Water Microdroplets Induce Heterocyclic Transmutation: Skeletal Editing of Aniline into Pyridine at the Air–Water Interface

Water microdroplets exhibit unique interfacial properties that can drive unconventional chemical transformations beyond those observed in a bulk solution. Here, we report an unprecedented heterocyclic transmutation in which aniline is converted directly into pyridine at the air-water interface of microdroplets under ambient conditions, without external catalysts, oxidants, or reagents. Within the millisecond lifetime of airborne microdroplets, aniline undergoes rapid skeletal reorganization, achieving up to ∼80% conversion to pyridine. Systematic variation of droplet size, charge, and pH reveals that the reaction is facilitated by the proton-rich, highly polar interface, with smaller microdroplets markedly enhancing reactivity. Mechanistic investigations, supported by high-resolution mass spectrometry, isotopic labeling, and radical trapping experiments, indicate a cooperative mechanism involving both interfacial protons and hydroxyl radicals. This work establishes microdroplet interfaces as powerful platforms for skeletal reprogramming and offers a green, reagent-free strategy for accessing pyridine scaffolds and pharmaceutically relevant molecules.