Nickel-catalyzed cross-coupling of functionalized difluoromethyl bromides and chlorides with aryl boronic acids: a general method for difluoroalkylated arenes

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.

Cu-Catalyzed Carbocyclization for General Synthesis of N-Containing Heterocyclics Enabled by BrCF2COOEt as a C1 Source

A practical and efficient copper-catalyzed carbocyclization of 2-functionalized anilines with ethyl bromodifluoroacetate has been developed. Ethyl bromodifluoroacetate is employed as the C1 source via quadruple cleavage in this transformation. This reaction can afford a variety of N-containing heterocyclics with satisfactory yields and excellent functional group compatibility.

Cobalt-catalyzed decarboxylative difluoroalkylation of nitrophenylacetic acid salts

The selective installation of fluorine-containing groups into biologically relevant molecules has been used as a common strategy for the development of pharmaceutically active molecules. However, the selective incorporation of gem-difluoromethylene groups next to sterically demanding secondary and tertiary alkyl groups remains a challenge. Herein, we report the first cobalt-catalyzed regioselective difluoroalkylation of carboxylic acid salts. The reaction allows for the facile construction of various difluoroalkylated products in good yields tolerating a wide range of functionalities on either reaction partner. The potential of the method is illustrated by the late-stage functionalization of molecules of biological relevance. Mechanistic studies support the in situ formation of a cobalt(i) species and the intermediacy of difluoroalkyl radicals, thus suggesting a Co(i)/Co(ii)/Co(iii) catalytic cycle.

Palladium-Catalyzed Decarbonylative Coupling of (Hetero)Aryl Boronate Esters with Difluorobenzyl Glutarimides

This report describes the Pd-catalyzed decarbonylative coupling of difluorobenzyl glutarimides with (hetero)aryl boronate esters to yield difluorobenzyl-substituted (hetero)arene products. The use of PAd2Bu as the phosphine ligand in combination with neopentylboronate ester nucleophiles proved critical for the selective formation of the decarbonylative coupling product versus analogous difluorobenzyl ketone. This transformation is effective for electronically diverse (hetero)aryl boronate esters and substituted difluorobenzyl glutarimides.

Controlled Synthesis of α-CF2H or α-CF2Cl Styrenes from the Same Precursors: Dehydrazinative Hydrogenation or Chlorination of 3,3-Difluoroallyl Hydrazines

By carefully choosing the reaction conditions, we have developed the controllable FeCl₃- or CuCl₂-mediated dehydrazinative hydrogenation or chlorination of 3,3-difluoroallyl hydrazines to access α-CF₂H or α-CF₂Cl styrenes. The current reaction provides for the first time a facile method for the direct and selective synthesis of α-CF₂H and α-CF₂Cl styrenes starting from the same precursors, which is easy to scale up and displays a broad substrate scope and good functional group tolerance. Moreover, product derivatization experiments demonstrated that the resulting α-CF₂Cl styrenes are practical and versatile building blocks for the diversified synthesis of fluorinated molecules.

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.

Palladium-Catalyzed Aryldifluoromethylation of Aryl Halides with Aryldifluoromethyl Trimethylsilanes

Diaryl difluoromethanes are valuable targets for medicinal chemistry because they are bioisosteres of diaryl ethers and can function as replacements for diaryl methane, ketone, and sulfone groups. However, methods to prepare diaryl difluoromethanes are scarce, especially methods starting from abundant aryl halides. We report the Pd-catalyzed aryldifluoromethylation of aryl halides with aryldifluoromethyl trimethylsilanes (TMSCF2 Ar). The reaction occurs when the catalyst contains a simple, but unusual, dialkylaryl phosphine ligand that promotes transmetallation of the silane. Computational studies show that reductive elimination following transmetallation occurs with a low barrier, despite the fluorine atoms on the α-carbon, due to coordination of the difluorobenzyl π-system to palladium. The co-development of a cobalt-catalyzed synthesis of the silanes broadened the scope of the process including several applications to the synthesis biologically relevant diaryl difluoromethanes.

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.

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.

