Synthesis of Sterically Hindered Dialkyl Ethers via Palladium-Catalyzed Fluoro-alkoxylation of gem-Difluoroalkenes

Organofluorine compounds are of high value in medicinal and agricultural chemistry. Herein, we report a palladium-catalyzed fluoro-alkoxylation of gem-difluoroalkenes for the synthesis of much more challenging sterically hindered ethers. This reaction represents a direct synthesis method for α-trifluoromethyl ethers with a broad functional group tolerance and excellent regioselectivity. This system employs N-fluorobenzenesulfonimide (NFSI) as an electrophilic fluorine source and alcohols as nucleophilic donors, including but not limited to sterically hindered tert-substituted alcohols.

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.

Visible-Light-Induced C-F Bond Activation for the Difluoroalkylation of Indoles

An aryl disulfide mediated C-F bond activation of the trifluoromethyl group to generate valuable gem-difluoroalkylindoles is described. This method relies on readily available commodity reagents under mild reaction conditions and represents the first transition-metal-free redox-neutral C-F bond activation strategy. The reaction employs various substituted indoles and α-fluoro-substituted esters. Further, this mode of C-F activation was also amenable to the activation of trifluoromethylated arenes for the preparation of bis-benzylic gem-difluoromethylenes between indole and arene substructures, providing access to a unique chemical space.

Recent advances in transition-metal catalyzed directed C–H functionalization with fluorinated building blocks

This review focuses on the advances in transition-metal catalyzed reactions with fluorinated building blocks via directed C–H bond activation for the construction of diverse organic molecules with an insight into the probable mechanistic pathway.

Rh(III)-Catalyzed Chemoselective C-H Alkenylation and [5 + 1] Annulation with Gem-Difluoromethylene Enabled by the Distinctive Fluorine Effect

The efficient couplings of diverse N-arylureas and gem-difluoromethylene alkynes have been realized via Rh(III)-catalyzed chemoselective C-H alkenylation and [5 + 1] annulation, which were induced by the distinctive fluorine effect to provide the different coordination mode of the Rh(III) catalyst binding to the directing group, thereby giving the direct access to difluorinated 2-alkenyl arylureas and 3,4-dihydroquinazolin-2(1H)-ones bearing both an α-quaternary carbon center and a monofluoroalkenyl moiety with broad substrate compatibility and good functional group tolerance. The synthetic application in C-H alkenylation of the N-pyridylaniline, the late-stage [3 + 2] annulation, and the derivation of the obtained products has been also demonstrated to further strengthen the synthetic utility of the chemodivergent transformations.

Synthesis of 2-aminobenzofurans via base-mediated [3 + 2] annulation of N-phenoxy amides with gem-difluoroalkenes

Efficient metal-free [3 + 2] annulation of N-phenoxy amides with gem-difluoroalkenes has been realized for the assembly of 2-aminobenzofuran derivatives with potent cytotoxicity against cancer cell lines and application potential for DELs.

Design and Synthesis of TY-Phos and Application in Palladium-Catalyzed Enantioselective Fluoroarylation of gem-Difluoroalkenes

The first example of highly enantioselective fluoroarylation of gem-difluoroalkenes with aryl halides is presented by using a new chiral sulfinamide phosphine (Sadphos) type ligand TY-Phos. N-Me-TY-Phos can be easily synthesized on a gram scale from readily available starting materials in three steps. Salient features of this work including readily available starting materials, good yields, high enantioselectivities as well as broad substrate scope make this approach very practical and attractive. Notably, the asymmetric synthesis of an analogue of a biologically active molecule is also reported.

Rhodium-Catalyzed Merging of 2-Arylquinazolinone and 2,2-Difluorovinyl Tosylate: Diverse Synthesis of Monofluoroolefin Quinazolinone Derivatives

An efficient method for the synthesis of 2-(o-monofluoroalkenylaryl)quinazolinone derivatives was developed. In this context, the quinazolinone ring served as the inherent directing group, 2,2-difluorovinyl tosylate was used as the monofluoroolefin synthon, and Rh(III)-catalyzed C-H bond difluorovinylation of 2-arylquinazolinons was performed to give the corresponding monofluoroalkene-containing quinazolinons in yields of 65-92%. The method is characterized by broad synthetic utility, mild conditions, and high efficiency.

The copper(ii)-catalyzed and oxidant-promoted regioselective C-2 difluoromethylation of indoles and pyrroles

A novel and efficient approach for the highly selective C-2 difluoromethylation of indole derivatives was developed by using sodium difluoromethylsulfinate (HCF₂SO₂Na) as the source of difluoromethyl groups and a Cu(ii) complex as the catalyst.

Silver-promoted decarboxylative radical addition/annulation of oxamic acids with gem-difluoroolefins: concise access to CF2-containing 3,4-dihydroquinolin-2-ones

Described is a silver-promoted decarboxylative radical addition/annulation of oxamic acids with gem-difluoroalkenes. This reaction proceeded under mild reaction conditions with broad functional group compatibility, enabling the convenient synthesis of various structurally diverse CF2-containing 3,4-dihydroquinolin-2-ones that might find applications in medical chemistry.

