Catalytic C-H Trifluoromethoxylation of Arenes and Heteroarenes

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.

Bactericidal and biofilm eradication efficacy of a fluorinated benzimidazole derivative, TFBZ, against methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is a major inducement of nosocomial infections and its biofilm formation render the high tolerance to conventional antibiotics, which highlights the requirement to develop new antimicrobial agents urgently. In this study, we identified a fluorinated benzimidazole derivative, TFBZ, with potent antibacterial efficacy toward planktonic MRSA (MIC = 4 μg/mL, MBC = 8 μg/mL) and its persistent biofilms (≥99%, MBEC = 8 μg/mL). TFBZ manifested significant irreversible time-dependent killing against MRSA as characterized by diminished cell viability, bacterial morphological change and protein leakage. Furthermore, the results from CBD devices, crystal violet assay in conjunction with live/dead staining and scanning electron microscopy confirmed that TFBZ was capable of eradicating preformed MRSA biofilms with high efficiency. Simultaneously, TFBZ reduced the bacterial invasiveness and exerted negligible hemolysis and cytotoxicity toward mammalian cells, which ensuring the robust therapeutic effect on mouse skin abscess model. The transcriptome profiling and quantitative RT-PCR revealed that a set of encoding genes associated with cell adhesion, biofilm formation, translation process, cell wall biosynthesis was consistently downregulated in MRSA biofilms upon exposure to TFBZ. In conclusion, TFBZ holds promise as a valuable candidate for therapeutic applications against MRSA chronic infections.

Catalyst-Free Trifluoromethoxylation of Silyl Enol Ethers and Allyl Silanes with Bis(trifluoromethyl)peroxide

Radical trifluoromethoxylation is an attractive approach to prepare compounds featuring the important OCF3 group, however most existing methods have focused on aromatic substrates. Here, we report novel methodologies with alkenyl substrates employing bis(trifluoromethyl)peroxide (BTMP) as a practical and comparatively atom economical trifluoromethoxylating reagent. With silyl enol ether substrates, switching reaction solvent allows for the synthesis of either α-(trifluoromethoxy)ketone products or unprecedented alkenyl-OCF3 species. Furthermore, allyl silanes have been employed as substrates for the first time, affording allyl(trifluoromethyl)ether products in good yields. In each case, the methods operate at room temperature without large excesses of the alkene substrate while, in contrast to previous radical trifluoromethoxylation reactions, no catalyst, light or other activators are required.

Silver-Enabled Dearomative Trifluoromethoxylation of Indoles

The only known method for the dearomative trifluoromethoxylation of indoles is preliminary, with only one substrate successfully undergoing the reaction. In this study, we not only developed a broadly applicable method for indole dearomative trifluoromethoxylation but also achieved divergent trifluoromethoxylation by fine-tuning the reaction conditions. Under optimized conditions, with a silver salt and an easily handled OCF3 reagent, various indoles smoothly underwent dearomatization to afford a diverse array of ditrifluoromethoxylated indolines in 50-84% isolated yields with up to 37:1 diastereoselectivity, and fluorinated trifluoromethoxylated indolines were obtained with exclusive trans selectivity. In addition, the reaction conditions were compatible with other heteroaromatic rings as well as styrene moieties.

Diversification of Complex Diaryl Ethers via Diaryliodonium Intramolecular Aryl Rearrangement

In this study, we present an efficient site-selective O-arylation method applicable to a broad range of complex arenes involving intramolecular aryl rearrangement. The reaction was facilitated by diaryliodonium salts bearing vicinal trifluoromethanesulfonate (OTf) groups. The procedure was initiated with selective C-H bond activation of arenes, which were then converted into diaryl ethers through nucleophilic aromatic substitution (SNAr). This synthetic method successfully affords complex diaryl ether derivatives, showcasing its practicality for the diversification of functionalized arenes and pharmaceutical agents.

