Nickel-Catalyzed Difluoroalkylation of (Hetero)Arylborons with Unactivated 1-Bromo-1,1-difluoroalkanes

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.

Recent advances on non-precious metal-catalysed fluorination, difluoromethylation, trifluoromethylation, and perfluoroalkylation of N-heteroarenes

This review highlights the recent advances, from 2015 to 2023, on the introduction of organo-fluorine derivatives at the N-heteroarene core. Notable features considering new technologies based on organofluorine compounds such as: (i) approaches based on non-precious metal catalysis (Fe, Co, Mn, Ni, etc.), (ii) the development of new strategies using non-precious metal-catalysts for the introduction of organo-fluorinine derivatives using N-heterocycles with one or more heteroatoms, (iii) newer reagents for fluorination, difluoromethylation, trifluoromethylation, or perfluoroalkylation of N-heteroarenes using different approaches, (iv) mechanistic studies on various catalytic transformations, as and when required, and (v) the synthetic applications of various bio-active organo-fluorine compounds, including post-synthetic drug derivatization, are discussed.

Visible-Light-Induced Cascade Cyclization of 1-Acryloyl-2-cyanoindole: Access of Difluoroalkylated Pyrrolo[1,2-a]indolediones

An effective method for accessing diverse difluoroalkylated pyrrolo[1,2-a]indolediones via visible-light-induced PhI(OAc)2-promoted cascade difluoroalkylation/cyclization reaction under mild conditions has been established. This method is noteworthy for its use of DMSO-H2O as a green medium at room temperature and avoidance of photocatalysts. The reactions are straightforward to execute and convenient to expand on, provide good to excellent yields, and have good functional group tolerance.

Silver-Promoted Radical Cascade Aryldifluoromethylation/Cyclization of 2-Allyloxybenzaldehydes for the Synthesis of 3-Aryldifluoromethyl-Containing Chroman-4-one Derivatives

A convenient silver-promoted radical cascade aryldifluoromethylation/cyclization of 2-allyloxybenzaldehydes has been developed. Experimental studies disclosed that the addition of aryldifluoromethyl radicals in situ produced from easily accessible gem-difluoroarylacetic acids to unactivated double bonds in 2-allyloxybenzaldehyde was an effective route to access a series of 3-aryldifluoromethyl-containing chroman-4-one derivatives in moderate to good yields under mild reaction conditions.

Nickel-Catalyzed Reductive Dicarbofunctionalizations of Alkenes for the Synthesis of Difluorocarbonyl Oxindoles and Isoquinoline-1,3-diones

A novel and efficient strategy for the construction of difluorocarbonyl-oxindole and difluorocarbonyl-isoquinoline-1,3-dione derivatives involving nickel-catalyzed intramolecular Heck-type cyclizations followed by intermolecular cross-couplings has been developed. This approach features high functional group tolerance, broad substrate scope, and operational simplicity under mild conditions, thus providing a new method for the rapid difluorocarbonyl-functionalization of alkenes to construct the structurally diversified five- and six-membered heterocycles.

A Base-Promoted Reductive Coupling Platform for the Divergent Defluorofunctionalization of Trifluoromethylarenes

We report a trifluoromethylarene reductive coupling method that dramatically expands the scope of difluorobenzylic substructures accessible via C-F bond functionalization. Catalytic quantities of a Lewis base, combined with a disilane reagent in formamide solvent, promotes the replacement of a single trifluoromethyl fluorine atom with a silylated hemiaminal functional group. The reaction proceeds through a difluorobenzyl silane intermediate that can also be isolated. Together, these defluorinated products are shown to provide rapid access to over 20 unique difluoroalkylarene scaffolds.

