Current Contributions of Organofluorine Compounds to the Agrochemical Industry

Fluorinated benzoxazinones designed via MIA-QSAR, docking and molecular dynamics as protoporphyrinogen IX oxidase inhibitors

BACKGROUND

Fluorine plays a significant role in agrochemical science because approximately 25% of herbicides licensed worldwide contain this element. In a pool of previously synthesized benzoxazinones, some compounds contained fluorine and demonstrated inhibitory activities against protoporphyrinogen IX oxidase (PPO). Therefore, three data sets of benzoxazinone derivatives with known inhibitory activity against PPO were employed to build a multivariate image analysis applied to a quantitative structure-activity relationships (MIA-QSAR) model to identify improved analogs with at least one fluorine substituent.

RESULTS

The QSAR model was vigorously validated and demonstrated to be highly predictive (r2 = 0.85, q2 = 0.71, and r2 pred = 0.88); thus, the model can provide reliable estimations for the PPO inhibitory activity of unknown derivatives. From these compounds, a couple of N-substituted benzoxazinones that contained the -CH2CHF2 group were found with predicted pKi values larger than 8 (Ki in mol L-1) and higher lipophilicity than the most active data set compounds. In addition, we carried out a systematic investigation of the binding mode of PPO by performing computational docking followed by molecular dynamics simulations. The proposed binding mode was consistent with experimental studies, and several potential key residues were identified.

CONCLUSION

Two new proposed benzoxazinones exhibited better performance than compounds of the data set, and fluorine substituents played pivotal roles in describing the biological activities. © 2024 Society of Chemical Industry.

Recent developments in fluorine-containing pesticides

To ensure ongoing sustainability, the modern agrochemical industry is faced with enormous challenges. These arise from provision of high-quality food to increasing water use and environmental impact as well as a growing world population. The loss of previous agrochemicals due to consumer perception, changing grower needs and ever-changing regulatory requirements is higher than the number of active ingredients that are being introduced into the crop protection market. Therefore, the development of novel agrochemicals is essential to provide improved efficacy and environmental profiles. In this context, the introduction of fluorine atoms and fluorine-containing motifs into a molecule is an important method to influence its physicochemical properties. These include, for example, small difluoro- and trifluoromethyl, or trifluoromethoxy groups at aryl or heterocyclic aryl moieties but also fragments like 2,2,2-trifluoroethoxycarbonyl, trifluoromethylsulfonyl, trifluoroacetyl, as well as the so far unusal rest like heptafluoro-iso-propyl. This review gives an overview of recent developments of fluorine-containing pesticides launched over the past 7 years and describes a selection of current fluorine-containing development candidates. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Visible-Light-Induced Hydrodifluoromethylation of Unactivated Alkenes with Difluoroacetic Anhydride

We herein described a practical and efficient protocol for hydrodifluoromethylation of unactivated alkenes using readily available difluoroacetic anhydride as a difluoromethyl source by merging photocatalysis and N-hydroxyphthalimide activation. This method features a wide substrate scope and excellent compatibility with various functional groups, as demonstrated by more than 50 examples, including bioactive molecules and pharmaceutical derivatives. Mechanism investigation indicated that N-hydroxyphthalimide may also serve as the hydrogen atom donor.

Selective Defluorination of Trifluoromethyl Substituents by Conformationally Induced Remote Substitution

The selective reduction of an aromatic trifluoromethyl substituent to a difluoromethyl substituent may be achieved by base-promoted elimination to form a difluoro-p-quinomethide which is trapped by an intramolecular nucleophile. High yields are obtained when the nucleophilic trap entails the conformationally favoured cyclisation of an aminoisobutyric acid (Aib) derivative. The resulting cyclised difluoromethyl-substituted arylimidazolidinone products are readily converted to versatile difluoromethyl-substituted aldehydes by reduction and hydrolysis. Defluorination is successful on a range of benzenoid (both para and ortho CF3-substituted) and heterocyclic substrates. Double defluorination may likewise be achieved sequentially, or in a single step, from an Aib dipeptide derivative.

Copper-Mediated Cyanodifluoromethylation of (Hetero)aryl Iodides and Activated (Hetero)aryl Bromides with TMSCF2CN

Molecules bearing fluorine are increasingly prevalent in pharmaceuticals, agrochemicals, and functional materials. The cyanodifluoromethyl group is unique because its size is closer than that of any other substituted difluoromethyl group to the size of the trifluoromethyl group, but its electronic properties are distinct from those of the trifluoromethyl group. In addition, the presence of the cyano group provides synthetic entry to a wide range of substituted difluoromethyl groups. However, the synthesis of cyanodifluoromethyl compounds requires multiple steps, highly reactive reagents (such as DAST, NSFI, or IF5), or specialized starting materials (such as α,α-dichloroacetonitriles or α-mercaptoacetonitriles). Herein, we report a copper-mediated cyanodifluoromethylation of aryl and heteroaryl iodides and activated aryl and heteroaryl bromides with TMSCF2CN. This cyanodifluoromethylation tolerates an array of functional groups, is applicable to late-stage functionalization of complex molecules, yields analogues of FDA-approved pharmaceuticals and fine chemicals, and enables the synthesis of a range of complex molecules bearing a difluoromethylene unit by transformations of the electron-poor CN unit. Calculations of selected steps of the reaction mechanism by Density Functional Theory indicate that the barriers for both the oxidative addition of iodobenzene to [(DMF)CuCF2CN] and the reductive elimination of the fluoroalkyl product from the fluoroalkyl copper intermediate lie in between those of [(DMF)CuCF3] and [(DMF)CuCF2C(O)NMe2].

