Synthesis of 2-Acylbenzo[b]thiophenes via Cu-Catalyzed α-C-H Functionalization of 2-Halochalcones Using Xanthate

An efficient protocol is described for the synthesis of 2-acylbenzo[b]thiophenes from easily accessible 2-iodochalcones through α-C-H functionalization using Cu(OAc)2 catalyst and xanthate as sulfur source. Less reactive 2-bromochalcones also yielded the corresponding 2-acylbenzothiophenes in good yield. The reaction proceeds via in situ incorporation of sulfur followed by copper-catalyzed cyclization to generate 2-acylbenzothiophenes without external acyl source. The synthetic importance is showcased by synthesis of 1-(5-hydroxybenzothiophene-2-yl)ethanone, which is a known pre-mRNA splicing modulator.