Synthesis of Phenol–Pyridinium Salts Enabled by Tandem Electron Donor–Acceptor Complexation and Iridium Photocatalysis

Herein, we describe a dual photocatalytic system to synthesize phenol–pyridinium salts using visible light. Utilizing both electron donor–acceptor (EDA) complex and iridium(III) photocatalytic cycles, the C–N cross-coupling of unprotected phenols and pyridines proceeds in the presence of oxygen to furnish pyridinium salts. Photocatalytic generation of phenoxyl radical cations also enabled a nucleophilic aromatic substitution (SNAr) of a fluorophenol with an electron-poor pyridine. Spectroscopic experiments were conducted to probe the mechanism and reaction selectivity. The unique reactivity of these phenol–pyridinium salts were displayed in several derivatization reactions, providing rapid access to a diverse chemical space.