Synthetic methods for compounds having CF3-S units on carbon by trifluoromethylation, trifluoromethylthiolation, triflylation, and related reactions

Clickable tryptophan modification for late-stage diversification of native peptides

As the least abundant residue in proteins, tryptophan widely exists in peptide drugs and bioactive natural products and contributes to drug-target interactions in multiple ways. We report here a clickable tryptophan modification for late-stage diversification of native peptides, via catalyst-free C2-sulfenylation with 8-quinoline thiosulfonate reagents in trifluoroacetic acid (TFA). A wide range of groups including trifluoromethylthio (SCF3), difluoromethylthio (SCF2H), (ethoxycarbonyl)difluoromethylthio (SCF2CO2Et), alkylthio, and arylthio were readily incorporated. The rapid reaction kinetics of Trp modification and full tolerance with other 19 proteinogenic amino acids, as well as the super dissolving capability of TFA, render this method suitable for all kinds of Trp-containing peptides without limitations from sequences, hydrophobicity, and aggregation propensity. The late-stage modification of 15 therapeutic peptides (1.0 to 7.6 kilodaltons) and the improved bioactivity and serum stability of SCF3- and SCF2H-modified melittin analogs illustrated the effectiveness of this method and its potential in pharmacokinetic property improvement.

Photocascade chemoselective controlling of ambident thio(seleno)cyanates with alkenes via catalyst modulation

Controlling the ambident reactivity of thiocyanates in reaction manifolds has been a long-standing and formidable challenge. We report herein a photoredox strategy for installing thiocyanates and isothiocyanates in a controlled chemoselective fashion by manipulating the ambident-SCN through catalyst modulation. The methodology allows redox-, and pot-economical 'on-demand' direct access to both hydrothiophene and pyrrolidine heterocycles from the same feedstock alkenes and bifunctional thiocyanomalonates in a photocascade sequence. Its excellent chemoselectivity profile was further expanded to access Se- and N-heterocycles by harnessing selenonitriles. Redox capability of the catalysts, which dictates the substrates to participate in a single or cascade catalytic cycle, was proposed as the key to the present chemodivergency of this process. In addition, detailed mechanistic insights are provided by a conjugation of extensive control experiments and dispersion-corrected density functional theory (DFT) calculations.

Synthesis of 18F-labeled Aryl Trifluoromethyl Sulfones, -Sulfoxides, and -Sulfides for Positron Emission Tomography

Positron emission tomography (PET) is becoming increasingly important in nuclear medicine and drug discovery. To date, the development of many potential PET tracers is hampered by the lack of suitable synthetic pathways for their preparation. This is particularly true for the highly desired radiolabeling of compounds bearing [18F]CF3-groups. For instance, S(O)nCF3-groups (n=0, 1, 2) serve as structural motif in a range of biologically active compounds, but their radiosynthesis remains largely unprecedented (for n=1, 2). Herein, we describe general methods for the radiosynthesis of 18F-labeled aryl trifluoromethyl sulfones, -sulfoxides, and -sulfides. All three methods are operationally straightforward, start from widely available precursors, i.e., sulfonyl fluorides and thiophenols, and make use of the recently established [18F]Ruppert-Prakash reagent. Further, the syntheses display good functional group tolerance as demonstrated by the 18F-labeling of more than 40 compounds. The applicability of the new method is demonstrated by the radiolabeling of three bioactive molecules, optionally to be used as PET tracers. In a broader context, this work presents a substantial expansion of the chemical space of radiofluorinated structural motifs to be used for the development of new PET tracers.

Transition-Metal-Free C-H Trifluoromethylthiolation of N,N-Disubstituted Enaminones To Access CF3S-Functionalized Enaminones and Their Application in the Synthesis of CF3S-Heteroaryls

The α-C-H trifluoromethylthiolation of N,N-disubstituted enaminones has been achieved with simple and cheap CF3SO2Na as the CF3S source. The reactions were run at mild temperature (0 °C to rt) using POCl3 as the only reducing reagent. The work represents the first example on the synthesis of α-trifluoromethylthio enaminones via direct C-H functionalization. In addition, the resulting CF3S-functionalized enaminones have been proven as useful building blocks in the synthesis of various CF3S-functionalized heteroaromatic compounds by simple annulation reactions.

