Recent Developments in the Trifluoromethylation of Alkynes

Synthesis of Z-gem-Cl,CF3-Substituted Alkenes by Stereoselective Cross-Metathesis and the Role of Disubstituted Mo Alkylidenes

Stereochemically defined organofluorine compounds are central to drug discovery and development. Here, we present a catalytic cross-metathesis method for the synthesis of Z-trisubstituted olefins that contain a Cl- and a CF3-bound carbon terminus. Notably, the process is stereoselective, which is in contrast to the existing stereoretentive strategies that also involve a trisubstituted olefin as starting material. Reactions are catalyzed by a Mo monoaryloxide pyrrolide alkylidene, involve a trisubstituted alkene and gem-Cl,CF3-substituted alkene, and are fully Z-selective. Catalytic cross-coupling can be used to convert the C-Cl bond of the trisubstituted olefin to C-B, C-D, and different C-C bonds. We elucidate the role of Cl,CF3-disubstituted Mo alkylidenes. Experimental and computational (DFT) data show that in some instances a disubstituted alkylidene is formed and then transformed to a more active complex. In other cases, the Cl,CF3-disubstituted alkylidene is a direct participant in a catalytic cycle. The studies described shed new light on the chemistry of high oxidation-state disubstituted alkylidenes-scarcely investigated entities likely to be pivotal to approaches for stereocontrolled synthesis of tetrasubstituted alkenes through olefin metathesis.

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.

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.

Highly regio- and stereocontrolled preparation of α-(trifluoromethyl)-β-(phenylthio) enamines by the hydroamination of in situ-synthesized 1-(trifluoromethyl)-2-(phenylthio)ethyne

Various nitrogen nucleophiles were easily added to in situ-generated 1-(trifluoromethyl)-2-(phenylthio)ethyne to afford the corresponding trifluoromethyl enamines in good-to-high yields and with high regio- and stereocontrol under very mild conditions.

Coordinating activation strategy enables 1,2-alkylamidation of alkynes

The radical 1,2-difunctionalization reaction of alkynes has been evolved into a versatile approach for expeditiously increasing the complexity of the common feedstock alkyne. However, intermolecular 1,2-carboamidation with general alkyl groups is an unsolved problem. Herein, we show that a coordinating activation strategy could act as an efficient tool for enabling radical 1,2-alkylamidation of alkynes. With the employment of diacyl peroxides as both alkylating reagents and internal oxidants, a large library of β-alkylated enamides is constructed in a three-component manner from readily accessible amides and alkynes. This protocol exhibits broad substrate scope with good functional group compatibility and is amenable for late-stage functionalization of natural molecules and biologically compounds.

Photoredox-Catalyzed gem-Difluoromethylenation of Aliphatic Alcohols with 1,1-Difluoroalkenes to Access α,α-Difluoromethylene Ethers

A switchable synthesis of alcohols and ketones bearing a CF2-OR scaffold using visible-light promotion is described. The method of PDI catalysis is characterized by its ease of operation, broad substrate scopes, and the ability to switch between desired products without the need for transition metal catalysts. The addition or absence of a base plays a key role in controlling the synthesis of the major desired products.

Development of Electrophilic Radical Perfluoroalkylation of Electron-Deficient Olefins

Fluorinated organic compounds have attracted significant attention over the past few decades owing to their unique properties and versatility. An established method for the synthesis of fluorinated organic compounds involves radical perfluoroalkylation reactions towards double bonds. In this radical pathway, electrophilic perfluoroalkyl radicals exhibit excellent reactivity towards electron-rich olefins. Therefore, several splendid perfluoroalkylation reactions of electron-rich olefins have been reported. However, there are only a few examples of reaction involving electron-deficient olefins because of their poor electronic compatibility with perfluoroalkyl radicals. This review focuses on the reports that challenge this long-standing issue. Radical perfluoroalkylation/bifunctionalization reactions of electron-deficient olefins are described according to the radical generation methods.

