Alkyl Fluorides Research Articles

Formation and reactivity of Electrogenerated Lewis acids by oxidation of Bu4NB(C6F5)4 under weakly coordinating conditions

This study explores the generation and application of electrogenerated Lewis acids (EGLA) through anodic oxidation of tetrakis(pentafluorophenyl)borate, B(C6F5)4−, in weakly coordinating electrolytes. Employing Bu4NB(C6F5)4/CH2Cl2 as the electrolyte, bis(perfluorophenyl)borane (PFB), a highly reactive Lewis acid, was generated and utilized in various organic transformations. Cyclic voltammetry confirmed the onset of oxidation at 1.8 V vs. Ag/AgNO3, which led to the formation of the EGLA species. The EGLA system was successfully applied for the defluorination of 1-fluoroadamantane and other alkyl fluorides in both batch and flow electrolysis systems. Additionally, EGLA was effective in catalyzing diverse reactions, including Friedel-Crafts dimerization, deoxygenation of triphenylmethanol, and carbonyl–olefin metathesis, outperforming traditional Lewis acids, such as PFB and tris(pentafluorophenyl)borane. The reactivity of EGLA is strongly dependent on the solvent environment, with weakly coordinating solvents being critical for maintaining activity. This study highlights the potential of EGLA as a versatile and highly active catalyst for a broad range of organic transformations, emphasizing the importance of solvent selection in maximizing its reactivity.

Photocatalytic Decarboxylative Fluorination by Quinone-Based Isoreticular Covalent Organic Frameworks.

The strategic incorporation of fluorine atoms into molecules has become a cornerstone of modern pharmaceuticals, agrochemicals, and materials science. Herein, we have developed a covalent organic framework (COF)-based, robust photocatalyst that enables the photofluorodecarboxylation reaction of diverse carboxylic acids, producing alkyl fluorides with remarkable efficiency. The catalytic activity of an anthraquinone-based COF catalyst TpAQ outperforms other structurally analogous β-ketoenamine COFs. Through comprehensive control experiments, photoluminescence, and electrochemical studies, we have elucidated the unique features of the material and the mechanistic pathway. This in-depth understanding has paved the way for optimizing the reaction conditions and achieving high yields of alkyl fluorides. The versatility of this protocol extends to a broad range of aliphatic acids with diverse functional groups and heterocycles. It also enabled the late-stage diversification of anti-inflammatory drugs and steroid derivatives. This opens up exciting possibilities for synthesizing novel pharmaceuticals and functionalized molecules. The methodology was also generalized to other light-mediated decarboxylative halogenation reactions. Furthermore, our method demonstrates scalability under both batch and continuous flow conditions, offering a promising approach for large-scale production. Additionally, the TpAQ catalyst exhibits exceptional durability and can be reused multiple times without significant activity loss (>80% yield after the eighth cycle), making it a sustainable and cost-effective solution. This work lays the foundation for developing efficient and sustainable light-driven synthesis methods using COFs as photocatalysts with potential applications beyond alkyl halide synthesis.

Evaluation of fluorous affinity using fluoroalkyl-modified silica gel and selective separation of poly-fluoroalkyl substances in organic solvents.

In this study, we focused on the fluorous affinity acting among fluorine compounds, and then developed a new separation medium and evaluated their performance. We prepared the stationary phases for a column using silica gel-modified alkyl fluoride and investigated the characteristics of fluorous affinity by comparing them with a typical stationary phase, which does not contain fluorine, using high-performance liquid chromatography (HPLC). In HPLC measurements, we confirmed that while all non-fluorine compounds were not retained, retention of fluorine compounds increased as the number of fluorine increased with the stationary phase. It also revealed that the strength of fluorous affinity changes depending on the types of the organic solvent; the more polar the solvent, the stronger the effect. Additionally, the stationary phase was employed to compare the efficiency of our column with that of a commercially available column, Fluofix-II. The retention selectivity was almost the same, but the absolute retention strength was slightly higher on our column, indicating that the column is available for practical use.

