The unique role of fluorine in the design of active ingredients for modern crop protection

Catalytic trifluoromethylation of aryl- and vinylboronic acids by 2-cyclopropyl-1-(trifluoromethyl)benzo[b]thiophenium triflate

Catalytic trifluoromethylation of aryl- and vinylboronic acids by 2-cyclopropyl-1-(trifluoromethyl)benzo[b]thiophenium triflate is described. In the presence of a catalytic amount of CuOAc and 2,4,6-collidine in ethyl acetate, the reaction proceeded in good to high yields for various substrates under mild reaction conditions at room temperature.

A highly regio- and stereoselective synthesis of α-fluorinated imides via fluorination of chiral enamides

A highly π-facial selective and regioselective fluorination of chiral enamides is described. The reaction involves an enantioselective fluorination exclusively at the electron-rich enamide olefin with N-F reagents such as Selectfluor and N-fluoro-benzenesulfonimide [NFSI] accompanied by trapping of the β-fluoro-iminium cationic intermediate with water. The resulting N,O-hemiacetal could be oxidized using Dess-Martin periodinane, leading to an asymmetric sequence for syntheses of chiral α-fluoro-imides and optically enriched α-fluoro-ketones.

Mechanisms and applications of cyclometalated Pt(ii) complexes in photoredox catalytic trifluoromethylation

The incorporation of a trifluoromethyl group into an existing scaffold can provide an effective strategy for designing new drugs and agrochemicals. Among the numerous approaches to trifluoromethylation, radical trifluoromethylation mediated by visible light-driven photoredox catalysis has gathered significant interest as it offers unique opportunities for circumventing the drawbacks encountered in conventional methods. A limited understanding of the mechanism and molecular parameters that control the catalytic actions has hampered the full utilization of photoredox catalysis reactions. To address this challenge, we evaluated and investigated the photoredox catalytic trifluoromethylation reaction using a series of cyclometalated Pt(ii) complexes with systematically varied ligand structures. The Pt(ii) complexes were capable of catalyzing the trifluoromethylation of non-prefunctionalized alkenes and heteroarenes in the presence of CF3I under visible light irradiation. The high excited-state redox potentials of the complexes permitted oxidative quenching during the cycle, whereas reductive quenching was forbidden. Spectroscopic measurements, including time-resolved photoluminescence and laser flash photolysis, were performed to identify the catalytic intermediates and directly monitor their conversions. The mechanistic studies provide compelling evidence that the catalytic cycle selects the oxidative quenching pathway. We also found that electron transfer during each step of the cycle strictly adhered to the Marcus normal region behaviors. The results are fully supported by additional experiments, including photoinduced ESR spectroscopy, spectroelectrochemical measurements, and quantum chemical calculations based on time-dependent density functional theory. Finally, quantum yields exceeding 100% strongly suggest that radical propagation significantly contributes to the catalytic trifluoromethylation reaction. These findings establish molecular strategies for designing trifluoromethyl sources and catalysts in an effort to enhance catalysis performance.

Efficient one-pot synthesis of 5-perfluoroalkylpyrazoles by cyclization of hydrazone dianions

A highly selective and efficient method for the synthesis of 5-trifluoromethylated and 5-perfluoroalkylated pyrazoles has been developed which relies on the cyclization of hydrazine dianions with ethyl perfluorocarboxylates.

Reactions of allyl alcohols and boronic acids with trifluoromethanesulfonyl hypervalent iodonium ylide under copper-catalysis

Trifluoromethylsulfinyl 3 and trifluoromethylthio 5 compounds are independently obtained by using the sulfone-type reagent 1 under Cu catalysis.

Silver-catalyzed Meerwein arylation: intermolecular and intramolecular fluoroarylation of styrenes

The first example of silver-catalyzed intermolecular and intramolecular Meerwein fluoroarylation of styrenes with aryl diazonium salts was reported.

Benzylic C–H trifluoromethylation of phenol derivatives

Phenol derivatives were trifluoromethylated using copper/Togni reagent. Reaction in DMF selectively gave benzylic trifluoromethylation products, whereas aromatic trifluoromethylation products were obtained in t-BuOH.

Regioisomerized atom transfer radical addition (ATRA) of olefins with dichlorofluorocarbons

The Cu(i) catalysed atom transfer radical addition of dichlorofluorocarbons to olefins via C–Cl bond homolysis is successfully carried out.

Transition-metal free oxidative aliphatic C–H fluorination

A mild and practical unactivated aliphatic C–H fluorination reaction was reported without the use of transition metals.

Metal-free radical perfluoroalkylation of (hetero)arenes

We report a metal-free radical perfluoroalkylation method which uses inexpensive and commercially available perfluorocarboxylic anhydrides as an easy to use source of perfluoroalkyl radicals.

Copper-catalyzed intermolecular and regioselective aminofluorination of styrenes: facile access to β-fluoro-N-protected phenethylamines

A copper-catalyzed regio- and intermolecular aminofluorination of styrenes has been developed.

