The unique role of fluorine in the design of active ingredients for modern crop protection

Deoxytrifluoromethylation/aromatization of cyclohexan(en)ones to access highly substituted trifluoromethyl arenes

Trifluoromethyl arenes (Ar-CF3) are amongst the commonly encountered fluorinated substructures in pharmaceutical, agrochemical, and material sciences. However, predominant methods to access Ar-CF3 possess several limitations, including harsh conditions, lack of availability of substrates, and poor regioselectivity, which combined restrict access to desirable highly functionalized Ar-CF3-containing compounds. To expand the scope of accessible Ar-CF3-based molecules, we present an orthogonal deoxyfluoroalkylation/aromatization approach that exploits readily accessible and programable cyclohexan(en)one substrates, which undergo a reliable 1,2-addition reaction with the Ruppert-Prakash reagent (TMSCF3) followed by aromatization to deliver highly functionalized Ar-CF3 compounds in a one/two-pot sequence. This general strategy enables access to highly substituted Ar-CF3-containing molecules that are difficult, expensive, and/or impossible to access by current synthetic methods.

Base-Mediated Regioselective [3 + 3] Annulation of Alkylidene Malononitriles with Trifluoromethyl Alkenes via Dual C-F Bond Cleavage

A base-mediated regioselective [3 + 3] annulation of alkylidene malononitriles with trifluoromethyl alkenes was described. The reaction proceeds through sequential intermolecular SN2' and intramolecular SNV-type cyclization by cleaving dual C-F bonds in a trifluoromethyl group, which discriminate multiple carbon-nucleophilic sites using a single base. Various bicycles bearing a monofluorocyclohexene motif were assembled from readily available starting materials under mild conditions via a one-pot cascade approach.

Recent advances in catalytic enantioselective construction of monofluoromethyl-substituted stereocenters

Chiral organofluorine compounds featuring a monofluoromethyl (CH2F)-substituted stereocenter are often encountered in a number of drugs and bioactive molecules. Consequently, the development of catalytic asymmetric methods for the enantioselective construction of CH2F-substituted stereocenters has made great progress over the past two decades, and a variety of enantioselective transformations have been accordingly established. According to the types of fluorinated reagents or substrates employed, these protocols can be divided into the following major categories: (i) enantioselective ring opening of epoxides or azetidinium salts by fluoride anions; (ii) asymmetric monofluoromethylation with 1-fluorobis(phenylsulfonyl)methane; (iii) asymmetric fluorocyclization of functionalized alkenes with Selectfluor; and (iv) asymmetric transformations involving α-CH2F ketones, α-CH2F alkenes, or other CH2F-containing substrates. This feature article aims to summarize these recent advances and discusses the possible reaction mechanisms, advantages and limitations of each protocol and their applications. Synthetic opportunities still open for further development are illustrated as well. This review article will be an inspiration for researchers engaged in asymmetric catalysis, organofluorine chemistry, and medicinal chemistry.

Palladium-Catalyzed Trifluoroacetylation of Arylboronic Acids Using a Trifluoroacetylation Reagent

A new trifluoroacetylation reagent was developed by using inexpensive and readily available trifluoroacetic anhydride and N-phenyl-4-methylbenzenesulfonamide for the first time. The reaction of (het)aryl boronic acids with the new trifluoroacetylation reagent, N-phenyl-N-tosyltrifluoroacetamide, proceeded smoothly in the presence of a palladium catalyst to provide trifluoromethyl ketones in satisfactory to excellent yields. Various groups, including the synthetically useful functional groups Cl, TMS, and PhCO, were tolerated well under the current reaction conditions. This new trifluoroacetylation reagent can be used in the large-scale synthesis of trifluoromethyl ketones, even at a low palladium catalyst loading.

Fingerprinting Organofluorine Molecules via Position-Specific Isotope Analysis

Organofluorine substances are found in a wide range of materials and solvents commonly used in industry and homes, as well as pharmaceuticals and pesticides. In the environment, organofluorine molecules are now recognized as an important class of anthropogenic pollutants. Fingerprinting organofluorine compounds via their carbon isotope ratios (13C/12C) is crucial for correlating molecules with their source. Here we apply a 19F nuclear magnetic resonance spectroscopy (NMR) technique to obtain the first position-specific carbon isotope ratios for a diverse set of organofluorine molecules. In contrast to traditional isotope ratio mass spectrometry, the 19F NMR method provides 13C/12C isotope ratios at each carbon position where a C-F bond is present, and does not require fragmentation or combustion to CO2, overcoming challenges posed by the robust C-F covalent bonds. The method was validated with 2,2,2-trifluoroethanol, and applied to analyze heptafluorobutanoic acid, 5-fluorouracil and fipronil. Results reveal distinct intramolecular carbon isotope distributions, enabling differentiation of chemically identical molecules. Notably, the NMR method accurately analyzes carbon isotopes within target molecules despite impurities. Potential applications include the detection of counterfeit products and drugs, and ultimately pollution tracking in the environment.

Regioselective fluorination of allenes enabled by I(I)/I(III) catalysis

The prominence and versatility of propargylic fluorides in medicinal chemistry, coupled with the potency of F/H and F/OH bioisosterism, has created a powerful impetus to develop efficient methods to facilitate their construction. Motivated by the well-established conversion of propargylic alcohols to allenes, an operationally simple, organocatalysis-based strategy to process these abundant unsaturated precursors to propargylic fluorides would be highly enabling: this would consolidate the bioisosteric relationship that connects propargylic alcohols and fluorides. Herein, we describe a highly regioselective fluorination of unactivated allenes based on I(I)/I(III) catalysis in the presence of an inexpensive HF source that serves a dual role as both nucleophile and Brønsted acid activator. This strategy enables a variety of secondary and tertiary propargylic fluorides to be prepared: these motifs are prevalent across the bioactive small molecule spectrum. Facile product derivatisation, concise synthesis of multi-vicinal fluorinated products together with preliminary validation of enantioselective catalysis are disclosed. The expansive potential of this platform is also demonstrated through the highly regioselective organocatalytic oxidation, chlorination and arylation of allenes. It is envisaged that the transformation will find application in molecular design and accelerate the exploration of organofluorine chemical space.