Recent Advances in Visible Light-Mediated Radical Fluoro-alkylation, -alkoxylation, -alkylthiolation, -alkylselenolation, and -alkylamination

In the last few years, many reagents and protocols have been developed to allow for the efficient fluorofunctionalization of a diverse set of scaffolds ranging from alkanes, alkenes, alkynes, and (hetero)arenes. The concomitant rise of organofluorine chemistry and visible light-mediated synthesis have synergistically expanded the fields and have mutually benefitted from developments in both fields. In this context, visible light driven formations of radicals containing fluorine have been a major focus for the discovery of new bioactive compounds. This review details the recent advances and progress made in visible light-mediated fluoroalkylation and heteroatom centered radical generation.

Tf2O as a CF3 Source for the Synthesis of Trifluoromethoxylation Reagent nC4F9SO3CF3

Described herein is the convenient synthesis of an efficient trifluoromethoxylation reagent, ⁿC₄F₉SO₃CF₃, by using cheap and widely available reagents and without the need of any tedious column chromatography purification procedure.

C-H Fluoromethoxylation of Arenes by Photoredox Catalysis

Redox-active N-(fluoromethoxy)benzotriazoles were made accessible from fluoroacetic acid and hydroxybenzotriazoles via electrodecarboxylative coupling. After alkylation, they become effective monofluoromethoxylation reagents, enabling the photocatalytic C-H functionalization of arenes. Thus, irradiation of 1-(OCH2 F)-3-Me-6-(CF3 )benzotriazolium triflate with blue LED light in the presence of [Ru(bpy)3 (PF6 )2 ] promotes the synthesis of diversely functionalized aryl monofluoromethyl ethers. This method allows the late-stage functionalization of biologically relevant structures without relying on ecologically problematic halofluorocarbons.

Mechanochemical Conversion of Aromatic Amines to Aryl Trifluoromethyl Ethers

Increased interest in the trifluoromethoxy group in organic synthesis and medicinal chemistry has induced a demand for new, selective, general, and faster methods applicable to natural products and highly functionalized compounds at a later stage of hit-to-lead campaigns. Applying pyrylium tetrafluoroborate, we have developed a mechanochemical protocol to selectively substitute the aromatic amino group with the OCF₃ functionality. The scope of our method includes 31 examples of ring-substituted anilines, including amides and sulfonamides. Expected S_NAr products were obtained in excellent yields. The presented concise method opens a pathway to new chemical spaces for the pharmaceutical industry.

Electrochemical Deconstructive Functionalization of Cycloalkanols via Alkoxy Radicals Enabled by Proton-Coupled Electron Transfer

Herein, we report a new electrochemical method for alkoxy radical generation from alcohols using a proton-coupled electron transfer (PCET) approach, showcased via the deconstructive functionalization of cycloalkanols. The electrochemical method is applicable across a diverse array of substituted cycloalkanols, accessing a broad range of synthetically useful distally functionalized ketones. The orthogonal derivatization of the products has been demonstrated through chemoselective transformations, and the electrochemical process has been performed on a gram scale in continuous single-pass flow.

Silver-Catalyzed Trifluoromethoxylation of Aziridines

We disclose a silver-catalyzed trifluoromethoxylation of N-tosyl aziridines with trifluoromethyl arylsulfonate. The protocol is characterized by its mild conditions, simple operations, and good chemo- and regioselectivity. In addition, the trifluoromethoxylation of trisubstituted aziridines could construct C-OCF₃ quaternary centers exclusively, which is quite rare. This method unlocks a new catalytic blueprint for accessing β-trifluoromethoxylated amines, which could be important building blocks in synthetic chemistry.

Advances in the Development of Trifluoromethoxylation Reagents

This review provides a short summary of the traditional methods for synthesis of CF3-O-containing compounds, followed by a critical overview of known trifluoromethoxylating reagents, focusing on their preparation, synthetic generality and limitations.

