Direct and Chemoselective Electrophilic Monofluoromethylation of Heteroatoms (O-, S-, N-, P-, Se-) with Fluoroiodomethane

O-Trifluoromethylation of Carboxylic Acids via the Formation and Activation of Acyloxy(phenyl)trifluoromethyl-λ3-Iodanes

Here we report the challenging O-trifluoromethylation of carboxylic acids via the formation and activation of acyloxy(phenyl)trifluoromethyl-λ3-iodanes. The method provides an easy access to various potentially valuable and hitherto elusive trifluoromethyl carboxylic esters. A remarkably wide range of substrates with commonly encountered functional groups are compatible with this reaction, including aromatic and aliphatic carboxylic acids, as well as Food and Drug Administration (FDA) approved drugs and pharmaceutically relevant molecules. The reaction mechanism and the origins of the enhanced reactivity by zinc chloride (ZnCl2) were discussed from experimental evidence and density functional theory (DFT) calculation.

Monofluoromethylation of N-Heterocyclic Compounds

The review focuses on recent advances in the methodologies for the formation or introduction of the CH2F moiety in N-heterocyclic substrates over the past 5 years. The monofluoromethyl group is one of the most versatile fluorinated groups used to modify the properties of molecules in synthetic medical chemistry. The review summarizes two strategies for the monofluoromethylation of N-containing heterocycles: direct monofluoromethylation with simple XCH2F sources (for example, ICH2F) and the assembly of N-heterocyclic structures from CH2F-containing substrates. The review describes the monofluoromethylation of pharmaceutically important three-, five- and six-membered N-heterocycles: pyrrolidines, pyrroles, indoles, imidazoles, triazoles, benzothiazoles, carbazoles, indazoles, pyrazoles, oxazoles, piperidines, morpholines, pyridines, quinolines and pyridazines. Assembling of 6-fluoromethylphenanthridine, 5-fluoromethyl-2-oxazolines, C5-monofluorinated isoxazoline N-oxides, and α-fluoromethyl-α-trifluoromethylaziridines is also shown. Fluoriodo-, fluorchloro- and fluorbromomethane, FCH2SO2Cl, monofluoromethyl(aryl)sulfoniummethylides, monofluoromethyl sulfides, (fluoromethyl)triphenylphosphonium iodide and 2-fluoroacetic acid are the main fluoromethylating reagents in recent works. The replacement of atoms and entire functional groups with a fluorine atom(s) leads to a change and often improvement in activity, chemical or biostability, and pharmacokinetic properties. The monofluoromethyl group is a bioisoster of -CH3, -CH2OH, -CH2NH2, -CH2CH3, -CH2NO2 and -CH2SH moieties. Bioisosteric replacement with the CH2F group is both an interesting task for organic synthesis and a pathway to modify drugs, agrochemicals and useful intermediates.

Access to 2-thio/selenoquinolines via domino reaction of isocyanides with sulfur and selenium in water

A domino reaction of o-alkenylaryl isocyanides with elemental sulfur and selenium in pure water was developed for the efficient and green synthesis of quinoline-2-thione and diquinolyl diselenide derivatives. Mechanistical investigation reveals that intramolecular nucleophilic addition of an alkenyl group to the in situ generated isothio/isoselenocyanate accounts for the formation of a quinoline-ring. Moreover, this transformation is also amendable for the convenient preparation of 2-fluoromethylthio-/seleno-quinolines by a one-pot three-component reaction.

Iron-Catalyzed Hydrobenzylation: Stereoselective Synthesis of (-)-Eugenial C

Metal-hydride hydrogen atom transfer (MHAT) has emerged as a useful tool to form quaternary carbons from alkenes via hydrofunctionalization. Methods to date that cross-couple alkenes with sp3 partners rely on heterobimetallic catalysis to merge the two cycles. Here, we report an iron-only cross-coupling via putative MHAT/SH2 steps that solves a key stereochemical problem in the synthesis of meroterpenoid eugenial C and obviates the need for nickel. The concise synthesis benefits from a conformationally locked o,o'-disubstituted benzyl bromide and a locally sourced chiral pool terpene coupling partner.

