Photoredox-Catalyzed\nAminolactonization of 2‑Styrylbenzoic\nAcids with <i>N</i>‑Aminopyridinium Salts to Access\n4‑Sulfonamino-3,4-dihydroisocoumarins

A photoredox-catalyzed aminolactonization of unsaturated\ncarboxylic\nacids was achieved using <i>N</i>-aminopyridinium salts\nas the amino radical precursor. The transformation features mild conditions\nand a remarkably broad substrate scope, offering an efficient approach\nto construct a wide range of 4-sulfonamino 3,4-dihydroisocoumarins.\nMechanistic studies indicate that the reaction proceeds via a distinctive <i>N</i>-aminopyridinium salt-promoted electrophilic amination\nof 2-styrylbenzoic acids.