The mild and highly efficient constructions of 2,5-disubstitued thiophenes, selenophenes and tellurophenes are achieved by using a one-pot, two-step protocol that combine Cu-catalyzed Glaser coupling with LiNH₂-mediated cycloaddition. And the DMSO/EtOH mixture solvent is found to short the reaction time and improve the reaction yield by promoting the production of S₃⋅⁻ and stabilizing the transition state.

Abstract

A mild and efficient method for the synthesis of 2,5-disubstituted chalcogenophenes is reported. This method involves two steps of reactions via one-pot approach by employing commercially available and cost-effective alkynes and element chalcogen. Further, by using LiNH₂ as the promoter and DMSO/EtOH as the solvent, Cu-catalyzed Glaser coupling-cycloaddition processes are dramatically enhanced that a diverse range of chalcogenophenes can be obtained in good to excellent yields under mild conditions. Controlled experiments show that trisulfur radical anion (S3⋅⁻) is the key intermediate and DMSO/EtOH serves as the hydrogen source, while alcohol may facilitate the transition state.