Exploring long-range fluorine-carbon J-coupling for conformational analysis of deoxyfluorinated disaccharides: A combined computational and NMR study

In this study, we investigated the potential of long-range fluorine-carbon J-coupling for determining the structures of deoxyfluorinated disaccharides. Three disaccharides, previously synthesized as potential galectin inhibitors, exhibited through-space fluorine-carbon J-couplings. In our independent conformational analysis of these disaccharide derivatives, we employed a combination of density functional theory (DFT) calculations and nuclear magnetic resonance (NMR) experiments. By comparing the calculated nuclear shieldings with the experimental carbon chemical shifts, we were able to identify the most probable conformers for each compound. A model comprising fluoromethane and methane molecules was used to study the relationship between molecular arrangements and intermolecular through-space J-coupling. Our study demonstrates the important effect of internuclear distance and molecular orientation on the magnitude of fluorine-carbon coupling. The experimental values for the fluorine-carbon through-space couplings (TSCs) of the disaccharides corresponded with values calculated for the most probable conformers identified by the conformational analysis. These results unlock the broader application of fluorine-carbon TSCs as powerful tools for conformational analysis of flexible molecules, offering valuable insights for future structural investigations.

Why •CF2H is nucleophilic but •CF3 is electrophilic in reactions with heterocycles

Radical substitution is a useful method to functionalize heterocycles, as in the venerable Minisci reaction. Empirically observed regiochemistries indicate that the CF2H radical has a nucleophilic character similar to alkyl radicals, but the CF3 radical is electrophilic. While the difference between •CH3 and •CF3 is well understood, the reason that one and two Fs make little difference but the third has a large effect is puzzling. DFT calculations with M06-2X both reproduce experimental selectivities and also lead to an explanation of this difference. Theoretical methods reveal how the F inductive withdrawal and conjugative donation alter radical properties, but only CF3 becomes decidedly electrophilic toward heterocycles. Here, we show a simple model to explain the radical orbital energy trends and resulting nucleophilicity or electrophilicity of fluorinated radicals.

The link between ancient microbial fluoride resistance mechanisms and bioengineering organofluorine degradation or synthesis

Fluorinated organic chemicals, such as per- and polyfluorinated alkyl substances (PFAS) and fluorinated pesticides, are both broadly useful and unusually long-lived. To combat problems related to the accumulation of these compounds, microbial PFAS and organofluorine degradation and biosynthesis of less-fluorinated replacement chemicals are under intense study. Both efforts are undermined by the substantial toxicity of fluoride, an anion that powerfully inhibits metabolism. Microorganisms have contended with environmental mineral fluoride over evolutionary time, evolving a suite of detoxification mechanisms. In this perspective, we synthesize emerging ideas on microbial defluorination/fluorination and fluoride resistance mechanisms and identify best approaches for bioengineering new approaches for degrading and making organofluorine compounds.

Controllable Synthesis of Cyclopenta[b]indolines via Photocatalytic Fluoroalkylative Radical Cyclization Cascade of Ynamides

A de novo method for direct construction of cyclopenta[b]indolines via a photocatalytic fluoroalkylative radical cyclization cascade of ynamides has been established, which proceeds via a sequence of radical addition, 1,5-HAT, 5-endo-trig cyclization, intramolecular arylation, and oxidative deprotonation. This protocol allows for the controllable assembly of a tricyclic architecture with three contiguous stereocenters, showcasing its high efficiency, compatibility, and regio- and diastereoselectivity for accessing pharmacologically significant fluoroalkylated cyclopenta[b]indolines. It represents one of the very few examples of tetrafunctionalization of alkynes.

Photoinduced metal-free trifluoro/perfluoroalkylation of heteroarenes

A practical and straightforward protocol to access trifluoromethylated/perfluoroalkylated heteroarenes via radical-type nucleophilic substitution rather than typical radical-type electrophilic substitution is described here. The substrate scope was observed to be broad and diverse-covering arenes, heteroarenes (containing N, O, S), bioactive cores, and allylic cores. Mechanistic studies confirmed a radical-mediated reaction pathway.

Synthesis of Fluorinated Nucleosides/Nucleotides and Their Antiviral Properties

The FDA has approved several drugs based on the fluorinated nucleoside pharmacophore, and numerous drugs are currently in clinical trials. Fluorine-containing nucleos(t)ides offer significant antiviral and anticancer activity. The insertion of a fluorine atom, either in the base or sugar of nucleos(t)ides, alters its electronic and steric parameters and transforms the lipophilicity, pharmacodynamic, and pharmacokinetic properties of these moieties. The fluorine atom restricts the oxidative metabolism of drugs and provides enzymatic metabolic stability towards the glycosidic bond of the nucleos(t)ide. The incorporation of fluorine also demonstrates additional hydrogen bonding interactions in receptors with enhanced biological profiles. The present article discusses the synthetic methodology and antiviral activities of FDA-approved drugs and ongoing fluoro-containing nucleos(t)ide drug candidates in clinical trials.

10-Phenylphenothiazine-Organophotocatalyzed Bromo-Perfluoroalkylation of Unactivated Olefins

In this study, we have developed a smooth metal-free visible-light-induced bromo-perfluoroalkylation of unactivated olefins with the aid of 10-phenylphenothiazine (PTH) as an organic photoredox catalyst. The reaction is 100% atom-economic redox-neutral and proceeds with stoichiometric amounts of olefin and perfluoroalkyl bromide. To show the potential of these unexplored motifs, we carried out various postfunctionalizations taking advantage of the bromine atom, including gram-scale experiments.

