Transition-Metal (Cu, Pd, Ni)-Catalyzed Difluoroalkylation via Cross-Coupling with Difluoroalkyl Halides

Copper difluorocarbene-involved catalytic gem-difluoropropargylation

The use of metal for catalytic difluorocarbene transfer reactions has long been hindered by the lack of understanding of metal difluorocarbene chemistry, despite the potential implications for medicinal chemistry and advanced materials science. Here, we report a copper-catalyzed difluorocarbene transfer reaction via 1,1-migration of copper difluorocarbene, in contrast to the previous nucleophilic addition of copper difluorocarbene pathway. This reaction enables the development of a modular catalytic gem-difluoropropargylation reaction using a variety of simple and widely available potassium propiolates, terminal alkynes, and allyl/propargyl electrophiles to couple difluorocarbene, opening an avenue to the precise synthesis of organofluorine compounds without tedious synthetic procedures. The impact of this protocol is demonstrated by the efficient synthesis of complex fluorinated skeletons and the rapid synthesis of key intermediates for pheromone derivatives and PGF2 agonists. Mechanistic studies reveal that the migratory insertion of difluorocarbene into the C-Cu bond of the alkynylcopper species is a key step in the reaction.

Difluorocarbene/H2O Serving as a CO2 Equivalent for Insertion into Oxiranes

A difluorocarbene-enabled regioselective C(sp3)-O bond cleavage of oxiranes has been developed. The protocol provides an efficient and practical approach to cyclic carbonates under mild conditions. Significantly, the generation of difluorocarbene with BrCF2CO2Et/H2O serving as a CO2 equivalent under metal-free conditions has been disclosed.

[18F]Radiolabeling fluorination of monofluoroalkyl triflates for the synthesis of [18F]difluoromethylated alkanes

An efficient method for the synthesis of [18F]-difluoromethylated alkanes by the combination of [18F]radio-fluoride with monofluoroalkyl triflates has been developed. This method uses [18F]KF/K2.2.2 as the fluorine source. It features synthetic simplicity without tedious precursor preparation, high RCC and RCY, good functional group tolerance, and is silver salt-free, providing potential for developing new PET agents.

Photoinduced Copper-Mediated Difluoroalkylation of Arylsulfonium Salts with XCF2COR

Photoredox fluoroalkylation has emerged as a powerful method and have unlocked new possibilities in organic chemistry. In this work, the green-light-induced copper-mediated difluoroalkylation of arylsulfonium salts with different XCF2COR reagents is described. The reaction proceeded smoothly at ambient temperature under mild conditions and allowed the formation of a variety of difluoroalkylated arenes in good yields. The photocatalyst, visible-light, and Cu(I) salt played a synergetic role in the reduction of arylsulfonium salt and XCF2COR to the respective radical intermediates. This metallophotoredox protocol was applicable to the late-stage difluoroalkylation of multifunctionalized bioactive molecules, offering opportunities to the discovery of new medicinal agents. The transformation showed advantages of mildness, simple operation, good functional group tolerance, a wide range of substrates, and excellent regioselectivity, which provided an interesting alternative to other difluoroalkylation reactions in terms of structural diversity, selectivity, and availability by the application of arylsulfonium platforms.

Photo-induced decarboxylative radical cascade cyclization of unactivated alkenes: access to CF- and CF2-substituted ring-fused imidazoles

A mild and effective visible-light-induced decarboxylative radical cascade reaction of olefin-containing imidazoles with α-fluorinated carboxylic acids as building blocks containing CF or ArCF2 moieties, has been developed to afford a series of monofluoromethylated or aryldifluoromethylated polycyclic imidazoles in medium to excellent yields with features of simple operation, available raw materials, and wide substrate scopes. In addition, the mechanistic experiments indicated that the methodology involved a radical pathway.

Photoinduced Iron-Catalyzed Decarboxylation/Isomerization of gem-Difluoroallyl Carboxylic Acid to Access Vinyl Difluoromethylene Units

Vinyl difluoromethylene units (-CF-) significantly enhance the bioactivity and physical and chemical properties of compounds. Despite recent advances in introducing vinyl difluoromethylene units, radical-mediated formation of these motifs remains largely unexplored. A novel serial catalytic strategy for selective defluoroalkylation of trifluoromethyl alkenes has been developed, utilizing photocatalytic defluorocarboxylation followed by photoinduced iron-catalyzed decarboxylation/isomerization. The defluoroalkylation reaction involves generating difluoroallyl radicals, tautomerizing to vinyl difluoromethylene radicals, and proceeding through radical addition and alkylation.

Visible-Light Mediated, Dual-Catalysis Enabled Allylic Difluoroalkylation via Halogen Atom Transfer

A visible-light-mediated protocol employing a halogen atom transfer strategy (XAT) has been developed for the synthesis of homoallylic difluorinated compounds. Employing a dual-catalysis reactivity manifold, which includes a cobaloxime catalyst, the reaction occurs without exogenous oxidant and under mild conditions. The applicability of unactivated olefins, a wide variety of halogenated precursors, and access to a diverse family of difluoromethylated molecular architectures are the highlights of this method.