Silver-Catalyzed Carbofluorination of Olefins and α-Fluoroolefins with Carbamoyl Radicals

The reactivity of carbamoyl radicals, generated in situ from sodium oxamate salts, has been investigated in the context of radical carbofluorination reactions of olefins and α-fluoroolefins, respectively. Both transformations are catalyzed by silver salts and required the presence of potassium persulfate (K2S2O8) and SelectfluorTM as a radicophilic fluorine source. The reported methods provide a direct access to β-fluoroamides and β,β-difluoroamides.

Recyclable V2O5/g-C3N4 Heterojunction-Catalyzed Visible-Light-Promoted C3-H Trifluoromethylation of Quinoxalin-2-(1H)-ones

A visible-light-initiated C-H trifluoromethylation of quinoxalin-2(1H)-ones was established using a Z-scheme V2O5/g-C3N4 heterojunction as a recyclable photocatalyst in an inert atmosphere at room temperature under additive-free and mild conditions. A variety of trifluoromethylated quinoxalin-2-(1H)-one derivatives were heterogeneously generated in moderate to high yields, exhibiting good functional group tolerance. Remarkably, the recyclable V2O5/g-C3N4 catalyst could be reused five times with a slight loss of catalytic activity.

Palladium(II)-Catalyzed Nondirected Late-Stage C(sp2)-H Deuteration of Heteroarenes Enabled Through a Multi-Substrate Screening Approach

The importance of deuterium labelling in a variety of applications, ranging from mechanistic studies to drug-discovery, has spurred immense interest in the development of new methods for its efficient incorporation in organic, and especially in bioactive molecules. The five-membered heteroarenes at the center of this work are ubiquitous motifs in bioactive molecules and efficient methods for the deuterium labelling of these compounds are therefore highly desirable. However, the profound differences in chemical properties encountered between different heteroarenes hamper the development of a single set of broadly applicable reaction conditions, often necessitating a separate optimization campaign for a given type of heteroarene. In this study we describe the use of a multi-substrate screening approach to identify optimal reaction conditions for different classes of heteroarenes from a minimal number of screening reactions. Using this approach, four sets of complementary reaction conditions derived from our dual ligand-based palladium catalysts for nondirected C(sp2)-H activation were identified, that together enable the deuteration of structurally diverse heteroarenes, including bioactive molecules.

Diverse role, structural trends, and applications of fluorinated sulphonamide compounds in agrochemical and pharmaceutical fields

Our knowledge of fluorine's unique and complex properties has significantly increased over the past 20 years. Consequently, more sophisticated and innovative techniques have emerged to incorporate this feature into the design of potential drug candidates. In recent years, researchers have become interested in synthesizing fluoro-sulphonamide compounds to discover new chemical entities with distinct and unexpected physical, chemical, and biological characteristics. The fluorinated sulphonamide molecules have shown significant biomedical importance. Their potential is not limited to biomedical applications but also includes crop protection. The discovery of novel fluorine and Sulfur compounds has highlighted their importance in the chemical sector, particularly in the agrochemical and medicinal fields. Recently, several fluorinated sulphonamide derivatives have been developed and frequently used by agriculturalists to produce food for the growing global population. These molecules have also exhibited their potential in health by inhibiting various human diseases. In today's world, it is crucial to have a steady supply of innovative pharmaceutical and agrochemical molecules that are highly effective, less harmful to the environment, and affordable. This review summarizes the available information on the activity of Fluorine and Sulphonamide compounds, which have proven active in pharmaceuticals and agrochemicals with excellent environmental and human health approaches. Moreover, it focuses on the current literature on the chemical structures, the application of fluorinated sulphonamide compounds against various pathological conditions, and their effectiveness in crop protection.

Nucleophilic fluorine substitution reaction of α-carbonyl benzyl bromide, phenylthiofluoroalkyl bromide, and 2-bromo-2-phenoxyacetonitrile

We herein describe a new method for nucleophilic fluorine substitution of alkylbromides using Et3N·3HF. The process is characterized by a broad substrate scope, good functional-group compatibility, and mild conditions and provides a variety of alkylfluorides including tertiary alkylfluorides that are versatile and structurally attractive.

In situ Diazonium Salt Formation and Photochemical Aryl-Aryl Coupling in Continuous Flow Monitored by Inline NMR Spectroscopy

A novel class of diazonium salts is introduced for the photochemical aryl-aryl coupling to produce (substituted) biphenyls. As common diazonium tetrafluoroborate salts fail, soluble and safe aryl diazonium trifluoroacetates are applied. In this mild synthesis route no catalysts are required to generate an aryl-radical by irradiation with UV-A light (365 nm). This reactive species undergoes direct C-H arylation at an arene, forming the product in reasonable reaction times. With the implementation of a continuous flow setup in a capillary photoreactor 13 different biphenyl derivatives are successfully synthesized. By integrating an inline 19F-NMR benchtop spectrometer, samples are reliably quantified as the fluorine-substituents act as a probe. Here, real-time NMR spectroscopy is a perfect tool to monitor the continuously operated system, which produces fine chemicals of industrial relevance even in a multigram scale.

Photoinduced Decarboxylative Difluoroalkylation and Perfluoroalkylation of α-Fluoroacrylic Acids

Herein, a novel and practical methodology for the photoinduced decarboxylative difluoroalkylation and perfluoroalkylation of α-fluoroacrylic acids is reported. A wide range of α-fluoroacrylic acids can be used as applicable feedstocks, allowing for rapid access to structurally important difluoroalkylated and polyfluoroalkylated monofluoroalkenes with high Z-stereoselectivity under mild conditions. The protocol demonstrates excellent functional group compatibility and provides a platform for modifying complex biologically active molecules.

