Synthesis of 3-aryl- and 3-alkynyl benzofurans in the presence of a supported palladium catalyst

Suzuki and Sonogashira coupling reactions of 3-iodo-2-phenylbenzofuran, leading to the corresponding 3-aryl- and 3-alkynyl derivatives, respectively, were carried out using a silica supported pyridinium ionic liquid based heterogeneous catalyst. Under optimized reactions conditions, arylboronic acids with either electron withdrawing or -donating substituents as well as terminal alkynes with aromatic or aliphatic groups could be coupled to the benzofuran skeleton efficiently. The application of this catalyst made it possible to carry out the reaction under phosphine-free and, in case of the Sonogashira coupling, under copper-free conditions. The catalyst retained its activity in at least 7 subsequent runs in both types of reactions. Palladium leaching of less than 1% of the original amount used in the catalytic reaction was observed under optimized conditions in most cases. The methodology was applied successfully in the synthesis of nine different 3-aryl- and ten different 3-alkynyl benzofuran derivatives in moderate to high yields.