Synthesis, structure, and electrochemical properties of [LNi(Rf)(C4F8)]- and [LNi(Rf)3]- complexes

The new anionic nickelate complexes [(MeCN)Ni(C₄F₈)(CF₃)]^-, [(MeCN)Ni(C₄F₈)(C₂F₅)]^-, [(IMes)Ni(C₄F₈)(CF₃)]^-, [(IMes)Ni(CF₃)₃]^- (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene), and [(F-NHC)Ni(R_f)₃]^- (F-NHC = 1,3-bis(2,4-F₂Ph), 2,4,6-F₃Ph- or 3,4,5-F₃Ph)imidazol-2-ylidene; (R_f = CF₃ or C₂F₅) were synthesized and structurally characterized. The electrochemical properties of all new compounds were revealed by cyclic voltammetry studies and compared to the known CF₃ analogue [(MeCN)Ni(CF₃)₃]^-. The IMes-coordinated complexes exhibited initial oxidation events that were well-separated from a second oxidation process in the cyclic voltammograms. The complexes containing F-substituted NHC ligands [(F-NHC)Ni(CF₃)₃]^- are structurally quite similar to the IMes derivative and reveal also two separated oxidation waves in their cyclic voltammograms. The absolute potentials as well as the separation between the two waves vary with the substitution pattern, suggesting that the NHC ligand environment (NHC = N-heterocyclic carbene) is an interesting platform for the development of new redox-triggered reactions that release trifluoromethyl and perfluoroalkyl radicals upon oxidation.

H-F bond insertions into α-diazo carbonyl compounds

A reaction for H-F bond insertion into α-diazo carbonyl compounds is reported. The protocol describes a simple reaction setup employing commercially available HF·pyr (Olah reagent) as the fluorine source. The method is rapid and practical, and allows access to a broad range of α-fluorinated carbonyl compounds in generally good yields.

(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.

Synthesis of 2,2-difluoro-2-arylethylamines as fluorinated analogs of octopamine and noradrenaline

A series of 2,2-difluoro-2-arylethylamines was synthesized as fluorinated analogs of octopamine and noradrenaline with the expectation of bioisosteric OH/F exchanges. The syntheses of these compounds were performed by a Suzuki–Miyaura cross-coupling reaction of 4-(bromodifluoroacetyl)morpholine with aryl boronic acids to produce the intermediate 2,2-difluoro-2-arylacetamides, followed by transformation of difluoroacetamide to difluoroethylamine.

Visible-Light-Induced para-Difluoroalkylation of Aniline Derivatives

Visible-light-induced, iridium catalyzed, para-selective C-H difluoroalkylation of aniline derivatives under mild reaction conditions is reported. Various substrates and bioactive compounds, such as precursors of vorinostat and chlorpropham, were all well tolerated. This protocol features a wide substrate scope, high regioselectivity, low catalyst usage, and operational simplicity.

Copper-Catalyzed Cross-Coupling of Arylacetylenes with Bromodifluoroacetamides

A copper-catalyzed radical difluoroalkylation of arylacetylenes with bromodifluoroamides has been developed. The reaction exhibits good functional group tolerance and allows acceA copper-catalyzed radical difluoroalkylation of arylacetylenes with bromodifluoroamides has been developed. The reaction exhibits good functional group tolerance and allows access to a variety of substituted α-alkynyl-α, α-difluoroacetamides in moderate to good yields. The potential for scale-up reaction and products derivatization also makes this method attractive for practical applications. Preliminary mechanistic studies suggest that a radical reaction pathway might be involved in the catalytic system.ss to a variety of substituted α-alkynyl-α, α-difluoroacetamides in moderate to good yields. The potential for scale-up reaction and products derivatization also makes this method attractive for practical applications. Preliminary mechanistic studies suggest that a radical reaction pathway might be involved in the catalytic system.

Hypervalent iodine-mediated β-difluoroalkylboron synthesis via an unusual 1,2-hydrogen shift enabled by boron substitution

A hypervalent iodine-mediated gem-difluorination allows the facile synthesis of β-difluoroalkylborons. An unusual 1,2-hydrogen migration, triggered by boron substitution, is involved.

Selective electrophilic di- and mono-fluorinations for the synthesis of 4-difluoromethyl and 4-fluoromethyl quinazolin(thi)ones by Selectfluor-triggered multi-component reaction

A simple and efficient domino protocol for the selective synthesis of 4-difluoromethyl and 4-fluoromethyl quinazolin(thi)ones was established from readily available 2-aminoacetophenones and iso(thio)cyanates mediated by Selectfluor. The reaction outcomes are...

Directed nickel-catalyzed regio- and diastereoselective arylamination of unactivated alkenes

Few methods have been reported for intermolecular arylamination of alkenes, which could provide direct access to important arylethylamine scaffolds. Herein, we report an intermolecular syn-1,2-arylamination of unactivated alkenes with arylboronic acids and O-benzoylhydroxylamine electrophiles with Ni(II) catalyst. The cleavable bidentate picolinamide directing group facilitates formation of stabilized 4-, 5- or 6-membered nickelacycles and enables the difunctionalization of diverse alkenyl amines with high levels of regio-, chemo- and diastereocontrol. This general and practical protocol is compatible with broad substrate scope and high functional group tolerance. The utility of this method is further demonstrated by the site-selective modification of pharmaceutical agents.