Nickel-Catalyzed Umpolung Difluoroalkylation of Imines Enables General Access to β-Difluoroalkylated Amines

Fluoroalkylated amines play a pivotal role in medicinal chemistry, yet the general and efficient synthesis of β-difluoroalkylated amines remains elusive. Here, we developed a nickel-catalyzed umpolung strategy that enables the difluoroalkylation of 2-azaallyl anions generated from aliphatic and aromatic imines, effectively overcoming the previous limitations. By inverting the polarity of imines, this strategy allows for the coupling of a variety of readily accessible difluoroalkyl bromides and iodides. This approach is characterized by its high efficiency, broad substrate scope, high functional group tolerance, and ease of synthesis. The rapid modification of bioactive molecules by the efficient synthesis of difluorinated analogs of key amine moieties present in bioactive molecules, including amphetamine, using the current approach shows the promising potential of this protocol in advancing drug discovery and development.

Dialkylation of Alkenes to Fluorinated δ-Lactams Enabled by Nickel-Electron-Shuttle Catalysis

The δ-lactam motif is a privileged pharmacophore in drug design and development. While these biologically relevant molecules could be assembled through two-component cyclization, a modular approach to constructing these structures via a multicomponent reaction with unactivated alkenes as starting materials is rare. Herein, we report a tandem reaction that integrates alkene-dialkylation with radical-involved ring-opening and cyclization under a single metal-electron-shuttle catalysis, which represents the most expeditious access to fluorinated δ-lactams from unactivated simple alkenes.

Photocatalytic Synthesis of Difluorinated Glycoamino Acids and Neoglycopeptides via Hydrodifluoroacetamidation of Vinyl-C-glycosides

A photocatalytic approach for the synthesis of difluorinated glycoamino acids and neoglycopeptides from bromodifluoroacetamides and sugar-derived olefins is presented. This method stands out because of its simplicity, atomic economy, and mild reaction conditions, allowing compatibility with both natural and unnatural amino acids and peptides. Additionally, it demonstrates efficacy across a variety of carbohydrates, including furanoses, pyranoses, pentose, hexoses, and disaccharides, accommodating an extensive range of protecting groups, even in their deprotected forms.

Oxygen Migration-Defluorination Strategy Enables the Aminocarbonylation of Enaminones with o-Aminobenzamides and CF2Br2

The development of different concept approaches and user-friendly carbonyl surrogates for aminocarbonylation is highly desirable. Herein, we report the photocatalytic aminocarbonylation of enaminones with easily available o-aminobenzamides and CF2Br2 through an oxygen migration-defluorination strategy. The reaction features switchable transformation for the construction of carbamoyl-substituted enaminones and enol products and allows the expedient synthesis of fully substituted maleimides under mild reaction conditions.

Nickel-catalyzed reductive cross-coupling of difluoromethylated secondary alkyl bromides with organohalides

We present a highly efficient and versatile nickel-catalyzed protocol for the reductive cross-coupling of unactivated CF2H-substituted electrophiles with a wide variety of aryl and alkenyl halides. This novel approach offers high catalytic reactivity and broad functional group compatibility, enabling late-stage fluoroalkylation of drug molecules.

Nickel-Catalyzed Difluoroalkylation of β,γ-Unsaturated α-Amino Nitrile Derived Lithium Reagents

Organolithium reagents, known for their low cost, ready availability, and high reactivity, allow fast cross-coupling under ambient conditions. However, their direct cross-coupling with fluoroalkyl electrophiles remains a formidable challenge due to the easy formation of thermo-unstable fluoroalkyl lithium species during the reaction, which are prone to decomposition via rapid α/β-fluoride elimination. Here, we exploit heteroatom-stabilized allylic anions to harness the exceptional reactivity of organolithium reagents, enabling the compatibility of difluoroalkyl halides and facilitating versatile and precise fluorine functionality introduction under mild conditions. In this process, a nickel-catalyzed difluoroalkylation of β,γ-unsaturated α-amino nitrile derived lithium reagents (N-stabilized allyl lithium reagents) with various difluoroalkyl bromides has been developed, opening a new avenue to access fluorinated compounds through catalytic cross-coupling of organolithium reagents with fluoroalkyl electrophiles. This approach allows for the efficient and precise construction of secondary C(sp3)-CF2R bonds, previously challenging in transition-metal-catalyzed fluoroalkylation reactions due to β-hydride elimination. The rapid fluorine-editing of drugs demonstrates the synthetic versatility and utility of this protocol, showing the perspective in modern drug discovery.

