Benzothiazoles and thiazolopyridines are widely prevalent in pharmaceuticals and organic materials. Herein, we report a metal-and reagent-free method for the uniform synthesis of benzothiazoles and thiazolopyridines through 2,2,6,6-tetramethylpiperidine-N-oxyl radical (TEMPO)-catalyzed electrolytic C−H thiolation. This dehydrogenative coupling process provides access to a host of benzothiazoles and thiazolopyridines from N-(hetero)arylthioamides. Mechanistic studies suggested that the thioamide substrate was oxidized with the electrochemically generated TEMPO + through an inner-sphere electron transfer to afford a thioamidyl radical, which undergoes homolytic aromatic substitution to form the key C−S bond.

A catalyst- and supporting electrolyte-free method for electrochemical dehydrogenative C-S bond formation in continuous flow has been developed. A broad range of N-arylthioamides have been converted to the corresponding benzothiazoles in good to excellent yields and with high current efficiencies. This transformation is achieved using only electricity and laboratory grade solvent, avoiding degassing or the use of inert atmosphere. This work highlights three advantages of electrochemistry in flow, which is (i) a supporting electrolyte-free reaction, (ii) an easy scale-up of the reaction without the need for a larger reactor and, (iii) the important and effective impact of having a good mixing of the reaction mixture, which can be achieved effectively with the use of flow systems. This clearly improves the reported methods for the synthesis of benzothiazoles.

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Reported herein is the synthesis of benzofused six‐membered S‐heterocycles by intramolecular dehydrogenative C−S coupling using a modular flow electrolysis cell. The continuous‐flow electrosynthesis not only ensures efficient product formation, but also obviates the need for transition‐metal catalysts, oxidizing reagents, and supporting electrolytes. Reaction scale‐up is conveniently achieved through extended electrolysis without changing the reaction conditions and equipment.