Changes in Metabolism and Content of Chlorophyll in Common Duckweed (Lemna minor L.) Caused by Environmental Contamination with Fluorides

The impact of fluorine on plants remains poorly understood. We examined duckweed growth in extracts of soil contaminated with fluorine leached from chicken manure. Additionally, fluorine levels were analyzed in fresh manure, outdoor-stored manure, and soil samples at varying distances from the manure pile. Fresh manure contained 37-48 mg F- × kg-1, while soil extracts contained 2.1 to 4.9 mg F- × kg-1. We evaluated the physiological effects of fluorine on duckweed cultured on soil extracts or in 50% Murashige-Skoog (MS) medium supplemented with fluorine concentrations matching those in soil samples (2.1 to 4.9 mg F- × L-1), as well as at 0, 4, and 210 mg × L-1. Duckweed exposed to fluorine displayed similar toxicity symptoms whether in soil extracts or supplemented medium. Fluoride at concentrations of 2.1 to 4.9 mg F- × L-1 reduced the intact chlorophyll content, binding the porphyrin ring at position 32 without affecting Mg2+. This reaction resulted in chlorophyll a absorption peak shifted towards shorter wavelengths and formation of a new band of the F--chlorophyll a complex at λ = 421 nm. Moreover, plants exposed to low concentrations of fluorine exhibited increased activities of aminolevulinic acid dehydratase and chlorophyllase, whereas the activities of both enzymes sharply declined when the fluoride concentration exceeded 4.9 mg × L-1. Consequently, fluorine damages chlorophyll a, disrupts the activity of chlorophyll-metabolizing enzymes, and diminishes the plant growth rate, even when the effects of these disruptions are too subtle to be discerned by the naked human eye.

Binary Organic Solar Cells with Exceeding 19% Efficiency via the Synergy of Polyfluoride Polymer and Fluorous Solvent

Rational molecular design and suitable device engineering are two important strategies to boost the efficiencies in organic solar cells (OSCs). Yet these two approaches are independently developed, while their synergy is believed to be more productive. Herein, a branched polyfluoride moiety, heptafluoroisopropoxyl group, is introduced into the side chains of conjugated polymers for the first time. Compared with the conventional alkyl chain, this polyfluoride chain can endow the resulting polymer namely PF7 with highly packing order and strong crystallinity owing to the strong polarization and fluorine-induced interactions, while good solubility and moderate miscibility are retained. As a result, PF7 comprehensively outperforms the state-of-the-art polymer PM6 in photovoltaic properties. More importantly, based on the solubility of heptafluoroisopropoxyl groups in fluorous solvents, a new post-treatment denoted as fluorous solvent vapor annealing (FSVA) is proposed to match PF7. Differing from the existing post-treatments, FSVA can selectively reorganize fluoropolymer molecules but less impact small molecules in blend films. By employing the synergy of fluoropolymer and fluorous solvent, the device achieves a remarkable efficiency of 19.09%, which is among the best efficiencies in binary OSCs. The polymer PF7 and the FSVA treatment exhibit excellent universality in various OSCs with different material combinations or device architectures.

Pd-Catalyzed Direct C7 Trifluoromethylation of Indolines with Umemoto's Reagent

An efficient palladium-catalyzed region-selective C7-trifluoromethylation of indolines using commercially available Umemoto's reagent was reported. The reaction utilizing Umemoto's reagent as CF3 radical precursor, pyrimidine as a removable directing group, Pd(II) as a catalyst, and Cu(II) as an oxidant furnished the required products with excellent regioselectivities and good yields. The present strategy has good region-selectivity, broad substrate scope, and scale-up application. Additionally, the present method was underlined by the direct C-1 trifluoromethylation of carbazoles. Furthermore, C7 trifluoromethylated indole can also be easily obtained via Pd-catalyzed direct C-7 trifluoromethylation/oxidation/deprotection sequential reactions.

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.

N-Heteroaromatic Fluoroalkylation through Ligand Coupling Reaction of Sulfones

Ligand coupling on hypervalent main group elements has emerged as a pivotal methodology for the synthesis of functionalized N-heteroaromatic compounds in recent years due to the avoidance of transition metals and the mildness of the reaction conditions. In this direction, the reaction of N-heteroaryl sulfur(IV) and N-heteroaryl phosphorus(V) compounds has been well studied. However, the ligand coupling of sulfur(VI) is still underdeveloped and the reaction of alkyl N-heteroarylsulfones is still elusive, which does not match the high status of sulfones as the chemical chameleons in organic synthesis. Here we present a ligand coupling-enabled formal SO2 extrusion of fluoroalkyl 2-azaheteroarylsulfones under the promotion of Grignard reagents, which not only enriches the chemistry of sulfones, but also provides a novel and practical synthetic tool towards N-heteroaromatic fluoroalkylation.

Stereoselective Nucleophilic Halogenation at CF3-Substituted Nonclassical Carbocation

CF3-substituted cyclopropyl carbinol derivatives undergo regioselective and diastereoselective nucleophilic halogenation at the quaternary carbon center to provide acyclic products as a single diastereomer. The selectivity of the substitution is rationalized by the formation of a nonclassical cyclopropylcarbinyl cation intermediate, reacting at the most-substituted carbon center. Tertiary alkyl chlorides, bromides, and fluorides adjacent to a stereogenic C-CF3-motif are diastereomerically pure and can be obtained in few catalytic steps from commercially available alkynes.