General access to furan-substituted gem-difluoroalkenes enabled by PFTB-promoted cross-coupling of ene-yne-ketones and difluorocarbene

Replacement of a carbonyl group with fluorinated bioisostere (e.g., CF2[double bond, length as m-dash]C) has been adopted as a key tactical strategy in drug design and development, which typically improves potency and modulates lipophilicity while maintaining biological activity. Consequently, new gem-difluoroalkenation reactions have undoubtedly accelerated this shift, and conceptually innovative practices would be of great benefit to medicinal chemists. Here we describe an expeditous protocol for the direct assembly of furan-substituted gem-difluoroalkenes via PFTB-promoted cross-coupling of ene-yne-ketones and difluorocarbene. In this multi-step tandem reaction process, the furan ring and the gem-difluorovinyl group are constructed simultaneously in an efficient manner. These products can serve as bioisosteres of the α-carbonyl furan core, which is an important scaffold present in natural products and drug candidates. The broad generality and practicality of this method for late-stage modification of bioactive molecules, gram-scale synthesis and versatile derivatisation of products has been described. Biological activity evaluation showed that the gem-difluoroalkene skeleton exhibited dramatic antitumor activity.

Copper-Catalyzed Difluoromethylation of Alkenyl Thianthrenium Salts

We have developed a novel and straightforward protocol that facilitates the transformation of alkenylsulfonium salts leading to the direct synthesis of E-difluoromethylated alkenes. The success of this method relies on the use of copper catalysis and Vicic-Mikami reagent (DMPU)2Zn(CF2H)2. These mild protocols offer the advantage of selectively synthesizing either aromatic or aliphatic difluoromethylated alkenes. Furthermore, our methodology extends to the perfluoroalkylation of alkenylsulfonium salts. Notably, this approach is conducive to large-scale synthesis and holds promise for diverse applications.

Difluoroenoxysilanes in Catalytic Asymmetric Allylic Alkylation

An allylic substitution with difluoroenoxysilanes as the nucleophile is accomplished for the enantioselective synthesis of α-allylic α,α-difluoroketones. With racemic branched allylic alcohols as the easily accessible allylic electrophile, this branched-selective and enantioconvergent allylic alkylation reaction is catalyzed by an Ir(I)/(P,olefin) complex and overcomes the low nucleophilicity of difluoroenoxysilanes to furnish β-chiral α,α-difluoroketones in moderate to good yields with high enantioselectivity (up to >99.9:0.1 er).

Defluorinative Multicomponent Cascade Reaction of Trifluoromethylarenes via Photoexcited Palladium Catalysis

The incorporation of aromatic difluoromethyl motifs has proven to be a fruitful strategy for enhancing the therapeutic profiles of modern pharmaceutical candidates. While the defluorofunctionalization of trifluoromethylarenes offers a promising pathway toward diverse aromatic difluoromethyl compounds, current methods are predominantly limited to two-component reactions. Multicomponent cascade reactions (MCRs) involving a transient aromatic difluoromethyl radical are still uncommon and highly sought after, owing to their capacity to rapidly generate challenging molecular structures. In this study, we present a photocatalytic manifold that combines commercially available trifluoromethylarenes, feedstock dienes, and various nucleophiles to achieve a modular defluorinative MCR. This method features mild reaction conditions and a broad substrate scope with excellent functional group compatibility. Furthermore, this protocol enables a previously unreported process of defluorinative editing for the resulting MCR aromatic difluoromethyl adducts. Preliminary mechanistic studies support the proposed photoexcited palladium catalytic cycle.

Recent advances in the applications of gem-difluoromethylene alkynes

As a special class of alkynes, gem-difluoromethylene alkynes exhibit a variety of fascinating properties due to the presence of the gem-difluoro substitution. This substitution highlights the distinctive fluorine effects in influencing the chemoselectivity of reactions. As a result, chemical scientists have shown great interest and enthusiasm for investigating their reactions. In this review, we briefly summarize recent advances in transition metal-catalysed reactions of gem-difluoromethylene alkynes with multiple reaction pathways. Their mechanistic studies and challenges will be highlighted. The purpose of this review is to provide illustrations of elegant gem-difluoromethylene alkynes and thereby elicit further interest among synthetic chemists in developing innovative transformations of gem-difluoromethylene alkynes.

Highly Enantioselective Decarboxylative Difluoromethylation

Organofluorine molecules that contain difluoromethyl groups (CF2H) at stereogenic centers have gained importance in pharmaceuticals due to the unique ability of CF2H groups to act as lipophilic hydrogen bond donors. Despite their potential, the enantioselective installation of CF2H groups into readily available starting materials remains a challenging and underdeveloped area. In this study, we report a nickel-catalyzed decarboxylative difluoromethylation reaction that converts alkyl carboxylic acids into difluoromethylated products with exceptional enantioselectivity. This Ni-catalyzed protocol exhibits broad functional group tolerance and is applicable for synthesizing fluorinated bioisosteres of biologically relevant molecules.