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

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

Ru(II)-Catalyzed Hydroarylation of in situ Generated 3,3,3-Trifluoro-1-propyne by C-H Bond Activation: A Facile and Practical Access to β-Trifluoromethylstyrenes

In this study, a practical and straightforward synthesis of β-(E)-trifluoromethylstyrenes by ruthenium-catalyzed C-H bond activation was developed. The readily available and inexpensive 2-bromo-3,3,3-trifluoropropene (BTP), a non-ozone depleting reagent, was used as a reservoir of 3,3,3-trifluoropropyne. With this approach, the monofunctionalization of a panel of heteroarenes was possible in a safe and scalable manner (23 examples, up to 87 % yield). Mechanistic investigations and density functional theory (DFT) calculations were also conducted to get a better understanding of the mechanism of this transformation. These studies suggested that 1) a cyclometallated ruthenium complex enabled the transformation, 2) this complex exhibited high efficiency in this transformation compared to the commercially available [RuCl2 (p-cymene)]2 and 3) the mechanism proceeded through a bis-cyclometallated ruthenium intermediate for the carboruthenation step.

Perfluoroalkylation of Terminal Alkynes with Perfluoroalkyl Iodides Catalyzed by an Iron Salt

The one-step, direct perfluoroalkylation of terminal alkynes with perfluoroalkyl iodides has been developed in which a simple ligandless iron salt is employed as the catalyst. Various perfluoroalkylated alkynes could be afforded in good to excellent yields with good functional group compatibility. Preliminary mechanistic studies suggest the involvement of the perfluoroalkyl radical in the catalytic cycle and the perfluoroalkylated alkenyl iodides as intermediates. The method provides straight, streamlined, and sustainable access to perfluoroalkylated acetylenes.

Radical hydrotrifluoromethylation of ynamides: a route toward β-CF3 enamides

We report here a radical hydrotrifluoromethylation of ynamides to provide an alternative route toward β-CF3 enamides.

Recent Advances in Transition-Metal Mediated Trifluoromethylation Reactions

Fluorine compounds are known for their abundance in more than 20% of pharmaceutical and agrochemical products mainly due to the enhanced lipophilicity, metabolic stability and pharmacokinetic properties of organofluorides. Consequently,...

Access to cyclopentenones via copper-catalyzed 5-endo trifluoromethylcarbocyclization of ynones

A copper-catalyzed 5-endo-selective trifluoromethylcarbocyclization of ynones is realized for the direct construction of trifluoromethylated cyclopentenones.

A diastereoselective synthesis of cyclopentanones via photocatalytic reductive alkyltrifluoromethylation of ynones

A photocatalytic reductive alkyltrifluoromethylation of ynones with the Langlois reagent is developed, providing a regio- and diastereoselective access to trifluoromethylated cyclopentanones under mild conditions.

Radical-induced denitration of N-(p-nitrophenyl)propiolamides coupled with dearomatization: access to phosphonylated/trifluoromethylated azaspiro[4.5]-trienones

A robust dearomative denitration of nitroarene derivatives induced by a radical ipso-cyclization process has been developed, delivering valuable phosphonated or trifluoromethylated azaspiro[4.5]trienones with good functional group tolerance. This represents a convenient and powerful approach to activate nitroarenes in a radical manner.

Radical-mediated vicinal addition of alkoxysulfonyl/fluorosulfonyl and trifluoromethyl groups to aryl alkyl alkynes

The addition of sulfonyl radicals to alkenes and alkynes is a valuable method for constructing useful highly functionalized sulfonyl compounds. The underexplored alkoxy- and fluorosulfonyl radicals are easily accessed by CF₃ radical addition to readily available allylsulfonic acid derivatives and then β-fragmentation. These substituted sulfonyl radicals add to aryl alkyl alkynes to give vinyl radicals that are trapped by trifluoromethyl transfer to provide tetra-substituted alkenes bearing the privileged alkoxy- or fluorosulfonyl group on one carbon and a trifluoromethyl group on the other. This process exhibits broad functional group compatibility and allows for the late-stage functionalization of drug molecules, demonstrating its potential in drug discovery and chemical biology.

