Photoredox Catalysis Mediated Application of Methyl Fluorosulfonyldifluoroacetate as the CF2CO2R Radical Source

A facile access to aliphatic trifluoromethyl ketones via photocatalyzed cross-coupling of bromotrifluoroacetone and alkenes

Biological molecules incorporating trifluoromethyl ketones (TFMKs) have emerged as reversible covalent inhibitors, aiding in the management and treatment of inflammatory diseases, cancer, and respiratory conditions. TFMKs, renowned for their versatile binding properties and adaptability, are pivotal in the rational design of novel drugs for diverse diseases. The photocatalytic insertion of alkenes, abundant feedstocks, into the α-carbon of trifluoromethylacetone represents a highly effective and atom-economical method for synthesizing valuable TFMKs. However, these processes typically necessitate high-energy photoirradiation (λ > 300 nm, Hg lamp) and stoichiometric oxidants to generate the acetonyl radical from acetone. In our study, we demonstrate the visible-light photocatalytic radical addition into olefins using bromotrifluoroacetone as the trifluoroacetonyl radical precursor under mild conditions. Aliphatic trifluoromethyl ketones or the corresponding bromo-substituted products can be obtained by selecting an appropriate photocatalyst and solvent. Comprehensive experimental investigations, including cyclic voltammetry, Stern-Volmer quenching studies, and kinetic isotope effects, corroborate the synthesis of trifluoroacetonyl radical species from bromotrifluoroacetone under photoredox conditions. Further, we demonstrate the efficient synthesis of an oseltamivir derivative bearing a trifluoromethylketone moiety, which shows promising biological activity. Hence, this methodology will streamline the direct introduction of trifluoromethyl ketone into biological target molecules during drug discovery.

Photoredox-Catalysis Fluorosulfonyldifluoromethylation of Unactivated Alkenes and (Hetero)arenes with ICF2SO2F

The fluorosulfonyldifluoromethylation of unactivated alkenes and (hetero)arenes with iododifluoromethanesulfonyl fluoride (ICF2SO2F) under visible light photoredox catalysis was successfully developed. Key to the successful fluorosulfonyldifluoromethylation of aromatic compounds was the usage of AgOTf as an additive to promote the formation of the CF2SO2F radical. The protocol provided a straightforward way to introduce the interesting and useful CF2SO2F group on sp3 and sp2 carbons.

Review and Theoretical Analysis of Fluorinated Radicals in Direct CAr-H Functionalization of (Hetero)arenes

We highlight key contributions in the field of direct radical CAr- H (hetero)aromatic functionalization involving fluorinated radicals. A compilation of Functional Group Transfer Reagents and their diverse activation mechanisms leading to the release of radicals are discussed. The substrate scope for each radical is analyzed and classified into three categories according to the electronic properties of the substrates. Density functional theory computational analysis provides insights into the chemical reactivity of several fluorinated radicals through their electrophilicity and nucleophilicity parameters. Theoretical analysis of their reduction potentials also highlights the remarkable correlation between electrophilicity and oxidizing ability. It is also established that highly fluorinated radicals (e.g. ⋅OCF3) are capable of engaging in single-electron transfer (SET) processes rather than radical addition, which is in good agreement with experimental literature data. A reactivity scale, based on activation barrier of addition of these radicals to benzene is also elaborated using the high accuracy DLPNO-(U)CCSD(T) method.

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.

Difluoroalkylation of Anilines via Photoinduced Methods

The development of sustainable and mild protocols for the fluoroalkylation of organic backbones is of current interest in chemical organic synthesis. Herein, we present operationally simple and practical transition-metal-free methods for the preparation of difluoroalkyl anilines. First, a visible-light organophotocatalytic system working via oxidative quenching is described, providing access to a wide range of difluoroalkyl anilines under mild conditions. In addition, the formation of an unprecedented electron donor-acceptor (EDA) complex between anilines and ethyl difluoroiodoacetate is reported and exploited as an alternative, efficient, and straightforward strategy to prepare difluoroalkyl derivatives.