Iron photocatalysis via Brønsted acid-unlocked ligand-to-metal charge transfer

Reforming sustainable 3d-metal-based visible light catalytic platforms for inert bulk chemical activation is highly desirable. Herein, we demonstrate the use of a Brønsted acid to unlock robust and practical iron ligand-to-metal charge transfer (LMCT) photocatalysis for the activation of multifarious inert haloalkylcarboxylates (CnXmCOO−, X = F or Cl) to produce CnXm radicals. This process enables the fluoro-polyhaloalkylation of non-activated alkenes by combining easily available Selectfluor as a fluorine source. Valuable alkyl fluorides including potential drug molecules can be easily obtained through this protocol. Mechanistic studies indicate that the real light-harvesting species may derive from the in situ-assembly of Fe3+, CnXmCOO−, H+, and acetonitrile solvent, in which the Brønsted acid indeed increases the efficiency of LMCT between the iron center and CnXmCOO− via hydrogen-bond interactions. We anticipate that this Brønsted acid-unlocked iron LMCT platform would be an intriguing sustainable option to execute the activation of inert compounds.

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.

Selective Hydrofunctionalization of Alkenyl Fluorides Enabled by Nickel-Catalyzed Hydrogen Atoms and Group Transfer: Reaction Development and Mechanistic Study.

Due to the unique effect of fluorine atoms, the efficient construction of high-value alkyl fluorides has attracted significant interest in modern drug development. However, enantioselective catalytic strategies for the efficient assembly of highly functionalized chiral C(sp3)-F scaffolds from simple starting materials have been underutilized. Herein, we demonstrate a nickel-catalyzed radical transfer strategy for the efficient, modular, asymmetric hydrogenation and hydroalkylation of alkenyl fluorides with primary, secondary, and tertiary alkyl halides under mild conditions. The transformation provides facile access to various structurally complex secondary and tertiary α-fluoro amide products from readily available starting materials with excellent substrate compatibility and distinct selectivity. Furthermore, the utility of this method is demonstrated by late-stage modifications and product derivatizations. Detailed mechanistic studies and DFT calculations have been conducted, showing that the rate-determining step for asymmetric hydrogenation reaction is NiH-HAT toward alkenyl fluorides and the stereo-determining step is alcohol coordination to Ni-enolates followed by a barrierless protonation. The mechanism for the asymmetric hydroalkylation reaction is also delivered in this investigation.

Editing Tetrasubstituted Carbon: Dual C-O Bond Functionalization of Tertiary Alcohols Enabled by Palladium-Based Dyotropic Rearrangement.

Many elegant asymmetric syntheses of enantioenriched tertiary alcohols have been developed, and both the transition metal-catalyzed and the radical-based peripheral functionalization of tertiary alcohols have attracted intensive research interest in recent years. However, directly editing tetrasubstituted carbons remains challenging. Herein, we report a Pd-catalyzed migratory fluoroarylation reaction that converts tertiary alcohols to α-fluorinated tertiary alkyl ethers in good to excellent yields. An unprecedented 1,2-aryl/PdIV dyotropic rearrangement along the C-O bond, integrated in a PdII-catalyzed domino process, is key to the dual functionalization of both the hydroxyl group and the tetrasubstituted carbon. This reaction, which is compatible with a broad range of functional groups, generates a tertiary alkyl fluoride and an alkyl-aryl ether functional group with inversion of the absolute configuration at the tetrasubstituted stereocenter.

Radical dehydroxymethylative fluorination of aliphatic primary alcohols and diverse functionalization of α-fluoroimides via BF3·OEt2-catalyzed C‒F bond activation

Ag2CO3-promoted dehydroxymethylative fluorination of aliphatic alcohols has been achieved with Selectfluor as both oxidant and fluorine source. The reaction involves β-fragmentation of primary alkoxy radicals, followed by the fluorination of the resulting C-centered radical intermediates. The transformation proceeds under mild reaction conditions and exhibits a broad substrate scope, thus opening up a new entrance to the synthesis of fluorinated constructs including α-fluoroimides and 1-fluoroalkyl benzoates as well as secondary and tertiary alkyl fluorides like versatile 2-fluoro-2-alkyl 1,3-propandiol derivatives. The divergent functionalization of the obtained α-fluoroimides enables an efficient access to amine derivatives through C–F bond activation under the action of BF3·OEt2.

