Electrochemical cascade sequences for remote C7-H bond thiocyanation of quinoxalin-2(1H)-ones with ammonium thiocyanate

The syntheses of C3-substituted quinoxalin-2(1H)-one derivatives have been extensively studied for decades, while the methods for direct functionalization at the embedded aromatic ring have rarely been achieved. Herein, it is reported that such a remote C-H functionalization can be enabled by electrochemical cascade sequences. Thus, quinoxalin-2(1H)-ones can be converted into 7-thiocyanatoquinoxalin-2(1H)-ones in a CH3CN/H2O solvent mixture by using an undivided cell at a constant current with inexpensive graphite electrodes and commercially cheap ammonium thiocyanate as the thiocyanate source. These cascade sequences consist of sequential cathodic reduction at the CvN double bond utilizing NH4SCN and H2O as the hydrogen atom donors, regioselective oxidative C7-thiocyanation, and anodic oxidation of the C-N single bond. The proposed mechanism has been supported by detailed cyclic voltammetry studies and control experiments. This oxidant-free strategy not only offers benefits in terms of sustainability and efficiency toward excellent functional group compatibility but also enables the synthesis of C3-deuterated derivatives.