Applications of Transition Metal-Catalyzed ortho-Fluorine-Directed C-H Functionalization of (Poly)fluoroarenes in Organic Synthesis

The synthesis of organic compounds efficiently via fewer steps but in higher yields is desirable as this reduces energy and reagent use, waste production, and thus environmental impact as well as cost. The reactivity of C-H bonds ortho to fluorine substituents in (poly)fluoroarenes with metal centers is enhanced relative to meta and para positions. Thus, direct C-H functionalization of (poly)fluoroarenes without prefunctionalization is becoming a significant area of research in organic chemistry. Novel and selective methodologies to functionalize (poly)fluorinated arenes by taking advantage of the reactivity of C-H bonds ortho to C-F bonds are continuously being developed. This review summarizes the reasons for the enhanced reactivity and the consequent developments in the synthesis of valuable (poly)fluoroarene-containing organic compounds.

Pd-Catalyzed Oxidative C-H Arylation of (Poly)fluoroarenes with Aryl Pinacol Boronates and Experimental and Theoretical Studies of its Reaction Mechanism

We report the synergistic combination of Pd(OAc)2 and Ag2O for the oxidative C-H arylation of (poly)fluoroarenes with aryl pinacol boronates (Ar-Bpin) in DMF as the solvent. This procedure can be conducted easily in air, and without using additional ligands, to afford the fluorinated unsymmetrical biaryl products in up to 98 % yield. Experimental studies suggest that the formation of [PdL2(C6F5)2] in DMF as coordinating solvent does not take place under the reaction conditions as it is stable to reductive elimination and thus would deactivate the catalyst. Thus, the intermediate [Pd(DMF)2(ArF)(Ar)] must be formed selectively to give desired arylation products. DFT calculations predict a low barrier (5.87 kcal/mol) for the concerted metalation deprotonation (CMD) process between C6F5H and the Pd(II) species formed after transmetalation between the Pd(II)X2 complex and aryl-Bpin which forms a Pd-Arrich species. Thus a Pd(Arrich)(Arpoor) complex is generated selectively which undergoes reductive elimination to generate the unsymmetrical biaryl product.

C-F Bond Insertion: An Emerging Strategy for Constructing Fluorinated Molecules

C-F Insertion reactions, where an organic fragment formally inserts into a carbon-fluorine bond in a substrate, are highly attractive, yet largely unexplored, methods to prepare valuable fluorinated molecules. The inherent strength of C-F bonds and the resulting need for a large thermodynamic driving force to initiate C-F cleavage often leads to sequestering of the released fluoride in an unreactive by-product. Recently, however, several groups have succeeded in overcoming this challenge, opening up the study of C-F insertion as an efficient and highly atom-economical approach to prepare fluorinated compounds. In this article, the recent breakthroughs are discussed focusing on the key conceptual advances that allowed for both C-F bond cleavage and subsequent incorporation of the released fluoride into the product.

Mechanism of Asymmetric Homologation of Alkenylboronic Acids with CF3-Diazomethane via Borotropic Rearrangement

Density functional theory calculations have been performed to investigate the mechanism for the BINOL-catalyzed asymmetric homologation of alkenylboronic acids with CF3-diazomethane. The reaction proceeds via a chiral BINOL ester of the alkenylboronic acid substrate. The calculations reveal a complex scenario for the formation of the chiral BINOL-alkenylboronate species, which is the key intermediate in the catalytic process. The aliphatic alcohol additive plays an important role in the reaction. This study provides a rationalization of the stereoinduction step of the reaction, and the enantioselectivity is mainly attributed to the steric repulsion between the CF3 group of the diazomethane reagent and the γ-substituent of the BINOL catalyst. The complex potential energy surface obtained by the calculations is analyzed by means of microkinetic simulations.

Sequential C-F Bond Transformation of the Difluoromethylene Unit in Perfluoroalkyl Groups: A Combination of Fine-Tuned Phenothiazine Photoredox Catalyst and Lewis Acid

A sequential process via photoredox catalysis and Lewis acid mediation for C-F bond transformation of the CF2 unit in perfluoroalkyl groups has been achieved to transform perfluoroalkylarenes into complex fluoroalkylated compounds. A phenothiazine-based photocatalyst promotes the defluoroaminoxylation of perfluoroalkylarenes with (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) under visible light irradiation, affording the corresponding aminoxylated products. These products undergo a further defluorinative transformation with various organosilicon reagents mediated by AlCl3 to provide highly functionalized perfluoroalkyl alcohols. Our novel phenothiazine catalyst works efficiently in the defluoroaminoxylation. Transient absorption spectroscopy revealed that the catalyst regeneration step is crucial for the photocatalytic aminoxylation.

Synthesis and Evaluation of New Phytotoxic Fluorinated Chalcones as Photosystem II and Seedling Growth Inhibitors

The development of novel phytotoxic compounds has been an important aim of weed control research. In this study, we synthesized fluorinated chalcone derivatives featuring both electron-donating and electron-withdrawing groups. These compounds were evaluated both as inhibitors of the photosystem II (PSII) electron chain as well as inhibitors of the germination and seedling growth of Amaranthus plants. Chlorophyll a (Chl a) fluorescence assay was employed to evaluate their effects on PSII, while germination experiments were conducted to assess their impact on germination and seedling development. The results revealed promising herbicidal activity for (E)-3-(4-bromophenyl)-1-(4-fluorophenyl)prop-2-en-1-one (7 a) and (E)-1-(4-fluorophenyl)-3-phenylprop-2-en-1-one (7 e). Compounds 7 a and 7 e exhibited a reduction in Chl a parameters associated with performance indexes and electron transport per reaction center. This reduction suggests a decrease in PSII activity, attributed to the blockage of electron flow at the quinone pool. Molecular docking analyses of chalcone derivatives with the D1 protein of PSII revealed a stable binding conformation, wherein the carbonyl and fluorine groups interacted with Phe265 and His215 residues, respectively. Additionally, at a concentration of 100 μM, compound 7 e demonstrated pre- and post-emergent herbicidal activity, resulting in a reduction of the seed germination index, radicle and hypocotyl lengths of Amaranthus weeds.

