Catalytic charge transfer complex enabled difluoromethylation of enamides with difluoromethyltriphenylphosphonium bromide

Photoredox-Enabled Direct and Three-Component Difluoroalkylative Modification of N-Aryl Glycinates

A Cu(I) photoredox-enabled reaction that selectively incorporates a difluoroalkyl group into N-aryl glycine derivatives has been established. Using a bench-stable [Ph3PCF2H]+Br- salt, the -CF2H group could be installed either directly on the α-carbon of the glycine backbone or in a three-component fashion using an alkene as a bridge. A series of glycine derivatives have been evaluated, providing access to diverse unnatural amino esters and dipeptides with a -CHF2 unit. The studies of the compatibility of other perfluorinated alkyl radical precursors showed that the selectivity of direct α-coupling is closely associated with the electronic property of the radical, while the three-component reaction works well in most cases.

Visible Light-Induced Radical Cascade Difluoromethylation/Cyclization of Unactivated Alkenes: Access to CF2H-Substituted Polycyclic Imidazoles

An efficient and mild protocol for the visible light-induced radical cascade difluoromethylation/cyclization of imidazoles with unactivated alkenes using easily accessible and bench-stable difluoromethyltriphenylphosphonium bromide as the precursor of the -CF2H group has been developed to afford CF2H-substituted polycyclic imidazoles in moderate to good yields. This strategy, along with the construction of Csp3-CF2H/C-C bonds, is distinguished by mild conditions, no requirement of additives, simple operation, and wide substrate scope. In addition, the mechanistic experiments have indicated that the difluoromethyl radical pathway is essential for the methodology.

Photoredox Catalyzed Radical Fluoroalkylation with Non-Classical Fluorinated Reagents

The emergence of photocatalysis has greatly advanced radical fluoroalkylation reactions. Central to this advancement is the introduction and refinement of radical reagents, which play a pivotal role in driving these reactions forward. Intriguingly, some of these reagents, previously not recognized for their radical properties, have emerged as key players in this area. In this Perspective, we provide an overview of four representative reagents pioneered by our laboratory, which have subsequently garnered extensive application in broader research contexts, including difluorocarbene precursors bromodifluoromethylphosphonium bromide, electrophilic sulfonylation reagent triflic anhydride, and nucleophilic trifluoromethylation reagent methyl fluorosulfonyldifluoroacetate (Chen's reagent). The integration of phosphonium reagents, triflic anhydride, and methyl fluorosulfonyldifluoroacetate into photocatalysis has enabled some unexpected reactivities and now notably expanded the capabilities in radical difluoromethylation, trifluoromethylation, and difluoroalkylation. Our discussion highlights how these atypical reagents have enriched the toolkit available for radical fluoroalkylations, offering insights that could inspire future research and application in this area.

Visible-Light Promoted Radical Fluoroalkylation of O- and N-Substituted Alkenes

Interaction of enol ethers enol acetates, enamides and enamines with fluorinated reagents may be considered as a reliable method for the synthesis of organofluorine compounds. While classic nucleophile/electrophile substitution or addition mechanisms cannot be realized for coupling of these components, their intrinsic reactivities are revealed with the aid of photoredox catalysis. A combination of these electron donating and accepting components provides a perfect balance needed for individual redox steps, which in some cases may proceed even without a photocatalyst. The same electronic factors also support the key C,C-bond forming event involving addition of fluorinated radical at the electron rich double bond.

Visible-light photoredox-catalyzed radical aryldifluoromethylation of N-arylacrylamides with S-(difluoromethyl)sulfonium salt

A facile and highly efficient visible-light photoredox-catalyzed protocol for aryldifluoromethylation of acrylamides was developed using S-(difluoromethyl)sulfonium salt as the difluoromethyl source. With this method, pharmaceutically interesting CF₂H-containing oxindoles were readily accessed from N-arylacrylamides, and this method featured mild reaction conditions, a broad scope of substrates, good tolerance of functional groups, and good to excellent yields. Control experiments revealed that this protocol proceeded through a difluoromethylation/cyclization cascade process.