Organoboron Reagent-Controlled Selective (Deutero)Hydrodefluorination

(Deuterium-labeled) CF₂ H- and CFH₂ -moieties are of high interest in drug discovery. The high demand for the incorporation of these fluoroalkyl moieties into molecular structures has witnessed significant synthetic progress, particularly in the (deutero)hydrodefluorination of CF₃ -containing compounds. However, the controllable replacement of fluorine atoms while maintaining high chemoselectivity remains challenging. Herein, we describe the development of a selective (deutero)hydrodefluorination reaction via electrolysis. The reaction exhibits a remarkable chemoselectivity control, which is enabled by the addition of different organoboron sources. The procedure is operationally simple and scalable, and provides access in one step to high-value building blocks for application in medicinal chemistry. Furthermore, density functional theory (DFT) calculations have been carried out to investigate the reaction mechanism and to rationalize the chemoselectivity observed.

C-H Fluoromethoxylation of Arenes by Photoredox Catalysis

Redox-active N-(fluoromethoxy)benzotriazoles were made accessible from fluoroacetic acid and hydroxybenzotriazoles via electrodecarboxylative coupling. After alkylation, they become effective monofluoromethoxylation reagents, enabling the photocatalytic C-H functionalization of arenes. Thus, irradiation of 1-(OCH₂ F)-3-Me-6-(CF₃ )benzotriazolium triflate with blue LED light in the presence of [Ru(bpy)₃ (PF₆ )₂ ] promotes the synthesis of diversely functionalized aryl monofluoromethyl ethers. This method allows the late-stage functionalization of biologically relevant structures without relying on ecologically problematic halofluorocarbons.

The synthetic versatility of fluoroiodomethane: recent applications as monofluoromethylation platform

In recent years, fluoroiodomethane (CH₂FI) has emerged as an easy-to-handle, non-ozone depleting agent and readily available platform for monofluoromethylation strategies. Recent applications in nucleophilic substitutions, lithiation reactions, transition-metal catalyzed transformations, radical processes, and ¹⁸F-radiolabelling chemistry showcase the potential of this reagent for the preparation of organofluorine compounds. In this minireview, we provide an update to the field covering the recent relevant literature on the use of CH₂FI.

Synthesis of 1,3-Dioxepine-Fused (Tricyclic) Bispyrazoles Involved with Pyrazolone Derivatives and Dichloromethane

A simple and novel method for the synthesis of novel 1,3-dioxepine-fused (tricyclic) bispyrazoles is described. It involves a Cs₂CO₃-mediated O-alkylation of readily available pyrazolone derivatives with dichloromethane as the methylene source followed by PhI(OAc)₂-mediated intramolecular oxidative biheteroaryl coupling under mild conditions. This scalable protocol was applied for the preparation of valuable and novel 1,3-dioxepine-fused (tricyclic) bispyrazoles that could find applications in medicinal or material chemistry.

Difunctionalization of gem-Difluoroalkenes via Photoredox Catalysis: Synthesis of Diverse α,α-Difluoromethyl-β-alkoxysulfones

Visible-light-promoted alkoxysulfonylation of gem-difluoroalkenes using sulfonyl chlorides and alcohols has been developed. The reaction exhibits a relatively broad substrate scope with excellent functional group compatibility. This synthesis method includes an atom transfer radical addition-like process. The products can be used as platform molecules for further modification.

29th Annual GP2A Medicinal Chemistry Conference

The 29th Annual GP₂A (Group for the Promotion of Pharmaceutical chemistry in Academia) Conference was a virtual event this year due to the COVID-19 pandemic and spanned three days from Wednesday 25 to Friday 27 August 2021. The meeting brought together an international delegation of researchers with interests in medicinal chemistry and interfacing disciplines. Abstracts of keynote lectures given by the 10 invited speakers, along with those of the 8 young researcher talks and the 50 flash presentation posters, are included in this report. Like previous editions, the conference was a real success, with high-level scientific discussions on cutting-edge advances in the fields of pharmaceutical chemistry.

Innovative Strategies for the Construction of Diverse 1'-Modified C-Nucleoside Derivatives

Modified C-nucleosides have proven to be enormously successful as chemical probes to understand fundamental biological processes and as small-molecule drugs for cancer and infectious diseases. Historically, the modification of the glycosyl unit has focused on the 2'-, 3'-, and 4'-positions as well as the ribofuranosyl ring oxygen. By contrast, the 1'-position has rarely been studied due to the labile nature of the anomeric position. However, the improved chemical stability of C-nucleosides allows the modification of the 1'-position with substituents not found in conventional N-nucleosides. Herein, we disclose new chemistry for the installation of diverse substituents at the 1'-position of C-nucleosides, including alkyl, alkenyl, difluoromethyl, and fluoromethyl substituents, using the 4-amino-7-(1'-hydroxy-d-ribofuranosyl)pyrrolo[2,1-f][1,2,4]triazine scaffold as a representative purine nucleoside mimetic.