Metallomimetic C-F Activation Catalysis by Simple Phosphines

Delivering metallomimetic reactivity from simple p-block compounds is highly desirable in the search to replace expensive, scarce precious metals by cheap and abundant elements in catalysis. This contribution demonstrates that metallomimetic catalysis, involving facile redox cycling between the P(III) and P(V) oxidation states, is possible using only simple, cheap, and readily available trialkylphosphines without the need to enforce unusual geometries at phosphorus or use external oxidizing/reducing agents. Hydrodefluorination and aminodefluorination of a range of fluoroarenes was realized with good to very good yields under mild conditions. Experimental and computational mechanistic studies show that the phosphines undergo oxidative addition of the fluoroaromatic substrate via a Meisenheimer-like transition state to form a fluorophosphorane. This undergoes a pseudotransmetalation step with a silane, via initial fluoride transfer from P to Si, to give experimentally observed phosphonium ions. Hydride transfer from a hydridosilicate counterion then leads to a hydridophosphorane, which undergoes reductive elimination of the product to reform the phosphine catalyst. This behavior is analogous to many classical transition-metal-catalyzed reactions and so is a rare example of both functional and mechanistically metallomimetic behavior in catalysis by a main-group element system. Crucially, the reagents used are cheap, readily available commercially, and easy to handle, making these reactions a realistic prospect in a wide range of academic and industrial settings.

Iodonium based regioselective double nucleophilic alkene functionalization of a hydrofluoroolefin scaffold

Herein, we report a modular regioselective alkene difunctionalization strategy based on the use of hydrofluoroolefin (HFO) gas as fluorous feedstock material. The transformation of the HFO gas to iodonium salt creates vicinal electrophilic sites readily available for a broad range of nucleophiles.

Electrochemical Fluorination Functionalization of gem-Difluoroalkenes with CsF as a Fluorine Source: Access to Fluoroalkyl Building Blocks

Using easily handled CsF as a fluorine source, an electrochemically metal-free protocol for chemo- and regioselective synthesis of various types of long-chain perfluoroalkyl aromatics with gem-difluoroalkene as a substrate and an alcohol or azole as an additional nucleophile was developed. The eletrochemical transformation could tolerate several functional groups, such as halogens, cyanos, benzyls, and heterocycles, and is amenable to gram-scale. The application of this electrochemical method in radiofluorination was also tested.

Why Nonheme Iron Halogenases Do Not Fluorinate C-H Bonds: A Computational Investigation

Selective halogenation is necessary for a range of fine chemical applications, including the development of therapeutic drugs. While synthetic processes to achieve C-H halogenation require harsh conditions, enzymes such as nonheme iron halogenases carry out some types of C-H halogenation, i.e., chlorination or bromination, with ease, while others, i.e., fluorination, have never been observed in natural or engineered nonheme iron enzymes. Using density functional theory and correlated wave function theory, we investigate the differences in structural and energetic preferences of the smaller fluoride and the larger chloride or bromide intermediates throughout the catalytic cycle. Although we find that the energetics of rate-limiting hydrogen atom transfer are not strongly impacted by fluoride substitution, the higher barriers observed during the radical rebound reaction for fluoride relative to chloride and bromide contribute to the difficulty of C-H fluorination. We also investigate the possibility of isomerization playing a role in differences in reaction selectivity, and our calculations reveal crucial differences in terms of isomer energetics of the key ferryl intermediate between fluoride and chloride/bromide intermediates. While formation of monodentate isomers believed to be involved in selective catalysis is shown for chloride and bromide intermediates, we find that formation of the fluoride monodentate intermediate is not possible in our calculations, which lack additional stabilizing interactions with the greater protein environment. Furthermore, the shorter Fe-F bonds are found to increase isomerization reaction barriers, suggesting that incorporation of residues that form a halogen bond with F and elongate Fe-F bonds could make selective C-H fluorination possible in nonheme iron halogenases. Our work highlights the differences between the fluoride and chloride/bromide intermediates and suggests potential steps toward engineering nonheme iron halogenases to enable selective C-H fluorination.

Synthetic Advantages of Defluorinative C-F Bond Functionalization

Much progress has been made in the development of methods to both create compounds that contain C-F bonds and to functionalize C-F bonds. As such, C-F bonds are becoming common and versatile synthetic functional handles. This review summarizes the advantages of defluorinative functionalization reactions for small molecule synthesis. The coverage is organized by the type of carbon framework the fluorine is attached to for mono- and polyfluorinated motifs. The main challenges, opportunities and advances of defluorinative functionalization are discussed for each class of organofluorine. Most of the text focuses on case studies that illustrate how defluorofunctionalization can improve routes to synthetic targets or how the properties of C-F bonds enable unique mechanisms and reactions. The broader goal is to showcase the opportunities for incorporating and exploiting C-F bonds in the design of synthetic routes, improvement of specific reactions and advent of new methods.

Nickel-Catalyzed Aminofluoroalkylative Cyclization of Styrenes with Ethyl Fluoroacetate and Anilines toward Fluoro-γ-Lactams

A novel method for the nickel-catalyzed multicomponent aminofluoroalkylation/cyclization of styrenes with ethyl fluoroacetate and anilines has been developed. This protocol provides general and efficient access to a diverse range of fluoro-γ-lactams from simple and readily available starting materials. Control experiments prove the involvement of radical intermediates and excluded the presence of 2-fluoro-N-phenylacetamide.