An unprecedented method for vicinal addition of alkoxysulfonyl/fluorosulfonyl and trifluoromethyl groups to aryl alkyl alkynes has been developed to afford useful alkenylsulfonate esters and alkenylsulfonyl fluorides.

Recent progress in the radical α-C(sp3)-H functionalization of ketones

The direct use structurally simple ketones as α-ketone radical sources for α-C(sp³)-H functionalization is a sustainable and powerful approach for constructing complex and multifunctional chemical scaffolds with diverse applications. The reactions of α-ketone radicals with alkenes, alkynes, enynes, imides, and imidazo[1,2-a]pyridines have broadened the structural diversity and complexity of ketones. Through chosen illustrative examples, we outline the recent progress in the development of methods that enable the radical α-C(sp³)-H functionalization of ketones, with an emphasis on radical initiation systems and possible mechanisms of the transformations. The application of these strategies is illustrated by the synthesis of several biologically active molecules and drug molecules. Further subdivision is based on substrate type and reaction type.

Generation of zwitterionic trifluoromethyl N-allylic ylides and their use in switchable divergent annulations

The previously unreported zwitterionic N-allylic ylide species from the corresponding Morita-Baylis-Hillman carbonates of trifluoromethyl ketones and acrylonitrile are generated under the catalysis of cinchona-derived tertiary amines, and subsequently participate in switchable asymmetric [3+2] or [4+1] annulations with 1-azadienes in chemo-, regio-, and stereodivergent manners via catalyst or substrate control. A diverse range of frameworks, having a trifluoromethylated all-carbon quaternary stereogenic centre or a tetrasubstituted alkene moiety, are generally constructed in good yields with excellent enantioselectivity.

Hydrogenation of fluorinated molecules: an overview

The review aims at providing an overview on the developments made in hydrogenation reactions of molecules having various fluorinated groups (F, CF3, CF2H, CF2Rf). Indeed, the hydrogenation of fluorine-containing molecules is a straightforward and atom-economical way to access challenging (chiral) fluorinated scaffolds. This promising field is still in its infancy and milestones are expected in the coming years. To illustrate that, the review will highlight the major contributions made in that field and will be organized by fluorinated groups.

Radical-Promoted Distal C-H Functionalization of C(sp3 ) Centers with Fluorinated Moieties

Due to their unique properties, fluorinated scaffolds are pivotal compounds in pharmaceuticals, agrochemicals, and materials science. Over the last years, the development of versatile strategies for the selective synthesis of fluorinated molecules by direct C-H bond functionalization has attracted a lot of attention. In particular, the design of novel transformations based on a radical process was a bottleneck for distal C-H functionalization reactions, offering synthetic solutions for the selective introduction of fluorinated groups. This Minireview highlights the major contributions in this blossoming field. The development of new methodologies for the remote functionalization of aliphatic derivatives with various fluorinated groups based on a 1,5-hydrogen atom transfer process and a β-fragmentation reaction will be showcased and discussed.

Vicinal halo-trifluoromethylation of alkenes

Both trifluoromethyl and halide groups are widely found in medicinally and pharmaceutically important compounds and, moreover, organohalides are commonly used as versatile intermediates in synthetic organic chemistry. Due to their prevalence and easy accessibility, alkene halo-trifluoromethylation provides a convenient way to install these valuable functionalities in complex targets. In this review, we summarize recent advances and achievements in this fast-growing research field. For clarity, the reactions were classified according to the type of halogen atom.

Design, synthesis, and biological evaluation of nitroisoxazole-containing spiro[pyrrolidin-oxindole] derivatives as novel glutathione peroxidase 4/mouse double minute 2 dual inhibitors that inhibit breast adenocarcinoma cell proliferation

A series of highly active CF₃-containing 3'-(nitroisoxazole)spiro[pyrrolidin-3,2'-oxindoles] were synthesized and found to be novel glutathione peroxidase 4 (GPX4)/mouse double minute 2 (MDM2) dual inhibitors. Bioactive spirooxindole and isoxazole skeletons were combined, and the resulting compounds exhibited strong activities against both targets. In particular, compound 3d displayed excellent activity in the suppression of MDM2-mediated degradation of p53, as well as levels of GPX4, in MCF-7 breast cancer cells. Moreover, 3d also exhibited inhibitory effects on MDM2 and GPX4 in MCF-7 xenograft model to trigger ferroptotic and apoptotic cell death in in vivo experiments, which was consistent with the results of in vitro experiments.

