Stereodivergent Palladium-Catalyzed C-F Bond Functionalization of gem-Difluoroalkenes

We herein describe a stereodivergent C-F bond functionalization of gem-difluoroalkenes. Using trisubstituted β,β-difluoroacrylates, both E and Z monofluoroalkene products can be obtained with excellent diastereoselectivities. The design of two different reaction manifolds, i.e., Pd(II)- versus Pd(0)-catalyzed cross-coupling of boronic acids, is the key to stereocontrol.

Borane-Catalyzed Coupling of Diazooxindoles and Difluoroenoxysilanes to Tetrasubstituted Monofluoroalkenes

A highly stereoselective coupling reaction of diazooxindoles with difluoroenoxysilanes catalyzed by Lewis acidic boranes has been developed. The reaction proceeded at ambient temperature under transition metal-free conditions with wide functional group tolerance. By using this simple procedure, a series of tetrasubstituted monofluoroalkenes can be accessed in good yield with high selectivity.

Photoinduced decarboxylative germylation of α-fluoroacrylic acids: access to germylated monofluoroalkenes

Herein, a novel strategy is presented for the photoinduced decarboxylative and dehydrogenative cross-coupling of a wide range of α-fluoroacrylic acids with hydrogermanes. This methodology provides an efficient and robust approach for producing various germylated monofluoroalkenes with excellent stereoselectivity within a brief photoirradiation period. The feasibility of this reaction has been demonstrated through gram-scale reaction, conversion of germylated monofluoroalkenes, and modification of complex organic molecules.

Silver-Catalyzed (Z)-β-Fluoro-vinyl Iodonium Salts from Alkynes: Efficient and Selective Syntheses of Z-Monofluoroalkenes

Monofluoroalkenes are stable and lipophilic amide bioisosteres used in medicinal chemistry. However, efficient and stereoselective methods for synthesizing Z-monofluoroalkenes are underdeveloped. We envisage (Z)-β-fluoro-vinyl iodonium salts (Z-FVIs) as coupling partners for the diverse and stereoselective synthesis of Z-monofluoroalkenes. Disclosed herein is the development and application of a silver(I)-catalyzed process for accessing a broad scope of (Z)-FVIs with exclusive Z-stereoselectivity and regioselectivity from alkynes in a single step. Experimental and computational studies provide insight into the mechanism of the catalytic cycle and the role of the silver(I) catalyst, and the reactivity of (Z)-FVIs is explored through several stereospecific derivatizations.

Rhodium-Catalyzed Enantio- and Regioselective Allylation of Indoles with gem-Difluorinated Cyclopropanes

The use of gem-difluorinated cyclopropanes (gem-DFCPs) as fluoroallyl surrogates under transition-metal catalysis has drawn considerable attention recently but such reactions are restricted to producing achiral or racemic mono-fluoroalkenes. Herein, we report the first enantioselective allylation of indoles under rhodium catalysis with gem-DFCPs. This reaction shows exceptional branched regioselectivity towards rhodium catalysis with gem-DFCPs, which provides an efficient route to enantioenriched fluoroallylated indoles with wide substrate scope and good functional group tolerance.

DFT Calculations Rationalize Unconventional Regioselectivity in PdII-Catalyzed Defluorinative Alkylation of gem-Difluorocyclopropanes with Hydrazones

Density functional theory (DFT) calculations have been conducted to gain insight into the unique formation of the branched alkylation product in the PdII-catalyzed defluorinative alkylation of gem-difluorocyclopropanes with hydrazones. The reaction is established to occur in sequence through oxidative addition, β-F elimination, η1-η3 isomerization, transmetalation, η3-η1 isomerization, 3,3'-reductive elimination, deprotonation/N2 extrusion, and proton abstraction. The rate-determining step of the reaction is identified as the β-F elimination, featuring an energy barrier of 28.6 kcal/mol. The 3,3'-reductive elimination transition states are the regioselectivity-determining transition states. The favorable noncovalent π-π interaction between the naphthyl group of gem-difluorocyclopropane and the phenyl group of hydrazone is found to be mainly responsible for the observed regioselectivity.

