathode materials involving Zn, C, Pt, Ni, and so on, has been investigated for the electrochemical allylation of acetone [543]. 

Since the catalytic effect of Cu ions with Fenton s reagent has been recognized, continuing interest has been focused on the role of the Cu species in oxidizing systems. The electrochemical alkyltransfer reaction of trialkylboranes to carbonyl compounds has been performed in an undivided cell by using the sacrificial Cu anode in a DMF-BU4NI system, giving the alkylated products in 62 77% yields [580]. 

The anodic oxidation of substituted allenes [76-79] and hetero-allenes [80-85] has been extensively studied by Becker and coworkers. Oxidation of secondary and tertiary alkyl isothiocyanates resulted in an ot-cleavage processes [77]. Primary alkyl isocyanates yielded amides and carbonyl compounds due to the nucleophilic involvement of either acetonitrile or water [80]. Primary alkyl isothiocyanates 48 afforded five-membered thiadiazolidine 49 and 50 and... 

Reduction of a range of allyl and benzyl chlorides at a stainless steel cathode in dimethylformamide in the presence of carbonyl compounds and using a sacrificial anode of aluminium or zinc, leads to a Reformatsky-type reaction in 40-80 % yields. Allyl halide give products by reaction at both the a- and y-positions. Tetra-chioromethane and bromotrifluoromethane take part in similar reactions provided a... 

Generation of the carbon based radical in these processes involves the prior formation of a complex between manganese(lll) and the enol of the carbonyl reactant. Intramolecular electron transfer occurs within this complex. Addition to the olefin then takes place within the co-ordination sphere of manganese. When manganese is present in catalytic amount, the relative values of the equlibrium constants between manganese and both the carbonyl compound and the alkene arc important. If the olefm is more strongly complexed then no radical can form and reaction ceases. Reactions are usually carried out at constant current and the current used must correspond to less than the maximum possible rate for the overall chemical steps involved. Excess current caused the anode potential to rise into a region where Kolbe reaction of acetate can occur and this leads to side reactions [28]. 

A pioneering electrochemical investigation was undertaken by Masui and coworkers . They showed that HPI is an efficient electron carrier (viz. mediator) in the electrochemical oxidation of alcohols to the corresponding carbonyl compounds. The anodic one-electron... 

D.F. Andres, U. Dietrich, E.G. Laurent, B.S. Marquet, Anodic fluorination of vinyl sulfides - synthesis of a-fluoro- -thio-a, -unsaturated carbonyl compounds. Tetrahedron 53 (1997) 647-658. 

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... 

An analogous non-electrochemical Ni(0)-catalysed process, exploited in a Mannich/ Reformatsky multicomponent process58, will be discussed in Section III (equation 41). In the third study, the a-bromoester Id is simply electrolysed in the presence of a carbonyl compound in DMF/THF in a 1 2 ratio using both indium and zinc rods as sacrificial anodes. While aldehydes afford the expected 3-hydroxyesters in high yield, aliphatic, aromatic and cyclic ketones, with the exception of acetone, directly afford /3-lactones,... 

Other organic mediators act as hydride atom-abstracting agents. This is true, for example, with 2,2-dichloro-5,6-dicyano-p-benzoquinone (DDQ) and the oxoammonium ion which is anodically accessible from 2,2,6,6-tetramethylpiperidyl oxide (TEMPO). DDQ has been electrochemically regenerated either externally or internally The in situ electrochemical oxidation, of TEMPO to the active oxoammonium ion is performed in lutidine-containing acetonitrile. Thus, primary alcohols can be oxidized to the aldehydes, while secondary ones are stable Primary amines are transformed to nitriles. If water is present, the amines are cleaved via the Schiff bases to the corresponding carbonyl compounds... 

Silyl-l,3-dienes undergo anodic methoxylation in methanol to give 1,4-addition products with an allylsilane structure as intermediates. Therefore, they are further oxidized to give l,l,4-trimethoxy-2-butene derivatives as the final products. The products are easily hydrolyzed to provide the corresponding y-methoxy-a, /t-unsaUirated aldehydes. Since 1-trimethylsilyl-l,3-dienes are readily prepared by the reaction of the anion of l,3-bis(trimethylsilyl)propene with aldehydes or ketones, l,3-bis(trhnethylsilyl)propene offers a, /i-formylvinyl anion equivalent for the reaction with carbonyl compounds (equation 15)16. 

Electrochemical properties of tosylhydrazones of acylsilanes were also investigated. A decrease in the oxidation potential of tosylhydrazones caused by silylation is much smaller than that for carbonyl compounds (see Tables 7 and Section n.E., Table 9). Anodic oxidation of tosylhydrazones of acylsilanes provides the corresponding nitriles with consumption of a catalytic amount of electricity (equation 29)34. 

One of the few anodic transformations of ketones in the presence of halogen derivatives which appears to involve anodic oxidation of the carbonyl compound itself is shown in... 

Anodic Oxidation of Carbonyl Compounds 3.1.6.1 Kolbe Reaction... 

Lund 12°) was first in applying cpe in the oxidation of a primary alcohol to an aldehyde (which under constant current conditions would be partly or completely oxidized to the corresponding carboxylic acid) 121 Anisyl alcohol displays two anodic waves in acetonitrile-sodium perchlorate withiTj /2 of 1.22 and 1.64 V vs. Ag/0.1 M Ag Cpe at the plateau of the first wave (1.35 V) in the same medium consumed only 5 % of the theoretically calculated amount of electricity and no carbonyl compound was formed. Addition of a three-fold excess of pyridine (to act as a proton acceptor) gave a 72 % of anisaldehyde ... 

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. 

The anodic oxidation of 1,2-diols and their ether derivatives is a simple and clean mediod for the fission of glycols to the corresponding carbonyl compounds (equation 1). The reaction is carried out using carbon electrodes in methanol containing tetraediylammonium p-toluenesulfonate as a supporting electrolyte.2 ... 

The direct anodic oxidation of aliphatic saturated alcohols to the corresponding carbonyl compounds is not always effective, because the high oxidation potentials of these alcohols make difficult Ae direct removal of an electron from the lone pair electrons on the oxygen atom. 

The anodic oxidation method is highly efficient for the oxidative cleavage of glycols (22) and related compounds. The oxidation of glycols and glycol ethers in methanol results in a clean cleavage to the corresponding carbonyl compounds (equation 44). ... 

The anodic oxidation of enol ethers in methanol yields a-methoxylated carbonyl conqKxinds, which are useful intermediates for the synthesis of carbonyl compounds utilizing the technique of oxidative cleavage of glycols (equation 4S). ... 

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