Decarboxylation electrochemical

During electrochemical fluorination retention of important functional groups or atoms in molecules is essential. Acyl fluorides and chlorides, but not carboxylic acids and anhydrides (which decarboxylate), survive perfluorination to the perfluorinated acid fluorides, albeit with some cyclization in longer chain (>C4) species [73]. Electrochemical fluorination of acetyl fluoride produces perfluoro-acetyl fluoride in 36-45% yields [85]. Electrochemical fluorination of octanoyl chloride results in perfluorinated cyclic ethers as well as perfluorinated octanoyl fluonde. Cyclization decreases as initial substrate concentration increases and has been linked to hydrogen-bonded onium polycations [73]. Cyclization is a common phenomenon involving longer (>C4) and branched chains. a-Alkyl-substituted carboxylic acid chlorides, fluorides, and methyl esters produce both the perfluorinated cyclic five- and six-membered ring ethers as well as the perfluorinated acid... 

Beneficial Micro Reactor Properties for Electrochemical Decarboxylations... 

Electrochemical Decarboxylations Investigated in Micro Reactors Organic synthesis 86 [OS 86] Electrochemical cecarboxylation of D-gluconic acid... 

OS 86] ]R 29] ]P 66] A model is able to describe experimental results obtained for the electrochemical decarboxylation of D-gluconic acid (1 A mT ) [65]. At an average electrical current of 5 A m the model predicts better performance than is actually achieved. 

With type iii-e reactions compounds (71) are formed. A radical tandem reaction initiated by the Kolbe electrolysis of (88) gave tricyclic compounds (89) in a one pot reaction (Scheme 32) [111]. The electrochemical decarboxylation avoids the usually applied toxic tin hydride as reagent and... 

Oxidative decarboxylation of a-amino carboxylic acid The electrochemical oxidation of Al-acyl-a-amino acids (96) in MeOH affords N, O-acetals (98) through acyliminium intermediates (97) (Scheme 36) [121]. 

The second important class of reducing agents is generated by means of oxidative decarboxylation of carboxylic acids. Electrochemical oxidation of oxalate ion C2042 produces, in aqueous as well as in acetonitrile solutions containing Ru... 

Oxidative cleavage by means of electrochemically generated cation-radicals is also possible thus benzyl ethers may be cleaved and carboxylates decarboxylated using cation-radicals of brominated triphenylamines in acetonitrile containing a weak base.34 35 Such as indirect reaction makes it... 

An interesting transformation of carbamoylaspartic acid (30a) or ethoxy-carbonylasparagine (30b) to uracil (31) was performed by electrochemical oxidative decarboxylation.77 The same ring-closure reaction occurs in a biological system via an enzyme-catalyzed oxidation. Good yields and mild conditions of the electrochemical transformations give promise of wide application [Eq. (34)]. 

Anodic oxidation of l,3-diaryl-5-methyl-A2-pyrazoline-5-carboxylic acids in CH3CN-Et4NBF4 proceeded with decarboxylation to the aromatized pyrazoles in high yield.414 Similarly, electrochemical oxidation of N-acetyl-2,3-substituted A4-pyrroline-2-carboxylic acids in water-tetrahydrofuran (3 1) containing KOH forms the corresponding pyrroles (80-98%).415... 

At low light flux, the semiconductor sensitization is constrained to one electron routes, since the valence band hole is annihilated by a single electron transfer. Presumably after decarboxylation the resulting alkyl radical can be reduced to the observed monodecarboxylate more rapidly than it can transfer a second electron to form the alkene. In a conventional electrochemical cell, in contrast, the initially formed radical is held at an electrode poised at the potential of the first oxidation so that two-electron products cannot be avoided and alkene is isolated in fair chemical yield. Other contrasting reactivity can be expected for systems in which the usual electrochemistry follows multiple electron paths. 