Recent advances in catalytic enantioselective construction of monofluoromethyl-substituted stereocenters

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

Oxy-difluoroallylation of Ynamides by Nickel-Catalyzed Tandem Alkoxylation/Claisen Rearrangement

A nickel-catalyzed tandem alkoxylation/claisen rearrangement strategy for the oxy-difluoroallylation of ynamides has been developed. In this reaction, 3,3-difluoroallyl alcohol was used as a fluorine-containing building block to construct the C-CF2 bond for the first time. This approach is recognized for its robust tolerance of functional groups, impressive yields, and excellent atomic efficiency, all achieved under mild reaction conditions. A series of β,β-difluoromethyleneamide derivatives were efficiently obtained through simple operations, and their practicality was confirmed through gram-scale synthesis and product derivatization.

Selective Functionalization of Alkenes and Alkynes by Dinuclear Manganese Catalysts

ConspectusAlkenes and alkynes are fundamental building blocks in organic synthesis due to their commercial availability, bench-stability, and easy preparation. Selective functionalization of alkenes and alkynes is a crucial step for the synthesis of value-added compounds. Precise control over these reactions allows efficient construction of complex molecules with new functionalities. In recent decades, second- and third-row precious transition metal catalysts (palladium, platinum, rhodium, ruthenium) have been pivotal in the development of metal-catalyzed synthetic methodology. These metals exhibit excellent catalytic activity and selectivity, enabling efficient synthesis of functionalized organic molecules. However, recovery and reuse of precious metals have long been a challenge in this field. In recent years, exploration of earth-abundant metal-catalyzed organic reactions has interested both academic and industrial researchers. The development of such catalytic systems offers a promising approach to overcome the limitations of precious metal catalysts. For example, manganese is the third most naturally abundant transition metal with minimal toxicity and excellent biocompatibility. It exhibits good catalytic activity in several organic reactions, including C-H bond functionalization, selective reduction, and radical reactions. This Account outlines our recent progress in dinuclear manganese catalysis for selective functionalization of alkenes and alkynes. We have established the elementary manganese(I)-catalysis in transmetalation with R-B(OH)2. This finding has enabled us to apply the catalyst for the selective 1,2-difunctionalization of structurally diverse alkenes and alkynes. Mechanistic studies suggest a double manganese center synergistic activation model, as superior to Mn(CO)5Br in some cases. In addition, we have developed a ligand-tuned metalloradical strategy of dinuclear manganese catalysts (Mn2(CO)10), bridging the gap between the organometallics and radical chemistry, highlighting the unique radical functionalization of alkenes. Interestingly, using the same starting materials, different ligands can deliver completely different products. Meanwhile, a cooperative catalysis strategy involving manganese and other catalysts (e.g., cobalt, iminium) has also been developed and is briefly discussed. For manganese/iminium synergistic catalysis, a new mechanism for migratory insertion and demetalization-isomerization in synergistic HOMO-LUMO activation was disclosed. This strategy expands the application of low-valent manganese catalysts for enantioselective C-C bond-forming reactions. New reaction discovery is outpacing mechanism studies for dinuclear manganese catalysis, and future studies with time-resolved spectroscopy will improve understanding of the mechanism. Based on these intriguing findings, the precise functionalization of alkenes and alkynes by dinuclear manganese catalysts will expedite a novel activation model to enable late-stage functionalization of complex molecules.

Palladium-catalyzed difluorocarbene transfer enables access to enantioenriched chiral spirooxindoles

We disclose herein an unprecedented Pd-catalyzed difluorocarbene transfer reaction, which assembles a series of structurally interesting chiral spiro ketones with generally over 90% ee. Commercially available BrCF2CO2K serves as the difluorocarbene precursor, which is harnessed as a user-friendly and safe carbonyl source in this transformation. Preliminary mechanistic studies exclude the formation of free CO in the reaction process, and importantly, we also find that BrCF2CO2K outcompete gaseous CO and several common CO surrogates in this asymmetric process. The reaction mechanism, including the in-situ progressive release of the difluorocarbene, the rapid migratory insertion of ArPd(II) = CF2 species, and subsequent defluorination hydrolysis by water to introduce the carbonyl group, accounts for the overall high efficiency and uniqueness. This work clearly showcases the advantage and potential of the difluorocarbene in synthesis and supplies a mechanistically distinct route for asymmetric carbonylative cyclization reactions.

Photo-Induced Difluoromethylation-Cyclization and Domino Amination-Defluorination to 4-(Aminomethyl)-3-fluoro-quinolinones

Herein, we report a visible light-induced difluoromethylation cyclization and subsequent amination-defluorination reaction. This protocol allows efficient to valuable 3-fluoro-quinolinones in moderate to excellent yields. A sequential difluoromethylation-cyclization-amination-defluorination mechanism was proposed based on a mechanism study. Further density functional theory (DFT) calculations revealed that the base K2HPO4 could lower the energy due to the C═O···K+ electrostatic interaction to assist the elimination process, while the six-membered transition state located in situ was essential for the cleavage of N-H and C-F bonds during this SN2'-type process.