Asymmetric Synthesis of SCF3-Substituted Alkylboronates by Copper-Catalyzed Hydroboration of 1-Trifluoromethylthioalkenes

A synthetic method for preparation of optically active trifluoromethylthio (SCF3) compounds by a copper-catalyzed regio- and enantioselective hydroboration of 1-trifluoromethylthioalkenes with H-Bpin has been developed. The enantioselective hydrocupration of an in situ generated CuH species and subsequent boration reaction generate a chiral SCF3-containing alkylboronate, of which Bpin moiety can be further transformed to deliver various optically active SCF3 molecules. Computational studies suggest that the SCF3 group successfully controls the regioselectivity in the reaction.

Unveiling the Use of 1,1-Bis(triflyl)ethylene as CF3SO2CH═CH2 Source with the Assistance of (n-Bu)4NF: Synthesis of 3-[(Trifluoromethyl)sulfonyl]cyclobut-1-enes

Allylic sulfone-embedded cyclobutenes have been prepared in one pot from alkynes. The carbocycle and the alkenyl sulfone moieties were installed through consecutive bis(triflyl)cyclobutenylation of a triple bond and tetra-n-butylammonium fluoride (TBAF)-assisted hydrodesulfonylation of an allylic bis(sulfone). It is noteworthy that 1,1-bis(triflyl)ethylene acts as a CF3SO2CH═CH2 source for the first time.

Design, Synthesis, and Bioactivity of Trifluoroethylthio-Substituted Phenylpyrazole Derivatives

As the first marketed phenylpyrazole insecticide, fipronil exhibited remarkable broad-spectrum insecticidal activity. However, it poses a significant threat to aquatic organisms and bees due to its high toxicity. Herein, 35 phenylpyrazole derivatives containing a trifluoroethylthio group on the 4 position of the pyrazole ring were designed and synthesized. The predicted physicochemical properties of all of the compounds were within a reasonable range. The biological assay results revealed that compound 7 showed 69.7% lethality against Aedes albopictus (A. albopictus) at the concentration of 0.125 mg/L. Compounds 7, 7g, 8d, and 10j showed superior insecticidal activity for the control of Plutella xylostella (P. xylostella). Notably, compound 7 showed similar insecticidal activity against Aphis craccivora (A. craccivora) compared with fipronil. Potential surface calculation and molecular docking suggested that different lipophilicity and binding models to the Musca domestica (M. domestica) gamma-aminobutyric acid receptors may be responsible for the decreased activity of the tested derivatives. Toxicity tests indicated that compound 8d (LC50 = 14.28 mg/L) induced obviously 14-fold lower toxicity than fipronil (LC50 = 1.05 mg/L) on embryonic-juvenile zebrafish development.

Ligand-Controlled Regiodivergent Alkoxycarbonylation of Trifluoromethylthiolated Internal Alkynes

Controlling the regioselectivity for the alkoxycarbonylation of unsymmetric internal alkynes is challenging. Herein, a palladium-catalyzed ligand-controlled regiodivergent alkoxycarbonylation of internal trifluoromethylthiolated alkynes was achieved. A series of α- or β-SCF3 acrylates from the same trifluoromethylthiolated alkyne were obtained with moderate to high yield and regioselectivity.

I2-Cs2CO3 Mediated Intramolecular C2-Amination and Oxidative Rearrangement Cascade of C-3 Phenylthio Indoles: A Route to Synthesize Thiosulfonate-Embedded 2-Iminoindolin-3-ones

An efficient, transition-metal-free protocol employing I2/Cs2CO3 for the synthesis of thiosulfonate containing 2-iminoindolin-3-ones motifs has been developed from C-3 phenylthio indoles. The reaction proceeded through intramolecular cyclization involving C-N bond formation, leading to the formation of indole-fused benzothiazines as a key intermediate. Remarkably, Cs2CO3 played a crucial role in the reaction as an oxygen source, enabling oxidative rearrangement with [1,4]-sulfonyl migration to furnish the final products with the formation of multiple functional groups such as C═O, C═N, and S-SO2.