A case in point involves the electrochemical oxidation of vicinal diacids. A standard synthetic method for the preparation of carbon-carbon double bonds occurs by the bis-decarboxylation of such diacids. Even relatively strained, synthetically inaccessible double bonds have been introduced in this way, e.g., eqn 6. 

This reaction resembles the decarboxylation of carboxylates during electrode one-electron oxidation. The Kolbe electrochemical reaction also consists of one-electron oxidation, decarboxylation, and culminates in dimerization of alkyl radicals formed intermediately. 

The electrochemical behavior of malonyl-a-aminopyridines 661 was investigated by Gullu et al. in acetonitrile or a mixture of trifluoroacetic acid and dichloromethane containing tetrabutylammonium tetrafluoro-borate or triethylammonium trifluoroacetate in a water-jacketed, two-compartment glass cell equipped with a platinum disk anode at 1.50 V (Ag/ Ag+) and a carbon-rod secondary electrode (91T675). Controlled potential anodic oxidation of 661 afforded labile coupled carboxylic acids 662 (R2 = COOH), which easily decarboxylated to compounds 662 (R2 = H) under the work-up conditions. Sometimes, the carboxylic acid 662 (R2 = COOH) could be isolated or when the reaction mixture was treated with methanol, methyl ester 662 (R = H, R1 = Bu, R2 = COOMe) was obtained in 40% yield. 

The electrochemical oxidative decarboxylation of carboxylic acid salts that leads to radicals, which dimerize. It is best applied to the synthesis of symmetrical dimers, but in some cases can be used with a mixture of two carboxylic acids to furnish unsymmetrical dimers. 

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... 

Seebach, D., Charczuk, R., Berber, C., Renaud, P, Bener, H and Schneider, H. (1989) Electrochemical decarboxylation of L-threonine and oligopeptide derivatives with formation of A-acyl-A, O-acetals preparation of oligopeptides with amide or phosphonate C-terminus. Helv. Chim. Acta 72,401 125. 

The glow electrolysis technique (electrolysis with an anode immersed in the solution and the cathode above the surface) at 600-800 V dc and 300-500 mA converts a solution of starch into ethylene, methane, hydrogen, and both carbon mono- and dioxides.323 Electrochemical methods for converting polysaccharides and other biomass-derived materials have been reviewed briefly by Baizer.324 These methods are mainly oxidations along a potential gradient, which decreases the activation energy of the reactants. Starch in 5 M NaOH solution is oxidized on platinum electrodes to carboxylic acids with an activation energy of about 10 kcal/mol. In acidic media oxidation takes place at C-l followed by decarboxylation and oxidation at the C-2 and C-6 atoms.325... 

Hofer-Moest reaction. We do not attempt this discrimination as the electrochemical decarboxylation of carboxylates is always a blend of both pathways. 

Eberson has comprehensively reviewed the mechanism of electrochemical decarboxylation 14 An extensive list of Kolbe electrolyses leading to predominant formation of substitution products has been compiled by Weinberg 10. Therefore this mode of anodic substitution, though comprehending a wealth of reactions, can be treated briefly and the reader is referred to these articles for more details. 

Very similar product mixtures are obtained from electrochemical decarboxylations or deoxidations 201 and deaminations 202 of the corresponding alcohols or amines. Anodic oxidation of cyclobutanecarboxylic acid affords in 30% yield a mixture of cyclopropylcarbinol, cyclobutanol and allylcarbinol identical in composition with that obtained from deamination of cyclobutylamine 203 Electrolysis of exo- or encfo-norbornane-2-carboxylic acid gave exo-norbornyl-2-... 

The mode of cation formation in electrochemical decarboxylation appears not to be uniform. Skcll 204 found two discrete 1 e-steps for oxidation of car-boxylates by chronopotentiometry. He attributed the second electron transfer to oxidation of the alkyl radical (path b, Eq. (94) ) as the carboxylate radical RC02 is to shortlived (r 10 10 sec) to survive for the second oxidation step. 

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