General alkyl fluoride functionalization via short-lived carbocation-organozincate ion pairs

Fluorinated organic compounds are frequently used across the chemical and life sciences. Although a large, structurally diverse pool of alkyl fluorides is nowadays available, synthetic applications trail behind the widely accepted utility of other halides. We envisioned that C(sp2)-C(sp3) cross-coupling reactions of alkyl fluorides with fluorophilic organozinc compounds should be possible through a heterolytic mechanism that involves short-lived ion pairs and uses the stability of the Zn-F bond as the thermodynamic driving force. This would be mechanistically different from previously reported radical reactions and overcome long-standing limitations of organometallic cross-coupling methodology, including competing β-hydride elimination, homodimerization and hydrodefluorination. Here, we show a practical Csp3-F bond functionalization method that expands the currently restricted synthetic space of unactivated primary, secondary and tertiary C(sp3)-F bonds but also uses benzylic, propargylic and acyl fluorides. Many functional groups and sterically demanding substrates are tolerated, which allows practical carbon-carbon bond formation and late-stage functionalization.

A silylboronate-mediated strategy for cross-coupling of alkyl fluorides with aryl alkanes: mechanistic insights and scope expansion.

The construction of C(sp3)-C(sp3) bonds is pivotal in organic synthesis; however, traditional methods involving alkyl halides are often limited by substrate tolerance and bond dissociation energies, particularly with alkyl fluorides. Herein, we report a silylboronate-mediated cross-coupling strategy that circumvents these challenges, enabling the efficient formation of C(sp3)-C(sp3) bonds between alkyl fluorides and aryl alkanes under mild conditions. Various alkyl fluorides have also been effectively utilized, demonstrating the versatility and broad applicability of this approach. The use of diglyme is critical for this transformation which encapsulates potassium cations and enhances the reaction efficiency. Conventional alkyl halides, including chlorides, bromides, and iodides, are also suitable for this transformation. Density functional theory (DFT) calculations were conducted on the silylboronate-mediated coupling reactions for the first time. Interestingly, while experimental results suggest a radical mechanism, DFT calculations indicate a preference for an ionic pathway.

Direct arylation of alkyl fluorides using in situ mechanochemically generated calcium-based heavy Grignard reagents

Direct arylation of alkyl fluorides using in situ mechanochemically generated calcium-based heavy Grignard reagents

Photoinduced copper-catalyzed alkoxycarbonylation of alkyl fluorides

A photoinduced copper-catalyzed alkoxycarbonylation of alkyl fluorides with phenols to synthesize various esters has been developed.

Recent Advancements in Typical Friedel–Crafts Alkylation Reactions Focused on Targeting Arene Nucleophiles

AbstractThis review delves into recent advances and significant breakthroughs in the field of the catalytic Friedel–Crafts alkylation of targeted arenes or heteroarenes. Though a few earlier literatures are referenced, the main emphasis of this review focuses on the literature mainly published between 2015 and March 2023.1 Introduction2 History and Background3 Alcohols as Alkylating Agents4 Aldehydes and Ketones as Alkylating Agents5 Alkyl Fluorides as Alkylating Agents6 Epoxides as Alkylating Agents7 Cyclopropanes as Alkylating Agents8 Conclusion and Outlook

Metal‐Free and Visible Light‐Induced Difunctionalizations of α‐CF3 Styrenes with Aryl Diazonium Salts and Hetero Nucleophiles

AbstractMetal‐free, visible light‐induced difunctionalizations of α‐CF3 styrenes with aryl diazonium salts and various hetero nucleophiles (ROH, H2O, N3− and F−) are described. This concise protocol provided easy access to the α‐CF3 tertiary alkyl ethers, alcohol and fluorides with good yields and excellent functional group tolerance. In addition, the four‐component “SO2” insertion reaction also worked efficiently to produce the α‐CF3, β‐sulfonyl ethers in moderate to good yields. A radical‐polar crossover coupling pathway was proposed for the C−O bond formation.

Chemo-, Regio-, and Stereoselective Access to (E)-Boryl-Substituted Allyl Fluorides via Electrophilic Fluorodesilylation

AbstractHerein, we report a transition-metal-free chemo-, regio-, and stereoselective electrophilic fluorodesilylation of α-silyl-substituted allylboronate esters. α-Silyl-substituted allylboronate esters can be chemoselectively coupled with Selectfluor, resulting in a variety of (E)-boryl-substituted allyl fluorides in good yields with γ- and (E)-selectivities. The utilities of the obtained (E)-boryl-substituted allyl fluorides are highlighted by further modifications to afford allyl or alkyl fluoride derivatives.