Access to Multifunctionalized Tetrasubstituted Carbon Centers Bearing up to Three Different Heteroatoms via Tandem Geminal Chlorofluorination of 1,2-Dicarbonyl Compounds

The incorporation of noncarbon heteroatoms into organic molecules typically instills characteristic and often valuable functionalities. The copresence of different heteroatoms can further broaden their utility through the synergistic cooperative effects, which may even lead to the discovery of formerly unavailable properties that are not just a simple accumulation of each function. However, despite increasing interest in the controllable installation of heteroatoms, it has been extremely challenging to construct carbon centers having three different heteroatoms in a synthetically useful manner. In this work, our group's tandem geminal chlorofluorination (Cl, F) strategy was applied to rationally designed heteroatom-bearing 1,2-dicarbonyl substrates, including α-keto thioesters (S), α-keto N-acylindoles (N), and α-keto acylsilane (Si), which resulted in the practical production of doubly or triply heterofunctionalized tetrasubstituted carbon centers with excellent site-selectivity.

Applications of Bioisosteres in the Design of Biologically Active Compounds

The design of bioisosteres represents a creative and productive approach to improve a molecule, including by enhancing potency, addressing pharmacokinetic challenges, reducing off-target liabilities, and productively modulating physicochemical properties. Bioisosterism is a principle exploited in the design of bioactive compounds of interest to both medicinal and agricultural chemists, and in this review, we provide a synopsis of applications where this kind of molecular editing has proved to be advantageous in molecule optimization. The examples selected for discussion focus on bioisosteres of carboxylic acids, applications of fluorine and fluorinated motifs in compound design, some applications of the sulfoximine functionality, the design of bioisosteres of drug-H2O complexes, and the design of bioisosteres of the phenyl ring.

Expanding the chemical space of enol silyl ethers: catalytic dicarbofunctionalization enabled by iron catalysis

Enol silyl ethers are versatile, robust, and readily accessible substrates widely used in chemical synthesis. However, the conventional reactivity of these motifs has been limited to classical two electron (2-e) enolate-type chemistry with electrophilic partners or as radical acceptors in one electron (1-e) reactivity leading, in both cases, to exclusive α-monofunctionalization of carbonyls. Herein we describe a mild, fast, and operationally simple one-step protocol that combines readily available fluoroalkyl halides, silyl enol ethers, and, for the first time, hetero(aryl) Grignard reagents to promote selective dicarbofunctionalization of enol silyl ethers. From a broader perspective, this work expands the synthetic utility of enol silyl ethers and establishes bisphosphine-iron catalysis as enabling technology capable of orchestrating selective C-C bond formations with short-lived α-silyloxy radicals with practical implications towards sustainable chemical synthesis.

Uranyl Polyoxotungstate Cluster for Visible-Light-Driven Heterogeneous C-H Selective Fluorination

The selective fluorination of C-H bonds at room temperature using heterogeneous visible-light catalysts is both interesting and challenging. Herein, we present the heterogeneous sandwich-type structure uranyl-polyoxotungstate cluster Na17{Na@[(SbW9O33)2(UO2)6(PO3OH)6]}·46H2O (denoted as U6P6) to regulate the selective fluorination of the C-H bond under visible light and room temperature. This is the first report in which uranyl participates in the fluorination reaction in the form of an insoluble substance. U6P6 is capable of the effective selective fluorination of cycloalkanes and the recyclability of the photocatalyst due to the synergistic effect of multiple uranyl (UO2)2+ and the insolubility of organic reagents of polyoxotungstate. In situ electron paramagnetic resonance spectroscopy captured the generation of cycloalkane radicals during the photoreaction, confirming the mechanism of direct hydrogen atom transfer.

Synthesis of Alkylated Polyfluorobenzenes through Decarboxylative Giese Addition of Aliphatic N-Hydroxyphthalimide Esters with Polyfluorostyrene

Polyfluoroaromatic compounds play crucial roles in medicinal and material science. However, the synthesis of alkylated polyfluoroarenes has been relatively underdeveloped. In this study, we devised a novel decarboxylative coupling reaction between aliphatic N-hydroxyphthalimide esters and polyfluorostyrene, leveraging the photochemical activity of electron donor-acceptor (EDA) complexes. This method offers simple reaction conditions, a broad substrate scope, and excellent functional group tolerance. Furthermore, we have demonstrated the practicality of this protocol through late-stage polyfluoroaryl modification of biologically active molecules using readily available carboxylic acids as starting materials, thus providing an important supplement to the current toolbox for accessing alkylated polyfluoroaryl motifs.

Activation of robust bonds by carbonyl complexes of Mn, Fe and Co

Metal carbonyl complexes possess among the most storied histories of any compound class in organometallic chemistry. Nonetheless, these old dogs continue to be taught new tricks. In this Feature, we review the historic discoveries and recent advances in cleaving robust bonds (e.g., C-H, C-O, C-F) using carbonyl complexes of three metals: Mn, Fe, and Co. The use of Mn, Fe, and Co carbonyl catalysts in controlling selectivity during hydrofunctionalization reactions is also discussed. The chemistry of these earth-abundant metals in the field of robust bond functionalization is particularly relevant in the context of sustainability. We expect that an up-to-date perspective on these seemingly simple organometallic species will emphasize the wellspring of reactivity that continues to be available for discovery.

