Catalysis by palladium salts. Part 2. Palladium-catalysed carboxylation with carbon monoxide of aromatic compounds working under mild conditions

Abstract

The carboxylation with CO of aromatic C–H bonds, catalysed by palladium acetate, occurs with good yields and under mild conditions (1 atm † of CO and 20—50 °C), with trifluoroacetic acid as solvent and sodium acetate as co-catalyst. The reaction, which is stoicheiometric with respect to palladium, can be transformed into a pseudo-catalytic process by addition of an excess of a specific oxidant, which is consumed stoicheiometrically to regenerate palladium(II) continuously. The more efficient oxidants are mercury(II) acetate, thallium(III) trifluoroacetate, and sodium nitrate. With substituted aromatic derivatives, such as toluene and anisole, or condensed aromatic systems such as naphthalene, the pattern of the ring substitution is typical of electrophilic reactions, but in the presence of specific oxidants the regioselectivity of the ring substitution is increased with respect to the stoicheiometric reaction.