Palladium-catalyzed direct 5-arylation of formyl- or acetyl-halothiophene derivatives

Pd(OAc)₂ was found to catalyze 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-3-chlorothiophene, 2-acetyl-4-chlorothiophene, 2-acetyl-3-bromothiophene diethylacetal or 2-(4-bromothiophen-2-yl)-[1,3]dioxolane, and a variety of aryl bromides, the 5-arylation products were obtained in moderate to high yields employing only 0.5 mol% catalyst. On the other hand, the use of 2-formyl-3-chlorothiophene, 2-acetyl-3-bromothiophene or 2-formyl-3-bromothiophene gave disappointing results.