Silica gel-assisted synthesis of benzo[b]thiophenes from o-(alkylsulfanyl)(ethynyl)benzenes

A variety of 2-substituted benzo[b]thiophenes were prepared from o-(alkylsulfanyl)(ethynyl)benzenes in the presence of silica gel under thermal conditions. Tertiary alkyl-substituted sulfanyl derivatives gave good results. Methylsulfanyl-substituted precursors also afforded benzo[b]thiophenes at higher temperature. Effect of modified silica gel was evaluated and the mechanism of this method was discussed. This method was also applied to preparation of 2-substituted thieno[3,2-b]thiophenes, which gave moderate yields.