Direct C(sp³)–H difluoromethylation via radical–radical cross-coupling by visible-light photoredox catalysis

Abstract

Herein, the radical-radical cross-coupling strategy for direct difluoromethylation of C(sp3)−H bond is reported. This transformation was readily accomplished under transition metal-free photoredox catalysis in the presence of 3 mol% of...

State of knowledge in photoredox-catalysed direct difluoromethylation

“…A variety of 1,4-dihydroquinoxalin-2-ones were subjected to these conditions to afford the desired products under blue LED irradiation (Scheme 47). 61 The mechanism was elucidated, giving evidence of a radical–radical cross-coupling process. The CF 2 H radical was formed by single-electron transfer reduction by the excited photocatalyst PC*; the resulting PC + species then wrested an electron to the substrate to give the cationic nitrogen radical A , which via deprotonation by lithium hydroxide rendered the C(sp 3 ) radical B .…”

Photocatalytic Functionalization of Dihydroquinoxalin‐2‐Ones with Pyrazolones

“…In this context, visible‐light photoredox catalysis [7] has been emerged as a powerful and versatile tool in organic synthesis for direct C−H functionalization of quinoxalin‐2‐one derivatives because its green, sustainable and environmentally friendly characteristics. Several methods have been described for the nucleophilic photofunctionalization of dihydroquinoxalin‐2‐ones with indoles, [8] alkynes, [9] peroxides [10] or ketones, [11] as well as electrophilic photofunctionalizations with ketones, [12] alkenes, [13] dialkyl azodicarboxylates [14] or difluoroalkylation with S ‐(difluoromethyl) diarylsulfonium salts [15] . In view of the bibliographic antecedents on the use of dihydroquinoxalin‐2‐ones in photocatalytic conditions we decided to test other nucleophiles to expand the functionalization of such compounds.…”

“…Several methods have been described for the nucleophilic photofunctionalization of dihydroquinoxalin-2-ones with indoles, [8] alkynes, [9] peroxides [10] or ketones, [11] as well as electro- philic photofunctionalizations with ketones, [12] alkenes, [13] dialkyl azodicarboxylates [14] or difluoroalkylation with S-(difluoromethyl) diarylsulfonium salts. [15] In view of the bibliographic antecedents on the use of dihydroquinoxalin-2-ones in photocatalytic conditions we decided to test other nucleophiles to expand the functionalization of such compounds.…”

Difluoromethylation of heterocyclesviaa radical process

“…In this context, Liu and coworkers developed a direct C(sp 3 )–H difluoromethylation via radical–radical cross-coupling by visible-light photoredox catalysis (Scheme 20). 77 In the presence of 3 mol% organic photocatalyst, this conversion could be smoothly performed to produce a variety of 1,4-dihydroquinoxalin-2-ones 180–187 in moderate to good yields. The mechanism study supported the radical–radical cross-coupling between the C(SP 3 ) radical and the difluoromethyl radical.…”