Photochemical C(sp2)−H Pyridination via Arene–Pyridinium Electron Donor–Acceptor Complexes

This report describes the development of a photochemical method for C(sp2)−H pyridination that leverages the photoexcitation of electron donor–acceptor (EDA) complexes. Experimental and DFT studies show that black light (λmax≈350 nm) irradiation of solutions of protonated pyridines (acceptors) and aromatic C−H substrates (donors) results in single electron transfer to form aryl radical cation intermediates that can be trapped with pyridine nucleophiles under aerobic conditions. With some modification of the reaction conditions, this EDA activation mode is also effective for promoting the oxidatively triggered SNAr pyridination of aryl halides. Overall, this report represents an inexpensive and atom‐economical approach to photochemical pyridination reactions that eliminates the requirement of an exogenous photocatalyst. We leverage the photoexcitation of arene–pyridinium electron donor–acceptor (EDA) complexes to achieve C(sp2)−H pyridination. Black light irradiation of the simple combination of arene substrate, pyridine, acid (to generate a pyridinium acceptor in situ), and O2 (terminal oxidant) affords N‐arylpyridinium products. This transformation proceeds without an exogenous photocatalyst, complementing prior photochemical C(sp2)−H amination methods.