Electrochemical Trifluoromethoxylation of (Hetero)aromatics with a Trifluoromethyl Source and Oxygen

Trifluoromethoxylated aromatics (ArOCF₃ ) are valuable structural motifs in the area of drug discovery due to the enhancement of their desired physicochemical properties upon the introduction of the trifluoromethoxy group (CF₃ O). Although significant progress has been made recently in the introduction of CF₃ O group into aromatics, current methods either require the use of expensive trifluoromethoxylation reagents or require harsh reaction conditions. We present a conceptually new and operationally simple protocol for the direct C-H trifluoromethoxylation of (hetero)aromatics by the combination of the readily available trifluoromethylating reagent and oxygen under electrochemical reaction conditions. This reaction proceeds through the initial generation of CF₃ radical followed by conversion to CF₃ O radical, addition to (hetero)aromatics and rearomatization. The utility of this electrochemical trifluoromethoxylation is illustrated by the direct incorporation of CF₃ O group into a variety of (hetero)aromatics as well as bio-relevant molecules.

Nucleophilic and Radical Heptafluoroisopropoxylation with Redox-Active Reagents

The heptafluoroisopropyl group (CF(CF₃ )₂ ) is prevalent in pharmaceuticals and agrichemicals. However, heptafluoroisopropoxylated (OCF(CF₃ )₂ ) compounds remain largely underexplored, presumably due to the lack of efficient access to these compounds. Herein, we disclose the practical and efficient heptafluoroisopropoxylation reactions through the invention of a series of redox-active N-OCF(CF₃ )₂ reagents. These reagents were readily prepared from the oxidative heptafluoroisopropylation of hydroxylamines with AgCF(CF₃ )₂ . The substitutions on the nitrogen atom significantly affected the properties and reactivities of N-OCF(CF₃ )₂ reagents. Accordingly, two types of N-OCF(CF₃ )₂ reagents including N-OCF(CF₃ )₂ phthalimide A and N-OCF(CF₃ )₂ benzotriazolium salt O' were used as OCF(CF₃ )₂ anion and radical precursors, respectively. This protocol enables the direct heptafluoroisopropoxylation of a range of substrates, delivering the corresponding products in moderate to excellent yields.

Alkoxy Radicals See the Light: New Paradigms of Photochemical Synthesis

Alkoxy radicals are highly reactive species that have long been recognized as versatile intermediates in organic synthesis. However, their development has long been impeded due to a lack of convenient methods for their generation. Thanks to advances in photoredox catalysis, enabling facile access to alkoxy radicals from bench-stable precursors and free alcohols under mild conditions, research interest in this field has been renewed. This review comprehensively summarizes the recent progress in alkoxy radical-mediated transformations under visible light irradiation. Elementary steps for alkoxy radical generation from either radical precursors or free alcohols are central to reaction development; thus, each section is categorized and discussed accordingly. Throughout this review, we have focused on the different mechanisms of alkoxy radical generation as well as their impact on synthetic utilizations. Notably, the catalytic generation of alkoxy radicals from abundant alcohols is still in the early stage, providing intriguing opportunities to exploit alkoxy radicals for diverse synthetic paradigms.

Photocatalysis in the Life Science Industry

In the pursuit of new pharmaceuticals and agrochemicals, chemists in the life science industry require access to mild and robust synthetic methodologies to systematically modify chemical structures, explore novel chemical space, and enable efficient synthesis. In this context, photocatalysis has emerged as a powerful technology for the synthesis of complex and often highly functionalized molecules. This Review aims to summarize the published contributions to the field from the life science industry, including research from industrial-academic partnerships. An overview of the synthetic methodologies developed and strategic applications in chemical synthesis, including peptide functionalization, isotope labeling, and both DNA-encoded and traditional library synthesis, is provided, along with a summary of the state-of-the-art in photoreactor technology and the effective upscaling of photocatalytic reactions.