Base-Dependent Divergent Carbodifluoroalkylation and Halodifluoroalkylation of Alkenes under Visible-Light Irradiation

Organic molecules containing a difluoroalkyl group are valuable and versatile chemicals because of their unique physicochemical and biological properties. Accordingly, the development of efficient and practical difluoroalkylation for the preparation of these compounds is important and attractive. Herein, we demonstrate photoredox-catalyzed and base-dependent selective carbodifluoroalkylation and halodifluoroalkylation of alkenes using readily available 2-(allyloxy)arylaldehydes [or 2-(allylamino)arylaldehydes] and XCF2COOEt (or BrCF2CONR1R2) as starting materials. The developed reaction enables convenient and accurate synthesis of difluoroalkylated chroman-4-ones and aldehydes and features broad substrate scope, mild conditions, and operational simplicity. Moreover, gram-scale product preparation and application of the title protocol in late-stage functionalization of pharmaceutical molecules are accomplished.

Near-Infrared-Light-Induced Iron(I) Dimer-Enabled Radical Cascade Reactions of Fluoroalkyl Bromides for the Synthesis of Ring-Fused Quinazolinones

The use of an earth-abundant and inexpensive iron complex as a catalyst, coupled with near-infrared (NIR) light as the energy source, for radical reactions with alkyl halides has been far less developed. In this study, we report NIR light-mediated iron(I) dimer-catalyzed radical cascade reactions of fluoroalkyl bromides for the synthesis of ring-fused quinazolinones bearing a difluoromethyl group. In this process, the 3-bromo-1,10-phenanthroline ligand facilitates the reactivity of [CpFe(CO)2]2, thereby improving the efficiency of the reaction.

Dialkylation of CF2 unit enabled by cobalt electron-shuttle catalysis

The incorporation of difluoromethylene (CF2) group into chemical molecules often imparts desirable properties such as lipophilicity, binding affinity, and thermal stability. Consequently, the increasing demand for gem-difluoroalkylated compounds in drug discovery and materials science has continued to drive the development of practical methods for their synthesis. However, traditional synthetic methods such as deoxofluorination often confront challenges including complicated substrate synthesis sequences and poor functional group compatibility. In this context, we herein report a metal electron-shuttle catalyzed, modular synthetic methodology for difluoroalkylated compounds by assembling two C(sp3) fragments across CF2 unit in a single step. The approach harnesses a difluoromethylene synthon as a biradical linchpin, achieving the construction of two C(sp3)-CF2 bonds through radical addition to two different π-unsaturated molecules. This catalytic protocol is compatible with broad range of coupling partners including diverse olefins, iminiums, and hydrazones, supporting endeavors in the efficient construction of C(sp3)-rich difluoroalkylated molecules.

General Defluoroalkylation of Trifluoromethylarenes with Both Electron-Donating and -Withdrawing Alkenes

The incorporation of gem-difluoromethylene units into organic molecules remains a formidable challenge. Conventional methodologies for constructing aryldifluoromethyl derivatives relied on the use of high-functional fluorinating regents under harsh conditions. Herein, we report general and efficient photoredox catalytic systems for defluoroalkylation of readily available trifluoromethylarenes through selective C-F cleavage to deliver gem-difluoromethyl radicals which proceed through reductive addition to both electron-donating and withdrawing alkenes under transition-metal free conditions. Mechanistic studies reveal that thiol serves as both photocatalyst and HAT reagent under visible light irradiation. This synergistic photocatalysis and HAT catalysis protocol exhibits ample and salient features such as high chemo- and regioselectivity, broad substrate scope, amenable gram-scale synthesis and late-stage modification of bioactive molecules.

Nickel-catalyzed regiodivergent sulfonylarylation of 1,3-enynes to access allenes and dienes

The radical-mediated difunctionalization of 1,3-enynes facilitates rapid access to structurally diverse allenes and dienes. Whereas, owing to the existence of multiple active sites in conjugated 1,3-enynes, regulating selectivity in difunctionalized addition via a single transition-metal-catalyzed radical tandem process remains elusive. Herein, we disclose an intriguing protocol of substrate-controlled nickel-catalyzed regiodivergent sulfonylarylation of 1,3-enynes with the assistance of sulfonyl chlorides and arylboronic acids. This valuable synthetic utility respectively delivers a series of highly functionalized and synthetically challenging allenyl sulfones and dienyl sulfones from fine-tuned 1,3-enynes by one step, which provides a facile approach for complex sulfone-containing drug molecules synthesis.

