A highly efficient and simple route for the synthesis of 2-substituted benzo[b]furans has been developed by Palladium catalyzed the cross-coupling reaction of 2-halobenzo[b]furans with aryl, alkynyl and alkylaluminum reagents. Various 2-aryl, 2-alkynyl and 2-alkyl substituted benzo[b]furans derivatives can be obtained with 23-97% isolated yields using 2-3 mol% PdCl2/ 4-6 mol% XantPhos as the catalyst under mild reaction conditions. The aryls bearing electron-donating or electron-withdrawing groups in 2-halobenzo[b]furans gave products in 40-97% isolated yields. In addition, aluminum reagents containing thienyl, furanyl trimethylsilanyl and benzyl groups worked efficiently with 2-halobenzo[b]furans as well, and three bioactive molecules with 2-substituted benzo[b]furan skeleton were synthesized. Furthermore, the broad substrates scope and the typical maintenance of vigorous efficiency on gram scale make this protocol a potentially practical method to synthesize 2-substituted benzo[b]furans derivatives. On the basis of the experimental results, a possible catalytic cycle has been proposed.
Palladium catalyzed Suzuki cross-coupling of benzyltrimethylammonium salts via C–N bond cleavage
