Electrochemical Oxidative Rearrangement of Tetrahydro-β-carbolines in Zero-gap Flow Cell

Oxidative rearrangement of tetrahydro-β-carbolines (THβCs) is one of the most widely used reactions for the synthesis of biologically active spirooxindoles (natural products and drug molecules). While enzymatic and chemical oxidation methods have been well established for this transformation, the corresponding electrochemical approach remain unknown. Herein, we reported the first electrochemical oxidative rearrangement of THβCs in a zero-gap flow cell. Under the optimal condition, the reaction can afford the desired spirooxindoles with up to 97% yield at a Faradaic efficiency (FE) of 96% and a productivity of 0.144 mmol/(h*cm2), which is the best among similar organic electrochemical reactions. Additionally, we discovered lithium ion played a key role in improving the reaction yield.