Radical α-Trifluoromethoxylation of Ketones under Batch and Flow Conditions by Means of Organic Photoredox Catalysis

The first light-driven method for the α-trifluoromethoxylation of ketones is reported. Enol carbonates react with N-trifluoromethoxy-4-cyano-pyridinium, using the photoredox catalyst 4-CzIPN under 456 nm irradiation, affording the α-trifluoromethoxy ketones in ≤50% isolated yield and complete chemoselectivity. As shown by 29 examples, the reaction is general and proceeds very rapidly under batch (1 h) and flow conditions (2 min). Diverse product manipulations demonstrate the synthetic potential of the disclosed method in accessing elusive trifluoromethoxylated bioactive ingredients.

Radical C-H Trifluoromethoxylation of (Hetero)arenes with Bis(trifluoromethyl)peroxide

Trifluoromethoxylated (hetero)arenes are of great interest for several disciplines, especially in agro- and medicinal chemistry. Radical C-H trifluoromethoxylation of (hetero)arenes represents an attractive approach to prepare such compounds, but the high cost and low atom economy of existing . OCF3 radical sources make them unsuitable for the large-scale synthesis of trifluoromethoxylated building blocks. Herein, we introduce bis(trifluoromethyl)peroxide (BTMP, CF3 OOCF3 ) as a practical and efficient trifluoromethoxylating reagent that is easily accessible from inexpensive bulk chemicals. Using either visible light photoredox or TEMPO catalysis, trifluoromethoxylated arenes could be prepared in good yields under mild conditions directly from unactivated aromatics. Moreover, TEMPO catalysis allowed for the one-step synthesis of valuable pyridine derivatives, which have been previously prepared via multi-step approaches.

Late-stage C–H functionalization offers new opportunities in drug discovery

Over the past decade, the landscape of molecular synthesis has gained major impetus by the introduction of late-stage functionalization (LSF) methodologies. C-H functionalization approaches, particularly, set the stage for new retrosynthetic disconnections, while leading to improvements in resource economy. A variety of innovative techniques have been successfully applied to the C-H diversification of pharmaceuticals, and these key developments have enabled medicinal chemists to integrate LSF strategies in their drug discovery programmes. This Review highlights the significant advances achieved in the late-stage C-H functionalization of drugs and drug-like compounds, and showcases how the implementation of these modern strategies allows increased efficiency in the drug discovery process. Representative examples are examined and classified by mechanistic patterns involving directed or innate C-H functionalization, as well as emerging reaction manifolds, such as electrosynthesis and biocatalysis, among others. Structurally complex bioactive entities beyond small molecules are also covered, including diversification in the new modalities sphere. The challenges and limitations of current LSF methods are critically assessed, and avenues for future improvements of this rapidly expanding field are discussed. We, hereby, aim to provide a toolbox for chemists in academia as well as industrial practitioners, and introduce guiding principles for the application of LSF strategies to access new molecules of interest.

Trifluoromethyl Nonaflate: A Practical Trifluoromethoxylating Reagent and its Application to the Regio- and Stereoselective Synthesis of Trifluoromethoxylated Alkenes

The trifluoromethoxy group has elicited much interest among drug and agrochemical discovery teams because of its unique properties. We developed trifluoromethyl nonafluorobutanesulfonate (nonaflate), TFNf, an easy-to-handle, bench-stable, reactive, and scalable trifluoromethoxylating reagent. TFNf is easily and safely prepared in a simple process in large scale and the nonaflyl part of TFNf can easily be recovered as nonaflyl fluoride after usage and recycled. The synthetic potency of TFNf was showcased with the underexplored synthesis of various trifluoromethoxylated alkenes, through a high regio- and stereoselective hydro(halo)trifluoromethoxylation of alkyne derivatives such as haloalkynes, alkynyl esters, and alkynyl sulfones. The synthetic merits of TFNf were further underscored with a high-yielding and smooth nucleophilic trifluoromethoxylation of alkyl triflates/bromides and primary/secondary alcohols.

