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

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