Using Chlorotrifluoroethane for Trifluoroethylation of (Hetero)aryl Bromides and Chlorides via Nickel Catalysis

A nickel-catalyzed reductive cross-coupling between industrial chemical CF₃CH₂Cl and (hetero)aryl bromides and chlorides has been reported. The reaction is synthetically simple without the preparation of arylmetals and exhibits high functional group tolerance. The utility of this protocol has been demonstrated by the late-stage modification of pharmaceuticals, providing a facile route for medicinal chemistry.

Nickel-catalysed fluoromethylation reactions

This review highlights important developments in nickel-catalysed mono-, di- and tri-fluoromethylation, trifluoromethylthiolation and trifluoromethylselenolation.

Utilization of Unsymmetric Diaryliodonium Salts in α-Arylation of α-Fluoroacetoacetamides

The use of unsymmetric diaryliodonium salts as a versatile class of arylating agents has been demonstrated by developing a novel strategy to quickly access α-arylated α-fluoroacetoacetamides. The protocol provides a convenient metal-free method for the α-arylation of a diverse class of fluorinated acetoacetamides, and the products are obtained in good yields. The strategy, upon use of electron-deficient diaryliodonium salts as an arylating agent, provides α-fluoroacetamides through a spontaneous arylation/deacylation cascade.

Recent progress on selective deconstructive modes of halodifluoromethyl and trifluoromethyl-containing reagents

Halodifluoromethyl and trifluoromethyl-containing compounds are widely employed in organic chemistry, pharmaceuticals and materials science. Therefore, their applications and transformations have received significant attention during the past few decades. The single, double, triple and quadruple cleavage of halodifluoromethyl compounds and various deconstructive modes of trifluoromethyl-containing compounds could generate a variety of synthons to prepare more valuable products. Herein, we summarize the most significant achievements in this field with an intriguing focus on results from the last decade.

Desymmetrization of difluoromethylene groups by C-F bond activation

Tertiary stereogenic centres containing one fluorine atom are valuable for medicinal chemistry because they mimic common tertiary stereogenic centres containing one hydrogen atom, but they possess distinct charge distribution, lipophilicity, conformation and metabolic stability1-3. Although tertiary stereogenic centres containing one hydrogen atom are often set by enantioselective desymmetrization reactions at one of the two carbon-hydrogen (C-H) bonds of a methylene group, tertiary stereocentres containing fluorine have not yet been constructed by the analogous desymmetrization reaction at one of the two carbon-fluorine (C-F) bonds of a difluoromethylene group3. Fluorine atoms are similar in size to hydrogen atoms but have distinct electronic properties, causing C-F bonds to be exceptionally strong and geminal C-F bonds to strengthen one another4. Thus, exhaustive defluorination typically dominates over the selective replacement of a single C-F bond, hindering the development of the enantioselective substitution of one fluorine atom to form a stereogenic centre5,6. Here we report the catalytic, enantioselective activation of a single C-F bond in an allylic difluoromethylene group to provide a broad range of products containing a monofluorinated tertiary stereogenic centre. By combining a tailored chiral iridium phosphoramidite catalyst, which controls regioselectivity, chemoselectivity and enantioselectivity, with a fluorophilic activator, which assists the oxidative addition of the C-F bond, these reactions occur in high yield and selectivity. The design principles proposed in this work extend to palladium-catalysed benzylic substitution, demonstrating the generality of the approach.

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.

The Fascinating Chemistry of α-Haloamides

The aim of this review is to highlight the rich chemistry of α-haloamides originally mainly used to discover new C-N, C-O and C-S bond forming reactions, and later widely employed in C-C cross-coupling reactions with C(sp3), C(sp2) and C(sp) coupling partners. Radical-mediated transformations of α-haloamides bearing a suitable located unsaturated bond has proven to be a straightforward alternative to access diverse cyclic compounds by means of either radical initiators, transition metal redox catalysis or visible light photoredox catalysis. On the other hand, cycloadditions with α-halohydroxamate-based azaoxyallyl cations have garnered significant attention. Moreover, in view of the important role in life and materials science of difluoroalkylated compounds, a wide range of catalysts has been developed for the efficient incorporation of difluoroacetamido moieties into activated as well as unactivated substrates.

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.

Metal-free α-arylation of α-fluoro-α-nitroacetamides employing diaryliodonium salts

Herein, we present a mild and efficient metal-free arylation of α-fluoro-α-nitroacetamides employing diaryliodonium salts. A broad range of diaryliodonium salts and α-fluoro-α-nitroacetamides containing sensitive functional groups was successfully employed in this protocol to yield the arylated products in good yields. The synthetic value of this novel protocol was further highlighted by extending the α-arylation to α-cyano-α-fluoroacetamides.