Direct Trifluoromethylation of Alcohols Using a Hypervalent Iodosulfoximine Reagent

The direct trifluoromethylation of a variety of aliphatic alcohols using a hypervalent iodosulfoximine reagent afforded the corresponding ethers in moderate to good yields (14-72 %). Primary, secondary, and even tertiary alcohols, including examples derived from natural products, underwent this transformation in the presence of catalytic amounts of zinc bis(triflimide). Typical reaction conditions involved a neat mixture of 6.0 equivalents of the alcohol with 1.0 equivalent of the reagent, with the majority of reactions complete within 2 h with 2.5 mol % of the Lewis acid catalyst. Furthermore, experimental evidence was provided that the C-O bond-forming process occurred via the coordination of the alcohol to the iodine atom and subsequent reductive elimination.

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.

Redox-Neutral TEMPO Catalysis: Direct Radical (Hetero)Aryl C-H Di- and Trifluoromethoxylation

Applications of TEMPO. catalysis for the development of redox-neutral transformations are rare. Reported here is the first TEMPO. -catalyzed, redox-neutral C-H di- and trifluoromethoxylation of (hetero)arenes. The reaction exhibits a broad substrate scope, has high functional-group tolerance, and can be employed for the late-stage functionalization of complex druglike molecules. Kinetic measurements, isolation and resubjection of catalytic intermediates, UV/Vis studies, and DFT calculations support the proposed oxidative TEMPO. /TEMPO+ redox catalytic cycle. Mechanistic studies also suggest that Li2 CO3 plays an important role in preventing catalyst deactivation. These findings will provide new insights into the design and development of novel reactions through redox-neutral TEMPO. catalysis.

Insights into Ruthenium(II/IV)-Catalyzed Distal C-H Oxygenation by Weak Coordination

C-H hydroxylation of aryl acetamides and alkyl phenylacetyl esters was accomplished via challenging distal weak O-coordination by versatile ruthenium(II/IV) catalysis. The ruthenium(II)-catalyzed C-H oxygenation of aryl acetamides proceeded through C-H activation, ruthenium(II/IV) oxidation and reductive elimination, thus providing step-economical access to valuable phenols. The p-cymene-ruthenium(II/IV) manifold was established by detailed experimental and DFT-computational studies.

Silver-Catalyzed Trifluoromethoxylation of Alkyl Trifluoroborates

A silver-catalyzed trifluoromethoxylation of alkyl trifluoroborates with trifluoromethyl arylsulfonate as the trifluoromethoxylation reagent has been reported for the first time. This reaction is performed under mild reaction conditions and has wide functional group compatibility. In addition, the mechanism of this site-specific trifluoromethoxylation is proposed as a radical pathway.

Photocatalytic trifluoromethoxylation of arenes and heteroarenes in continuous-flow

The first example of photocatalytic trifluoromethoxylation of arenes and heteroarenes under continuous-flow conditions is described. Application of continuous-flow microreactor technology allowed to reduce the residence time up to 16 times in comparison to the batch procedure, while achieving similar or higher yields. In addition, the use of inorganic bases was demonstrated to increase the reaction yield under batch conditions.

Selective C-H trifluoromethoxylation of (hetero)arenes as limiting reagent

Methods for direct C-H trifluoromethoxylation of arenes and heteroarenes are rare, despite the importance of trifluoromethoxylated compounds for pharmaceuticals, agrochemicals, and material sciences. Especially selective C-H trifluoromethoxylation of pyridines remains a formidable challenge. Here we show a general late-stage C-H trifluoromethoxylation of arenes and heteroarenes as limiting reagent with trifluoromethoxide anion. The reaction is mediated by silver salts under mild reaction conditions, exhibiting broad substrate scope and wide functional-group compatibility. In addition, ortho-position selective C-H trifluoromethoxylation of pyridines is observed. The method is not only applicable to the gram-scale synthesis of trifluoromethoxylated products but also allows efficient late-stage C-H trifluoromethoxylation of marketed small-molecule drugs, common pharmacophores and natural products.