Nickel-catalyzed regiodivergent hydrosilylation of α-(fluoroalkyl)styrenes without defluorination

The fluoroalkyl-containing organic molecules are widely used in drug discovery and material science. Herein, we report ligand regulated nickel(0)-catalyzed regiodivergent hydrosilylation of α-(fluoroalkyl)styrenes without defluorination, providing an atom- and step-economical synthesis route of two types of fluoroalkyl substituted silanes with exclusive regioselectivity. The anti-Markovnikov addition products (β-fluoroalkyl substituted silanes) are formed with monodentate phosphine ligand. Noteworthy, the bidentate phosphine ligand promote the generation of the more challenging Markovnikov products (α-fluoroalkyl substituted silanes) with tetrasubstituted saturated carbon centers. This protocol features with easy available starting materials and commercially available nickel catalysis, a wide range of substrates and excellent regioselectivity. The structure divergent products undergo a variety of transformations. Comprehensive mechanistic studies including the inverse kinetic isotope effects demonstrate the regioselectivity controlled by ligand structure through α-CF3 nickel intermediate. DFT calculations reveal a distinctive mechanism involving an open-shell singlet state, which is crucial for generating intricate tetra-substituted Markovnikov products.

Fluorine-Effect-Enabled Photocatalytic 4-Exo-Trig Cyclization Cascade to Access Fluoroalkylated Cyclobutanes

Cyclobutanes are popular structural units in bioactive compounds and versatile intermediates in synthetic chemistry, but their synthesis is challenging owing to high ring strain. In this study, a novel method for highly regio- and diastereoselective synthesis of fluoroalkylcyclobutanes bearing vicinal quaternary and tertiary stereocenters is realized by a photocatalytic 4-exo-trig cyclization cascade of thioalkynes or trifluoromethylalkenes. Density functional theory calculations reveal that a unique fluorine effect, arising from hyperconjugative π→σ*C-F interactions, accounts for the regio-reversed radical addition at the sterically hindered alkene carbon, which facilitates an unprecedented 4-exo-trig ring closure. This chemistry enables the direct and controllable construction of medicinally valuable quaternary-carbon-containing cyclobutanes from readily available raw materials, nicely complementing the existing methods.

Electrochemical synthesis of β-difluoromethylamide compounds by N-benzenesulfonylacrylamide with difluorine reagents

A mild and efficient electrochemical method for radical addition, cyclization, and migration reaction was described in this work. A difluoromethyl radical was produced by anodizing CF2HSO2Na. The resulting product was then added to olefin, underwent Smiles cyclization, and migrated to form β-difluoromethamide compounds after the release of SO2. The process was free from metals and catalysts, gram-grade, and resistant to a variety of electron-rich substrates.

Tetrafluoroisopropylation of alkenes and alkynes enabled by photocatalytic consecutive difluoromethylation with CF2HSO2Na

Direct assembly of complex fluorinated motifs from simple fluorine sources is an attractive frontier of synthetic chemistry. Reported herein is an unconventional protocol for achieving tetrafluoroisopropylation by using commercially available CF2HSO2Na as a convenient source of the tetrafluoroisopropyl [(CF2H)2CH] group, which finds widespread applications in life science and material science. Visible-light-induced hydrotetrafluoroisopropylation of alkenes and carbotetrafluoroisopropylation of alkynes have been thus developed. Various structurally diverse α-tetrafluoroisopropyl carbonyls and cyclopentanones are selectively constructed under mild conditions. A photocatalytic triple difluoromethylation cascade, driven by consecutive reductive radical/polar crossover processes, leads to the direct assembly of a tetrafluoroisopropyl moiety from CF2HSO2Na. This C1-to-C3 fluoroalkylation protocol provides a practical strategy for the rapid construction of polyfluorinated compounds that are otherwise difficult to access, thus significantly enhancing the boundary of fluoroalkylation chemistry.

Visible Light-Induced Copper-Catalyzed Regio- and Stereoselective Difluoroalkylthiocyanation of Alkynes

The first regio- and stereoselective difluoroalkylthiocyanation of alkynes with BrCF2R and KSCN has been disclosed under visible light-induced copper catalysis. The copper complex photosensitizer formed in situ not only promotes the generation of CF2-alkyl radicals but also facilitates the construction of C-SCN bonds, allowing the reaction to proceed smoothly without any additional photocatalysts or radical initiators. Moreover, the challenging internal alkynes can also be transformed to deliver CF2-derived tetrasubstituted olefins with potential applications in agricultural and medicinal chemistry.

One-pot C(sp3)-H difluoroalkylation of tetrahydroisoquinolines and isochromans via electrochemical oxidation and organozinc alkylation

The C(sp3)-H difluoroalkylation for the introduction of carbonylated CF2 groups into tetrahydroisoquinolines (THIQs) and isochromans has been achieved by using electrochemical oxidation and organozinc alkylation. This one-pot process proceeded smoothly under transition-metal catalyst- and chemical oxidant-free conditions, and the desired products were obtained in good to high yields with a broad scope, except for N-Boc-THIQ. In addition, the gram-scale experiment successfully demonstrated the promising scalability. This is the first example of an electrochemical method for C(sp3)-H difluoroalkylation of amines and ethers.