Synthesis of Selectively gem-Difluorinated Molecules; Chiral gem-Difluorocyclopropanes via Chemo-Enzymatic Reaction and gem-Difluorinated Compounds via Radical Reaction

The incorporation of fluorine atoms into an organic compound can alter the chemical reactivity or biological activity of the resulting compound due to the strong electron withdrawing nature of the fluorine atom. We have synthesized many original gem-difluorinated compounds and described the results in four sections. The first section describes the synthesis of optically active-gem-difluorocyclopropanes via the chemo-enzymatic reaction; we applied these compounds to liquid crystalline molecules, then further discovered a potent DNA cleavage activity for the gem-difluorocyclopropane derivatives. The second section describes the synthesis of selectively gem-difluorinated compounds via a radical reaction; we synthesized fluorinated analogues of a sex pheromone of the male African sugarcane borer, Eldana saccharina, and used the compounds as proof for investigating the origin of pheromone molecule recognition on the receptor protein. The third involves the synthesis of 2,2-difluorinated-esters by visible light-driven radical addition of 2,2-difluoroacetate with alkenes or alkynes in the presence of an organic pigment. The last section describes the synthesis of gem-difluorinated compounds via the ring-opening of gem-difluorocyclopropanes. We further developed a novel method of synthesizing gem-difluorohomoallylic alcohols via the ring-opening of gem-difluorocyclopropane and aerobic oxidation by photo-irradiation in the presence of an organic pigment. Since gem-difluorinated compounds that were prepared by the present method have two olefinic moieties with a different reactivity at the terminal position, we accomplished the synthesis of four types of gem-difluorinated cyclic alkenols via the ring-closing-metathesis (RCM) reaction.

Visible-Light-Induced Difluoroalkylation of Alkenes and Alkynes with Fluoro-Containing Hypervalent Iodane (III) Reagents Under Photo-Catalyst-Free Conditions

A visible-light-induced difluoroalkylation of unactivated alkenes by fluoro-containing hypervalent iodine-based difluoroalkylation reagent was achieved for the first time under photo-catalyst-free conditions. Moreover, the same reaction conditions were applicable to the difluoroalkylation of alkynes to give the hydrodifluoroalkylation products in moderate to excellent yields. The readily available reagent, broad substrate scope, and photo-catalyst-free conditions make this protocol an efficient and environmental friendly method for the hydrodifluoroalkylation of alkenes and alkynes.

Visible-light-induced Mn(0)-catalyzed direct C-3 mono-, di- and perfluoroalkylation reactions of 2H-indazoles

A general and efficient method for visible-light-driven fluoroalkylation, such as difluoromethylphosphonation, difluoroacetamidation, monofluoromethylation, difluoromethylation, and perfluoroalkyalation, of 2H-indazoles using an inexpensive Mn₂(CO)₁₀ photocatalyst has been developed. The present methodology affords a new series of C-3 fluoroalkylated 2H-indazole derivatives with wide functional group tolerance in good to excellent yields. Difluoromethylenated indiazoles are also prepared from difluoroester derivatives. Our mechanistic investigations support a radical pathway for the reaction.

Visible-Light-Induced C-F Bond Activation for the Difluoroalkylation of Indoles

An aryl disulfide mediated C-F bond activation of the trifluoromethyl group to generate valuable gem-difluoroalkylindoles is described. This method relies on readily available commodity reagents under mild reaction conditions and represents the first transition-metal-free redox-neutral C-F bond activation strategy. The reaction employs various substituted indoles and α-fluoro-substituted esters. Further, this mode of C-F activation was also amenable to the activation of trifluoromethylated arenes for the preparation of bis-benzylic gem-difluoromethylenes between indole and arene substructures, providing access to a unique chemical space.