The wide presence of fluorinated compounds in common chemical products and the environment: a review

The C-F bonds, due to their many unique features, have been incorporated into numerous compounds in countless products and applications. These fluorinated compounds eventually are disposed of and released into the environment through different pathways. In this review, we analyzed the occurrence of these fluorinated compounds in seven types of products (i.e., refrigerants/propellants, aqueous film-forming foam, cosmetics, food packaging, agrochemicals, pharmaceuticals, coating materials) and discussed their fate in the environment. This is followed by describing the quantity of fluorinated compounds from each source based on available data. Total on- and off-site disposal or other releases of 536 fluorinated compounds in 2021 were analyzed using the data sourced from the U.S. EPA Toxics Release Inventory (TRI). Among the chemicals examined, chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) were the primary contributors in terms of total mass. Upon examining the seven sources of fluorinated compounds, it became evident that additional contributors are also responsible for the presence of organofluorine compounds in the environment. Although various toxic degradation products of fluorinated compounds could form in the environment, trifluoroacetic acid (TFA) was specifically highlighted in this review given the fact that it is a common dead-end degradation product of > 1 million chemicals. This paper ended with a discussion of several questions raised from this study. The path forward was elaborated as well for the purpose of protecting the environment and human health.

A Strategic Synthesis of Fluoroethers via Ring-Opening Fluorinative Beckmann Fragmentation

An SN1-type fluorination method for monofluoroethers is developed. The key to this reaction is fluorinative C-C bond cleavage that is driven by oxygen-assisted Beckmann fragmentation. To enable this transformation, cyclic α-aryloxyoximes derived from 3-coumaranone and 1-indanones were investigated as substrates, using N,N-diethylaminosulfur trifluoride (DAST) as a dual-role reagent of an oxime activator and fluoride donor. This method features the synthesis of an underdeveloped chemical motif with simple and mild operating conditions.

Hypervalent Fluoro-iodane-Triggered Semipinacol Rearrangements: Synthesis of α-Fluoro Ketones

Hypervalent fluoro-λ3-iodanes have emerged as versatile reagents that provide unusual fluorination selectivities under mild reaction conditions. Here, we report on adding a semipinacol rearrangement, fluorination, and aryl migration cascade reaction of styrene derivatives. Thus, various cyclopentanones became accessible in up to 96% yield, all bearing tertiary C,F-carbon centers adjacent to the ketone group. Such fluorinated structural motifs are difficult to build with previously established methods. Preliminary experiments on enantioselective processes validated that asymmetric transformations are likewise feasible.

Fluoroalkylations and Fluoroalkenylations with Iodonium Salts

Synthesis and applications of fluoroalkyl and fluoroalkenyliodonium salts are summarized in this account article, focusing preferably to the reagents designed in our laboratory in the last decade. Among these reagents trifluoroethyl(aryl)iodonium salts have been used most frequently to build carbon-carbon and carbon-heteroatom bonds in simple nucleophilic substitutions and through transition metal catalyzed coupling reactions. Iodonium salts equipped with unsaturated fluorinated function showed diverse reactivity due to their electron deficient character, and these molecular motifs enable cycloadditions and nucleophilic additions to prepare fluorinated carbo- and heterocyclic molecules. Beyond the overview of existing transformations, with the presented collection, we aim to inspire future developments of iodonium reagents and their application in organic synthesis.

Visible Light-Induced Metal-Free Fluoroalkylations

Fluoroalkylation is a crucial synthetic process that enables the modification of molecules with fluoroalkyl groups, which can enhance the properties of compounds and have potential applications in medicine and materials science. The utilization of visible light-induced, metal-free methods is of particular importance as it provides an environmentally friendly alternative to traditional methods and eliminates the potential risks associated with metal-catalyst toxicity. This Account describes our studies on visible light-induced, metal-free fluoroalkylation processes, which include the use of organic photocatalysts or EDA complexes. We have utilized organophotocatalysts such as Nile red, tri(9-anthryl)borane, and an indole-based tetracyclic complex, as well as catalyst-free EDA chemistry through photoactive halogen bond formation or an unconventional transient ternary complex formation with nucleophilic fluoroalkyl source. A variety of π-systems including arenes/heteroarenes, alkenes, and alkynes have been successfully fluoroalkylated under the developed reaction conditions.

Practical Synthesis of Terminal Vinyl Fluorides

The synthesis of di- and trisubstituted vinyl fluorides with high isomeric purity remains a challenge for organic synthesis. While many methods exist to access these compounds, the separation of the desired isomer from the minor isomer and/or starting materials often is difficult. Herein, we report a practical method to access di- and trisubstituted vinyl fluorides via a selective Horner-Wadsworth-Emmons olefination/hydrolysis, which provides crystalline 2-fluoroacrylic acids in high (>98%) E-isomeric purity. A subsequent silver-catalyzed stereoretentive decarboxylation provides the title substances with high isomeric purity and without the need for tedious chromatography to remove the minor isomer. The process was amenable to a variety of aldehydes and ketones and provided a diverse array of di- and trisubstituted vinyl fluorides. The sequence was applied to the synthesis of antibacterial and anti-inflammatory compounds.

Fluorinated covalent-organic polymers as stationary phase for analysis of organic fluorides by open-tubular capillary electrochromatography

Fluorinated porous materials, which can provide specific fluorine-fluorine interaction, hold great promise for fluoride analysis. Here, a novel fluorinated covalent-organic polymer was prepared by using 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 2,3,5,6-tetrafluorotelephtal aldehyde as the precursors and introduced as stationary phase for open-tubular capillary electrochromatography. The as-synthesized fluorinated covalent-organic polymer and the modified capillary column were characterized by infrared spectroscopy, scanning electron microscopy, and energy dispersive X-ray spectrometry. Based on strong hydrophobic interaction and fluorine-fluorine interaction provided by fluorinated covalent-organic polymer coating layer, the modified column showed powerful separation selectivity toward hydrophobic compounds, organic fluorides, and fluorinated pesticides. Additionally, the fluorinated covalent-organic polymer with good porosity and regular shape was uniformly and tightly coated on the capillary inner wall. The obtained highest column efficiency could reach up to 1.2 × 105 plates⋅m-1 for fluorophenol. The loading capacity of the modified column can reach 141 pmol for trifluorotoluene. Besides, the relative standard deviations of retention times for intraday run (n = 5), interday run (n = 3), and between columns (n = 3) were all less than 2.55%. Significantly, this novel fluorinated material-based stationary phase shows great application potential in fluorides analysis.

