Decarboxylative dimerization

Scheme 7 Synthesis of iV -tert-Butoxycaibonyl-D-a-aminosuberic Acid a-re/7-Butyl Ester to-Methyl Ester by the Kolbe Electrolytic Decarboxylation Dimerization Reaction 271 NHBoc...

Decarboxylative Dimerization. The Kolbe Reaction De-carboxylide-coupling... 

Desulfurization of sulfur compounds 4-38 Decarboxylative dimerization (Kolbe)... 

Chromanones,4 In the presence of this amine 4-mcthyl-6-hydroxy-2-pyrone (1) undergoes decarboxylative dimerization to form a coumarochromanone (2) in 42 yield. The pyrone group in 2 undergoes decarboxylative Diels Alder reactions (8, 32G 9, 175 176) with acetylenes to form 4-chromanoncs (3). 

The mechanism of the Kolbe reaction involves electrochemical decarboxylation-dimerization via radicals (Scheme 2.34). 

Decarboxylative dimerization of maleic anhydride (2). When maleic anhydride (2 equiv.) and 1 (1 equiv.) are heated in HO Ac at 110°, CO2 is evolved, and on acidification dimethyhnaleic anhydride (3) is obtained in 75% yield. ... 

The alkyl groups of two identical carboxylic acids can be coupled to symmetrical dimers in the presence of a fair number of functional groups (equation 1). Since free radicals are the reactive intermediates, polar substituents need not be protected. This saves the steps for protection and deprotection that are necessary in such cases when electrophilic or nucleophilic C—C bond-forming reactions are involved. Furthermore, carboxylic acids are available in a wide variety from natural or petrochemical sources, or can be readily prepared from a large variety of precursors. Compared to chemicd methods for the construction of symmetrical compounds, such as nucleophilic substitution or addition, decomposition of azo compounds or of diacyl peroxides, these advantages make the Kolbe electrolysis the method of choice for the synthesis of symmetrical target molecules. No other chemical method is available that allows the decarboxylative dimerization of carboxylic acids. 

Kolbe electrolytic synthesis. Formation of hydrocarbons by the electrolysis of alkali salts of carboxylic acids (decarboxylative dimerization). 

Electrochemical decarboxylation-dimerization (via free radicals) (see 1st edition). 

There is a close structural affinity between ibotenic acid and its dihydro derivative, tricholomic acid (mp 207°C). Nevertheless the chemical interrelation between these compounds appeared to be difficult to prove because of the reactivity of the N—O bond which undergoes hydrogenolysis on mild catalytic hydrogenation of ibotenic acid (Scheme 13). The a-amino ketone formed in this way undergoes decarboxylation, dimerization, and reduction, becoming a trans derivative of piperazine 48). Tricholomic acid and its threo isomer have been synthesized from erythro- and f/ireo-diethyl D,L-3-hydroxyglutamate, respectively, by Iwasaki et al. 49). 

Scheme 1 Decarboxylative dimerization pathway for the biosynthesis of the CP-moiecuies (1 and 2).

Formation of symmetrical dimers by the electrolysis of carboxylates (decarboxylative dimerization). The coupling of two distinct carboxylates yields unsymmetrical products ... 

Electrode modification can be carried out by methods that vary greatly. A reaction can be affected simply by addition to the electrolysis solution of a substance that is readily adsorbed onto the electrode surface. Thus, additimi of a thiocyanate salt to the medium diverts the anodic oxidatimi of carboxylates frran decarboxylative dimerization (Kolbe reaction) to peracid formation [1]. Often, a polymer solutimi containing an electrocatalyst is placed on a surface, and the solvent evaporated or a monomer is electrochemicaUy polymerized in situ from solution mito the surface. Electrocatalysts deposited in this manner include organometallic electrocatalyst complexes such as vitamin B12 [2], oxidizable heterocycles such as pyrrole or thiophene, or metal ions [3]. Successive layers of complementary materials may be laid down on an electrode to achieve the desired immobilization effect. Thus, a polymer (PDAA polydimethyldiallyl ammonium chloride) bearing... 

In 1834, while studying the conductivity of acetates, M. Faraday observed that an inflammable gas was produced at the anode [1]. However, being more interested in physics than in chemistry, he reported this phenomenon but did not identify the gas. Fifteen years later, in 1849, W.H. Kolbe reinvestigated this transformation [2]. He characterized ethane as the product formed at the anode and recognized the nature and utility of this electrochemical process. The Kolbe reaction, the electrochemical oxidative decarboxylation-dimerization of carboxylic acids, is a powerful method for the generation of C-C bonds under particularly mild conditions (Scheme 1). 

Electrolysis of carboxylates to afford the coupled products. Homocoupling product is obtained if two carboxylates are the same — decarboxylative dimerization unsymmetrical product will be produced if the two carboxylates are different. 

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