Copper decarboxylative coupling

Since then, experiments have been reported which indicate that (1) organocopper compounds will couple with aryl halides (2) arylcopper compounds can be oxidatively and thermally dimerized (3) arylcopper compounds are intermediates in the Ullmann reaction (4) organocopper compounds are intermediates in copper-catalyzed decarboxylations and (5) copper-promoted coupling reactions are not restricted to aromatic halides. The copper(I) oxide-promoted coupling reactions, however, have still to yield firm evidence of a copper intermediate. 

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... 

In 2010, Xue and coworkers [41] reported the viability of a copper-catalyzed decarboxylative coupling of alkynyl carboxylic acids with aryl h llides under relatively mild reaction conditions (Scheme 3.24a). On the basis of computation2il investigations, the authors proposed that in the initial step of the catalytic cycle, the copper(I) precursor was oxidized to a copper(lll) complex. 

Monometallic copper complexes were also found to mediate decarboxylative couplings, but these reactions have a rather limited scope as well [60]. They are advantageous particularly for the coupling of polyfluorinated benzoic acids with aryl halides (Scheme 17). 

Potassium perfluorobenzoates were shown to undergo decarboxylative coupling with aryl hahdes using copper as catalyst without needing to use Pd [7] (Scheme 4.3). 

The oxidative coupling of a benzoic acid with phenylboronic acid is achievable (Scheme 4.9) [13]. Thus, in the presence of a palladium catalyst together with a silver salt oxidant, decarboxylative coupling takes place selectively to produce 2,4,6-trimethoxybiphenyl. In contrast, under conditions using a copper catalyst in place of Pd, a Chan-Evans-Lam type reaction proceeds to afford phenyl 2,4,6-trimethoxybenzoate. 

The copper-catalyzed decarboxylative coupling of cinnamic acids with benzylic hydrocarbons through sp C-H bond cleavage can proceed by a radical mechanism (Scheme 4.60) [61]. 

The copper-catalyzed decarboxylative coupling of a-keto carboxylic acids with indoles can proceed through C-H bond cleavage at their C3-position (Scheme 4.76) [78]. In contrast, the coupling with Ar-(pyrimidin-2-yl)indoles occurs at their C2-position under palladium catalysis [79]. 

Huang et al. described paUadium/copper-cocatalyzed cascade halopalladation/ decarboxylation/carbon-carbon fonning reactions for the synthesis of 5-halo-6-substituted benzo[it]naphtho[2,l-d]furans 267 [95] (Scheme 6.71). The protocol represents the first example of trapping the a-vinylpalladium intermediate, generated from halopalladation of alkynes, by the decarboxylative coupling reaction. 

A copper/A,A-diisopropyl-ethylamine (DIPEA)-catalyzed, aldehyde-induced intermolecular decarboxylative coupling reaction of proline and... 

Reactions of phosphonic acids and their derivatives A copper catalysed intermolecular, decarboxylative coupling reaction of natural a-amino acids (583) and phosphites or secondary phosphine oxides (584) with aldehydes (585), has been developed in the synthesis of unnatural amino acid derivatives (586) (Scheme 145). ... 

The majority of examples of metal-assisted hydrolysis of peptides which have been reported recently involve the use of cobalt(II) centers. However, use of copper(II) for the specific hydrolysis of the C-terminal residue of polypeptides has been reported. The polypeptides coordinate to the copper with concomitant deprotonation of the amido group of the C-terminal residue. Treatment with persulfate results in an oxidative decarboxylation to yield an iV-acylimine, which undergoes subsequent hydrolysis to generate a carbonyl compound and carboxamide. This results in an overall process, Eq. (3). In contrast, treatment with [IrCl ] results in the alternative reaction (4), although this process is dependent upon the redox potential of the copp r(II)/copper(III) couple. 

The pyrolysis of perfluoro carboxylic salts can result both in mono and bimolecular products At 210-220 °C, silver salts give mostly the coupled products, at 160-165 °C in A -methylpyrrolidinone, the corresponding copper salts also give the simple decarboxylated compounds in nearly equal amounts The decomposition of the copper salts m the presence of lodobenzene at 105-125 °C results m a phenyl derivative, in addition to the olefin and coupled product [94] (equations 60-62)... 

Finally perfluorinated alkenes, prepared according to various routes (decarboxylation of perfluorinated acids or anhydrides, action of organolithium, magnesium reagents or metallic zinc-copper couple to perfluoroalkyl iodides, oligomerisation of TFE and of HFP, addition of perfluoroalkyl iodides to per-fluoroallyl chloride [304], addition of KF to perhalogenated esters or alkanes... 

GooBen LJ, Zimmermann B, Knauber T (2008) Palladium/copper-catalyzed decarboxylative cross-coupling of aryl chlorides with potassium carboxylates. Angew Chem Int Ed 47 7103-7106... 

A novel copper-catalyzed decarboxylative arylation of a variety of benzoxazoles with 2-nitrocarboxyhc acids (218) was reported to be most effective with electron-rich benzoxazoles by Hoover and coworkers (2015CC15059). Moreover, the presence of the ortho-nitro group was found to be essential for coupling, suggesting that this group plays a role in faciH-tating the decarboxylation step. 

Besides the synthesis of various triazoles, the synthetic potential of the copper flow system was further demonstrated by the catalytic decarboxylation of the propargyhc add 11 (Scheme 4, Reaction 2) and the C—O coupling in the synthesis of benzopyranone 14 (Scheme 4, Reaction 3) (2010SL2009). 

The dibromofuran 2.40 was subjected to a sequence of Stille coupling reactions, the second one requiring a more robust catalyst, leading to rosefuran 2.43 after hydrolysis and copper-catalysed thermal decarboxylation (Scheme 2.15). A quite different synthesis of rosefuran may be found in Scheme 11.48. 

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