Remote Radical Trifluoromethylation: A Unified Approach to the Selective Synthesis of γ-Trifluoromethyl α,β-Unsaturated Carbonyl Compounds

Radical photochemical difluorosulfoximination of alkenes and propellanes

Herein, we report a metal-free divergent visible-light driven method for the synthesis of fluorinated sulfoximines. Both olefins and propellanes efficiently undergo difluorosulfoximination with yields up to 77% (65 examples). The process is general and robust and tolerates diverse functional groups, including esters, ethers, ketones, silyl groups, silyl ethers or boronic esters. The functionalization of diverse bioactive ingredients (8 examples) and various product manipulations demonstrate the synthetic usefulness of the developed synthetic platform. Finally, we rationalized the divergent reaction mechanism by performing Stern-Volmer quenching and EPR experiments that revealed the key activity of a difluoroalkyl sulfoximine radical.

Nickel/Photo-Cocatalyzed Cross-Coupling of Enol Silyl Ethers with α-Trifluoromethyl Bromides to Access β-CF3-Substituted Ketones

Herein, we introduce a nickel-photocatalyzed cross-coupling reaction between enol silyl ethers and CF3-substituted alkyl bromides. This method provides a streamlined approach for synthesizing a wide array of structurally diverse β-CF3-substituted ketones, achieving favorable yields under mild conditions. The practicality of this methodology is further underscored by its successful application in the late-stage functionalization of various pharmaceuticals and natural products.

Site-Selective γ-Trihalomethylation and γ-Dihalomethylidenation of Silyl Dienol Ethers under Organophotoredox Catalysis

We report a general remote tribromo- and trichloromethylation process using CBr4 and CBrCl3 as ready available sources of trihalomethyl radicals. This method operates under mild and metal-free photocatalyzed conditions and enables the access to γ-trihalomethylated enals with complete regioselectivity in up to 71 % isolated yield. Importantly, this protocol is easily adapted to the selective one-pot synthesis of the corresponding γ-dihalomethylidenated enals in up to 49 % overall yield. Mechanistic studies are in favor of a radical chain propagation initiated by an oxidative quenching of the photocatalyst.

Cyclic Sulfoximines as Methyl and Perdeuteromethyl Transfer Agents and Their Applications in Photoredox Catalysis

Benzo[1,3,2]dithiazole-1,1,3-trioxides are bench-stable and easy-to-use reagents. In photoredox catalysis, they generate methyl and perdeuteromethyl radicals which can add to a variety of radical acceptors, including olefins, acrylamides, quinoxalinones, isocyanides, enol silanes, and N-Ts acrylamide. As byproduct, a salt is formed which can be regenerated to the original methylating agent. Flow chemistry provides an option for reaction scale-up further underscoring the synthetic usefulness of these methylation reagents. Mechanistic investigations suggest a single-electron transfer (SET) pathway induced by photoredox catalysis.

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.

Electrophilic Fluorination of Silyl Dienol Ethers: a General and Selective Access to γ-Fluoro Enals

We describe the direct synthesis of γ-fluoro enals from the corresponding silyl dienol ethers. This simple process operates under mild conditions and is compatible with a wide range of functionalities. The high γ regioselectivity of this protocol was rationalized by means of theoretical calculations.

Chemo-divergent Cyano Group Migration: Involving Elimination and Substitution of the Key α-Thianthrenium Cyano Species

Herein, we report a light-driven, radical-type cyano migration in the absence of a photocatalyst, enabling a chemo-divergent synthesis of (Z)-alkenyl nitriles and ketones. Trifluoromethyl thianthrenium salt (TT-CF3+OTf-) plays multiple roles: (a) absorbing light to generate trifluoromethyl radicals to initiate the reaction and (b) forming α-thianthrenium cyano species by in situ capture of TT• +. (Z)-Alkenyl nitriles were formed through the elimination of thianthrenium salts, and aryl ketones were obtained via the nucleophilic substitution of thianthrenium salts.

Fluoroalkyl Sulfoximines for Versatile Photocatalytic Radical Fluoroalkylations

Fluoroalkyl sulfoximines, which serve as electron-accepting fluoroalkyl radical sources, are easy-to-handle, solid, and bench-stable chemicals. Fluoroalkyl radicals can be generated from sulfoximine reagents using strong one-electron injectors, such as a highly reducing photoredox catalyst in the excited state. Our group has developed photocatalytic radical di- and mono-fluoromethylation and α-monofluoroalkylation of olefins with the corresponding fluoroalkyl sulfoximines. In this personal account, appropriate combinations of fluoroalkyl sulfoximines and photoredox catalysts, leading to successful radical fluoroalkylation, have been discussed.

The Revival of Enantioselective Perfluoroalkylation - Update of New Synthetic Approaches from 2015-2022

Over the last years, methods devoted to the synthesis of asymmetric molecules bearing a perfluoroalkylated chain have been limited in number. Among them, only a few can be used on a large variety of scaffolds. This microreview aims at summarizing these recent advances in enantioselective perfluoroalkylation (-CF3 , -CF2 H, -Cn F2n+1 ) and highlights the need for new enantioselective methods to easily synthesize chiral fluorinated molecules which would be useful for the pharmaceutical and agrochemical industries. Some perspectives are also mentioned.

Enantioselective catalytic remote perfluoroalkylation of α-branched enals driven by light

Herein, we report a photochemical organocatalytic method for the asymmetric introduction of perfluoroalkyl fragments (including the valuable trifluoromethyl moiety) at the remote γ-position of α-branched enals. The chemistry exploits the ability of extended enamines (dienamines) to form photoactive electron donor-acceptor (EDA) complexes with perfluoroalkyl iodides, which under blue light irradiation generate radicals through an electron transfer mechanism. The use of a chiral organocatalyst, derived from cis-4-hydroxy-l-proline, secures a consistently high stereocontrol while inferring complete site selectivity for the more distal γ position of the dienamines.