Streamlining Fluoroalkenyl Arene Synthesis Illuminated with Mechanistic Insights

Fluorinated compounds are a staple of modern-day chemical innovation, and efficient strategies for their synthesis are highly valuable. In this chemical space, fluoroalkenes continue to be the object of much interest across diverse fields, including drug development and pharmaceuticals with active roles as bioisosteres. Herein, in expanding chemists' synthetic toolbox for constructing valuable organofluorine compounds, we report a "pipeline" strategy for the synthesis of fluorinated olefins, viz., gem-difluoroalkenyl and monofluoroalkenyl arenes with high E-isomeric selectivity. The advantages of this streamlined synthetic protocol include mild reaction conditions, operational simplicity, broad substrate scope, and good to excellent yields, even at gram scales. Critical to this robust procedure is the use of widely available and inexpensive "scavenger" solid-support Merrifield peptide resin for removing phosphine impurities. Further computational investigations offering clarity into this reactivity are disclosed.

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.

Rapid reaction optimization by robust and economical quantitative benchtop 19F NMR spectroscopy

The instrumental analysis of reaction mixtures is usually the rate-determining step in the optimization of chemical processes. Traditionally, reactions are analyzed by gas chromatography, HPLC or quantitative NMR spectroscopy on high-field spectrometers. However, chromatographic methods require elaborate work-up and calibration protocols, and high-field NMR spectrometers are expensive to purchase and operate. This protocol describes an inexpensive and highly effective analysis method based on low-field benchtop NMR spectroscopy. Its key feature is the use of fluorine-labeled model substrates that, because of the wide chemical shift range and high sensitivity of 19F, enable separate, quantitative detection of product and by-product signals even on low-field, permanent magnet spectrometers. An external lock/shim device obviates the need for deuterated solvents, permitting the direct, noninvasive measurement of crude reaction mixtures with minimal workup. The low field-strength facilitates a homogeneous excitation over a wide chemical shift range, minimizing systematic integration errors. The addition of the optimal amount of the nonshifting relaxation agent tris(acetylacetonato) iron(III) minimizes relaxation delays at full resolution, reducing the analysis time to 32 s per sample. The correct choice of processing parameters is also crucial. A step-by-step guideline is provided, the influence of all parameters, including adjustments needed when using high-field spectrometers, is discussed and potential pitfalls are highlighted. The wide applicability of the analytical protocol for reaction optimization is illustrated by three examples: a Buchwald-Hartwig amination, a Suzuki coupling and a C-H arylation reaction.

High-Valent Copper Catalysis Enables Regioselective Fluoroarylation of Gem-Difluorinated Cyclopropanes

Transition-metal (TM) catalyzed reaction of gem-difluorinated cyclopropanes (gem-DFCPs) has drawn much attention recently. The reaction generally occurs via the activation of the distal C─C bond in gem-DFCPs by a low-valent TM through oxidative addition, eventually producing mono-fluoro olefins as the coupling products. However, achieving regioselective activation of the proximal C─C bond in gem-DFCPs that overcomes the intrinsic reactivity via TM catalysis remains elusive. Here, a new reaction mode of gem-DFCPs enabled by high-valent copper catalysis, which allows exclusive activation of the congested proximal C─C bond is presented. The reaction that achieves fluoroarylation of gem-DFCPs uses NFSI (N-fluorobenzenesulfonimide) as electrophilic fluoro reagent and arenes as the C─H nucleophiles, enabling the synthesis of diverse CF3-containing scaffolds. It is proposed that a high-valent copper species plays an important role in the regioselective activation of the proximal C─C bond possibly via a σ-bond metathesis.

Electrocatalysis-Enabled Stereoselective Synthesis of Monofluoroalkenes via Hydrodefluorination of gem-Difluoroakenes

We report a simple and economical method to synthesize monofluoroalkenes via the electrochemical hydrodefluorination of gem-difluoroalkenes. This reaction proceeds efficiently at room temperature, eliminating the requirement for a costly transition metal catalyst, ligand, and external reducing agent. The monofluoroalkene products can be obtained in medium to good yields and up to 99:1 E/Z selectivity. The reaction is easily scalable to gram scale.

Electrocatalysis-Enabled Defluorinative Cross-Coupling of gem-Difluoroalkenes with Aldehydes and Ketones

An electrochemical defluorinative cross-coupling of gem-difluoroalkenes with carbonyl compounds was described, by which highly stereoselective monofluoroalkene allyl alcohols were synthesized. The reaction tolerates a broad range of functional groups and has successfully been applied to synthesize complex molecules. Mechanistic studies indicate that the reaction starts from electron reduction of gem-difluoroalkenes to generate radical negative ions, which undergo β-fluoride elimination and subsequent reduction to form anions. These anions are subsequently trapped by carbonyl compounds to furnish target products.

