Access to Substituted Thiophenes through Xanthate-Mediated Vinyl C(sp)-Br Bond Cleavage and Heterocyclization of Bromoenynes.

An environmentally sustainable strategy for the chemoselective heterocyclization of bromoenynes through a transition-metal-free sulfuration/cyclization process is reported. Using inexpensive and safe EtOCSK as a thiol surrogate and tetrabutylphosphonium bromide and HO as a mixed solvent, the reaction provided a range of substituted thiophenes in moderate to good yields. In addition, 2,3,4,5-tetrasubstituted thiophenes were able to be prepared under mild reaction conditions by electrophilic heterocyclization with NHI and EtOCSK in good yields.