Solvent-controlled nucleophilic trifluoromethylthiolation of Morita–Baylis–Hillman carbonates: dual roles of DABCO in activating the Zard's trifluoromethylthiolation reagent and the MBH carbonates

A novel amine-catalyzed nucleophilic trifluoromethylthiolation between Morita–Baylis–Hillman carbonates and O-octadecyl-S-trifluorothiolcarbonate has been developed.

Fluorination of 2-substituted benzo[b]furans with Selectfluor™

An efficient protocol was developed to access 3-fluoro-2-hydroxy-2-substituted benzo[b]furans with Selectfluor™ as the fluorinating reagent in MeCN and water. By utilizing SOCl₂/Py as the dehydrating agent, the compounds above were readily converted to 3-fluorinated, 2-substituted benzo[b]furans in high yields.

Silver-catalyzed C-H trifluoromethylation of arenes using trifluoroacetic acid as the trifluoromethylating reagent

Direct trifluoromethylation of arenes using TFA as the trifluoromethylating reagent was achieved with Ag as the catalyst. This reaction not only provides a new protocol for aryl C-H trifluoromethylation, but the generation of CF3· from TFA may prove useful in other contexts and could potentially be extended to other trifluoromethylation reactions.

Asymmetric fluorocyclizations of alkenes

CONSPECTUS: The vicinal fluorofunctionalization of alkenes is an attractive transformation that converts feedstock olefins into valuable cyclic fluorinated molecules for application in the pharmaceutical, agrochemical, medical, and material sectors. The challenges associated with asymmetric fluorocyclizations induced by F(+) reagents are distinct from other types of halocyclizations. Processes initiated by the addition of an F(+) reagent onto an alkene do not involve the reversible formation of bridged fluoronium ions but generate acyclic β-fluorocationic intermediates. This mechanistic feature implies that fluorocyclizations are not stereospecific. A discontinuity exists between the importance of this class of fluorocyclization and the activation modes currently available to implement successful catalysis. Progress toward fluorocyclization has been achieved by investing in neutral and cationic [NF] reagent development. The body of work on asymmetric fluorination using chiral cationic [NF](+) reagents prepared by fluorine transfer from the dicationic [NF](2+) reagent Selectfluor to quinuclidines, inspired the development of asymmetric F(+)-induced fluorocyclizations catalyzed by cinchona alkaloids; for catalysis, the use of N-fluorobenzenesulfonimide, which is less reactive than Selectfluor, ensures that the achiral F(+) source remains unreactive toward the alkene. These organocatalyzed enantioselective fluorocyclizations can be applied to indoles to install the fluorine on a quaternary benzylic stereogenic carbon center and to afford fluorinated analogues of natural products featuring the hexahydropyrrolo[2,3-b]indole or the tetrahydro-2H-furo[2,3-b]indole skeleton. In an alternative approach, the poor solubility of dicationic Selectfluor bis(tetrafluoroborate) in nonpolar solvent was exploited with anionic phase transfer catalysis as the operating activation mode. Exchange of the tetrafluoroborate ions of Selectfluor with bulky lipophilic chiral anions (e.g., TRIP and derivatives) brings into solution the resulting chiral Selectfluor reagent, now capable of asymmetric fluorocyclization. This strategy is best applied to a subset of substrates bearing a nucleophilic pendent group (benzamide is best) capable of hydrogen bonding for association with the chiral phosphate catalyst. These contributions focused on fluoroheterocyclization involving either O- or N-nucleophiles. As for other halocyclizations, alkenes armed with π C-nucleophiles represent the most demanding class of substrates for asymmetric F(+)-induced electrophilic fluorination-cyclization. Successful implementation required the design of new chiral Selectfluor reagents featuring stereogenicity on the DABCO core. These reagents, accessible from chiral vicinal diamines, allowed the synthesis of unusual chiral fluorine-containing tetracyclic compounds, some composed of carbon, hydrogen, and fluorine exclusively. The challenges associated with F(+)-induced fluorocarbocyclizations prompted methodologists to consider chemistry where the Csp(3)-F bond formation event follows a catalyst-controlled cyclization. An exciting development built on in the area of transition metal π-cyclization of polyenes leading to cationic metal-alkyl intermediates. When intercepted by oxidative fluorodemetalation with a F(+) source, the resulting products are complex polycyclic structures emerging from an overall catalytic cascade fluorocarbocyclization. Complementing F(+)-based reactions, examples of fluorocyclizations with fluoride in the presence of an oxidant were reported. Despite some exciting developments, the field of asymmetric fluorocyclizations is in its infancy and undoubtedly requires new activation modes, catalysts, as well as F(+) and F(-) reagents to progress into general retrosynthetic approach toward enantioenriched fluorocycles. Numerous opportunities emerge, not least the use of a latent fluorine source as a means to minimize background fluorination.