Pd/IPrBIDEA-Catalyzed Hydrodefluorination of gem-Difluorocyclopropanes: Regioselective Synthesis of Terminal Fluoroalkenes

Developing new strategies to enable chemo- and regioselective reductions is an important topic in chemical research. Herein, an efficient and regioselective Pd/IPrBIDEA-catalyzed ring-opening hydrodefluorination of gem-difluorocyclopropanes to access terminal fluoroalkenes is developed. The success of this transformation was attributed to the use of 3,3-dimethylallyl Bpin as a novel hydride donor. DFT calculations suggest that a direct 3,4'-hydride transfer via a 9-membered cyclic transition state is more favorable, which combined with the irreversibility of the reaction enables the unusual selectivity for the less thermodynamically stable terminal alkene isomer. This reaction mode is also applicable to a variety of regioselective allylic and propargyl reductions.

Palladium-Catalyzed Diversified Synthesis of Monofluorinated Alkenes from Allylic gem-Difluorides through Pd-OH Intermediate

Significant advancements in synthesis of monofluoroalkenes via palladium-catalyzed reactions involving allylic gem-difluorides and diverse nucleophiles have been achieved. This method allows regioselective arylation, alkylation, allylation, alkenylation, and hydrogenation of allylic gem-difluorides, yielding high Z-selectivity and favorable product yields under mild conditions. Tolerating various functional groups, these transformations utilize a common Pd-OH intermediate. Additionally, employing triple Pd-catalyzed cross-coupling yields diverse trisubstituted alkenes efficiently.

Palladium-Catalyzed Cross-Coupling of gem-Difluorocyclopropanes with gem-Diborylalkanes for the Synthesis of Boryl-Substituted Fluorinated Alkenes

This study presents a novel method for the regioselective coupling of gem-difluorinated cyclopropanes with gem-diborylmethane, utilizing a Pd-catalyst system. This innovative approach enables the synthesis of 2-fluoroalkenyl monoboronate scaffolds with high Z-selectivity. The resulting products undergo further transformations, including oxidation, Suzuki cross-coupling, and trifluoroborylation, all of which are achieved with good yields. This work introduces a valuable synthetic pathway to access important fluorinated compounds for various applications in organic chemistry.

Recent Advances in Monofluorinated Carbenes, Carbenoids, Ylides, and Related Species

The synthesis of monofluorinated compounds is of great interest because of the vast applications of organofluorine compounds. Recently, the introduction of monofluorocarbene synthons has emerged as an important strategy for the synthesis of fluorine-containing products. In contrast to direct fluorination, in which C-F bonds are formed, the use of monofluorinated carbenes and related reactive species involves C-C or C-X bond formation while delivering valuable fluorine atoms into the target structure. Owing to increased knowledge on carbon-carbon and carbon-heteroatom bond formations, monofluorinated carbenes have enormous potential for the synthesis of organofluorine compounds, which, in our opinion, has not yet been fully exploited. This review summarizes the recent advances in the synthetic applications of monofluorinated carbenes, carbenoids, ylides, and related species.

Hydrofluorination of Alkynes: From (E) to (Z)

The hydrofluorination of alkynes is an efficient synthetic route to monofluoroalkenes or difluoroalkanes. Both fluorinated motifs have found applications in medicinal chemistry and beyond. This review explores the recent advances in the hydrofluorination of diverse alkynes through various activation methods, from classical coinage metal catalysis to metal-free conditions. The range of alkynes goes from the simplest unactivated alkynes to activated ones (ynones and derivatives, ynamides, alkynyl sulfides and sulfones as much as haloalkynes). Regio- and stereoselective methods exists, but there is still room for improvement depending on the type of alkyne.

