Practical and Site‐Selective Photoinitiated C( <i>sp</i> ^<i>3</i> )–H Bond Chlorination of Ketones, ( <i>E</i> )‐1,3‐Enones, and Alkylbenzenes by Chloramine‐T and <i>N</i> ‐Chlorosuccinimide

Comprehensive Summary A practical photoinitiated synthetic method for the site‐selective γ ‐ and α ‐chlorination of C( sp 3 )–H bonds of ketones, ( E )‐1,3‐enones, and alkylbenzenes by chloramine‐T (CAT) and N ‐chlorosuccinimide (NCS) under blue LED ( λ max = 456 nm) light irradiation is reported. Mechanistic studies suggest the reaction to proceed via a radical pathway where the chlorination reagent dichloramine‐T (DCT) is generated in situ from the reaction of CAT with NCS. Its premised controlled formation along with that of the carbon‐centered radical species derived from the substrate is thought to contribute to product site‐selectivity. The developed protocol operates under mild reaction conditions at room temperature and demonstrates excellent functional group tolerance as exemplified by the site‐selective γ ‐C( sp 3 )–H bond chlorination of carboxylic esters and amides, and late‐stage functionalization of several bioactive natural products and drug molecules. The study also highlights the potential of CAT for the first time as a versatile and controllable chlorine radical atom source for site‐selective halogenation reactions, expanding its synthetic utility beyond traditional applications.