Synthesis of α-Fluorinated Areneacetates through Photoredox/Copper Dual Catalysis

The development of mild and practical conditions for the fluoroalkylation of arenes is an ongoing challenge in chemical organic synthesis. Herein, we report a metallaphotoredox method for the preparation of fluoroalkyl arenes based on the synergistic combination of Ir/Cu dual catalysis from boronic acids. The mild conditions allow broad functional group tolerance, including substrates containing aldehydes, free phenols, and N-Boc-protected amines. Mechanistic investigations support a process proceeding via photoredox/copper dual catalysis.

Visible-Light-Induced para-Difluoroalkylation of Aniline Derivatives

Visible-light-induced, iridium catalyzed, para-selective C-H difluoroalkylation of aniline derivatives under mild reaction conditions is reported. Various substrates and bioactive compounds, such as precursors of vorinostat and chlorpropham, were all well tolerated. This protocol features a wide substrate scope, high regioselectivity, low catalyst usage, and operational simplicity.

Photoredox catalyzed C-H trifluoroethylamination of heteroarenes

The first C-H trifluoroethylamination of heteroarenes with previously unknown N-trifluoroethyl hydroxylamine reagents was achieved under photoredox catalyzed conditions. In the presence of an iridium(III) photoredox catalyst, a variety of heteroarenes, such as indoles, benzofurans, and benzothiophenes, were smoothly converted to the trifluoroethylaminated products in moderate to high yields and with excellent regioselectivity.

Photoredox-Catalyzed Addition of Dibromofluoromethane to Alkenes: Direct Synthesis of 1-Bromo-1-fluoroalkanes

Reported herein is a direct and efficient route to 1-bromo-1-fluoroalkanes through the reaction of unactivated alkenes with dibromofluoromethane under photoredox catalysis. The key to the success of these addition reactions is the employment of a suitable photoredox catalyst. In particular, hydro- and bromo-bromofluoromethylated products were chemoselectively formed using THF and DMF/H₂O as solvents, respectively. Furthermore, the synthetic application of the prepared 1-bromo-1-fluoroalkanes has been demonstrated by their transformation into a variety of fluorine-containing compounds.

Visible light photocatalysis in the late-stage functionalization of pharmaceutically relevant compounds

The late stage functionalization (LSF) of complex biorelevant compounds is a powerful tool to speed up the identification of structure-activity relationships (SARs) and to optimize ADME profiles. To this end, visible-light photocatalysis offers unique opportunities to achieve smooth and clean functionalization of drugs by unlocking site-specific reactivities under generally mild reaction conditions. This review offers a critical assessment of current literature, pointing out the recent developments in the field while emphasizing the expected future progress and potential applications. Along with paragraphs discussing the visible-light photocatalytic synthetic protocols so far available for LSF of drugs and drug candidates, useful and readily accessible synoptic tables of such transformations, divided by functional groups, will be provided, thus enabling a useful, fast, and easy reference to them.

Iridium-Catalyzed Enantioselective Synthesis of α-Chiral Bicyclo[1.1.1]pentanes by 1,3-Difunctionalization of [1.1.1]Propellane

Bicyclo[1.1.1]pentanes (BCPs) have found application as bioisosteres of aromatic rings in drug development. However, catalytic construction of this motif with adjacent stereocenters with high enantioselectivity from readily available starting materials still constitutes a significant synthetic challenge. Herein we report a direct stereoselective synthesis of α-chiral allylic BCPs by 1,3-difunctionalization of [1.1.1]propellane with Grignard reagents and allyl carbonates using iridium catalysis. This mild protocol proceeds via initial organometallic addition to [1.1.1]propellane followed by asymmetric allylic substitution, providing the products with high enantioselectivities over a broad range of substrates. Further derivatization of the products demonstrates the applicability of this method to the preparation of structurally diverse libraries of chiral BCP derivatives.

Cascade cyclization reactions of alkylidenecyclopropanes for the construction of polycyclic lactams and lactones by visible light photoredox catalysis

A facile method for the synthesis of seven- and eight-membered ring-containing polycyclic lactams and lactones by visible light photocatalysis has been developed.