Discovery of Novel Diamides Scaffold Containing Monofluoro-acrylamides Activating the Insect Ryanodine Receptor

The research and development of organofluorine chemistry has flourished; in particular, monofluoroalkene has aroused considerable interest from medicinal and organic chemists. It is a significant attempt to introduce monofluoroalkene into agrochemicals. In this study, monofluoroalkene was introduced into diamide molecules and inserted between the aliphatic amide and benzene ring, and 44 compounds have been successfully synthesized. The bioassay results showed that compounds with monofluoro-acrylamide moiety (Z-isomers) had excellent larvicidal activity against lepidopteran pests at 5 mg·L-1. The LC50 values of compounds B16, B18, and B21 against Mythimna separata were 1.02, 1.32, and 0.78 mg·L-1, respectively. 3D-QSAR analysis including the CoMFA model and the CoMSIA model was conducted to illustrate the contributions of steric, electrostatic, hydrophobic, and hydrogen bond fields on the bioactivity. Moreover, typical symptoms caused by chlorantraniliprole including dehydration, shrinkage, and blackening were also observed on the test larvae treated with monofluoro-acrylamide diamide compounds. M. separata central neurons calcium imaging experiment of compound B18 indicated that the monofluoro-acrylamide diamide compounds were potential insect ryanodine receptor activators. The molecular docking was performed in the CHL binding domain of Plutella xylostella RyR and revealed that the predicted binding mode of compound B21 was slightly different from that of CHL. The MM|GBSA dG Bind values of B21 and CHL with P. xylostella RyR were respectively -85.797 and -95.641 kcal·mol-1. The present work explored the insecticidal properties of a new diamide scaffold containing a monofluoro-acrylamide fragment and extended the application of monofluoroalkene in the agrochemical field.

Tunable Synthesis of Monofluoroalkenes and Gem-Difluoroalkenes via Solvent-Controlled Rhodium-Catalyzed Arylation of 1-Bromo-2,2-difluoroethylene

Divergent synthesis of fluorine-containing scaffolds starting from a suite of raw materials is an intriguing topic. Herein, we report the solvent-controlled rhodium-catalyzed tunable arylation of 1-bromo-2,2-difluoroethylene. The selection of the reaction solvents provides switchable defluorinated or debrominated arylation from readily available feedstock resources (both arylboronic acids/esters and 1-bromo-2,2-difluoroethylene are commercially available). This switch is feasible because of the difference in coordination ability between the solvent (CH2 Cl2 or CH3 CN) and the rhodium center, resulting in different olefin insertion. This protocol allows the convenient synthesis of monofluoroalkenes and gem-difluoroalkenes, both of which are important scaffolds in the fields of medicine and materials. Moreover, this newly developed solvent-regulated reaction system can be applied to the site-selective dechlorinated arylation of trichloroethylene. Overall, this study provides a useful strategy for the divergent synthesis of fluorine-containing scaffolds and provides insight into the importance of solvent selection in catalytic reactions.

Pd-IHept-Catalyzed Ring-Opening of gem-Difluorocyclopropanes with Malonates Via Selective C-C Bond Cleavage: Synthesis of Monofluoroalkenes

Monofluoroalkene scaffolds are frequently found in various functional molecules. Herein, we report a Pd-IHept-catalyzed (NHC = N-heterocyclic carbene) defluorinative functionalization approach for the synthesis of monofluoroalkenes from gem-difluorocyclopropanes and malonates. The flexible yet sterically hindered N,N'-bis(2,6-di(4-heptyl)phenyl)imidazol-2-ylidene ligand plays a key role in ensuring the high reaction efficiency. In addition, sterically hindered 1,1- and 1,2-disubstituted gem-difluorocyclopropanes could also be used in this transformation.

Defluorinative Thiolation of gem-Difluoroalkenes by Convergent Paired Electrolysis

Herein, we have successfully developed a convergent paired electrolysis strategy for the defluorinative thiolation process utilizing thiols and gem-difluoroalkenes as precursors. This protocol exhibits remarkable tolerance toward a wide range of functional groups, as exemplified by the successful late-stage defluorothiolation of complex molecules. Additionally, this strategy is amenable to gram-scale synthesis, making use of both anodic oxidation and cathodic reduction processes in an efficient manner. Several control studies were conducted and suggested a convergent paired electrolysis mechanism.

Au(I)-Catalyzed Regioselective Hydrofluorination of Propargylamines Using Aqueous HF

Gold-catalyzed regioselective hydrofluorination of alkynes using aqueous HF has been achieved by employing an amide directing group. For both aryl- and alkyl-substituted propargylamines, the fluorination occurred at the site distal to the amino group.

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.