First-Principles Study of Adsorption of CH4 on a Fluorinated Model NiF2 Surface

Electrochemical fluorination on nickel anodes, also known as the Simons' process, is an important fluorination method used on an industrial scale. Despite its success, the mechanism is still under debate. One of the proposed mechanisms involves higher valent nickel species formed on an anode acting as effective fluorinating agents. Here we report the first attempt to study fluorination by means of first principles investigation. We have identified a possible surface model from the simplest binary nickel fluoride (NiF2). A twice oxidized NiF2(F2) (001) surface exhibits higher valent nickel centers and a fluorination source that can be best characterized as an [F2]- like unit, readily available to aid fluorination. We have studied the adsorption of CH4 and the co-adsorption of CH4 and HF on this surface by means of periodic density functional theory. By the adsorption of CH4, we found two main outcomes on the surface. Unreactive physisorption of CH4 and dissociative chemisorption resulting in the formation of CH3F and HF. The co-adsorption with the HF gave rise to four main outcomes, namely the formation of CH3F, CH2F2, CH3 radical, and also physisorbed CH4.

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.

Zinc 1,1,2,2-Tetrafluoroethanesulfinate: A Synthetically Useful Oxidative and Photoredox Source of the 1,1,2,2-Tetrafluoroethyl Radical

1,1,2,2-Tetrafluoroethyl-containing molecules are of potential importance in drug discovery, but the efficient synthesis of such compounds is still relatively unexplored due to the lack of readily available reagents for the incorporation of the HCF2CF2 group. Herein, we introduce a new reagent, zinc 1,1,2,2-tetrafluoroethanesulfinate, which can be useful for the oxidative tetrafluoroethylation of arylboronic acids and heteroarenes as well as for a novel photoredox, three component hydro-tetrafluoroethylation of two alkenes of complementary reactivity.

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.

eFluorination of Activated Alcohols Using Collidinium Tetrafluoroborate

Tertiary C-F bonds are important structural designs; however, they suffer from challenging synthesis. Current methodologies use corrosive amine-HF salts or expensive and hazardous catalysts and reagents. Our group recently introduced collidinium tetrafluoroborate as an efficient fluorinating agent for anodic decarboxyfluorination reactions. Nevertheless, tertiary carboxylic acids are less readily available and more challenging to prepare than their alcohol analogues. Herein we report a practical, mild, and cheap electrochemical method to achieve deoxyfluorination of hindered carbon centers.

Cobalt(III) Halide Metal-Organic Frameworks Drive Catalytic Halogen Exchange

The selective halogenation of complex (hetero)aromatic systems is a critical yet challenging transformation that is relevant to medicinal chemistry, agriculture, and biomedical imaging. However, current methods are limited by toxic reagents, expensive homogeneous second- and third-row transition metal catalysts, or poor substrate tolerance. Herein, we demonstrate that porous metal-organic frameworks (MOFs) containing terminal Co(III) halide sites represent a rare and general class of heterogeneous catalysts for the controlled installation of chlorine and fluorine centers into electron-deficient (hetero)aryl bromides using simple metal halide salts. Mechanistic studies support that these halogen exchange (halex) reactions proceed via redox-neutral nucleophilic aromatic substitution (SNAr) at the Co(III) sites. The MOF-based halex catalysts are recyclable, enable green halogenation with minimal waste generation, and facilitate halex in a continuous flow. Our findings represent the first example of SNAr catalysis using MOFs, expanding the lexicon of synthetic transformations enabled by these materials.

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.

Synthesis of difluoromethylated spiropyrazolones via [3 + 2] cycloaddition of difluoroacetohydrazonoyl bromides with alkylidene pyrazolones

An effective [3 + 2] cycloaddition reaction of difluoromethyl or trifluoromethyl hydrazonoyl bromides with alkylidene pyrazolones was disclosed. This method provides an efficient approach for accessing a variety of highly functionalized fluoroalkyl spiropyrazolones in good yields. This protocol also features some advantages such as easily available and stable substrates, simple operation procedures, and atom and step economy. The formation of (cis)- and (trans)-products was discussed.

Cross-coupling of organic fluorides with allenes: a silyl-radical-relay pathway for the construction of α-alkynyl-substituted all-carbon quaternary centres

Controlling the transformation of versatile and reactive allenes is a considerable challenge. Herein, we report an efficient silylboronate-mediated cross-coupling reaction of organic fluorides with allenes to construct a series of sterically demanding α-ethynyl-containing all-carbon quaternary centers (ACQCs), using catalyst-free silyl-radical-relay reactions to selectively functionalize highly inert C-F bonds in organic fluorides. The key to the success of this transformation lies in the radical rearrangement of an in situ-generated allenyl radical to form a bulky tertiary propargyl radical; however, the transformation does not show efficiency when using the propargyl isomer directly. This unique reaction enables the cross-coupling of a tertiary carbon radical center with a C(sp2)-F bond or a benzylic C(sp3)-F bond. α-Ethynyl-containing ACQCs with (hetero)aromatic substituents and benzyl were efficiently synthesized in a single step using electronically and sterically diverse organic fluorides and allenes. The practical utility of this protocol is showcased by the late-stage functionalization of bioactive molecules and the modification of a liquid crystalline material.

Palladium-catalysed aryl/monofluoroalkylation of allenamides: access to fluoroalkyl indoles and isoquinolones

A palladium catalysed construction of fluoroalkyl indoles and isoquinolones through aryl/monofluoroalkylation of allenamides has been developed. Monofluoromethyl-substituted heterocycles could be accessed under mild conditions with broad functional group tolerance. In addition, indole-oxindole bisheterocyclic scaffolds bearing a fluorine atom were successfully synthesized with 3-fluoro-oxindole as the nucleophile by applying this method.

