Decarboxylative coupling tricyclohexylphosphine

Silver(I) carbonate is responsible for generating an aryl silver species, which can subsequently undergo transmetalation with Pd. To prevent protodecarboxylation and decarboxylative homocoupling, tricyclohexylphosphine was required to accelerate transmetalation and reductive elimination. Electron-rich, electron-deficient, and heterocyclic benzoic acids were compatible coupling partners and a wide range of functional groups were tolerated for both thiophene and carboxylic acid moieties. Additional heterocycles such as benzothiophenes and 2-methylfuran could also be arylated. 

Decarboxylative couplings were accomplished using polyfluo-rinated arenes and heteroaryl carboxylic acids using silver(I) carbonate and tricyclohexylphosphine as a Ugand (eq 39). ... 

Silver(I) carbonate functioned as an cooxidant with TEMPO. Tricyclohexylphosphine was employed to suppress homocoupling between heteroarenes. Substituted thiophenes, furans, and indoles could be selectively olefinated (C5-alkenylation for thiophenes and furans, C3-alkenylation for indoles, E/Z > 99 1). Unsubstituted thiophenes produced poor yields (24%) however, formyl, acetyl, and ketyl substituents were well tolerated. For electron-deficient substrates, tricyclohexylphosphine was reduced to 10 mol % to achieve good conversions. A variety of ketones could be employed using 2-methyl thiophene as a coupling partner. A related methodology employing saturated ketones and heterocyclic carboxylic acids via a Pd-catalyzed decarboxylative process was also reported (eq 44). ... 

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See also in sourсe #XX -- [ ]

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