Electrochemical Difunctionalization of gem-Difluoroalkenes: A Metal-Free Synthesis of α-Difluoro(alkoxyl/azolated) Methylated Ethers

A scalable electrochemical difunctionalization of gem-difluoroalkenes to structurally versatile difluoro motifs was achieved. This methodology features reagent-free conditions, good functional group tolerance, and a relatively broad substrate scope. Meanwhile, the electrolysis protocol is easy to handle, and the products show good regio- and chemoselectivity. The reaction mechanism was also preliminarily studied.

(Z)-Selective Synthesis of Bromofluoroalkenes via the TMSCF2Br-Mediated Tandem Reaction with para-Quinone Methides

We report herein a tandem reaction of para-quinone methides with TMSCF₂Br to construct bromofluoroalkenes in a Z-selective manner. While TMSCF₂Br has been documented as the precursor of difluoro carbene, it exhibits another possibility in this transformation, a formal bromofluoro carbene surrogate. The alkenyl bromide unit of the products could directly engage in a variety of transformations.

Visible-Light-Induced Monofluoroalkenylation and gem-Difluoroallylation of Inactivated C(sp3)-H Bonds via 1,5-Hydrogen Atom Transfer (HAT)

The direct monofluoroalkenylation of C(sp³)-H bonds is of great importance and quite challenging. Current methods have been restricted to the monofluoroalkenylation of activated C(sp³)-H bonds. Here, we reported the photocatalyzed C(sp³)-H monofluoroalkenylation of inactivated C(sp³)-H bonds with gem-difluoroalkenes via 1,5-hydrogen atom transfer. This process shows good functional group tolerance, such as halides (F, Cl), nitrile, sulfone, ester, and pyridine, and good γ-selectivity. Moreover, this method succeeds in the photocatalyzed gem-difluoroallylation of inactivated C(sp³)-H with α-trifluoromethyl alkenes.

Anthranilic Diamides Containing Monofluoroalkene Amide Linkers as Potential Insect RyR Activators: Design, Synthesis, Bio-evaluation, and Computational Study

In order to develop anthranilic diamides with novel chemotypes, a series of anthranilic diamides with acrylamide linkers were designed and synthesized. The results of preliminary bioassays indicated that compounds with a monofluoroalkene amide linker (Z-isomer) exhibited good larvicidal activity against lepidopteran pests. The LC₅₀ values of compound A23 against Mythimna separata and Plutella xylostella were 1.44 and 3.48 mg·L^-1, respectively, while those of chlorantraniliprole were 0.08 and 0.06 mg·L^-1, respectively. Compound A23 also exhibited the same level of lethal potency against resistant and susceptible strains of Spodoptera frugiperda at 50 mg·L^-1. Compound A23 exhibited similar symptoms as chlorantraniliprole in test larvae. Comparative molecular field analysis was conducted to demonstrate the structure-activity relationship. Central neuron calcium imaging experiments indicated that monofluoroalkene compounds were potential ryanodine receptor (RyR) activators and activated calcium channels in both the endoplasmic reticulum and the cell membrane. Molecular docking suggested that A23 had a better binding potency to P. xylostella RyR than chlorantraniliprole. The MM|GBSA dG bind value of A23 with P. xylostella RyR was 117.611 kcal·mol^-1. Monofluoroalkene was introduced into anthranilic diamide insecticides for the first time and brought a novel chemotype for insect RyR activators. The feasibility of fluoroalkenes as insecticide fragments was explored.

Cu-catalyzed cascade difluoroalkylation/5-endo cyclization/β-fluorine cleavage of ynones

A copper-catalyzed, redox-neutral cascade difluoroalkylation/5-endo annulation/β-fluorine cleavage of ynones is developed, providing a direct and stereoselective method to access synthetically important α-monofluoroalkenyl cyclopentanones. Mechanistic studies suggest an unprecedented Cu^II-assisted β-fluorine fragmentation, which may be valuable for the challenging but important C-F bond activation. Moreover, the in situ generated difluorocarbene was found to serve as an effective reductant for the regeneration of copper(I) catalyst, thus avoiding the addition of external reductants.