Highly regio- and enantioselective Cu/Pd co-catalyzed allylic alkylation of α-pyridyl-α-fluoroesters: construction of quaternary C-F stereocenters.

New methods for preparation of chiral alkyl fluorides have been studied intensively in recent years due to the favorable physicochemical and biological properties of those structures. Herein, we describe the regio- and enantioselective allylic alkylation of α-pyridyl-α-fluoroesters with allyl acetates promoted by Cu/Pd synergistic catalysis, constructing the carbon- fluorine quaternary stereocenters. In this co-catalytic system, palladium catalyst mainly constructed the C-C bond, while chiral copper catalyst controlled the enantioselectivity. A series of aryl- and aliphatic-substituted allyl acetates are applied, giving the corresponding products in high yield, excellent enantioselectivity and E/Z (up to 98% yield, 98:2 er, E/Z >20:1).

Cationic Rhodium(I) Tetrafluoroborate Catalyzed Intramolecular Carbofluorination of Alkenes via Acyl Fluoride C-F Bond Activation.

C-F bonds of acyl fluorides can be cleaved and added across tethered alkenes in the presence of a cationic rhodium(I) tetrafluoroborate catalyst. This 1,2-carbofluorination reaction offers a powerful method for the synthesis of tertiary alkyl fluoride derivatives with atom economy of 100%. Mechanistic studies indicate that the concerted action of a rhodium cation and a tetrafluoroborate anion is the key for the success of this catalytic cleavage and formation of C-F bonds in a controlled manner.

Cationic Rhodium(I) Tetrafluoroborate Catalyzed Intramolecular Carbofluorination of Alkenes via Acyl Fluoride C−F Bond Activation**

AbstractThe C−F bond of acyl fluorides can be cleaved and added across tethered alkenes in the presence of a cationic rhodium(I) tetrafluoroborate catalyst. This 1,2‐carbofluorination reaction offers a powerful method for the synthesis of tertiary alkyl fluoride derivatives with an atom economy of 100 %. Mechanistic studies indicate that the concerted action of a rhodium cation and a tetrafluoroborate anion is key for the success of this catalytic cleavage and formation of C−F bonds in a controlled manner.

Cross- and Multi-Coupling Reactions Using Monofluoroalkanes.

Carbon-fluorine bonds are stable and have demonstrated sluggishness against various chemical manipulations. However, selective transformations of C-F bonds can be achieved by developing appropriate conditions as useful synthetic methods in organic chemistry. This review focuses on C-C bond formation at monofluorinated sp3 -hybridized carbons via C-F bond cleavage, including cross-coupling and multi-component coupling reactions. The C-F bond cleavage mechanisms on the sp3 -hybridized carbon centers can be primarily categorized into three types: Lewis acids promoted F atom elimination to generate carbocation intermediates; nucleophilic substitution with metal or carbon nucleophiles supported by the activation of C-F bonds by coordination of Lewis acids; and the cleavage of C-F bonds via a single electron transfer. The characteristic features of alkyl fluorides, in comparison with other (pseudo)halides as promising electrophilic coupling counterparts, are also discussed.

Enantioselective and stereodivergent hydromonofluoroalkylation of conjugated and remote dienes

Because of the widespread applications of optically active alkyl fluorides in medicinal and agro chemicals, enantioselective and even stereodivergent construction of alkyl fluorides remains highly desirable but underdeveloped. Transition-metal-catalyzed asymmetric hydrofluoroalkylation of readily available dienes represents a novel route to achieve this goal, yet receives scarce study. Here we report an intriguing palladium-catalyzed enantioselective hydromonofluoroalkylation reaction of conjugated dienes. Both monosubstituted and internal dienes proceed well with the transformation and furnish alkyl fluorides in generally >80% yield and >90% ee. A stereodivergent hydromonofluoroalkylation protocol via Pd/Cu co-catalysis is also established for the access to all four stereoisomers of corresponding moieties bearing a fully-substituted F-stereogenic center and vicinal tertiary carbon center. In addition, asymmetric migratory hydromonofluoroalkylation of skipped dienes is developed to realize the direct allylic CH fluoroalkylation. A compound library of enantioenriched cyclic fluorides is thus built to highlight the transformation potential of present methodology.