Single‐Particle Spectro‐Catalytic Platform Enabling High‐Efficiency Synthesis and Mechanistic Tracking of Cu‐Driven Radical N‐Heterocyclization

Conventional benzimidazole synthesis faces several challenges, including harsh reaction conditions, the formation of aldehyde‐related byproducts, and a lack of comprehensive mechanistic insights. To address these limitations, we engineered a bifunctional Cu/ZnO catalyst that facilitates high‐efficiency synthesis of benzimidazole while enabling in situ mechanistic monitoring. The spherical ZnO superstructure enhances Lewis acidity (91.2 µmol g −1 ) optimizing the adsorption of o‐arylenediamines. Concurrently, Cu nanoparticles (NPs) promote charge separation, evidenced by a 6‐fold increase in photocurrent and a carrier lifetime of 1.57 ns, while selectively cleaving the α‐C─H bonds of alcohols to generate • CH(R 2 )OH radicals such as • CH(CH 3 )OH. Notably, this radical‐driven pathway circumvents the formation of aldehyde intermediates, achieving a record 2‐methylbenzimidazole (2MBZ) productivity of 3.28 mmol g −1 h −1 with a yield of 98% yield and over 95% stability across five cycles. Furthermore, integrated surface‐enhanced Raman scattering (SERS) spectroscopy provides detailed insights at the single‐particle level, directly capturing transient species, such as radical intermediates (1170 cm −1 ) and Schiff bases (1568 cm −1 ). These findings elucidate the dual role of Cu NPs in both radical adsorption/cross‐coupling and Lewis acid‐mediated stabilization of intermediates. Thus, this work establishes a synergistic strategy that combines high‐efficiency photocatalysis with in situ mechanistic tracking for sustainable heterocycle synthesis.