Synthesis of aryldifluoromethyl aryl ethers via nickel-catalyzed suzuki cross-coupling between aryloxydifluoromethyl bromides and boronic acids

As a unique organofluorine fragment, gem-difluoromethylated motifs have received widespread attention. Here, a convenient and efficient synthesis of aryldifluoromethyl aryl ethers (ArCF₂OAr') was established via Nickel-catalyzed aryloxydifluoromethylation with arylboronic acids. This approach features easily accessible starting materials, good tolerance of functionalities, and mild reaction conditions. Diverse late-stage difluoromethylation of many pharmaceuticals and natural products were readily realized. Notably, a new difluoromethylated PD-1/PD-L1 immune checkpoint inhibitor was conveniently synthesized and showed both improved metabolic stability and enhanced antitumor efficacy. Preliminary mechanistic studies suggested the involvement of a Ni(I/III) catalytic cycle.

Synthesis of α-Fluorinated Areneacetates through Photoredox/Copper Dual Catalysis

The development of mild and practical conditions for the fluoroalkylation of arenes is an ongoing challenge in chemical organic synthesis. Herein, we report a metallaphotoredox method for the preparation of fluoroalkyl arenes based on the synergistic combination of Ir/Cu dual catalysis from boronic acids. The mild conditions allow broad functional group tolerance, including substrates containing aldehydes, free phenols, and N-Boc-protected amines. Mechanistic investigations support a process proceeding via photoredox/copper dual catalysis.

Coupling of Heteroaryl Halides with Chlorodifluoroacetamides and Chlorodifluoroacetate by Nickel Catalysis

A nickel-catalyzed cross-coupling of heteroaryl halides with chlorodifluoroacetamides and chlorodifluoroacetate has been developed. The combination of NiCl₂  ⋅ DME with 4,4'-diNon-bpy, co-ligand PPh₃ , and additive LiCl renders the catalytic system efficient for the synthesis of medicinal interest heteroaryldifluoroacetamides. The application of the method leads to short and highly efficient synthesis of biologically active molecules, providing a facile route for applications in medicinal chemistry and agrochemistry.

(Fluoro)alkylation of alkenes promoted by photolysis of alkylzirconocenes

Difluoroalkylated compounds have important applications in pharmaceutical, agrochemical, and materials science. However, efficient methods to construct the alkylCF₂–alkyl bond are very limited, and the site-selective introduction of a difluoromethylene (CF₂) group into an aliphatic chain at the desired position remains challenging. Here, we report an unprecedented example of alkylzirconocene promoted difluoroalkylation of alkyl- and silyl-alkenes with a variety of unactivated difluoroalkyl iodides and bromides under the irradiation of visible light without a catalyst. The resulting difluoroalkylated compounds can serve as versatile synthons in organic synthesis. The reaction can also be applied to activated difluoroalkyl, trifluoromethyl, perfluoroalkyl, monofluoroalkyl, and nonfluorinated alkyl halides, providing a general method to controllably access fluorinated compounds. Preliminary mechanistic studies reveal that a single electron transfer (SET) pathway induced by a Zr(iii) species is involved in the reaction, in which the Zr(iii) species is generated by the photolysis of alkylzirconocene with blue light.

An unprecedented example of alkylzirconocene promoted difluoroalkylation of alkyl- and silyl-alkenes with a variety of fluoroalkyl and nonfluoroalkyl halides under the irradiation of visible light has been reported.

Nickel-catalyzed alkyl-arylation of 3,3,3-trifluoropropene

Owing to the versatile synthetic utility of its carbon-carbon double bond, low-cost industrial chemical 3,3,3-trifluoropropene (TFP) represents one of the most straightforward and cost-efficient precursors to prepare trifluoromethylated compounds. However, only limited methods for the efficient transformations of TFP have been reported so far. Here, we report a nickel-catalyzed dicarbofunctionalization of TFP. The reaction uses inexpensive NiCl2·6H2O as the catalyst and 4,4'-biMeO-bpy and PCy2Ph as the ligands, allowing the alkyl-arylation of TFP with a variety of tertiary alkyl iodides and arylzinc reagents in high efficiency. This nickel-catalyzed process overcomes the previous challenges by suppressing β-H and β-F eliminations from TFP, rendering this strategy effective for the transformations of TFP into medicinal interest trifluoromethylated compounds.

