Acetoxylation electrochemical

The electrochemical oxidation is often more sensitive to the reaction conditions than to the substituents. Platinum electrodes are recommended for methoxylation and the equivalent acetoxylation procedures.290 In acetonitrile buffered by hydrogen carbonate ion, 3,4-diethylfuran affords the 2,5-dihydroxy-2,5-dihydro derivative (84%) and Jones oxidation readily leads to diethylmaleic anhydride in what is claimed to be the best general method for such conversions.291 In unbuffered methanol and under current density control, the oxidation of 2-methylfuran appears to eliminate the methyl group since the product is the acetal-ester 111 also obtained from methyl 2-furoate.292 If sodium acetate buffer is used, however, the methyl group is retained but oxidized in part to the aldehyde diacetate 112 in a... 

These methoxylated and acetoxylated seknides are a-perfluoroalkyl mono-selenoacetals, which seem to be useful building blocks similar to those of the sulfur analogues described above. So far, only limited methods have been developed for the preparation of monoselenoacetals and they require rather complicated procedures or special reagents. In this regard, this electrochemical method has advantages since monoselenoacetals can be prepared in a one step reaction under mild conditions. 

BASF has developed a direct electrochemical process based on anodic acetoxylation for the production of aromatic aldehydes on industrial scale [40,146,147]. The reaction passes smoothly through the benzyl acetate stage. 

Allylic acetoxylation of cyclohexene (96) at 80 °C affords 3-acetoxycyclohexene (97) in 67% yield (Scheme 36). It was found that the catalytic double-bond isomerization of 3-phenylpropene proceeds by the action of an electrochemically generated 17-electron Co(II) species [132]. The cobalt(III)-mediated electrooxidative decomposition of chlorinated organics, that is, l,3-dichloro-2-propanol, 2-monochloro-propanol, and so on, has been performed... 

Pd-hydroquinone-mediated electrochemical 1,4-diacetoxylation of cyclohexa-1,3-diene (118), leading to 1,4-diacetoxycyclo-hex-2-ene (119), has been investigated (Scheme 46) [156]. Palladium-catalyzed indirect electrochemical monoacetoxylation of olefins has been attained in an MeCN/Ac0H-NaC104/Ac0Na/Pd(0Ac)2-Cu(OAc)2-(C) system. The acetoxylation of cyclohexene produces unsaturated esters with less current efficiency, giving a 1 1 mixture of allylic and vinylic products [118]. 

Electrochemical oxidation of indole [202] and N-methylindole [203] in acetonitrile gives rise to dimers and trimers. These are oxidised further to polymers. Oxidation of N-acetylindoles in acetic acid results in acetoxylation of the heterocyclic... 

Highly selective formation of phenyl acetate was observed in the oxidation of benzene with palladium promoted by heteropoly acids.694 Lead tatraacetate, in contrast, usually produces acetoxylated aromatics in low yields due to side reac-tions. Electrochemical acetoxylation of benzene and its derivatives and alkoxylation of polycyclic aromatics789 790 are also possible. Thermal or photochemical decomposition of diacyl peroxides, when carried out in the presence of polycyclic aromatic compounds, results in ring acyloxylation.688 The less reactive... 

Electrochemical acetoxylation of Af-acetylindolines (141) in AcOH-Et3N at a platinum electrode afforded the corresponding 2,3-diacetoxyindolines (143).205 The reaction goes in a stepwise manner and the intermediate N-acetylindole (142) can be isolated [Eq. (94)]. 

Cells such as those described in References 23, 24, and 29 are particularly suited to study of short-lived intermediates requiring in situ generation at accurately controlled potentials. When a conventional electrochemical cell was used to study the Kolbe synthesis oxidation of triphenylacetic acid [53], it was concluded that the initially formed radical was triphenylacetoxyl (3-CCOO ), based on the assignment of two para- and four ortho-proton splittings. A more careful study [54] using the cell described in Reference 23 showed that it is in fact the triphenylmethyl radical that is formed initially the identity of the other species was not established, although it is clearly not the acetoxyl radical. 