Influence of conditioner and straw on the herbaceous plant-based phytoremediation copper tailings: a field trial at Liujiagou tailings pond, China

A field trial was performed to carry out an enhanced phytoremediation technique for multi-metal contaminated copper tailings by Sudan grass (Sorghum Sudanese), ryegrass (Lolium perenne L.), and Bermuda grass (Cynodon dactylon), using conditioner (TH-LZ01) and straw combination into composite amendments as soil amendments, aimed to obtain the maximum of phytoremediation effect. The results showed that compared with untreated herbaceous plants, the application of conditioner and straw planted with herbaceous plants reduced the pH and conductivity and increased the organic matter and water content of the copper tailings to different degrees. With the addition of conditioner and straw, the DTPA-Cd, DTPA-Cu, DTPA-Pb, and DTPA-Zn contents in the copper tailings showed a decreasing trend compared with the untreated group. The herbaceous plants were promoted to reduce the percentage contents of acid soluble fractions Cd, Cu, Pb, and Zn and to increase the percentage contents of reducible, oxidizable, and residual fractions heavy metals (Cd, Cu, Pb, and Zn) in the copper tailings to different degrees. The contents of Cd, Cu, Pb, and Zn in the underground part of herbaceous plants were higher than those in the aboveground part, and the contents of Cd, Cu, Pb, and Zn in the aboveground part and underground part decreased after adding conditioner and straw, which indicated that the conditioner and straw inhibited the transport of heavy metals in the plant. Furthermore, the principal component analysis showed that the application of conditioner and straw with planting ryegrass had more potential for improving the physicochemical properties of copper tailings and reducing heavy metal toxicity, followed by Bermuda grass and Sudan grass.

FluoroFusion: NHC-Catalyzed Nucleophilic Aromatic Substitution Reaction Unveils Functional Perfluorinated Diarylmethanones

A mild, facile, and metal-free approach via the N-heterocyclic carbene-catalyzed SNAr reaction between aryl aldehydes with perfluoroarenes to obtain the coveted functional perfluorinated diarylmethanones is disclosed. This method accommodates a diverse substrate range and exhibits notable tolerance toward various functional groups. Our success in modifying biologically relevant molecules, crafting a fully fluorinated bioisosteric analogue of drug candidate D1, and highlighting the potential of these ketones as valuable electrolyte additives for lithium-ion batteries (LIBs) underscores the versatility of our methodology.

Silver-Catalyzed Decarboxylative Remote Fluorination via a Zwitterion-Promoted 1,4-Heteroaryl Migration

A silver-catalyzed decarboxylative remote fluorination via a zwitterion-promoted 1,4-heteroaryl migration has been developed. A variety of heteroaryl-tethered benzyl fluorides have been readily synthesized with good regioselectivity under mild conditions. The zwitterion of the substrate is suggested to accelerate the 1,4-heteroaryl migration, which determines the regioselectivity of this transformation.

Synthetic Utilization of 2H-Heptafluoropropane: Ionic 1,4-Addition to Electron-Deficient Carbon-Carbon Unsaturated Bonds

We have found a novel method for introducing heptafluoro-2-propyl CF(CF3)2 groups into carbon-carbon unsaturated bonds via a nucleophilic reaction using 2H-heptafluoropropane as the source of CF(CF3)2 groups. The reaction involves the nucleophilic addition of a heptafluoro-2-propyl anion, generated by treating 2H-heptafluoropropane with a fluoride ion, to various electron-deficient unsaturated compounds. This allows the easy synthesis of various aliphatic compounds containing heptafluoro-2-propyl groups.

Organo-Photoredox Catalyzed gem-Difluoroallylation of Glycine and Glycine Residue in Peptides

An organo-photoredox catalyzed gem-difluoroallylation of glycine with α-trifluoromethyl alkenes via direct C(sp3)-H functionalization of glycine and C-F bond activation of α-trifluoromethyl alkenes has been described. As a consequence, a broad range of gem-difluoroalkene-containing unnatural amino acids are afforded in moderate to excellent yields. This reaction exhibits multiple merits such as readily available starting materials, broad substrate scope, and mild reaction conditions. The feasibility of this reaction has been highlighted by the late-stage modification of several peptides as well as the improved in vitro antifungal activity of compound 3v toward Valsa mali compared to that with commercial azoxystrobin.

Multi-substituted trifluoromethyl alkene construction via gold-catalyzed fluoroarylation of gem-difluoroallenes

An unprecedented fluoroarylation of 1,1-difluoroallenes with a cost-effective nucleophilic fluoride reagent and aryldiazonium salts is reported. This visible light promoted gold-catalyzed reaction allows a stereo- and regioselective incorporation of both the fluorine atom and aryl group, enabling a straightforward construction of multi-substituted trifluoromethyl alkenes. Under the mild reaction conditions, a nice tolerance of diverse functional groups is achieved. The high regioselectivity for fluorine-incorporation is rationalized by considering the thermodynamic driving force of trifluoromethyl group formation, whereas the counterintuitive stereoselectivity that aryl is installed on the side of the bulkier γ-substituent is interpreted by alleviating the increasing 1,3-allylic interaction in the gold-coordinated allene intermediate en route to the product.

