Blue Light Promoted Difluoroalkylation of Aryl Ketones: Synthesis of Quaternary Alkyl Difluorides and Tetrasubstituted Monofluoroalkenes

Synthesis of fluoroalkenes and fluoroenynes via cross-coupling reactions using novel multihalogenated vinyl ethers

In this study, we develop the synthesis methods of fluoroalkenes and fluoroenynes via Suzuki-Miyaura and Sonogashira cross-coupling reactions using novel multihalogenated fluorovinyl ethers, which are easily prepared from the reaction between phenols and 2-bromo-2-chloro-1,1,1-trifluoroethane (halothane). These reactions make use of the unique structure of multihalogenated fluorovinyl ethers, which contains a reactive bromine atom, to afford a series of fluoroalkenes and fluoroenynes in moderate to high yields.

Mechanochemical Synthesis of α-halo Alkylboronic Esters

α-halo alkylboronic esters, acting as ambiphilic synthons, play a pivotal role as versatile intermediates in fields like pharmaceutical science and organic chemistry. The sequential transformation of carbon-boron and carbon-halogen bonds into a broad range of carbon-X bonds allows for programmable bond formation, facilitating the incorporation of multiple substituents at a single position and streamlining the synthesis of complex molecules. Nevertheless, the synthetic potential of these compounds is constrained by limited reaction patterns. Additionally, the conventional methods often necessitate the use of bulk toxic solvents, exhibit sensitivity to air/moisture, rely on expensive metal catalysts, and involve extended reaction times. In this report, a ball milling technique is introduced that overcomes these limitations, enabling the external catalyst-free multicomponent coupling of aryl diazonium salts, alkenes, and simple metal halides. This approach offers a general and straightforward method for obtaining a diverse array of α-halo alkylboronic esters, thereby paving the way for the extensive utilization of these synthons in the synthesis of fine chemicals.

Phototriggered Fluoroalkylation/Cyclization of Unactivated 1-Acryloyl-2-cyanoindoles: Synthesis of RCOCF2-Substituted Pyrrolo[1,2-a]indolediones

A photochemical approach toward RCOCF2-substituted pyrrolo[1,2-a]indolediones was developed by the radical cascade difluoroalkylation/cyclization reaction of unactivated 1-acryloyl-2-cyanoindoles with ethyl iododifluoroacetate or iododifluoramides under visible-light irradiation. This transition-metal- and photosensitizer-free protocol afforded diverse difluoroalkylated pyrrolo[1,2-a]indolediones in moderate to good yields under mild reaction conditions. Most appealingly, the reaction can proceed smoothly under sunlight irradiation, which opens a new avenue toward difluoroalkylated pyrrolo[1,2-a]indolediones.

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.

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.

Photocatalytic Alkyl Radical Addition Tandem Oxidation of Alkenyl Borates

Photocatalytic oxidation is a popular transformation way for organic synthesis and is widely applied in academia and industry. Herein, we report a blue light-induced alkylation-oxidation tandem reaction for the synthesis of diverse ketones by combining alkyl radical addition and oxidation of alkenyl borates. This reaction shows excellent functional group compatibility in acceptable yields, and diversity of radical precursors is applicable.

Cu-catalyzed cascade difluoroalkylation/5-endo cyclization/β-fluorine cleavage of ynones

A copper-catalyzed, redox-neutral cascade difluoroalkylation/5-endo annulation/β-fluorine cleavage of ynones is developed, providing a direct and stereoselective method to access synthetically important α-monofluoroalkenyl cyclopentanones. Mechanistic studies suggest an unprecedented Cu^II-assisted β-fluorine fragmentation, which may be valuable for the challenging but important C-F bond activation. Moreover, the in situ generated difluorocarbene was found to serve as an effective reductant for the regeneration of copper(I) catalyst, thus avoiding the addition of external reductants.

A highly efficient metal-free selective 1,4-addition of difluoroenoxysilanes to chromones

A highly efficient metal-free selective 1,4-addition reaction of difluoroenoxysilanes to chromones was developed using the low-cost and readily available HOTf as the catalyst, which is a facile and straightforward method to access valuable C2-difluoroalkylated chroman-4-one derivatives. Interestingly, the products could be readily converted to the difluorinated bioisostere of the natural product (S)-2,6-dimethylchroman-4-one and a difluorinated benzo-seven-membered heterocycle via the Schmidt rearrangement reaction. In addition, the in vitro anti-proliferative activities of these synthesized derivatives against human colon carcinoma cells (HCT116) revealed that compound 3g exhibited potent inhibitory effect on HCT116 cancer cells with an IC₅₀ value of 6.37 μM, representing a novel lead compound for further structural optimization and biological evaluation.

Visible-light-induced radical cascade reaction to prepare oxindoles via alkyl radical addition to N-arylacryl amides

A photochemical approach towards oxindoles with C3 quaternary centers by the radical cascade reaction of α,β-unsaturated N-arylacryl amides with alkyl bromides or iodides upon visible light irradiation under mild reaction conditions was developed.

Photochemical and electrochemical strategies in C–F bond activation and functionalization

The recent advances in photochemical or electrochemical C–F bond activation and functionalization have been summarized and discussed.

Bromine-radical-induced Csp2–H difluoroalkylation of quinoxalinones and hydrazones through visible-light-promoted Csp3–Br bond homolysis

Bromine radicals derived from photo-induced Csp3–Br bond homolysis can mediate H abstraction/imine radical formation from quinoxalinones and hydrazones, which in turn quench the in situ-generated difluoroalkyl radicals to furnish the products.

Gold-Catalyzed One-Pot Synthesis of Polyfluoroalkylated Oxazoles from N-Propargylamides Under Visible-Light Irradiation

A gold-catalyzed synthesis of polyfluoroalkylated oxazoles from N-propargylamides under visible-light irradiation has been developed. These reactions display excellent compatibility of radicals and gold catalysts under visible-light irradiation. Mechanistic experiments indicate that polyfluoroalkyl iodides play a dual role in enhanced compatibility of radicals and gold catalysts through assisted protodeauration of vinyl gold and reactivated the gold catalyst. In addition, PPh₃ AuNTf₂ not only activates N-propargylamide to generate vinyl gold intermediate, but also greatly promotes homolysis of polyfluoroalkyl iodides under blue light irradiation.

Visible-light-induced radical isocyanide insertion protocol for the synthesis of difluoromethylated spiro[indole-3,3'-quinoline] derivatives

Herein, we report the first protocol for visible-light-induced radical isocyanide insertion reactions between 3-(2-isocyanobenzyl)-indoles and bromodifluoroacetates or bromodifluoroacetamides. The protocol, which has good functional group tolerance and a broad substrate scope, constitutes an efficient and general route to difluoromethylated spiro[indole-3,3'-quinoline] derivatives.

Difluoroisoxazolacetophenone: A Difluoroalkylation Reagent for Organocatalytic Vinylogous Nitroaldol Reactions of 1,2-Diketones

Difluoroisoxazolacetophenone (DFIO) is developed as a new difluoroalkylation reagent that can be easily prepared from inexpensive starting materials. In situ remote C-C bond cleavage of DFIO affords γ,γ-difluoroisoxazole nitronate that undergoes base-catalyzed vinylogous nitroaldol additions to isatins, benzothiophene-2,3-dione, unsaturated-α-ketoesters, and cyclic 1,2-diketones. This organocatalytic debenzoate vinylogous nitroaldol reaction provides a new and mild approach for the preparation of various difluoroisoxazole-substituted 3-hydroxy-2-oxindoles.