Nucleophilic and Radical Heptafluoroisopropoxylation with Redox-Active Reagents

The heptafluoroisopropyl group (CF(CF₃ )₂ ) is prevalent in pharmaceuticals and agrichemicals. However, heptafluoroisopropoxylated (OCF(CF₃ )₂ ) compounds remain largely underexplored, presumably due to the lack of efficient access to these compounds. Herein, we disclose the practical and efficient heptafluoroisopropoxylation reactions through the invention of a series of redox-active N-OCF(CF₃ )₂ reagents. These reagents were readily prepared from the oxidative heptafluoroisopropylation of hydroxylamines with AgCF(CF₃ )₂ . The substitutions on the nitrogen atom significantly affected the properties and reactivities of N-OCF(CF₃ )₂ reagents. Accordingly, two types of N-OCF(CF₃ )₂ reagents including N-OCF(CF₃ )₂ phthalimide A and N-OCF(CF₃ )₂ benzotriazolium salt O' were used as OCF(CF₃ )₂ anion and radical precursors, respectively. This protocol enables the direct heptafluoroisopropoxylation of a range of substrates, delivering the corresponding products in moderate to excellent yields.

Hydrofluoromethylation of alkenes with fluoroiodomethane and beyond

A process for the direct hydrofluoromethylation of alkenes is reported for the first time. This straighforward silyl radical-mediated reaction utilises CH₂FI as a non-ozone depleting reagent, traditionally used in electrophilic, nucleophilic and carbene-type chemistry, but not as a CH₂F radical source. By circumventing the challenges associated with the high reduction potential of CH₂FI being closer to CH₃I than CF₃I, and harnessing instead the favourable bond dissociation energy of the C–I bond, we demonstrate that feedstock electron-deficient alkenes are converted into products resulting from net hydrofluoromethylation with the intervention of (Me₃Si)₃SiH under blue LED activation. This deceptively simple yet powerful methodology was extended to a range of (halo)methyl radical precursors including ICH₂I, ICH₂Br, ICH₂Cl, and CHBr₂F, as well as CH₃I itself; this latter reagent therefore enables direct hydromethylation. This versatile chemistry was applied to ¹⁸F-, ¹³C-, and D-labelled reagents as well as complex biologically relevant alkenes, providing facile access to more than fifty products for applications in medicinal chemistry and positron emission tomography.

Herein, we report the direct hydro(halo)methylation of alkenes from a variety of (halo)methyl iodides (including F-18, C-13, D-2 isotopologues), enabling the incorporation of a plethora of C-1 fragments into complex biologically active molecules.

Fluoromethyl-2,4,6-trinitrophenylsulfonate: A New Electrophilic Monofluoromethylating Reagent

Fluoromethyl-2,4,6-trinitrophenylsulfonate has been prepared for the first time and qualified as a simple to use monofluoromethylating reagent. Its molecular structure in the solid state has been determined by single-crystal X-ray diffraction studies. This reagent proves to be effective for the electrophilic introduction of a CH₂F group into selected chalcogen and nitrogen nucleophiles. Monofluoromethyl derivatives of various bifunctional N,O-nucleophiles have been synthesized using fluoromethyl-2,4,6-trinitrophenylsulfonate. Due to the good crystallizing properties of the anion, the fluoromethylated products as well as side products that are difficult to identify by nuclear magnetic resonance spectroscopy can readily be characterized by X-ray crystallographic techniques.

Optimized Monofluoromethylsulfonium Reagents for Fluoromethylene-Transfer Chemistry

An investigation of the properties and reactivity of fluoromethylsulfonium salts resulted in the redesign of the reagents for fluoromethylene transfer chemistry. The model reaction, fluorocyclopropanation of nitrostyrene, turned out to be a suitable platform for the discovery of more streamlined fluoromethylene transfer reagents. The incorporation of halides on one aryl ring increased the reactivity, and 2,4-dimethyl substitution on the other aryl ring provided a balance between the reactivity/crystallinity of the reagent as well as the atom economy. The utility of new reagents was demonstrated by the development of an efficient fluorocyclopropanation protocol to access a range of monofluorinated cyclopropane derivatives.