Organocatalytic difluorobenzylation of 1,2-diketones via mild cleavage of carbon–carbon bonds

Difluoroacetophenones (DFAPs) are developed as a class of novel and practical reagents for organocatalytic difluorobenzylation reactions.

Nucleophilic Substitution of Selenosulfonates with Me3SiCF2Br: Facile and Efficient Access to Bromodifluoromethylated Selenides under Metal-Free Conditions

A facile synthesis of bromodifluoromethylated selenides under metal-free conditions is described here. Commercially available Me₃SiCF₂Br and bench-stable selenosulfonates react smoothly to give a broad scope of alkyl- and aryl-substituted bromodifluoromethylated selenides in moderate to good yields via a difluorocarbene intermediate. This protocol features a short reaction time, the absence of toxic waste, good scalability, and successful late-stage modification of bioactive molecules. In addition, the title products can be easily converted to different fluorinated and ¹⁸F-labeled selenides.

Palladium-Catalyzed Carbonylative Cross-Coupling of Difluoroalkyl Halides with Alkylboranes under 1 atm of CO

A palladium catalyzed carbonylative cross-coupling of difluoroalkyl halides with alkyl-9-BBN under 1 atm of CO has been developed. The reaction shows broad substrate scope and high functional group tolerance, even toward complex pharmaceuticals, providing a general and straightforward method to access alkyldifluoroalkyl ketones. Preliminary mechanistic studies reveal that a radical pathway is involved in the reaction.

Visible-Light-Induced Palladium-Catalyzed Selective Defluoroarylation of Trifluoromethylarenes with Arylboronic Acids

Selective functionalization of inactive C(sp³)-F bonds to prepare medicinally interesting aryldifluoromethylated compounds remains challenging. One promising route is the transition-metal-catalyzed cross-coupling through oxidative addition of the C(sp³)-F bond in trifluoromethylarenes (ArCF₃), which are ideal precursors for this process due to their ready availability and low cost. Here, we report an unprecedented excited-state palladium catalysis strategy for selective defluoroarylation of trifluoromethylarenes with arylboronic acids. This visible-light-induced palladium-catalyzed cross-coupling proceeds under mild reaction conditions and allows transformation of a variety of arylboronic acids and ArCF₃. Preliminary mechanistic studies reveal that the oxidative addition of the C(sp³)-F bond in ArCF₃ to excited-state palladium(0) via a single electron transfer pathway is responsible for the C(sp³)-F bond activation.

3,3-Difluoroallyl ammonium salts: highly versatile, stable and selective gem-difluoroallylation reagents

The selective synthesis of fluorinated organic molecules continues to be of major importance for the development of bioactive compounds (agrochemicals and pharmaceuticals) as well as unique materials. Among the established synthetic toolbox for incorporation of fluorine-containing units, efficient and general reagents for introducing -CF2- groups have been largely neglected. Here, we present the synthesis of 3,3-difluoropropen-1-yl ammonium salts (DFPAs) as stable, and scalable gem-difluoromethylation reagents, which allow for the direct reaction with a wide range of fascinating nucleophiles. DFPAs smoothly react with N-, O-, S-, Se-, and C-nucleophiles under mild conditions without necessity of metal catalysts with exclusive regioselectivity. In this way, the presented reagents also permit the straightforward preparation of many analogues of existing pharmaceuticals.

Iron-Catalyzed Fluoroalkylation of Arylborates with Sulfone Reagents: Beyond the Limitation of Reduction Potential

The iron-catalyzed alkyl-aryl coupling reaction between sulfones and arylboron compounds has remained a challenge. We report the first iron-catalyzed radical difluoroalkylation of arylborates with N-heteroaryl sulfones. The coordination between the iron catalyst and the nitrogen atom of N-heteroaryl sulfones was identified to be important in overcoming the reduction potential limitation of sulfones in the intermolecular single-electron-transfer process, which enables both fluoroalkyl N-heteroaryl sulfones (with relatively high reduction potentials) and nonfluorinated alkyl N-heteroaryl sulfones (with low reduction potentials) to serve as powerful alkylation reagents.

