Decarboxylative Trifluoromethylation of Aliphatic Redox-Active Esters with 2-CF 3 -Benzimidazolium Salt via Copper/Photoredox Catalysis

The development of methods for constructing C(sp3)−CF3 bonds from simple, abundant alkyl substrates is of significance but remains less developed. Aliphatic redox-active esters (RAEs), readily derived from aliphatic carboxylic acids, have emerged as a versatile platform for bond formation. Their catalytic decarboxylative trifluoromethylation has remained elusive although monofluoromethylation and difluoromethylation were achieved. This is largely due to the lability and low reactivity of conventional nucleophilic trifluoromethylating reagents. Herein, a copper-catalyzed trifluoromethylation of aliphatic N-hydroxyphthalimide (NHPI) esters using a less-explored reagent, 2-CF3-benzimidazolium salts, via a redox-neutral process was reported. This reagent addressed key limitations by enabling a slow and tunable release of the nucleophilic CF3 species, ensuring high compatibility with copper catalysis. A wide range of primary, secondary, and some tertiary aliphatic NHPI esters were trifluoromethylated smoothly. Mechanistic studies support an alkyl radical intermediate and its subsequent trifluoromethylation with trifluoromethyl copper species. This work not only completes the puzzle of catalytic decarboxylative fluoroalkylation of aliphatic RAEs but also highlights the potential of 2-CF3-benzimidazolium salts as a versatile nucleophilic trifluoromethylating reagent for catalyzed trifluoromethylation of more alkyl electrophiles via redox-neutral catalysis.