Photoredox-Catalyzed Aminolactonization of 2‑Styrylbenzoic Acids with N‑Aminopyridinium Salts to Access 4‑Sulfonamino-3,4-dihydroisocoumarins

A photoredox-catalyzed aminolactonization of unsaturated carboxylic acids was achieved using N-aminopyridinium salts as the amino radical precursor. The transformation features mild conditions and a remarkably broad substrate scope, offering an efficient approach to construct a wide range of 4-sulfonamino 3,4-dihydroisocoumarins. Mechanistic studies indicate that the reaction proceeds via a distinctive N-aminopyridinium salt-promoted electrophilic amination of 2-styrylbenzoic acids.