Synthesis of the 2-alkynyl benzo[b]furanes/benzo[b]thiophenes from the cross-coupling reaction of benzo[b]furanyl/ benzo[b]thiophene aluminum reagents with gem-dibromoolefin derivatives catalyzed by palladium

A PdCl 2 (dppf) 2 /MePhos catalyzed synthesis of 2-alkynylbenzo[b]furanes/benzo[b]thiophenes by the crosscoupling of benzo[b]furan/benzo[b]thiophene aluminums with gem-dibromoviny derivatives at 80 degrees C in DMF solvent was developed. The aryls bearing electron-donating or-withdrawing groups in gem-dibromoviny derivatives give the corresponding coupling products 2-alkynylbenzo[b]furanes/benzo[b]thiophenes in moderate to good isolated yields up to 74 %. For electrically neutral, electron rich or electron deficient benzo[b]furanyl/ benzo[b]thiophene aluminum reagents, corresponding 2-alkynylbenzo[b]furane/benzo[b]thiophene compounds can also be obtained with moderate to good isolated yields. This process was simple and easily performed, which provides an efficient method for the synthesis of 2-alkynyl benzo[b]furane/benzo[b]thiophene derivatives. On the basis of the experimental results, a possible catalytic cycle has been proposed.