A Journey of the Development of Privileged Difluorocarbene Reagents TMSCF2X (X = Br, F, Cl) for Organic Synthesis

ConspectusAs fluorine has played an increasingly important role in modulating the physical, chemical, and biological properties of organic molecules, the selective introduction of fluorine atom(s) or fluorinated moieties into target molecules has become a powerful tool in the development of new pharmaceuticals, agrochemicals, and functional materials. In this context, the difluoromethylene (CF2) and difluoromethyl (CF2H) groups are of special interest because of their ability to serve as bioisosteres of ethereal oxygen atoms and hydroxyl (OH) and thiol (SH) groups, respectively. Difluorocarbene is one of the most versatile reactive intermediates to incorporate CF2 and CF2H groups; however, before 2006, most of the previously known difluorocarbene reagents suffered from several drawbacks such as using ozone-depleting substances (ODSs), difficult-to-handle reagents, or harsh reaction conditions or having narrow substrate scope and/or low yields. Moreover, the reactivity of difluorocarbene generated from different precursors (reagents) was often unpredictable, since the difluorocarbene generation conditions (activation modes) of various difluorocarbene precursors are different, and these conditions may mismatch those required for subsequent difluorocarbene-involved transformations. Therefore, the development of new environmentally friendly and versatile difluorocarbene reagents, as well as the investigation of the mechanistic insights into difluorocarbene-involved reactions, has been highly desirable.In this Account, we summarize our contributions to the development of new difluorocarbene reagents and their applications in organic synthesis since 2006. We have developed seven new difluorocarbene reagents, including 2-chloro-2,2-difluoroacetophenone (1), chlorodifluoromethyl phenyl sulfone (2), S-difluoromethyl-S-phenyl-N-tosylsulfoximine (3), difluoromethyltri(n-butyl)ammonium chloride (4), (chlorodifluoromethyl)trimethylsilane (TMSCF2Cl, 5), (bromodifluoromethyl)trimethylsilane (TMSCF2Br, 6), and (trifluoromethyl)trimethylsilane (TMSCF3, 7). In this journey, we realized the key factor for an ideal difluorocarbene reagent that can be used for a broad range of reactions, that is, the reagent should allow various activation modes for the generation of difluorocarbene species, such as under basic/acidic/neutral conditions, at wide range of temperatures, and in different solvents, which are compatible with a wide range of difluorocarbene-involved transformations. Among all known difluorocarbene reagents, silanes TMSCF2X (X = Br, F, Cl) have stood out as privileged ones, which paves a new avenue for further developing difluorocarbene chemistry. In particular, TMSCF2Br was recognized as an "all-rounder": TMSCF2Br can be applied in almost all common difluorocarbene-involved reactions, and more importantly, TMSCF2Br also enables many other novel transformations that other difluorocarbene reagents cannot achieve, thanks to its unique structure and rich activation modes of releasing difluorocarbene under different reaction conditions. It can be expected that with the commercial availability of TMSCF2X reagents (X = Br, F, Cl) now, the development of difluorocarbene chemistry will be accelerated in the years to come.

Transition-Metal-Free Approach for Z-Vinyl Fluorides by Hydrofluorination of Alkynes bearing SF4 and SF5 Groups

The synthesis of vinyl fluorides plays a crucial role in various scientific disciplines, including pharmaceutical and materials sciences. Herein, we present a direct and stereoselective hydrofluorination method for the synthesis of Z isomers of vinyl fluorides from alkynes containing unexplored SF5 and SF4 groups. Our strategy employed tetrabutylammonium fluoride (TBAF) as a fluorine source. It demonstrates high compatibility with aryls, biaryls, heteroaryls, and tert-alkyl groups, allowing facile incorporation of SF5 and SF4 groups across the triple bond without any transition-metal catalysts. This approach avoids the potential decomposition of the SF5 or SF4 units via coordination with transition metals or acidic protic sources. Remarkably, this transformation proceeded at room temperature without any additional additives, providing the Z isomer of vinyl fluorides in excellent yield and high selectivity. The presence of a water molecule as a hydrate in TBAF is essential for efficient conversion. This methodology opens new avenues for the synthesis of enchanting SF5 - and SF4 -containing fluorinated vinylic scaffolds, thereby providing advanced opportunities for novel drug discovery and fluorinated polymers.

Expanding the Frontier of Linear Drug Design: Cu-Catalyzed Csp -Csp 3 -Coupling of Electron-Deficient SF4 -Alkynes with Alkyl Iodides

Despite the attractive properties of tetrafluorosulfanyl (SF4 ) compounds in drug discovery, medicinal research on SF4 molecules is hindered by the scarcity of suitable synthetic methodologies. Drawing inspiration from the well-established Sonogashira cross-coupling of terminal alkynes under Pd-catalysis, it is envisioned that SF4 -alkynes can serve as effective coupling partners. To overcome the challenges associated with the electron-deficient nature of SF4 -alkynes and the lability of the SF4 unit under transition-metal catalysis, an aryl radical mediated Csp -Csp 3 cross-coupling reaction is successfully developed under Cu catalysis. This methodology facilitates the coupling of SF4 -alkynes with alkyl iodides, leading to the immediate synthesis of SF4 -attached drug-like molecules. These findings highlight the potential impact of SF4 -containing molecules in the drug industry, paving the way for further research in this emerging field.

Asymmetric Fluorocyclization of Difluoroalkenes with Concomitant Formation of a Trifluoromethyl Group

Asymmetric electrophilic fluorination of difluoroalkenes remains undeveloped because of the poor reactivity of difluoroalkenes with electrophiles. However, such reactions, if feasible, are expected to be useful for the synthesis of chiral heterocyclic compounds with a trifluoromethyl group at the stereogenic center. In this Letter, we disclose the first example of asymmetric fluoroamide cyclization of difluoroalkenes using our dianionic phase-transfer catalyst. This reaction provides unique chiral trifluoromethylated oxazoline derivatives at a synthetically useful level.