Several synthetic procedures for the preparation of C-2-acetoxy- and methoxy-cephalosporins have been reported20). The functionalization at the C-2 position of cephalosporin 15 can be started with the oxidation of the divalent sulfur atom which produces sulfenium cation intermediates, which are precursors of C-2-substituted cephalosporins. The electrochemical conversion of cephalosporins 15 into their C-2-substituted homologs has been realized 2,). For example, the electrochemical acetoxy-lation at the C-2 position of desacetoxycephalosporin 15 is carried out in an AcOH— Ba(OAc)2—(Pt) system to give the C-2-acetoxylated products 24 (R1 = CFL,OPh R2 = Me) in 70% yield (Scheme 2-8). Electromethoxylation at the C-2 position of 15 is performed in a MeOH/CHClj—BuEtjNCl—(Pt) system to give the compounds 25 (R1 = CH2OPh R2 = CH2Ph) in 43% yield. The methoxylated product 25 can lead to the further oxidized product 26 by electrolysis in a H20/CHClj—MgC —(Pt) two-layer system. 

Thiazoline-azetidinone 36 is a versatile intermediate for the synthesis of varieties of beta-lactam antibiotics 24>. The most straightforward route to 36 must be the removal of the feta-lactam A-substituents of thiazoline-azetidinone 35, which is readily obtained from penicillins by Copper s method 4>. This has usually been done by the two-step operation, involving ozonolysis and subsequent methanolysis 25). Direct transformation of 35 to 36 also has been achieved by oxidation with potassium permanganate or osminum tetraoxide, but yields are unsatisfactory (—37%)25). An efficient method for the removal of A-substituents of 35 is the electrochemical acetoxylation procedure which may lead to the compound 36 along with 37 (Scheme 2-12)3). For example, the... 

An alternative electrochemical route to the thiazoline-azetidinone 36 also has been developed. Carboxylic acid 39 prepared from penicillin G can be converted to 36 via 40 by electrochemical decarboxylative acetoxylation followed by hydrolysis (Scheme 2-13)The electrolysis of 39 in an AcOH/DME—AcONa—(C) system at 0 °C... 

A variety of alkylbenzenes undergo anodic acetoxylation, in which the loss of an a proton and solvation of the radical cation intermediate form the basis of side-chain and nuclear acetoxylation, respectively.30Sa b The nucleophilicity of the solvent can be diminished by replacing acetic acid with TFA. The attendant increase in the lifetimes of aromatic radical cations has been illustrated in anodic oxidations.308 Radical cations also appear to be intermediates in the electrochemical oxidation of alkanes and alkenes.309a-c... 

Electrochemical acetoxylation of A-acetylindoline (337) in acetic acid in the presence of DBU using platinum foil electrodes gave the 2,3-diacetoxy derivative 338 in 77% yield, together with two minor products—339 and 340—in 3 and 2% yields, respectively (78JOC2882). 

Electrochemical a-acetoxylation of octyl phenyl sulfide, methyl octyl sulfide, and several a-sulfanylated esters and ketones was achieved in HOAc-NaOAc solutions at Pt electrodes using high concentrations of the sulfur compounds [103]. Phenylthio derivatives produce a single a-acetoxy compound, whereas with the methylthio compounds two regioisomers are formed [Eqs. (55)-(56)]. 

Anodic a-methoxylation of phenyl 2,2,2-trifluoroethyl sulfide was carried out using various solid-supported bases as shown in Equation 12.6. Polystyrene and silica -gel are suitable as the solid support for an organic base such as piperidine. It is noteworthy that anodic methoxylation was successfully carried out even after 10 recycles of the solid-supported base. The method has also been successfully applied to electrochemical acetoxylation in acetic add/acetonitrile. 

Horii D, Atobe M, Fuchigami T et al (2006) Self-supported methoxylation and acetoxylation electrosynthesis using a simple thin-layer flow cell. J Electrochem Soc 153 D143-D147... 

Electrochemical a-acetoxylation or a-methoxylation of cyclohexanones, followed by reduction or a Grignard reaction and finally acid-catalysed dehydration has been found to provide a convenient method for carbonyl 1,2-transposition. Thus 1-tetralone is converted into 2-tetraIone etc. 

Electrochemical oxidation of fiirans can also been carried out without intentionally added electrolyte using a microflow system. I n this case, an electrochemical thin-layer flow cell, which has a simple geometry with a glassy carbon anode and a platinum cathode directly facing each other at a distance of 80 pm apart is used (Figure 7.9) [65, 66]. 2,5-Dimethoxy-2,5-dihydrofuran is obtained in 98% yield by the oxidation of furan in methanol solvent. Similar electrochemical methoxylation and acetoxylation of various organic molecules can also be carried out using this system. 

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