Fluorocarbonylation via palladium/phosphine synergistic catalysis

Despite the growing importance of fluorinated organic compounds in pharmaceuticals, agrochemicals, and materials science, the introduction of fluorine into organic molecules is still a challenge, and no catalytic fluorocarbonylation of aryl/alkyl boron compounds has been reported to date. Herein, we present the development of palladium and phosphine synergistic redox catalysis of fluorocarbonylation of potassium aryl/alkyl trifluoroborate. Trifluoromethyl arylsulfonate (TFMS), which was used as a trifluoromethoxylation reagent, an easily handled and bench-scale reagent, has been employed as an efficient source of COF₂. The reaction operates under mild conditions with good to excellent yields and tolerates diverse complex scaffolds, which allows efficient late-stage fluorocarbonylation of marked small-molecule drugs. Mechanistically, the key intermediates of labile Brettphos-Pd(II)-OCF₃ complex and difluoro-Brettphos were synthesized and spectroscopically characterized, including X-ray crystallography. A detailed reaction mechanism involving the synergistic redox catalytic cycles Pd(II)/(0) and P(III)/(V) was proposed, and multifunction of phosphine ligand was identified based on ¹⁹F NMR, isotope tracing, synthetic, and computational studies.

Direct Fluoroacylation of Indole with Perfluoroalkyl Iodides

Functionalization of perfluoroalkyl compounds has shown huge potential in synthetic chemistry and drug development. Herein, we report a one-pot tandem perfluoroalkylation-defluorination reaction of indole, perfluoroalkyl iodide, and water in the presence of Na₂S₂O₄. A wide array of indole derivatives were efficiently accessed with good yields under mild reaction conditions. The reaction is believed to undergo perfluoroalkylation and follow the defluorination hydrolysis pathway. This study represents an alternative approach for defluorination functionalization.

Visible-Light Photoredox-Catalyzed Three-Component Reaction of Carbazoles with Alkenes and S-(Difluoromethyl)sulfonium Salt: A Practical Approach to Access Difluoroalkyl-Functionalized Carbazoles

A mild and elegant multicomponent protocol for construction of CF₂H-containing carbazoles was accomplished by visible-light photoredox catalysis with formation of two new C-C bonds in a single step to deliver a wide variety of structurally diverse difluoroalkylated carbazoles in moderate to good yields, featuring mild reaction conditions, synthetic simplicity, broad substrates, and good functional group tolerance.

Insecticidal and Repellent Properties of Rapid-Acting Fluorine-Containing Compounds against Aedes aegypti Mosquitoes

The development of safe and potent insecticides remains an integral part of a multifaceted strategy to effectively control human-disease-transmitting insect vectors. Incorporating fluorine can dramatically alter the physiochemical properties and bioavailability of insecticides. For example, 1,1,1-trichloro-2,2-bis(4-fluorophenyl)ethane (DFDT)─a difluoro congener of trichloro-2,2-bis(4-chlorophenyl)ethane (DDT)─was demonstrated previously to be 10-fold less toxic to mosquitoes than DDT in terms of LD50 values, but it exhibited a 4-fold faster knockdown. Described herein is the discovery of fluorine-containing 1-aryl-2,2,2-trichloro-ethan-1-ols (FTEs, for fluorophenyl-trichloromethyl-ethanols). FTEs, particularly per-fluorophenyl-trichloromethyl-ethanol (PFTE), exhibited rapid knockdown not only against Drosophila melanogaster but also against susceptible and resistant Aedes aegypti mosquitoes, major vectors of Dengue, Zika, yellow fever, and Chikungunya viruses. The R enantiomer of any chiral FTE, synthesized enantioselectively, exhibited faster knockdown than its corresponding S enantiomer. PFTE does not prolong the opening of mosquito sodium channels that are characteristic of the action of DDT and pyrethroid insecticides. In addition, pyrethroid/DDT-resistant Ae. aegypti strains having enhanced P450-mediated detoxification and/or carrying sodium channel mutations that confer knockdown resistance were not cross-resistant to PFTE. These results indicate a mechanism of PFTE insecticidal action distinct from that of pyrethroids or DDT. Furthermore, PFTE elicited spatial repellency at concentrations as low as 10 ppm in a hand-in-cage assay. PFTE and MFTE were found to possess low mammalian toxicity. These results suggest the substantial potential of FTEs as a new class of compounds for controlling insect vectors, including pyrethroid/DDT-resistant mosquitoes. Further investigations of FTE insecticidal and repellency mechanisms could provide important insights into how incorporation of fluorine influences the rapid lethality and mosquito sensing.

Vibronic and Cationic Features of 2-Fluorobenzonitrile and 3-Fluorobenzonitrile Studied by REMPI and MATI Spectroscopy and Franck-Condon Simulations