Defluorinative Transformation of (2,2,2-Trifluoroethyl)arenes Catalyzed by the Phosphazene Base t-Bu-P2

In this study, we demonstrated that 1-tert-butyl-2,2,4,4,4-pentakis(dimethylamino)-2λ5,4λ5-catenadi(phosphazene) (t-Bu-P2) catalyzes the defluorinative functionalization reactions of (2,2,2-trifluoroethyl)arenes with alkanenitriles to produce monofluoroalkene products. The reaction proceeds through HF elimination from a (2,2,2-trifluoroethyl)arene to form a gem-difluorostyrene intermediate, which is followed by nucleophilic addition of an alkanenitrile and elimination of a fluoride anion. The catalysis is compatible with a variety of functional groups.

Recent Advances in Alkenyl sp2 C-H and C-F Bond Functionalizations: Scope, Mechanism, and Applications

Alkenes and their derivatives are featured widely in a variety of natural products, pharmaceuticals, and advanced materials. Significant efforts have been made toward the development of new and practical methods to access this important class of compounds by selectively activating the alkenyl C(sp²)-H bonds in recent years. In this comprehensive review, we describe the state-of-the-art strategies for the direct functionalization of alkenyl sp² C-H and C-F bonds until June 2022. Moreover, metal-free, photoredox, and electrochemical strategies are also covered. For clarity, this review has been divided into two parts; the first part focuses on currently available alkenyl sp² C-H functionalization methods using different alkene derivatives as the starting materials, and the second part describes the alkenyl sp² C-F bond functionalization using easily accessible gem-difluoroalkenes as the starting material. This review includes the scope, limitations, mechanistic studies, stereoselective control (using directing groups as well as metal-migration strategies), and their applications to complex molecule synthesis where appropriate. Overall, this comprehensive review aims to document the considerable advancements, current status, and emerging work by critically summarizing the contributions of researchers working in this fascinating area and is expected to stimulate novel, innovative, and broadly applicable strategies for alkenyl sp² C-H and C-F bond functionalizations in the coming years.

Synthesis of remote fluoroalkenyl ketones by photo-induced ring-opening addition of cyclic alkoxy radicals to fluorinated alkenes

Fluoroalkenyl moieties are often used as carbonyl mimics in medicine preparation, and thus the development of facile routes for the synthesis of such compounds is of great importance. In this work, we report a photocatalytic ring-opening addition of cyclic alcohols to α-(trifluoromethyl)styrenes, which underwent a proton-coupled electron transfer and β-scission process, delivering a great variety of remote gem-difluoroalkenyl ketone derivatives. This methodology can also be applied in the reaction of gem-difluorostyrenes and 1,1,2-trifluorostyrenes to access monofluoro- and 1,2-difluoroalkenyl ketones.

Metal-free visible-light-induced hydroxy-perfluoroalkylation of conjugated olefins using enamine catalyst

We developed a simple and sustainable method for the hydroxy-perfluoroalkylation of electron-deficient conjugated olefins and styrenes. In this protcol, in situ generated enamine forms electron-donor-accepter (EDA) complexes with perfluoroalkyl iodide, and reaction proceed with visible-light irradiation. Tertiary amine also interacts with perfluoroalkyl iodide via halogen-bonding, promoting the perfluoroalkyl radical generation. This reaction does not require any transition-metal or photoredox catalyst, and gaseous oxygen is used as the green hydroxy source. Moreover, various commercially available substrates and perfluoroalkyl iodides were tolerated, affording the desired hydroxy-perfluoroalkylated products in good to moderate yields (>50 examples, up to 90%).

Photocatalytic Defluorinative Three-Component Reaction of α-Trifluoromethyl Alkenes, Alkenes, and Sodium Sulfinates: Synthesis of Monofluorocyclopentenes

A photocatalytic three-component reaction of α-trifluoromethyl alkenes, electron-rich alkenes, and sodium sulfinates for the synthesis of gem-difluoroalkenes in a radical/polar crossover manner was developed. Due to the strong electron-withdrawing nature of the sulfonyl group, the resultant gem-difluoroalkenes can be converted into various monofluorocyclopentenes via intramolecular base-mediated S_NV reactions in one pot.

