Palladium-Based Catalytic System for the Direct C3-Arylation of Furan-2-carboxamides and Thiophene-2-carboxamides

The palladium-catalyzed direct arylation of furans or thiophenes that contained secondary carboxamides at the C2 position proceeded regioselectively at either the C3 or C5 positions, depending on the reaction conditions. The nature of the base was crucial for controlling the regioselectivity of the reaction. We had previously observed that, in the presence of potassium acetate, direct arylation at the C5 position was favored. Herein, we report that the use of cesium carbonate as the base and xylene as the solvent selectively afforded the C3-arylated furans or thiophenes. The reactivity of furan-2-carboxamides and thiophene-2-carboxamides were similar. The reaction tolerated a range of functional groups on the aryl bromide and also heteroaryl bromide substrates.