Cross Dehydrogenative Coupling of SF4-Alkyne with Tetrahydroisoquinolines

This study introduces a dual-catalytic method for cross-dehydrogenative coupling (CDC) between tetrahydroisoquinolines and Py-SF4-alkyne using visible-light photoredox catalysis. This protocol enables selective C(sp3)-H alkynylation, expanding the synthetic toolkit for SF4-based molecules. Demonstrating efficiency and substrate versatility, this approach opens new avenues in hexacoordinated tetrafluorinated sulfur chemistry and CDC strategies and holds significant promise for drug discovery and materials science.

Late-stage gem-difluoroallylation of phenol in bioactive molecules and peptides with 3,3-difluoroallyl sulfonium salts

An efficient method for the late-stage selective O-fluoroalkylation of tyrosine residues with a stable yet highly reactive fluoroalkylating reagent, 3,3-difluoroallyl sulfonium salts (DFASs), has been developed. The reaction proceeds in a mild basic aqueous buffer (pH = 11.6) with high efficiency, high biocompatibility, and excellent regio- and chemoselectivity. Various oligopeptides and phenol-containing bioactive molecules, including carbohydrates and nucleosides, could be selectively O-fluoroalkylated. The added vinyl and other functional groups from DFASs can be valuable linkers for successive modification, significantly expanding the chemical space for further bioconjugation. The synthetic utility of this protocol has been demonstrated by the fluorescently labeled anti-cancer drug and the synthesis of O-link type 1,4,7,10-tetraazacyclododecane-N,N',N,N'-tetraacetic acid-tyrosine3-octreotate (DOTA-TATE), showing the prospect of the method in medicinal chemistry and chemical biology.

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

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

Comprehensive evaluation of chiral sedaxane with four stereoisomers for risk reduction: Bioactivity, toxicity, and stereoselective dissipation in crop planting systems

A comprehensive evaluation of chiral pesticide at the stereoisomeric level is an effective strategy to improve efficiency and reduce risk on foods. For chiral sedaxane with four stereoisomers, there were 517-1013 fold differences in bioactivity for three kinds of phytopathogens and 3.73 fold differences in toxicity against model organism (Danio rerio) between the best (trans-1R2S-sedaxane) and worst stereoisomer (cis-1S2S-sedaxane). Trans-1R2S-sedaxane had the strongest affinity with the active site than other stereoisomers, which might contribute to the highest bioactivity. Trans-sedaxane was 28.2-331 fold more effective than cis-sedaxane. The dissipation half-lives of sedaxane stereoisomers ranged from 3.28 to 30.7 d in the test crops and soils. Trans-1S2R-sedaxane and cis-1S2S-sedaxane were preferentially dissipated in corn plants, while the preferential dissipation of trans-1R2S-sedaxane was found in wheat plants, potato plants and corn soil. The preferential dissipation of trans-sedaxane in corn plants, wheat plants, potato plants and corn soil would be environmentally friendly.

Selective 1,2-Hydroarylation(Alkenylation) of gem-Difluoroalkenes to Access (-CF2 H) Motifs

An emerging class of C-C coupling transformations that furnish drug-like building blocks involves catalytic hydrocarbonation of alkenes. However, despite notable advances in the field, hydrocarbon addition to gem-difluoroalkenes without additional electronic activation remains largely unsuccessful. This owes partly to poor reactivity and the propensity of difluoroalkenes to undergo defluorinative side reactions. Here, we report a nickel catalytic system that promotes efficient 1,2-selective hydroarylation and hydroalkenylation, suppressing defluorination and providing straightforward access to a diverse assortment of prized organofluorides bearing difluoromethyl-substituted carbon centers. In contrast to radical-based pathways and reactions triggered by hydrometallation via a nickel-hydride complex, our experimental and computational studies support a mechanism in which a catalytically active nickel-bromide species promotes selective carbonickelation with difluoroalkenes followed by alkoxide exchange and hydride transfer, effectively overcoming the difluoroalkene's intrinsic electronic bias.

Palladium-Catalyzed Regioselective Synthesis of 2-SF5 -Indenols and Further Derivatizations

A palladium-catalyzed synthesis of 2-SF5 -indenols has been developed by reacting commercially available boronic acid derivatives and readily accessible SF5 -alkynes. The present methodology is fully regioselective thanks to the intrinsic polarization of SF5 -alkynes. A selection of downstream functionalizations has been performed to highlight the versatility of 2-SF5 -indenols and indenones as platforms for the design of more complex SF5 -containing molecules.

Fluorinated Pharmaceutical and Pesticide Photolysis: Investigating Reactivity and Identifying Fluorinated Products by Combining Computational Chemistry,19F NMR, and Mass Spectrometry

Fluorinated breakdown products from photolysis of pharmaceuticals and pesticides are of environmental concern due to their potential persistence and toxicity. While mass spectrometry workflows have been shown to be useful in identifying products, they fall short for fluorinated products and may miss up to 90% of products. Studies have shown that 19F NMR measurements assist in identifying and quantifying reaction products, but this protocol can be further developed by incorporating computations. Density functional theory was used to compute 19F NMR shifts for parent and product structures in photolysis reactions. Computations predicted NMR spectra of compounds with an R2 of 0.98. Computed shifts for several isolated product structures from LC-HRMS matched the experimental shifts with <0.7 ppm error. Multiple products including products that share the same shift that were not previously reported were identified and quantified using computational shifts, including aliphatic products in the range of -80 to -88 ppm. Thus, photolysis of fluorinated pharmaceuticals and pesticides can result in compounds that are polyfluorinated alkyl substances (PFAS), including aliphatic-CF3 or vinyl-CF2 products derived from heteroaromatic-CF3 groups. C-F bond-breaking enthalpies and electron densities around the fluorine motifs agreed well with the experimentally observed defluorination of CF3 groups. Combining experimental-computational 19F NMR allows quantification of products identified via LC-HRMS without the need for authentic standards. These results have applications for studies of environmental fate and analysis of fluorinated pharmaceuticals and pesticides in development.