Synthesis of Spirocycles via Ni-Catalyzed Intramolecular Coupling of Thioesters and Olefins

A nickel-catalyzed intramolecular coupling of thioesters and olefins has been developed for the efficient synthesis of spirocycles, a privileged scaffold commonly found in natural products. This transformation is characterized by the simultaneous transfer of both acyl and thiol moieties to the alkene, with the suppression of decarbonylation and β-hydrogen elimination. Initial mechanistic investigations are consistent with an oxidative addition/olefin insertion/reductive elimination mechanism. The incorporated methylene sulfide substituent can undergo a variety of further reactions to increase molecular diversity and complexity. These results demonstrate that thioester derivatives can be used as powerful building blocks for the assembly of complex scaffolds.

Direct Carbon Isotope Exchange of Pharmaceuticals via Reversible Decyanation

The incorporation of carbon-14 allows tracking of organic molecules and provides vital knowledge on their fate. This information is critical in pharmaceutical development, crop science, and human food safety evaluation. Herein, a transition-metal-catalyzed procedure enabling carbon isotope exchange on aromatic nitriles is described. By utilizing the radiolabeled precursor Zn([¹⁴C]CN)₂, this protocol allows the insertion of the desired carbon tag without the need for structural modifications, in a single step. By reducing synthetic costs and limiting the generation of radioactive waste, this procedure will facilitate the labeling of nitrile containing drugs and accelerate ¹⁴C-based ADME studies supporting drug development.

Synthetic applications of α,α-difluoroarylacetic acids and salts via decarboxylative functionalization

α,α-Difluoroarylacetic acids are stable, inexpensive and readily available building blocks which can be used to access various difluoromethylated aryl motifs via decarboxylative functionalization for the formation of carbon–carbon and carbon-heteroatom (F, O, S) bonds.

Arylation of gem-difluoroalkenes using a Pd/Cu Co-catalytic system that avoids β-fluoride elimination

Pd^II/Cu^I co-catalyze an arylation reaction of gem-difluoroalkenes using arylsulfonyl chlorides to deliver α,α-difluorobenzyl products. The reaction proceeds through a β,β-difluoroalkyl-Pd intermediate that typically undergoes unimolecular β-F elimination to deliver monofluorinated alkene products in a net C-F functionalization reaction. However to avoid β-F elimination, we offer the β,β-difluoroalkyl-Pd intermediate an alternate low-energy route involving β-H elimination to ultimately deliver difluorinated products in a net arylation/isomerization sequence. Overall, this reaction enables exploration of new reactivities of unstable fluorinated alkyl-metal species, while also providing new opportunities for transforming readily available fluorinated alkenes into more elaborate substructures.

Nickel-Catalyzed Four-Component Carbocarbonylation of Alkenes under 1 atm of CO

Transition-metal-catalyzed carbonylation is one of the most straightforward strategies to prepare carbonyl compounds. However, compared to well-established noble-metal-catalyzed carbonylation reactions, analogue coupling via base-metal, nickel catalysis has received less attention because of the easy formation of highly toxic and unreactive Ni(CO)₄ species between Ni(0) and CO. To date, the use of inexpensive and widely available carbon monoxide (CO) gas for nickel-catalyzed carbonylation reaction remains challenging, and nickel-catalyzed four-component carbonylative reaction has not been reported yet. Here, we report a highly selective nickel-catalyzed four-component carbocarbonylation of alkenes under 1 atm (1 atm) of CO gas to efficiently achieve an array of complex carbonyl compounds, including fluorinated amino acids and oligopeptides of great interest in medicinal chemistry and chemical biology. This reaction relies on a nickel-catalyzed one-pot cascade process to assemble CO, arylboronic acids, and difluoroalkyl electrophiles across the carbon-carbon double bond of alkenes, paving a new way for base-metal-catalyzed carbonylative cascade reaction.