A general and green fluoroalkylation reaction promoted via noncovalent interactions between acetone and fluoroalkyl iodides

The first example of visible light promoted fluoroalkylation reactions initiated via noncovalent interactions between solvents and R_FI is presented.

Visible-Light-Promoted Oxo-difluoroalkylation of Alkenes with DMSO as the Oxidant

Visible-light-promoted oxo-difluoroalkylation (acetylation and acetamidation) of alkenes with dimethyl sulfoxide as both the solvent and the oxidant was developed, affording the corresponding α,α-difluoro-γ-ketoacetates and acetamides in modest yields. Both terminal and internal alkenes worked well for the reaction. This reaction features simple starting materials, a green oxidant, mild reaction conditions, and highly functional products.

Progress in Difluoroalkylation of Organic Substrates by Visible Light Photoredox Catalysis

The selective incorporation of fluorinated motifs, in particular CF2FG (FG=a functional group) and CF2H groups, into organic compounds has attrracted increasing attention since organofluorine molecules are of the utmost importance in the areas of nuclear imaging, pharmaceutical, agrochemical, and material sciences. A variety of synthetic approaches has been employed in late-stage difluoroalkylation reactions. Visible light photoredox catalysis for the production of CF2FG and CF2H radicals has provided a more sustainable alternative to other conventional radical-triggered reactions from the viewpoint of safety, cost, availability, and "green" chemistry. A wide range of difluoroalkylating reagents has been successfully implemented in these organic transformations in the presence of transition metal complexes or organic photocatalysts. In most cases, upon excitation via visible light irradiation with fluorescent light bulbs or blue light-emitting diode (LED) lamps, these photocatalysts can act as both reductive and oxidative quenchers, thus enabling the application of electron-donor or electron-acceptor difluoroalkylating reagents for the generation of CF2FG and CF2H radicals. Subsequent radical addition to substrates and additional organic transformations afford the corresponding difluoroalkylated derivatives. The present review describes the distinct strategies for the transition metal- and organic-photocatalyzed difluoroalkylation of a broad range of organic substrates by visible light irradiation reported in the literature since 2014.

A metal-free desulfurizing radical reductive C–C coupling of thiols and alkenes

An intermolecular reductive C–C coupling of electrophilic alkyl radicals and alkenes has been developed.

Visible-light-triggered direct keto-difluoroacetylation of styrenes with (fluorosulfonyl)difluoroacetate and dimethyl sulfoxide leads to α-difluoroacetylated ketones

Photoredox-catalyzed direct keto-difluoroacetylation of styrenes with methyl (fluorosulfonyl)difluoroacetate and dimethyl sulfoxide to deliver various α-difluoroacetylated ketones are disclosed.

Synthesis of Elongated Esters from Alkenes

A convenient method for synthesizing elongated aliphatic esters from alkenes is reported. An (alkoxycarbonyl)methyl radical species is generated upon visible-light irradiation of an ester-stabilized phosphorus ylide in the presence of a photoredox catalyst. This radical species adds onto the carbon-carbon double bond of an alkene to produce an elongated aliphatic ester.

Trifluoromethanesulfonic Anhydride as a Low-Cost and Versatile Trifluoromethylation Reagent

A large number of reagents have been developed for the synthesis of trifluoromethylated compounds. However, an ongoing challenge in trifluoromethylation reaction is the use of less expensive and practical trifluoromethyl sources. We report herein the unprecedented direct trifluoromethylation of (hetero)arenes using trifluoromethanesulfonic anhydride as a radical trifluoromethylation reagent by merging photoredox catalysis and pyridine activation. Furthermore, introduction of both the CF₃ and OTf groups of the trifluoromethanesulfonic anhydride into internal alkynes to access tetrasubstituted trifluoromethylated alkenes was achieved. Since trifluoromethanesulfonic anhydride is a low-cost and abundant chemical, this method provides a cost-efficient and practical route to trifluoromethylated compounds.

Copper(ii)-catalyzed trifluoromethylation of iodoarenes using Chen's reagent

The utility of Chen's reagent in trifluoromethylation revisited.