Phosphine-free palladium-catalysed direct C2-arylation of benzothiophenes with aryl bromides

Ligand-free Pd(OAc)2 was found to catalyse very efficiently the direct C2-arylation of benzothiophene derivatives under low catalyst concentration. The reaction can be performed employing as little as 0.5–0.1 mol % catalyst with electron-deficient and some electron-rich aryl bromides. The presence of a methyl or a formyl substituent at C3 of benzothiophene has a minor influence on the reactivity, and even a bromo substituents at C3 is tolerated. A wide variety of functional groups on the aryl bromide, such as nitrile, nitro, acetyl, formyl, ester, chloro, fluoro or trifluoromethyl has been employed.