Visible Light-Mediated Monofluoromethylation/Acylation of Olefins by Dual Organo-Catalysis

Monofluoromethyl (CH2F) motifs exhibit unique bioactivities and are considered privileged units in drug discovery. The radical monofluoromethylative difunctionalization of alkenes stands out as an appealing approach to access CH2F-containing compounds. However, this strategy remains largely underdeveloped, particularly under metal-free conditions. In this study, we report on visible light-mediated three-component monofluoromethylation/acylation of styrene derivatives employing NHC and organic photocatalyst dual catalysis. A diverse array of α-aryl-β-monofluoromethyl ketones was successfully synthesized with excellent functional group tolerance and selectivity. The mild and metal-free CH2F radical generation strategy from NaSO2CFH2 holds potential for further applications in fluoroalkyl radical chemistry.

Quaternary ammonium fluorides and difluorosilicates as nucleophilic fluorination reagents

TBAT (tetrabutylammonium difluorotriphenylsilicate) is an excellent homogeneous nucleophilic fluorination reagent, but a high excess of the reagent was reported to be essential. We hence optimized the reaction conditions and compared its nucleophilic fluorination reactivity with that of other common commercial nucleophilic fluorination reagents, such as anhydrous TBAF and TASF (tris(dimethylamino)sulfonium difluorotrimethylsilicate). As the substrates, we employed a standard set of primary and secondary octyl substrates under identical conditions. To eliminate the possibility of hydrogen fluoride elimination in the above reagents, we prepared four quaternary ammonium fluorides lacking β-elimination possibility in the hydrocarbon chain, transformed them to the corresponding difluorotriphenylsilicates, and compared their reactivity with that of the commercial reagents. Furthermore, attempts to isolate analogous tetrabutylammonium difluoromethyldiphenylsilicate or difluorodimethylphenylsilicate failed, as was confirmed by comparison of the published experimental data with computed 19F NMR spectra. Finally, we studied the transition states of decomposition of various tetramethylammonium methylphenyldifluorosilicates by DFT methods and found that their relative energies increase with an increasing number of phenyl groups. The formation of difluorosilicates is a nearly barrierless process.

Controllable Fluorocarbon Chain Elongation: TMSCF2Br-Enabled Trifluorovinylation and Pentafluorocyclopropylation of Aldehydes

Controllable fluorocarbon chain elongation (CFCE) is a promising yet underdeveloped strategy for the well-defined synthesis of structurally novel polyfluorinated compounds. Herein, the direct and efficient trifluorovinylation and pentafluorocyclopropylation of aldehydes are described by using TMSCF2Br (TMS = trimethylsilyl) as the sole fluorocarbon source, accomplishing the goals of CFCE from C1 to C2 and from C1 to C3, respectively. The key to the success of these CFCE processes lies in the unique and diversified chemical reactivity of TMSCF2Br, which can serve as two different precursors, namely, a TMSCF2 radical precursor and a difluorocarbene precursor. Various functional groups are amenable to this new synthetic protocol, providing streamlined access to a broad range of alcohols containing trifluorovinyl or pentafluorocyclopropyl moieties from abundantly available aldehydes. The potential utility of these methods is further demonstrated by the gram-scale synthesis, derivatization, and measurement of log P values of the products.

Update on novel synthetic approaches towards the construction of carbazole nuclei: a review

The carbazole scaffold is a significant entity in organic compounds due to its variety of biological and synthetic applications. Traditionally, carbazole skeletons have been synthesized either via the Grabe-Ullman method, Clemo-Perkin method or Tauber method. With the passage of time, these methods have been modified and explored to accomplish the synthesis of target compounds. These methods include hydroarylations, C-H activations, annulations and cyclization reactions mediated by a variety of catalysts to construct carbazole-based compounds. This brief review article intends to provide recent updates on important methodological developments reported for the synthesis of carbazole nuclei covering 2019-2023.

Recombinant Pseudomonas growing on non-natural fluorinated substrates shows stress but overall tolerance to cytoplasmically released fluoride anion

IMPORTANCE

Society uses thousands of organofluorine compounds, sometimes denoted per- and polyfluoroalkyl substances (PFAS), in hundreds of products, but recent studies have shown some to manifest human and environmental health effects. As a class, they are recalcitrant to biodegradation, partly due to the paucity of fluorinated natural products to which microbes have been exposed. Another limit to PFAS biodegradation is the intracellular toxicity of fluoride anion generated from C-F bond cleavage. The present study identified a broader substrate specificity in an enzyme originally studied for its activity on the natural product fluoroacetate. A recombinant Pseudomonas expressing this enzyme was used here as a model system to better understand the limits and effects of a high level of intracellular fluoride generation. A fluoride stress response has evolved in bacteria and has been described in Pseudomonas spp. The present study is highly relevant to organofluorine compound degradation or engineered biosynthesis in which fluoride anion is a substrate.