Electrochemical Regioselective C(sp2)-H Bond Chalcogenation of Pyrazolo[1,5-a]pyrimidines via Radical Cross Coupling at Room Temperature

In this report, we disclose an electrochemical approach for the C(sp2)-H chalcogenation of pyrazolo[1,5-a]pyrimidines at room temperature via radical cross-coupling reaction. The reaction takes place within an undivided cell employing graphite electrodes, with TBABF4 acting as the supporting electrolyte. This technique offers a rapid, oxidant-free, and environmentally conscious protocol for achieving regioselective chalcogenation specifically at the C3 position of pyrazolo[1,5-a]pyrimidines. Furthermore, the procedure uses only 0.5 equivalents of diaryl chalcogenides which underscores the atom economy of the protocol. Key attributes of this methodology include mild reaction conditions, short reaction time, utilization of cost-effective electrode materials, and reliable achievement of yields ranging from good to excellent and environmentally friendly reaction conditions. Cyclic voltammetry studies and radical quenching experiments suggest a radical pathway for the reaction mechanism.