Selective C-H trifluoromethoxylation of pyridines remains a formidable synthetic challenge. Here, the authors report a silver-mediated late-stage C-H trifluoromethoxylation of arenes and heteroarenes as limiting reagents with trifluoromethoxide anion.

Nickel-Catalyzed, para-Selective, Radical-Based Alkylation of Aromatic Ketones

A direct, para-selective, radical-based alkylation of aromatic ketones with alkanes has been developed using a nickel catalyst with oxamide as the ligand. Acetophenones bearing electron-withdrawing substituents were functionalized directly with simple alkanes with high para-selectivity while acetophenones with electron-donating groups were mainly para-functionalized. A mechanistic study indicated that C-H bond activation of the aromatic ring may be the rate-determining step of the reaction.

Nucleophilic trifluoromethoxylation of alkyl halides without silver

The biological properties of molecules containing the trifluoromethoxy group have made these compounds important targets in pharmaceuticals and agrochemicals, yet their preparation is still a substantial challenge. Herein, we present a practical nucleophilic trifluoromethoxylation of alkyl halides with (E)-O-trifluoromethyl-benzaldoximes (TFBO) as a trifluoromethoxylation reagent in the absence of silver under mild reaction conditions. The trifluoromethoxylation reagent TFBO is easily prepared and thermally stable, and can release CF₃O⁻ species in the presence of a base. Furthermore, broad scope and good functional group compatibility are demonstrated by application of the method to the late-stage trifluoromethoxylation of alkyl halides in complex small molecules.

Trifluoromethyl ethers are important bioactive targets in pharmaceuticals and agrochemicals, however, their synthesis is often not straightforward. Here, the authors disclose a reagent for the nucleophilic trifluoromethoxylation of alkyl halides without silver and under mild conditions.

Sequential Xanthalation and O-Trifluoromethylation of Phenols: A Procedure for the Synthesis of Aryl Trifluoromethyl Ethers

Molecules containing trifluoromethoxyaryl groups are of interest in pharmaceutical, agrochemical, and materials science research, due to their unique physical and electronic properties. Many of the known methods to synthesize aryl trifluoromethyl ethers require harsh reagents and highly controlled reaction conditions and rarely occur when heteroaromatic units are present. The two-step O-trifluoromethylation of phenols via aryl xanthates is one such method that suffers from these drawbacks. Herein, we report a method for the synthesis of aryl trifluoromethyl ethers from phenols by the facile conversion of the phenol to the corresponding aryl and heteroaryl xanthates with newly synthesized imidazolium methylthiocarbonothioyl salts and conversion of these xanthates to the trifluoromethyl ethers under mild reaction conditions.

Oxidation of difluorocarbene and subsequent trifluoromethoxylation

As a versatile intermediate, difluorocarbene is an electron-deficient transient species, meaning that its oxidation would be challenging. Herein we show that the oxidation of difluorocarbene could occur smoothly to generate carbonyl fluoride. The oxidation process is confirmed by successful trifluoromethoxylation, ¹⁸O-trifluoromethoxylation, the observation of AgOCF₃ species, and DFT calculations.

Difluorocarbene is a versatile and efficient intermediate for fluorine incorporation. Here, the authors show that difluorocarbene can be oxidized to carbonyl fluoride and this process is confirmed in ¹⁸O-trifluoromethoxylation reactions, by observation of AgOCF₃ species and theory.

Manganese-Catalyzed Electrochemical Deconstructive Chlorination of Cycloalkanols via Alkoxy Radicals

A manganese-catalyzed electrochemical deconstructive chlorination of cycloalkanols has been developed. This electrochemical method provides access to alkoxy radicals from alcohols and exhibits a broad substrate scope, with various cyclopropanols and cyclobutanols converted into synthetically useful β- and γ-chlorinated ketones (40 examples). Furthermore, the combination of recirculating flow electrochemistry and continuous inline purification was employed to access products on a gram scale.