Chalcogenide-Catalyzed Intermolecular Electrophilic Thio- and Halofunctionalization of gem-Difluoroalkenes: Construction of Diverse Difluoroalkyl Sulfides and Halides

Thio- and halodifluoromethylated compounds are an important class of compounds in medicinal chemistry and organic synthesis. Herein, we report a facile method for the construction of these compounds via chalcogenide-catalyzed intermolecular electrophilic thio- and halofunctionalization of gem-difluoroalkenes. Simple treatment of gem-difluoroalkenes with electrophilic sulfur/halogen reagents and various O- or N-nucleophiles affords diverse multifunctionalized thio- and halodifluoromethylated compounds. This reaction features a relatively broad substrate scope, good functional group tolerance, and mild reaction conditions.

Regio- and Enantioselective Bromocyclization of Difluoroalkenes as a Strategy to Access Tetrasubstituted Difluoromethylene-Containing Stereocenters

Difluoromethylene-containing compounds have attracted substantial research interest over the past decades for their ability to mimic biological functions of traditional functional groups while providing a wide variety of pharmacological benefits bestowed by the C-F bond. We report a novel strategy to access RCF2Br-containing heterocycles by regio- and enantioselective bromocyclization of difluoroalkenes enabled by chiral anion phase-transfer catalysis. The utility of this methodology was highlighted through a synthesis of an analogue of efavirenz, a drug used for treating HIV. Additionally, the synthetic versatility of the CF2Br intermediates was showcased through functionalization to a variety of enantioenriched α,α-difluoromethylene-containing products.

Photoinitiated decarboxylative C3-difluoroarylmethylation of quinoxalin-2(1H)-ones with potassium 2,2-difluoro-2-arylacetates in water

An efficient and green strategy for the preparation of C3-difluoroarylmethylated quinoxalin-2(1H)-one via a visible-light-induced decarboxylative C3-difluoroarylmethylation of quinoxalin-2(1H)-one with potassium 2,2-difluoro-2-arylacetate in water at room temperature was developed. This photoinduced reaction generated the desired products in good yields under simple and mild conditions.

Silver-Catalyzed Decarboxylative Allylation of Difluoroarylacetic Acids with Allyl Sulfones in Water

A practical silver-catalyzed decarboxylative allylation of α,α-difluoroarylacetic acids with allyl sulfones is described, which provides a variety of β,β-difluorinated alkenes in good yields. Notably, the reaction proceeds smoothly in water with good functional group tolerance. The practicality and synthetic value of this process was demonstrated by scaled-up experiment and elaboration of the products via reduction or Heck reaction. Primary mechanism investigations suggest that a radical process might be involved.

Visible light promoted deaminative difluoroalkylation of aliphatic amines with difluoroenoxysilanes

A visible light promoted deaminative strategy for the difluoroalkylation reaction utilizing pyridinium-activated aliphatic primary amines and difluoroenoxysilane as substrates has been developed.

Controlling the Cleavage of Carbon-Carbon Bonds To Generate α,α-Difluorobenzyl Carbanions for the Construction of Difluoromethylbenzenes

Controlling the cleavage of carbon-carbon bonds during a chemical reaction is a substantial challenge; however, synthetic methods that accomplish this objective produce valuable and often unexplored reactivity. We have designed a mild process to generate α,α-difluorobenzyl carbanions in the presence of potassium carbonate by exploiting the cleavage of C-C bonds during the release of trifluoroacetate. The initiating reagent is potassium carbonate, which represents an improvement over existing protocols that require a strong base. Fragmentation studies across substituted arenes and heteroarenes were conducted along with computational analyses to elucidate reactivity trends. Furthermore, the mildly generated α,α-difluorobenzyl carbanions from electron-deficient aromatics and heteroaromatic rings can react with aldehydes to create derivatives of difluoromethylbenzenes, which are valuable synthetic targets.