Reversal of the Regioselectivity of Iron-Promoted Hydrogenation and Hydrohalogenation of gem-Difluoroalkenes

The reaction regioselectivity of gem-difluoroalkenes is dependent on the intrinsic polarity. Thus, the reversal of the regioselectivity of the addition reaction of gem-difluoroalkenes remains a formidable challenge. Herein, we described an unprecedented reversal of regioselectivity of hydrogen atom transfer (HAT) to gem-difluoroalkenes triggered by Fe-H species for the formation of difluoroalkyl radicals. Hydrogenation of the in situ generated radicals gave difluoromethylated products. Mechanism experiments and theoretical studies revealed that the kinetic effect of the irreversible HAT process resulted in the reversal of the regioselectivity of this scenario, leading to the formation of a less stable α-difluoroalkyl radical regioisomer. On basis of this new reaction of gem-difluoroalkene, the iron-promoted hydrohalogenation of gem-difluoroalkenes for the efficient synthesis of aliphatic chlorodifluoromethyl-, bromodifluoromethyl- and iododifluoromethyl-containing compounds was developed. Particularly, this novel hydrohalogenation of gem-difluoroalkenes provided an effect and large-scale access to various iododifluoromethylated compounds of high value for synthetic application.

Chemoselective Synthesis of α-Halo-α,α-difluoromethyl Ketones from Trimethyl(phenylethynyl)silane

Here, we describe a novel strategy for chemoselective synthesis of α-halo-α,α-difluoromethyl ketones (-COCF3 and -COClCF2 motifs) from trimethyl(phenylethynyl)silane under catalyst-free and mild conditions. Commercially available Selectfluor or additional NaCl as halogen reagent was employed to complete this transformation, thereby demonstrating the potential synthetic value of this new reaction in organic synthesis.

Hybrid Palladium-Catalyzed Intramolecular Carboamination of Conjugated Dienes: Synthesis of Functionalized Pyrrolidines via Selective Trifluoromethylarene Defluorination

The incorporation of difluoromethylene groups into aza-heterocycles represents a compelling yet underexplored avenue in contemporary chemical research. In this study, we unveil a hybrid palladium-catalyzed intramolecular gem-difluoroalkylamination of conjugated dienes, providing a versatile approach to the synthesis of diverse functionalized pyrrolidines. Noteworthy features include mild reaction conditions and a remarkable tolerance toward various functional groups. Additionally, the use of alkyl iodides as electrophiles facilitates the generation of the corresponding alkylamination products. Control experiments support a proposed hybrid palladium-catalyzed radical-polar crossover pathway, offering insights into the underlying chemical processes governing this transformation.

Masters of Mediation: MN(SiMe3)2 in Functionalization of C(sp3)-H Latent Nucleophiles

Organoalkali compounds have undergone a far-reaching transformation being a coupling partner to a mediator in unusual organic conversions which finds its spot in the field of sustainable synthesis. Transition-metal catalysis has always been the priority in C(sp3)-H bond functionalization, however alternatively, in recent times this has been seriously challenged by earth-abundant alkali metals and their complexes arriving at new sustainable organometallic reagents. In this line, the importance of MN(SiMe3)2 (M=Li, Na, K & Cs) reagent revived in C(sp3)-H bond functionalization over recent years in organic synthesis is showcased in this minireview. MN(SiMe3)2 reagent with higher reactivity, enhanced stability, and bespoke cation-π interaction have shown eye-opening mediated processes such as C(sp3)-C(sp3) cross-coupling, radical-radical cross-coupling, aminobenzylation, annulation, aroylation, and other transformations to utilize readily available petrochemical feedstocks. This article also emphasizes the unusual reactivity of MN(SiMe3)2 reagent in unreactive and robust C-X (X=O, N, F, C) bond cleavage reactions that occurred alongside the C(sp3)-H bond functionalization. Overall, this review encourages the community to exploit the untapped potential of MN(SiMe3)2 reagent and also inspires them to take up this subject to even greater heights.