Enhancing Flavins Photochemical Activity in Hydrogen Atom Abstraction and Triplet Sensitization through Ring-Contraction

The isoalloxazine heterocycle of flavin cofactors reacts with various nucleophiles to form covalent adducts with important functions in enzymes. Molecular flavin models allow for the characterization of such adducts and the study of their properties. A fascinating set of reactions occurs when flavins react with hydroxide base, which leads to imidazolonequinoxalines, ring-contracted flavins, with so far unexplored activity. We report a systematic study of the photophysical properties of this new chromophore by absorption and emission spectroscopy as well as cyclic voltammetry. Excited, ring-contracted flavins are significantly stronger hydrogen atom abstractors when compared to the parent flavins, which allowed the direct trifluoromethylthiolation of aliphatic methine positions (bond dissociation energy (BDE) of 400.8 kJ mol-1). In an orthogonal activity, their increased triplet energy (E(S0←T1)=244 kJ mol-1) made sensitized reactions possible which exceeded the power of standard flavins. Combining both properties, ring-contracted flavin catalysts enabled the one-pot, five-step transformation of α-tropolone into trans-3,4-disubstituted cyclopentanones. We envision this new class of flavin-derived chromophores to open up new modes of reactivity that are currently impossible with unmodified flavins.

Enantioselective Construction of C-SCF3 Stereocenters via Nickel Catalyzed Asymmetric Negishi Coupling Reaction

The construction of the SCF3-containing 1,1-diaryl tertiary carbon stereocenters with high enantioselectivities is reported via a nickel-catalyzed asymmetric C-C coupling strategy. This method demonstrates simple operations, mild conditions and excellent functional group tolerance, with newly designed SCF3-containing synthon, which can be easily obtained from commercially available benzyl bromide and trifluoromethylthio anion in a two-step manner. Further substrate exploration indicated that the reaction system could be extended to diverse perfluoroalkyl sulfide (SC2F5, SC3F7, SC4F9, SCF2CO2Et)-substituted 1,1-diaryl compounds with excellent enantioselectivities. The synthetic utility of this transformation was further demonstrated by convenient derivatization to optical SCF3-containing analogues of bioactive compounds without an apparent decrease in enantioselectivity.

Catalytic Asymmetric Difluoroalkylation Using In Situ Generated Difluoroenol Species as the Privileged Synthon

A robust and practical difluoroalkylation synthon, α,α-difluoroenol species, which generated in situ from trifluoromethyl diazo compounds and water in the presence of dirhodium complex, is disclosed. As compared to the presynthesized difluoroenoxysilane and in situ formed difluoroenolate under basic conditions, this difluoroenol intermediate displayed versatile reactivity, resulting in dramatically improved enantioselectivity under mild conditions. As demonstrated in catalytic asymmetric aldol reaction and Mannich reactions with ketones or imines in the presence of chiral organocatalysts, quinine-derived urea, and chiral phosphoric acid (CPA), respectively, this relay catalysis strategy provides an effective platform for applying asymmetric fluorination chemistry. Moreover, this method features a novel 1,2-difunctionalization process via installation of a carbonyl motif and an alkyl group on two vicinal carbons, which is a complementary protocol to the metal carbene gem-difunctionalization reaction.

Copper-Catalyzed, Interrupted Remote Fluoromethylthiolation of Unactivated C(sp3)-H Bonds

An efficient copper-catalyzed selective fluoromethylthiolation of an inert δ-C(sp3)-H bond in sulfonamides was reported. In the presence of a copper catalyst and PhSO2SRf, the radical generated through 1,5-hydrogen atom transfer (HAT) was sufficiently trapped by PhSO2SRf, instead of copper, which was prevalent in metal-catalyzed radical-relay processes, incorporating a fluoromethylthio group into molecules. The general substrate scope and mild conditions endowed the method with wide potential applications in pharmaceuticals and agrochemicals.

