Carboxylate-Assisted Carboxylation of Thiophene with CO2 in the Solvent-Free Carbonate Medium

Direct carboxylation of thiophene with CO2 has been achieved under a relatively mild solvent-free carbonate and carboxylate medium. This base-mediated medium can cleave the very weakly acidic C–H bond without using other limiting reagents, which is one indispensable step in reaction. Product yield varies different salts, cesium pivalate most suitable base additive among targeted simple salts. Furthermore, detailed mechanism this reaction studied, involves initial proton abstraction, rendered by C–C formation, inserting CO2. The activation energy barrier higher than following insertion step, whether for formation mono- and/or di-carboxylate, indicates that deprotonation induced slow resulting carbon-centered nucleophile reacts rapidly