Metal‐Free Electrosynthesis and Photoelectrosynthesis of N‐Aryl Phenothiazines via C–H Amination

ABSTRACT N‐Aryl phenothiazines are privileged scaffolds in materials science and medicinal chemistry, yet their synthesis often relies on transition metals or stoichiometric oxidants. Herein, we report a sustainable, metal‐free electrochemical (EC) method for the C–H amination of phenols and anilines with phenothiazines. This protocol employs stable platinum electrodes under mild, oxidant‐free conditions, enabling the late‐stage functionalization of pharmaceuticals and natural products with high efficiency (up to 97% yield) and excellent regioselectivity. Furthermore, we introduce a complementary photoelectrochemical (PEC) strategy that, for a subset of substrates, provides superior yields, including several near‐quantitative transformations. Mechanistic studies via cyclic voltammetry and EPR spectroscopy confirm the generation of a persistent phenothiazine radical cation (PTZ• + ) as the key electrophilic intermediate. The efficiency of both EC and PEC pathways is rationalized by the stability of these radical cations, which is tunable by substituent effects.