Electric-Field-Driven Dual-Pathway Click Coupling of Phenothiazines and Amines in Aqueous Microdroplets

"Click chemistry" offers an efficient strategy for molecular construction, yet S-N bond formation typically requires strong oxidants, leading to side reactions and poor compatibility with aromatic systems. Here, we report an oxidant-free click reaction between phenothiazines and amines within aqueous microdroplets at room temperature. This reaction is driven by the interfacial electric field and proceeds via two distinct pathways governed by the amine oxidation potential: amines with high oxidation potentials react via the phenothiazine dication intermediate, whereas those with lower oxidation potentials undergo coupling via nitrogen-centered radicals and phenothiazine radical cations. Isotopic labeling (H₂¹⁸O) together with intermediate-trapping experiments supports the involvement of phenothiazine dications and nitrogen-centered radical intermediates. Cyclic voltammetry measurements further reveal that the distinct pathways are fundamentally governed by the intrinsic redox properties of the organic substrates. This strategy expands the scope of microdroplet-based click transformations, overcoming previous limitations in aromatic amine reactivity and showcasing the utility of microdroplet environments for oxidative transformations.