Fluorinated organic compounds have superior physicochemical properties than general organic compounds due to the strong C-F single bond; they are widely used in medicine, biology, pesticides, and materials science. In order to gain a deeper understanding of the physicochemical properties of fluorinated organic compounds, fluorinated aromatic compounds have been investigated by various spectroscopic techniques. 2-fluorobenzonitrile and 3-fluorobenzonitrile are important fine chemical intermediates and their excited state S₁ and cationic ground state D₀ vibrational features remain unknown. In this paper, we used two-color resonance two photon ionization (2-color REMPI) and mass analyzed threshold ionization (MATI) spectroscopy to study S₁ and D₀ state vibrational features of 2-fluorobenzonitrile and 3-fluorobenzonitrile. The precise excitation energy (band origin) and adiabatic ionization energy were determined to be 36,028 ± 2 cm^-1 and 78,650 ± 5 cm^-1 for 2-fluorobenzonitrile and 35,989 ± 2 cm^-1 and 78,873 ± 5 cm^-1 for 3-fluorobenzonitrile, respectively. The density functional theory (DFT) at the levels of RB3LYP/aug-cc-pvtz, TD-B3LYP/aug-cc-pvtz, and UB3LYP/aug-cc-pvtz were used to calculate the stable structures and vibrational frequencies for the ground state S₀, excited state S₁, and cationic ground state D₀, respectively. Franck-Condon spectral simulations for transitions of S₁ ← S₀ and D₀ ← S₁ were performed based on the above DFT calculations. The theoretical and experimental results were in good agreement. The observed vibrational features in S₁ and D₀ states were assigned according to the simulated spectra and the comparison with structurally similar molecules. Several experimental findings and molecular features were discussed in detail.

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.

Studying Regioisomer Formation in the Pd-Catalyzed Fluorination of Cyclic Vinyl Triflates: Evidence for in situ Ligand Modification

Pd-catalyzed nucleophilic fluorination reactions are important methods for the synthesis of fluoroarenes and fluoroalkenes. However, these reactions can generate a mixture of regioisomeric products that are often difficult to separate. While investigating the Pd-catalyzed fluorination of cyclic vinyl triflates, we observed that the addition of a substoichiometric quantity of TESCF3 significantly improved the regioselectivity of the reaction. Herein, we report a combined experimental and computational study on the mechanism of this transformation focusing on the role of TESCF3 . The poor regioselectivity of the reaction in the absence of additives results from the formation of LPd-cyclohexyne complexes (L=biaryl monophosphine ligand). When TESCF3 is added to the reaction mixture, the generation of the Pd-cyclohexyne complexes is diminished by an unexpected pathway involving the dearomatization of the ligand by nucleophilic attack from a trifluoromethyl anion (CF3 - ).

Cobalt-catalysed nucleophilic fluorination in organic carbonates

The novel P-N ligand 1-((diphenylphosphaneyl)methyl)-1H-benzo-1,2,3-triazole (1), based on a benzotriazole scaffold, has been prepared. The reaction of 1 with [CoCp*(CH₃CN)₃][BF₄]₂ and [CoCp*(I)₂]₂ (Cp* = pentamethylcyclopentadienyl) affords the chelate complexes [CoCp*(CH₃CN)(P-N)][BF₄]₂ (2) and [CoCp*(I)(P-N)]I (3), respectively. Complexes 2 and 3 were studied as catalysts in the fluorination of aromatic and aliphatic acyl chlorides in CH₂Cl₂, with 3 showing notably higher activities than 2. Subsequently, organic carbonates (dimethyl carbonate and propylene carbonate) were also employed as solvents, which led to shorter reaction times and to the broadening of the substrate scope to a variety of aliphatic halides. Comparative studies between 3 and the analogous complex [CoCp*(I)₂(PMePh₂)], which features a monodentate phosphane ligand, showed that higher yields were obtained in the case of the former. DFT calculations and experimental studies were performed in order to shed light on the reaction mechanism, which entails the formation of a cobalt fluoride species that reacts via nucleophilic attack with the substrate to afford the corresponding fluorinated compounds.

Synthesis of novel glycerol-fluorinated triazole derivatives and evaluation of their phytotoxic and cytogenotoxic activities

The control of weeds in agriculture is mainly conducted with the use of synthetic herbicides. However, environmental and human health concerns and increased resistance of weeds to existing herbicides have increased the pressure on researchers to find new active ingredients for weed control which present low toxicity to non-target organisms, are environmentally safe, and can be applied at low concentrations. It is herein described the synthesis of glycerol-fluorinated triazole derivatives and evaluation of their phytotoxic and cytogenotoxic activities. Starting from glycerol, ten fluorinated triazole derivatives were prepared in four steps. The assessment of them on Lactuca sativa revealed that they present effects on phytotoxic and cytogenotoxic parameters with different degrees of efficiency. The compounds 4a, 4b, 4d, 4e, 4i, and 4j have pre-emergent inhibition behavior, while all the investigated compounds showed post emergent effect. Mechanism of action as clastogenic, aneugenic, and epigenetic were observed in the lettuce root meristematic cells, with alterations as stick chromosome, bridge, delay, c-metaphase, and loss. It is believed that glycerol-fluorinated triazole derivatives possess a scaffold that can be explored towards the development of new chemicals for the control of weed species.

Electrochemical trifluoromethylation of 2-isocyanobiaryls using CF3SO2Na: synthesis of 6-(trifluoromethyl)phenanthridines

An efficient trifluoromethylation of 2-isocyanobiaryls was developed through the constant current electrolysis, employing sodium trifluoromethanesulfinate (CF₃SO₂Na) as the trifluoromethyl source. The method enabled the syntheses of a series of 6-(trifluoromethyl)phenanthridine derivatives in moderate to high yields under metal- and oxidant-free conditions. A gram-scale synthesis highlights the synthetic versatility of the reported protocol.

P-Stereogenic Ir-MaxPHOX: A Step toward Privileged Catalysts for Asymmetric Hydrogenation of Nonchelating Olefins

The Ir-MaxPHOX-type catalysts demonstrated high catalytic performance in the hydrogenation of a wide range of nonchelating olefins with different geometries, substitution patterns, and degrees of functionalization. These air-stable and readily available catalysts have been successfully applied in the asymmetric hydrogenation of di-, tri-, and tetrasubstituted olefins (ee's up to 99%). The combination of theoretical calculations and deuterium labeling experiments led to the uncovering of the factors responsible for the enantioselectivity observed in the reaction, allowing the rationalization of the most suitable substrates for these Ir-catalysts.