Pd(OAc)2 catalysed the direct arylation of some functionalized halothiophene derivatives allowing the synthesis in only one step of polyfunctionalized arylated thiophenes. In the presence of 2-acetyl-4-chlorothiophene and various aryl bromides, the 5-arylation products were obtained in moderate to high yields employing only 0.5 mol% catalyst. Researchers studied the coupling of 2-acetyl-4-chlorothiophene with several aryl bromides employing 0.5 mol% Pd(OAc)2 as the catalyst and KOAc as the base. These phosphine-free catalyst reaction conditions allowed the successful coupling of several aryl bromides to more simple thiophene derivatives. Using such conditions, the 5-arylated thiophenes were obtained with high isolated yields. With this procedure, the priority for the arylation of this 2,4-disubstituted thiophene is the 5-position. Moreover, no formation of by-products, such as thiophene oligomers, due to the oxidative addition of this chlorothiophene to palladium was detected during these reactions[1].
