Paired electrolysis enables para-C-H amination of phenols with nitroarenes and mechanistic visualization via multifunctional electrochemical mass spectrometry.

Direct C-N bond formation from nitroarenes offers an appealing alternative to conventional routes that rely on aniline intermediates, yet existing metal-catalyzed approaches often suffer from narrow substrate scope and the need for stoichiometric additives. Herein, we report a paired electrolysis strategy that enables highly selective para-C-H amination of phenols with nitroarenes, delivering unprotected p-hydroxy diphenylamines in a single step without transition-metal catalysts or external reductants. Central to this advance is a multifunctional automated injection electrochemical mass spectrometry (AIEC-MS) platform, which accelerates reaction screening, identifies productive electrochemical conditions, and reveals broad compatibility with diverse phenolic and nitroarene substrates. Real-time EC-MS analysis captures key transient intermediates-including a putative aryl-nitrene species-thus providing mechanistic visualization that clarifies how anodic and cathodic events cooperatively generate the reactive partners. Together, these insights demonstrate both the synthetic utility and mechanistic distinctiveness of paired electrolysis for direct C-N bond construction.