Selective C-F bond carboxylation of gem-difluoroalkenes with CO2 by photoredox/palladium dual catalysis

The catalytic C-F bond carboxylation of organofluorines with CO2 gas remains a challenging problem in synthetic chemistry. Here, we describe a selective defluorinative carboxylation of gem-difluoroalkenes through photoredox/palladium dual catalysis. The C-F bond activation is enabled by single electron reduction through photoredox catalysis to generate a fluorovinyl radical, which subsequently participates in an unprecedented palladium-catalyzed carboxylation. This novel C-F functionalization proved applicable to a wide range of substituted gem-difluoroalkenes, providing a rapid access to valuable α-fluoroacrylic acids.

Stereoselective β-F Elimination Enabled Redox-Neutral [4 + 1] Annulation via Rh(III)-Catalyzed C-H Activation: Access to Z-Monofluoroalkenyl Dihydrobenzo[ d]isoxazole Framework

An efficient and practical Rh(III)-catalyzed redox-neutral [4 + 1] annulation of N-phenoxy amides with α, α-difluoromethylene alkynes has been realized to give direct access to the Z-configured monofluoroalkenyl dihydrobenzo[ d]isoxazole framework with broad substrate compatibility and good functional group tolerance, which was further enhanced by the late-stage C-H modification of complex bioactive compounds. Subsequent density functional theory calculations revealed that the stereoselective β-F elimination involving an allene species played a decisive role in determining the reaction outcome and such Z-selectivity.

Cp*Rh(III)-Catalyzed C-H Bond Difluorovinylation of Indoles with α,α-Difluorovinyl Tosylate

Unprecedented Rh(III)-catalyzed C-H bond difluorovinylation of indoles has been successfully developed, and this method provided an example of direct difluorovinylation reaction through C-H bond activation which was rarely reported. In this context, N-ethoxycarbamoyl served as the directing group and 2,2-difluorovinyl tosylates were used for the construction of difluorovinyl-substituted indoles. This method provided a practical strategy for difluorovinylation of indoles with moderate to good yields and is characterized by the broad synthetic utility, mild conditions, and high efficiency.

3d Transition Metals for C-H Activation

C-H activation has surfaced as an increasingly powerful tool for molecular sciences, with notable applications to material sciences, crop protection, drug discovery, and pharmaceutical industries, among others. Despite major advances, the vast majority of these C-H functionalizations required precious 4d or 5d transition metal catalysts. Given the cost-effective and sustainable nature of earth-abundant first row transition metals, the development of less toxic, inexpensive 3d metal catalysts for C-H activation has gained considerable recent momentum as a significantly more environmentally-benign and economically-attractive alternative. Herein, we provide a comprehensive overview on first row transition metal catalysts for C-H activation until summer 2018.

Nickel-Catalyzed Regioselective C(2)-H Difluoroalkylation of Indoles with Difluoroalkyl Bromides

Regioselective C(2)-H difluoroalkylation of C-3 unsubstituted indoles with commonly available fluoroalkyl bromides is successfully achieved employing a simple nickel catalyst system, (DME)NiCl₂ /Xantphos. This methodology shows excellent regioselectivity and exhibits a broad substrate scope. Various functional groups, such as -OMe, -F, and -Br, are tolerated on the indole backbone to give the difluoroalkylated products in moderate to good yields. Preliminary mechanistic findings demonstrate that the reaction is homogeneous in nature and involves a radical manifold. Synthetic utility of this nickel-catalyzed method is demonstrated by synthesizing melatonin receptor antagonist Luzindole derivative.

A Copper-Catalyzed Reductive Defluorination of β-Trifluoromethylated Enones via Oxidative Homocoupling of Grignard Reagents

An efficient copper-catalyzed reductive defluorination of β-trifluoromethylated enones via an oxidative homocoupling of Grignard reagents is reported. The reaction proceeded smoothly with a wide range of substrates, including the ones bearing aromatic heterocycles, such as furyl and thienyl ring systems in high yields (80-92%, except one example) under mild conditions. This provides a practical method for synthesis of gem-difluoroolefin ketones. It is also worth noting that this homocoupling process of Grignard reagents using β-trifluoromethylated enones as "oxidizing reagents" is effective for both the Csp²-Csp² and Csp³-Csp³ bond formations, including for substrates whose β-hydride elimination of the corresponding transition metal alkyl complex is particularly facile, affording coupling products with high yields (83-95%), simultaneously.

Synthesis of α-CF3 and α-CF2H amines via the aminofluorination of fluorinated alkenes

A novel synthesis of α-CF₃ and α-CF₂H amines via the aminofluorination of gem-difluoroalkenes and mono-fluoroalkenes, respectively, is reported.

Rh-Catalyzed C–H bond alkylation of indoles with α,α-difluorovinyl tosylate via indolyl group migration

An unprecedented C–H alkylation of indoles was achieved with α,α-difluorovinyl tosylate through an indolyl group shift process enabled by fluorine substituents.

Rh(iii)-Catalyzed α-fluoroalkenylation of N-nitrosoanilines with 2,2-difluorovinyl tosylates via C–H bond activation

Rh(iii)-Catalyzed α-fluoroalkenylation of N-nitrosoanilines with 2,2-difluorovinyl tosylates has been realized, leading to the synthesis of monofluoroalkenes with high Z-selectivity with respect to the olefin.