Platinum‐Catalyzed Hydrofluorination of Alkynes: Hydrogen Bonding to Indolylphosphine Ligands to Provide Fluoride Reactivity

The reaction of the Pt complexes cis‐[Pt(CH₃)₂{R₂P(Ind)}₂] (Ind=2‐(3‐methyl)indolyl, R=Ph (1 a), 4‐FC₆H₄ (1 b), 4‐CF₃C₆H₄ (1 c)) with HF afforded the fluorido complexes trans‐[Pt(F(HF)₂)(CH₃){R₂P(Ind)}₂] 2 a–c, which can be converted into trans‐[Pt(F)(CH₃){R₂P(Ind)}₂] (3 a–c) by treatment with CsF. Addition of 3‐hexyne to 2 a–c gave alkyne complexes trans‐[Pt(C,C‐η²‐C₂H₅C≡CC₂H₅)(CH₃){R₂P(Ind)}₂{F(HF)₂}] (4 a–c) at which a fluoride is stabilised as polyfluoride in the coordination sphere by hydrogen bonding to the indolyl‐substituted phosphine ligands. Subsequent heating of a solution of 4 a in the presence of PVPHF led to fluoroalkene formation. Selective catalytic hydrofluorination of alkynes to yield (Z)‐fluoroalkenes were developed. The ability of hydrogen bonding to polyfluoride favours the fluorination step as demonstrated by studies with complexes bearing no indolyl groups at the phosphine ligands.

Cobalt-Catalyzed Fluoroallyllation of Carbonyls via C-C Activation of gem-Difluorocyclopropanes

A new Co-catalyzed sequential C-C and C-F activation of gem-difluorinated cyclopropanes (gem-FCPs) to form nucleophilic fluoroallylcobalt, followed by addition to aldehydes, is reported. The protocol features the regioselective cleavage of dual chemical bonds of readily available gem-FCPs to prepare easily separable linear (Z)- and (E)-fluorinated homoallylic alcohols with a broad scope. This discovery established a new strategy for the efficient transformation of gem-FCPs as well as the synthesis of challenging fluorinated homoallylic alcohols.

Highly Selective C-F Bond Functionalization of Tetrasubstituted gem-Difluoroalkenes and Trisubstituted Monofluoroalkenes Using Grignard Reagents

We herein describe selective C-F bond functionalizations of tetrasubstituted gem-difluoroalkenes and trisubstituted monofluoroalkenes using Grignard reagents without the transition metal catalyst. β,β-Difluoroacrylates react with Grignard reagents under mild conditions to afford tetrasubstituted (E)-β-monofluoroacrylates. Experimental and computational studies revealed that the selectivity stems from the intrinsic reactivity difference between the (E)- and (Z)-isomers toward excess Grignard reagent, which leads to the resolution of the two products.

Stereoconvergent Synthesis of Monofluoroalkenes via Photoinduced Dual Decarboxylative Cross-Coupling of α-Fluoroacrylic Acids with Redox-Active Esters

Herein, a new strategy for the synthesis of monofluoroalkenes via employing α-fluoroacrylic acids and N-hydroxyphthalimide (NHPI) redox-active esters as coupling partners has been developed. This decarboxylative reaction enabled the formation of C(sp²)-C(sp³) bonds to provide a practical and efficient approach for the construction of a variety of monofluoroalkenes, which are key structural motifs in organic chemistry, under mild reaction conditions. The protocol exhibited excellent functional group compatibility and delivered monofluoroalkene products with excellent Z-stereoselectivity. This work also provides a platform for the modification of complex biologically active molecules containing carboxylic acids.

Au(I) Catalyzed HF Transfer: Tandem Alkyne Hydrofluorination and Perfluoroarene Functionalization

HF transfer reactions between organic substrates are potentially useful transformations. Such reactions require the development of catalytic systems that can promote both defluorination and fluorination steps in a single reaction sequence. Herein, we report a catalytic protocol in which an equivalent of HF is generated from a perfluoroarene | nucleophile pair and transferred directly to an alkyne. The reaction is catalyzed by [Au(IPr)NⁱPr₂] (IPr = N,N′-1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene). HF transfer generates two useful products in the form of functionalized fluoroarenes and fluoroalkenes. Mechanistic studies (rate laws, KIEs, density functional theory (DFT) calculations, competition experiments) are consistent with the Au(I) catalyst facilitating a catalytic network involving both concerted S_NAr and hydrofluorination steps. The nature of the nucleophile impacts the turnover-limiting step. The cS_NAr step is turnover-limiting for phenol-based nucleophiles, while protodeuaration likely becomes turnover-limiting for aniline-based nucleophiles. The approach removes the need for direct handling of HF reagents in hydrofluorination and offers possibilities to manipulate the fluorine content of organic molecules through catalysis.