Visible-light-driven thio-carboxylation of alkynes with CO2: facile synthesis of thiochromones.

Difunctionalizing carboxylation of alkynes with CO₂ is a sustainable and important strategy to generate valuable acrylate derivatives from both readily available starting materials. Such protocols, however, always suffer from the use of excess metallic reagents and transition metal residue. Herein, we report the first thio-carboxylation of alkynes with thiophenols and CO₂, which is a visible-light-driven and transition metal-free process. In contrast to previous carboxylations of alkynes via two-electron activation of CO₂, mechanistic and computational investigations suggest that the single-electron activation of CO₂ is involved in the thio-carboxylation, rendering unique β-carboxylation. The following cyclizing acylation affords important thiochromones efficiently. Moreover, the one-pot method features mild reaction conditions (room temperature, 1 atmosphere of CO₂), high chemo- and regio-selectivity, easy scalability and facile derivatization of products to bioactive compounds. [ABSTRACT FROM AUTHOR]