Photoinduced intramolecular carbosulfonylation of alkynes: access to sulfone-containing dibenzazepines from sulfur dioxide

A visible-light-driven three-component carbosulfonylation of terminal alkynes, DABCO (SO₂)₂ and aryldiazonium tetrafluoroborates is developed, leading to sulfone-containing dibenzazepines in moderate to good yields under mild conditions.

Synthesis of polysubstituted azetidines via cascade trifluoromethylation/cyclization of N-allyl ynamides

A cascade trifluoromethylation/cyclization of N-allyl sulfonylynamides is developed, providing a direct access to azetidine-fused tricyclic compounds at room temperature.

Recent trends in dehydroxylative trifluoro-methylation, -methoxylation, -methylthiolation, and -methylselenylation of alcohols

This review studies on the direct dehydroxylative trifluoromethylation, trifluoromethoxylation, trifluoromethylthiolation, and trifluoromethylselenylation of alcohols.

Internal Alkyne-Directed Fluorination of Unactivated C(sp3)-H Bonds

A silver-mediated internal alkyne-guided fluorination of unactivated C(sp³)-H bonds is described. The reaction provides a facile access to γ-fluorinated fluoroalkylated (Z)-alkenes from readily available alkynes in promising yields with excellent regioselectivity, stereoselectivity, and site selectivity.

Copper-Catalyzed Asymmetric Coupling of Allenyl Radicals with Terminal Alkynes to Access Tetrasubstituted Allenes

In contrast to the wealth of asymmetric transformations for generating central chirality from alkyl radicals, the enantiocontrol over the allenyl radicals for forging axial chirality represents an uncharted domain. The challenge arises from the unique elongated linear configuration of the allenyl radicals that necessitates the stereo-differentiation of remote motifs away from the radical reaction site. We herein describe a copper-catalyzed asymmetric radical 1,4-carboalkynylation of 1,3-enynes via the coupling of allenyl radicals with terminal alkynes, providing diverse synthetically challenging tetrasubstituted chiral allenes. A chiral N,N,P-ligand is crucial for both the reaction initiation and the enantiocontrol over the highly reactive allenyl radicals. The reaction features a broad substrate scope, covering a variety of (hetero)aryl and alkyl alkynes and 1,3-enynes as well as radical precursors with excellent functional group tolerance.

AIBN-Induced Remote Trifluoromethyl-Alkynylation of Thioalkynes

A novel α,α'-azobis(isobutyronitrile) (AIBN)-induced remote trifluoromethyl-alkynylation of thioalkynes with alkynyl triflones as both the trifluoromethyl and alkyne sources is described. Structurally diverse trifluoromethylated (Z)-enynes can be constructed with full control of regio-, stereo-, and site-selectivity, which serves as a highly selective method for the rapid construction of trifluoromethylated molecules.

Fluorofunctionalizations of C-C Multiple Bonds and C-H Bonds

In spite of only a few naturally occurring products having one or more fluorine atoms, organofluorine compounds have been widely utilized in pharmaceutical, agrochemical, and functional material science fields due to the characteristic properties of the fluorine atom. Therefore, the development of new methods for the introduction of fluorine-containing functional groups has been a long-standing research topic. This article discusses our contributions to this area. The first topic is on the trifluoromethylations of C-C multiple bonds using Togni reagent based on our working hypothesis that hypervalent iodine could be activated by coordination of the carbonyl moiety to the Lewis acid catalyst. The second topic relates to asymmetric fluorofunctionalization of alkenes. A newly designed phase-transfer catalyst consisting of a carboxylate anion functioning as a phase-transfer agent and a primary hydroxyl group as a site that captures the anionic substrate was revealed to be an effective catalyst for asymmetric fluorolactonization. Inspired by the mechanistic studies of fluorolactonization, we produced a linked binaphthyl dicarboxylate catalyst, which catalyzes the 6-endo-fluorocyclization and the deprotonative fluorination of allylic amides in a highly enantioselective manner. The third topic is on C-H fluorofunctionalizations using either catalysis or photoactivation. Benzylic trifluoromethylation, which is still a rare reaction, using Togni reagent and aromatic C-H trifluoromethylation using Umemoto reagent under simple photoirradiation conditions were achieved. In addition, the Csp³-H fluorination of alkyl phthalimide derivatives is demonstrated.

