Decarboxylative couplings

Similarly, biaryls, including sterically hindered ones, have more recently been obtained by decarboxylative coupling of arenecarboxylic acids and diaryliodonium triflates.93 The PdCla/DPEphos system in the presence of silver carbonate in DMSO was found to be the most efficient, giving yields ranging from 37% to 85% (Scheme 10.61). 

One typical radical reaction is a coupling reaction. Oxidative decarboxylation coupling reaction of carboxylic acids by electrolysis (Kolbe electrolysis), intramolecular coupling reaction of diesters with Na (acyloin condensation), formation of pinacols from ketones or aldehydes with Na or Mg are well known classical methods [1,2]. Recently, oxidative... 

The palladium-catalyzed decarboxylative coupling of allyl 2-(benzo[c(jthiazol-2-yl)acetates 118 provides a facile approach to 2-(but-3-enyl)benzo[c(jthiazoles 122 <07JA4138>. The reaction is initiated by nucleophilic attack of Pd(0) on the allyl ester to give Pd-7t-allyl complex 119, which undergoes nucleophilic attack at the less substituted allylic carbon from the benzothiazole nitrogen to produce 120. Decarboxylative dearomatization leads to intermediate 121, and a subsequent aza-Cope rearrangement driven by rearomatization affords the final product 122 and accounts for the unusual regioselectivity. This appears to be the first report of a tandem allylation/aza-Cope reaction driven by decarboxylative dearomatization/ rearomatization. 

The reactions between i-dinitrobenzene or 1,3,5-trinitrobenzene, aryl halides, and copper(I) oxide in quinoline 17-19, 21) provide a simple synthesis of nitrobiphenyls uncontaminated by symmetrical biphenyls. These couplings may be related to the Ullmann reaction, the decarboxylative coupling of benzoic acids with aryl halides, and the preparation of ethers from phenols 165). Although no intermediates... 

Electrolytic decarboxylative coupling of sodium salts of carboxylic acids takes place during their electrolysis. Carbon dioxide is eliminated, and the free radicals thus generated couple to form hydrocarbons or their derivatives. The reaction is referred to as the Kolbe electrosynthesis and is exemplified by the synthesis of 1,8-difluorooctane from 5-fluorovaleric acid (equation 469) [574]. Yields of homologous halogenated acids range from 31% to 82% [574]. 

The proper choice of the electrolysis medium may provide significant product selectivity in each reaction. For instance, in the electrolysis of cyclopropane carboxylic acids (I) [Eq. (9)], a dramatic change in products is observed [52] in a pyridine-H20-Et3N-(Pt) system the Kolbe dimer (II) is mainly obtained, but in an MeOH-MeONa-(Pt) system predominantly cyclopropane (III) is formed via hydrogen atom abstraction. The cyclopropane carboxylic acid (IV), however, undergoes decarboxylative coupling even in an MeOH-MeONa-(Pt) system to afford the dimer (V) as a major product along with the ester (VI) [Eq. (10)] [53] ... 

It has been shown that the metal-based oxidant hexachloro osmate (V) yields in some cases also decarboxylative coupling products [183c]. 

For e radical pair, 72a, derived from 70a, decarboxylation to the more stable phenoxyl radical should be much more rapid, probably in the nanosecond time domain. Therefore, any initially formed radical pair will be rapidly converted to either the ion pair, 71a, by electron transfer or to the new radical pair, 73a, by decarboxylation. Coupling of this radical pair then gives the other three products the yield of the product 74, Eq. (29), does not necessarily reflect its primary photochemical yield because it is rapidly converted to the other two coupling products by irradiation in methanol (Sec. IV.D.2). 

Goossen LJ, Deng G, Levy LM (2006) Synthesis of biaryls via catalytic decarboxylative coupling. Science 313 662-664... 

Goossen LJ, Rodriguez N, Melzer B, Linder C, Deng G, Levy LM (2007) Biaryl synthesis via Pd-catalyzed decarboxylative coupling of aromatic carboxylates with aryl halides. J Am Chem Soc 129 4824-4833... 

Coupling reactions. Electron-dehcient aroic acids undergo decarboxylative coupling with ArBr on heating with Pd(acac)2, CUCO3. ... 

Pyridine N-oxides will decarboxylatively couple with a-oxocarboxylic acids in the presence of a number of catalysts recently, a silver catalyst, which is cheaper and more readily available than the typical palladium catalysts, was shown to initiate this transformation under mild conditions (Scheme 38). The yields were moderate (43-81%) for a number of... 

Scheme 38 Ag-catalyzed decarboxylative coupling of a-oxocarboxylic acids and pyridine A/-oxides.

Decarboxylative coupling of allyl 4-methyl-3-carboxycoumarins results in y-allylation of the methyl group (Scheme 135). Intramolecular proton ttansfer from the 4-methyl group to the 3-carboxylate allows allylation of the remote methyl group and the resulting 4-butenyl-3-carboxyl coumarin undergoes Pd(0)-catalysed decarboxylation to give butenylcoumarin products. 

A metabolically important route for the neration of acyl coenzyme A derivatives is through the oxidation of a-keto adds. The a-keto add dehydrogenase complexes, of which pyruvate dehydrogenase complex is typical, are large multienzyme aggregates. They carry out a comidex reaction sequence to be discussed in section III.D on lipoic acid. The overall reaction given below is an oxidative decarboxylation coupled to thioester formation. 

The earliest electrochemical synthesis is the so-called Kolbe reaction involving the oxidation of carboxylic acids in forming decarboxylated coupling products (alkanes). At present, the electrochemical synthesis has become an independent discipline. A large number of organic reactions (synthesis) have been achieved by this technique. The essential requirement for conducting an electrochemical reaction is the conductivity of the reaction medium. The most commonly... 

Electrolysis of carboxylates in the presence of olefins may afford the radical addition products [5]. Intramolecular radical addition may furnish a simple and straightforward access to cyclic compounds. Mixed decarboxylative coupling of 6-alkenoic acids and various carboxylic acids giving cyclic compounds is utilized for synthesis of useful chemicals. For instance, a stereoselective synthesis of prostaglandin precursors is achieved successfully by mixed Kolbe-type decarboxylation [b](Fig.2). 

SCHEME 22.23 Synthesis of phenanthrenes by Pd-catalyzed decarboxylative coupling of 2-phenylbenzoic acids with alkynes. 

Another example of an ARCIS reaction is the efficient Rh(I)-catalyzed decarboxylative coupling of ethyl benzo[/j]quinoline-10-carboxylate with organoboron compounds, which proceeds through C-C and C-B cleavage with the assistance of an N-containing directing group (Scheme 22.35) [50]. 

SCHEME 22.40 Pd-catalyzed decarboxylative coupling of aromatic acids with aryl iodides. 

Voutchkova, A., Coplin, A., Leadbeater, N. E., Crabtree, R. H. (2008). Palladium-catalyzed decarboxylative coupling of aromatic acids with aryl halides or unactivated arenes using microwave heating. Chemical... 

Wang, Z., Ding, Q., He, X., Wu, J. (2009). Pd-catalyzed decarboxylative couplings of arenecarboxylic acids with aryl iodides. Tetrahedron, 65, 4635-4638. 

GooBen, L. J., Linder, C., Rodriguez, N., Lange, R P. (2009). Biaryl and aryl ketone synthesis via Pd-oatalyzed decarboxylative coupling of carboxylate salts with aryl triflates. Chemistry-An European Journal, 15, 9336-9349. 

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