Palladium-catalyzed carbonylation of aryl halides -: a detailed investigation of the alkoxycarbonylation of 4-bromoacetophenone

The palladium-catalyzed alkoxycarbonylation of 4-bromoacetophenon with n-butanol to give the corresponding benzoic acid ester has been studied systematically by evaluating the influence of critical reaction parameters such as temperature, CO pressure, solvent, base, catalyst precursor and ligand/palladium ratio. The highest catalyst efficiency was displayed at 130 degrees C and low CO pressures using the neat alcohol as the solvent, a trialkylamine as the base and Pd(PPh3)(4) or a PdCl2(PhCN)(2)/n PPh3-combination as the catalyst precursor. A strong dependence of the catalyst activity and stability on the phosphine concentration in the reaction mixture was found as demonstrated by the time/conversion behavior of the reaction. Thus, under the optimized conditions, catalyst productivities (turnover number = TON) of up to 7000 (70% yield of 2) were achieved. (C) 2000 Elsevier Science B.V. All rights reserved.