Synthesis of regioselectively functionalized benzo[b]thiophenes by combined ortho-lithiation-halocyclization strategies

An efficient synthesis of 3-halo-7-oxygen-functionalized benzob]thiophenes bearing different substituents at C-2 has been developed from N,N-diethyl O-3-halophenylcarbamates. The key steps are an ortho-lithiation reaction, which gives rise to 3-halo-2-sulfanylphenol derivatives, and a electrophilic cyclization. The subsequent functionalization of the prepared halobenzothiophenes allows the access of a wide variety of 2,3,7-regioselectively functionalized benzob]thiophenes in good overall yields.