Recent advances in transition-metal-catalyzed incorporation of fluorine-containing groups

Fluorine chemistry plays an increasingly important role in pharmaceutical, agricultural, and materials industries. The incorporation of fluorine-containing groups into organic molecules can improve their chemical and physical properties, which attracts continuous interest in organic synthesis. Among various reported methods, transition-metal-catalyzed fluorination/fluoroalkylation has emerged as a powerful method for the construction of these compounds. This review attempts to describe the major advances in the transition-metal-catalyzed incorporation of fluorine, trifluoromethyl, difluoromethyl, trifluoromethylthio, and trifluoromethoxy groups reported between 2011 and 2019.

Silver-Mediated Trifluoromethoxylation of (Hetero)aryldiazonium Tetrafluoroborates

Here we report a silver-mediated trifluoromethoxylation of (hetero)aryldiazonium tetrafluoroborates by converting an aromatic amino group into an OCF₃ group. This method, which can be considered to be a trifluoromethoxylation variation of the classic Sandmeyer-type reaction, uses readily available aryl and heteroaromatic amines as starting materials and AgOCF₃ as trifluoromethoxylating reagents. The broad substrate scope and simple, mild reaction condition made this transformation a valuable method in constructing aryl-OCF₃ bonds.

Synthesis of Tri- and Difluoromethoxylated Compounds by Visible-Light Photoredox Catalysis

Trifluoromethoxy (OCF3 ) and difluoromethoxy (OCF2 H) groups are fluorinated structural motifs that exhibit unique physicochemical characteristics. Incorporation of these substituents into organic molecules is a highly desirable approach used in medicinal chemistry and drug discovery processes to alter the properties of a parent compound. Recently, tri- and difluoromethyl ethers have received increasing attention and several innovative strategies to access these valuable functional groups have been developed. The focus of this Minireview is the use of visible-light photoredox catalysis in the synthesis of tri- and difluoromethyl ethers. Recent photocatalytic strategies for the formation of O-CF3 , C-OCF3, O-CF2 H, and C-OCF2 H bonds as well as other transformations leading to the construction of ORF groups are discussed herein.

Visible-Light Photoredox-Catalyzed and Copper-Promoted Trifluoromethoxylation of Arenediazonium Tetrafluoroborates

We report the development of photoredox-catalyzed and copper-promoted trifluoromethoxylation of arenediazonium tetrafluoroborates, with trifluoromethyl arylsulfonate (TFMS) as the trifluoromethoxylation reagent. This new method takes advantage of visible-light photoredox catalysis to generate the aryl radical under mild conditions, combined with copper-promoted selective trifluoromethoxylation. The reaction is scalable, tolerates a wide range of functional groups, and proceeds regioselectively under mild reaction conditions. Furthermore, mechanistic studies suggested that a Cs[Cu(OCF₃ )₂ ] intermediate might be generated during the reaction.

Catalytic radical difluoromethoxylation of arenes and heteroarenes

Intermolecular C-H difluoromethoxylation of (hetero)arenes remains a long-standing and unsolved problem in organic synthesis. Herein, we report the first catalytic protocol employing a redox-active difluoromethoxylating reagent 1a and photoredox catalysts for the direct C-H difluoromethoxylation of (hetero)arenes. Our approach is operationally simple, proceeds at room temperature, and uses bench-stable reagents. Its synthetic utility is highlighted by mild reaction conditions that tolerate a wide variety of functional groups and biorelevant molecules. Experimental and computational studies suggest single electron transfer (SET) from excited photoredox catalysts to 1a forming a neutral radical intermediate that liberates the OCF2H radical exclusively. Addition of this radical to (hetero)arenes gives difluoromethoxylated cyclohexadienyl radicals that are oxidized and deprotonated to afford the products of difluoromethoxylation.