Redox Relay-Induced C-S Radical Cross-Coupling Strategy: Application in Nontraditional Site-Selective Thiocyanation of Quinoxalinones

Oxidative cross-coupling is a powerful strategy to form C-heteroatom bonds. However, oxidative cross-coupling for constructing C-S bond is still a challenge due to sulfur overoxidation and poisoning transition-metal catalysts. Now, electrochemical redox relay using sulfur radicals formed in situ from inorganic sulfur source offers a solution to this problem. Herein, electrochemical redox relay-induced C-S radical cross-coupling of quinoxalinones and ammonium thiocyanate with bromine anion as mediator is presented. The electrochemical redox relay comprised initially the formation of sulfur radical via indirect electrochemical oxidation, simultaneous electrochemical reduction of the imine bond, electro-oxidation-triggered radical coupling involving dearomatization-rearomatization, and the reformation of the imine bond through anodic oxidation. Applying this strategy, various quinoxalinones bearing multifarious electron-deficient/-rich substituents at different positions were well compatible with moderate to excellent yields and good steric hindrance compatibility under constant current conditions in an undivided cell without transition-metal catalysts and additional redox reagents. Synthetic applications of this methodology were demonstrated through gram-scale preparation and follow-up transformation. Notably, such a unique strategy may offer new opportunities for the development of new quinoxalinone-core leads.

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.

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.

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.

Selective Mono-Defluorinative Cross-Coupling of Trifluoromethyl arenes via Multiphoton Photoredox Catalysis

A new cross-coupling of trifluoromethyl arenes has been realized via multiphoton photoredox catalysis. Trifluoromethyl arenes were demonstrated to undergo selective mono-defluorinative alkylation under mild reaction conditions providing access to a series of valuable α,α-difluorobenzylic compounds. The reaction shows broad substrate scope and general functional group tolerance. In addition to the electron-deficient trifluoromethyl arenes that are easily reduced to the corresponding radical anion, more challenging electron-rich substrates were also successfully applied. Steady-State Stern-Volmer quenching studies indicated that the trifluoromethyl arenes were reduced by the multiphoton excited Ir-based photocatalyst.

Palladium-Catalyzed Iodine Assisted Carbonylation of Indoles with ClCF2CO2Na and Alcohols

A palladium-catalyzed iodine-assisted carbonylation reaction of indoles with readily available ClCF2CO2Na and alcohols has been developed. This protocol provides a practical and efficient approach to highly regioselective indole-3-carboxylates via a preiodination strategy of indoles. Different from classic carbonylation using toxic and difficult-to-handle carbon monoxide, this operationally simple and scalable reaction employed difluorocarbene as the carbonyl surrogate.

Stereoselective Control of the Cu Activation of β,β-Diboryl Acrylates for Allylic Coupling Protocols with Concomitant Lactonization

The key to a successful C-B activation is to discriminate between two geminal boryl moieties that are exposed to the same reaction conditions. Here we describe a stereoselective C-B activation of β,β-diboryl acrylates forming exclusively the (Z)-α-borylalkenyl copper(I) key intermediate, for subsequent allylic alkylation reactions. The new borylated (Z)-skipped dienoates followed a feasible iodo-lactonization sequence for the preparation of borylated lactone cores, which can be used in drug discovery.

Catalytic Asymmetric Difluoroalkylation Using In Situ Generated Difluoroenol Species as the Privileged Synthon

A robust and practical difluoroalkylation synthon, α,α-difluoroenol species, which generated in situ from trifluoromethyl diazo compounds and water in the presence of dirhodium complex, is disclosed. As compared to the presynthesized difluoroenoxysilane and in situ formed difluoroenolate under basic conditions, this difluoroenol intermediate displayed versatile reactivity, resulting in dramatically improved enantioselectivity under mild conditions. As demonstrated in catalytic asymmetric aldol reaction and Mannich reactions with ketones or imines in the presence of chiral organocatalysts, quinine-derived urea, and chiral phosphoric acid (CPA), respectively, this relay catalysis strategy provides an effective platform for applying asymmetric fluorination chemistry. Moreover, this method features a novel 1,2-difunctionalization process via installation of a carbonyl motif and an alkyl group on two vicinal carbons, which is a complementary protocol to the metal carbene gem-difunctionalization reaction.

Access to CF2COR-Containing Quinazolinones via Visible-Light-Induced Domino Difluoroalkylation/Cyclization of N-Cyanamide Alkenes

A green and highly efficient visible-light-induced radical cascade difluoroalkylation/cyclization reaction of N-cyanamide alkenes has been developed. A variety of CF2COR-containing quinazolinones have been obtained in high yields with cheap non-metallic 4CzIPN as the photocatalyst. This photocatalytic reaction provides rapid, facile, and practical access to valuable polycyclic quinazolinone, and it is amenable to the gram scale.

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.

Synthesis of gem-Difluorinated 2,3-Dihydrobenzofurans Using Freon-22 via [4 + 1] Annulation of Difluorocarbene and Antitumor Activity Evaluation

As an inexpensive industrial chemical, chlorodifluoromethane (Freon-22), despite its relatively low reactivity, can serve as a practical CF2 source for the construction of gem-difluorinated ring structures. Here, we develop a protocol for the efficient assembly of valuable fluorinated 2,3-dihydrobenzofurans from the [4 + 1] annulation in good yields under basic conditions. The reliable practicability and scalability of the process have also been demonstrated by preparation at the multigram scale, late-stage modifications of pharmaceutical molecules, and potential antitumor potency.