Copper-Catalyzed Asymmetric Radical 1,2-Carboalkynylation of Alkenes with Alkyl Halides and Terminal Alkynes

A copper-catalyzed intermolecular three-component asymmetric radical 1,2-carboalkynylation of alkenes has been developed, providing straightforward access to diverse chiral alkynes from readily available alkyl halides and terminal alkynes. The utilization of a cinchona alkaloid-derived multidentate N,N,P-ligand is crucial for the efficient radical generation from mildly oxidative precursors by copper and the effective inhibition of the undesired Glaser coupling side reaction. The substrate scope is broad, covering (hetero)aryl-, alkynyl-, and aminocarbonyl-substituted alkenes, (hetero)aryl and alkyl as well as silyl alkynes, and tertiary to primary alkyl radical precursors with excellent functional group compatibility. Facile transformations of the obtained chiral alkynes have also been demonstrated, highlighting the excellent complementarity of this protocol to direct 1,2-dicarbofunctionalization reactions with C(sp²/sp³)-based reagents.

Phosphine-Free Ru-Catalyzed Regio- and Stereoselective Addition of Benzoic Acids to Trifluoromethylated Alkynes toward Facile Access to Trifluoromethyl Group-Substituted (E)-Enol Esters

A combination of ruthenium catalyst with silver salt and copper salt was proved to be a highly efficient protocol for the direct addition reaction of benzoic acids with unsymmetrical trifluoromethylated internal alkynes. Diverse trifluoromethyl group-substituted (E)-enol esters were readily obtained for a broad substrate scope in moderate to good yields with excellent regio- and stereoselectivities under mild reaction conditions.

Synthesis of difluoromethylated allenes through trifunctionalization of 1,3-enynes

Organofluorine compounds have shown their great value in many aspects. Moreover, allenes are also a class of important compounds. Fluorinated or fluoroalkylated allenes might provide an option as candidates for drug and material developments, as allenes allow a great number of valuable transformations. Herein, we report a metal-free synthesis of difluoromethylated allenes via regioselective trifunctionalization of 1,3-enynes. This method proceeds through double C–F bond formation with concomitant introduction of an amino group to the allene. Synthetic applications are conducted and preliminary mechanistic studies suggest that a two-step pathway is involved. DFT calculations revealed an unusual dibenzenesulfonimide-assisted fluorination/fluoroamination with NFSI. In addition, kinetic reaction study revealed the induction period of both major and side products to support the proposed reaction mechanism. This work offers a convenient approach for the synthesis of a range of difluoromethylated allenes and is also a rare example of trifunctionalization of 1,3-enynes.

Fluorinated or fluoroalkylated allenes are versatile building blocks for medicinal and material chemistry. Here, the authors show a regioselective trifunctionalization of 1,3-enynes proceeding through double C-F bond formation and concomitant installation of a -NSO₂Ph group to the allene moiety.

Practical fluorothiolation and difluorothiolation of alkenes using pyridine-HF and N-thiosuccinimides

Fluorothiolation and difluorothiolation of alkenes using pyridine-HF and N-thiosuccinimides.

Transition-metal-free trifluoromethylative difunctionalization of olefins and alkynes: approaches and challenges ahead

Transition metal free trifluoromethylative difunctionalization of olefins and alkynes represents one of the most efficient methods to generate pharmaceutically and agrochemically important organofluoride compounds.