A catalytic borylation/dehalogenation route to o-fluoro arylboronates

A two-step Ir-catalyzed borylation/Pd-catalyzed dehalogenation sequence allows for the net synthesis of fluoroarenes where the boronic ester is ortho to fluorine. Key elements of this approach include the use of a halogen para to the fluorine to block meta Ir-catalyzed borylation and the chemoselective Pd-catalyzed dehalogenation by KF activated polymethylhydrosiloxane (PMHS).

Mild silver-mediated geminal difluorination of styrenes using an air- and moisture-stable fluoroiodane reagent

An air- and moisture-stable fluoroiodane in the presence of AgBF4 is suitable for selective geminal difluorination of styrenes under mild reaction conditions. One of the CF bonds is formed by transfer of electrophilic fluorine from the hypervalent iodine reagent, while the other one arises from the tetrafluoroborate counterion of silver. Deuterium-isotope-labelling experiments and rearrangement of methyl styrene substrates suggest that the reaction proceeds through a phenonium ion intermediate.

Adhesion and friction properties of fluoropolymer brushes: on the tribological inertness of fluorine

The effects of fluorination on the adhesion and friction properties of covalently bound poly(fluoroalkyl methacrylate) polymer brushes (thickness ∼80 nm) were systematically investigated. Si(111) surfaces were functionalized with a covalently bound initiator via a thiol-yne click reaction to have a high surface coverage for initiator immobilization. Surface-initiated atom-transfer radical polymerization (SI-ATRP) was employed for the synthesis of four different fluoropolymer brushes (SPFx, where x = 0, 3, 7, or 17 F atoms per monomer), based on fluoroalkyl methacrylates. All polymer brushes were characterized with static contact angle measurements, X-ray photoelectron spectroscopy (XPS), and infrared absorption reflection spectroscopy (IRRAS). The polymer brushes exhibited an excellent hydrophobicity, with static water contact angles of up to 121° depending on the number of fluorine atoms per side chain in fluoroalkyl methacrylate. The degree of swelling was precisely studied by using ellipsometry in different solvents such as acetone, hexadecane, hexafluoroisopropanol, nonafluorobutyl methyl ether, and Fluorinert FC-40. The polymer brushes have shown nanoscale swelling behavior in all solvents except hexadecane. The grafting density decreased upon increasing fluorine content in polymer brushes from 0.65 chains/nm(2) (SPF0) to 0.10 chains/nm(2) (SPF17) as observed in Fluorinert FC-40 as a good solvent. Adhesion and friction force measurements were conducted with silica colloidal probe atomic force microscopy (CP-AFM) under ambient, dry (argon), and lubricating fluid conditions. SPF17 showed the lowest coefficient of friction 0.005 under ambient condition (RH = 44 ± 2%) and a further decrease with 50% under fluidic conditions. These polymer brushes also showed adhesion forces as low as 6.9 nN under ambient conditions, which further went down to 0.003 nN under fluidic conditions (Fluorinert FC-40 and hexadecane) at 10 nN force.

Cu(OTf)2-mediated fluorination of aryltrifluoroborates with potassium fluoride

This Communication describes the Cu(OTf)2-mediated fluorination of aryltrifluoroborates with KF. The reaction proceeds under mild conditions (at 60 °C over 20 h) and shows a broad substrate scope and functional group tolerance. The Cu is proposed to play two separate roles in this transformation: (1) as a mediator for the aryl–F coupling and (2) as an oxidant for accessing a proposed Cu(III)(aryl)(F) intermediate.

Activity of antifungal organobismuth(III) compounds derived from alkyl aryl ketones against S. cerevisiae: comparison with a heterocyclic bismuth scaffold consisting of a diphenyl sulfone

A series of hypervalent organobismuth(III) compounds derived from alkyl aryl ketones [XBi(5-R'C₆H₃-2-COR)(Ar)] was synthesized to investigate the effect of the compounds’ structural features on their antifungal activity against the yeast Saccharomyces cerevisiae. In contrast to bismuth heterocycles [XBi(5-RC₆H₃-2-SO₂C₆H₄-1'-)] derived from diphenyl sulfones, a systematic quantitative structure-activity relationship study was possible. The activity depended on the Ar group and increased for heavier X atoms, whereas lengthening the alkyl chain (R) or introducing a substituent (R') reduced the activity. IBi(C₆H₄-2-COCH₃)(4-FC₆H₄) was the most active. Its activity was superior to that of the related acyclic analogues ClBi[C₆H₄-2-CH₂N(CH₃)₂](Ar) and ClBi(C₆H₄-2-SO₂tert-Bu)(Ar) and also comparable to that of heterocyclic ClBi(C₆H₄-2-SO₂C₆H₄-1'-), which was the most active compound in our previous studies. Density function theory calculations suggested that hypervalent bismuthanes undergo nucleophilic addition with a biomolecule at the bismuth atom to give an intermediate ate complex. For higher antifungal activity, adjusting the lipophilicity-hydrophilicity balance, modeling the three-dimensional molecular structure around the bismuth atom, and stabilizing the ate complex appear to be more important than tuning the Lewis acidity at the bismuth atom.