Based on mechanistic investigations, it is established that it is not possible to invert the reactivity of aroyl halides, ArCO-X, and make them react with electrophiles, in the presence of a palladium catalyst and a source of electron. Indeed, the key intermediate ArCO-Pd-XL2 (L = PPh,) whose activation by electron transfer in the presence of an electrophile would produce the coupling product ArCO-E, is less easily reduced than the corresponding aroyl halide. [GRAPHICS] However, an indirect palladium catalyzed process for the synthesis of ArCO-E derivatives is proposed, from aryl halides, carbon monoxide and an electron source. [GRAPHICS] The efficiency of the second process comes from the fact that the intermediate ArCO-Pd-XL2, formed by reaction of CO with Ar-Pd-XL2, is more easily reduced than the aryl halide and the transient Ar-Pd-XL2 complex.