Nickel-Catalyzed Hydroarylation of Alkynes under Reductive Conditions with Aryl Bromides and Water

An operationally simple nickel-catalyzed hydroarylation reaction for alkynes is described. This three-component coupling reaction utilizes commercially available alkynes and aryl bromides, along with water and Zn. An air-stable and easily synthesized Ni(II) precatalyst is the only entity used in the reaction that is not commercially available. This reductive cross-coupling reaction displays a fairly unusual anti selectivity when aryl bromides with ortho substituents are used. In addition to optimization data and a preliminary substrate scope, complementary experiments including deuterium labeling studies are used to provide a tentative catalytic mechanism. We believe this report should inspire and inform other Ni-catalyzed carbofunctionalization reactions.

1,1-Difluoroethyl chloride (CH3CF2Cl), a novel difluoroalkylating reagent for 1,1-difluoroethylation of arylboronic acids

1,1-Difluoroethylated aromatics are of great importance in medicinal chemistry and related fields. 1,1-Difluoroethyl chloride (CH₃CF₂Cl), a cheap and abundant industrial raw material, is viewed as an ideal 1,1-difluoroethylating reagent, but the direct introduction of the difluoroethyl (CF₂CH₃) group onto aromatic rings using CH₃CF₂Cl has not been successfully accomplished. Herein, we disclose a nickel-catalyzed 1,1-difluoroethylation of arylboronic acids with CH₃CF₂Cl for the synthesis of (1,1-difluoroethyl)arenes.

1,1-Difluoroethylated aromatics are of great importance in medicinal chemistry and related fields.

Selective C-F Functionalization of Unactivated Trifluoromethylarenes

Fluorinated organic molecules are pervasive within the pharmaceutical and agrochemical industries due to the range of structural and physicochemical properties that fluorine imparts. Currently, the most abundant methods for the synthesis of the aryl-CF₂ functionality have relied on the deoxyfluorination of ketones and aldehydes using expensive and poorly atom economical reagents. Here, we report a general method for the synthesis of aryl-CF₂R and aryl-CF₂H compounds through activation of the corresponding trifluoromethyl arene precursors. This strategy is enabled by an endergonic electron transfer event that provides access to arene radical anions that lie outside of the catalyst reduction potential. Fragmentation of these reactive intermediates delivers difluorobenzylic radicals that can be intercepted by abundant alkene feedstocks or a hydrogen atom to provide a diverse array of difluoalkylaromatics.

Selective single C-F bond arylation of trifluoromethylalkene derivatives

Through an S_N2′ amination, N-alkylation and palladium-catalyzed allylic substitution sequence, we realized ipso-C–F bond arylation/alkenylation of trifluoromethylalkene derivatives.

A strategically novel single C–F bond functionalization of CF₃-derived molecules, which shows a prominent advantage for the expedient construction of difluoromethylene-bridged organic scaffolds, is disclosed. The reported protocol consists of S_N2′ amination, N-alkylation and palladium-catalyzed allylic substitution reactions, which enables straightforward arylation and alkenylation of vinyltrifluoromethane derivatives. Furthermore, this strategy is characterized by its broad substrate scope with respect to both CF₃-alkene and arylboronic acid derivatives.

Exploiting the trifluoroethyl group as a precatalyst ligand in nickel-catalyzed Suzuki-type alkylations

We report herein the exploitment of the partially fluorinated trifluoroethyl as precatalyst ligands in nickel-catalyzed Suzuki-type alkylation and fluoroalkylation coupling reactions. Compared with the [L n NiII(aryl)(X)] precatalysts, the unique characters of bis-trifluoroethyl ligands imparted precatalyst [(bipy)Ni(CH2CF3)2] with bench-top stability, good solubilities in organic media and interesting catalytic activities. Preliminary mechanistic studies reveal that an eliminative extrusion of a vinylidene difluoride (VDF, CH2[double bond, length as m-dash]CF2) mask from [(bipy)Ni(CH2CF3)2] is a critical step for the initiation of a catalytic reaction.