Copper-Catalyzed Enantioselective C(sp3 )-SCF3 Coupling of Carbon-Centered Benzyl Radicals with (Me4 N)SCF3

In contrast with the well-established C(sp2 )-SCF3 cross-coupling to forge the Ar-SCF3 bond, the corresponding enantioselective coupling of readily available alkyl electrophiles to forge chiral C(sp3 )-SCF3 bond has remained largely unexplored. We herein disclose a copper-catalyzed enantioselective radical C(sp3 )-SCF3 coupling of a range of secondary/tertiary benzyl radicals with the easily available (Me4 N)SCF3 reagent. The key to the success lies in the utilization of chiral phosphino-oxazoline-derived anionic N,N,P-ligands through tuning electronic and steric effects for the simultaneous control of the reaction initiation and enantioselectivity. This strategy can successfully realize two types of asymmetric radical reactions, including enantioconvergent C(sp3 )-SCF3 cross-coupling of racemic benzyl halides and three-component 1,2-carbotrifluoromethylthiolation of arylated alkenes under mild reaction conditions. It therefore provides a highly flexible platform for the rapid assembly of an array of enantioenriched SCF3 -containing molecules of interest in organic synthesis and medicinal chemistry.

Synthesis of gem-Difluoro-3,4-dihydro-2H-pyrans via a TfOH-Catalyzed [4 + 2] Annulation of Difluoroenoxysilanes with α-Cyano Chalcones

Difluoroenoxysilane, a commonly used difluoroallylating reagent, has attracted considerable attention in recent years. However, its application in the annulation reaction for the construction of fluorinated heterocyclic compounds remains relatively limited. Presented here is the Brønsted acid-catalyzed efficient formal [4 + 2] annulation of difluoroenoxysilanes with α-cyano chalcones. The developed protocol demonstrates tolerance to various substituents under mild reaction conditions, providing a reliable approach to construct gem-difluoro-3,4-dihydro-2H-pyrans in good to excellent yields with high diastereoselectivities.

ortho-Cyanomethylation of aryl fluoroalkyl sulfoxides via a sulfonium-Claisen rearrangement

We hereby report the ortho-cyanomethylation of aryl fluoroalkyl sulfoxides with acetonitrile through a sulfonium-Claisen-type rearrangement. This reaction enables the incorporation of two valuable functional groups, such as the cyanomethyl group and the fluoroalkylthio group, into arenes. Remarkably, fluoroalkylthio groups, such as SCFH2 and SCF2H, bearing active hydrogen, are well tolerated by the reaction. The success of the reaction relies on the use of an excess amount of acetonitrile and the electronegative effect of fluoroalkyl substituents, both of which promote the electrophilic assembly of sulfoxides with acetonitrile. Consequently, the sulfonium-Claisen rearrangement reaction tolerates a wide variety of fluoroalkyl sulfoxides bearing functional groups including halides, nitriles, ketones, sulfones, and amides, which are appealing for subsequent elaboration and exploration.

Trifluoromethylthiolation of Arenes Using Lewis Acid and Lewis Base Dual Catalysis

Incorporation of the highly lipophilic trifluoromethanesulfenyl group into bioactive molecules facilitates transport through lipid membranes, and thus, CF3S-containing compounds are important for drug discovery. Although reagents and procedures have been reported for arene trifluoromethylthiolation, methods are still required that are applicable to a diverse substrate scope and can be performed under mild conditions. Here, we describe a rapid and efficient approach for the trifluoromethylthiolation of arenes by catalytic activation of N-trifluoromethylthiosaccharin using a combination of iron(III) chloride and diphenyl selenide. This dual catalytic process allowed regioselective functionalization of a wide range of arenes and N-heterocycles under mild conditions and was used for the trifluoromethylthiolation of bioactive compounds such as tyrosine and estradiol.

Visible light-induced hydrogen atom transfer trifluoromethylthiolation of aldehydes with bismuth catalyst

By using a combination of BiCl3 and TBACl as a ligand-to-metal charge transfer (LMCT) photocatalyst, hydrogen atom transfer trifluoromethylthiolation of aldehydes was achieved under visible light irradiation. The present method provides economical and operationally simple access to trifluoromethylthioesters using low toxicity and cost-effective bismuth catalysts under mild reaction conditions. Based on the radical trapping experiments, the direct conversion of aldehydes to acyl radicals via chlorine radicals as HAT reagents was proposed as the reaction mechanism.

Synthesis of acyl fluorides through deoxyfluorination of carboxylic acids

A direct deoxyfluorination of carboxylic acids by utilizing inorganic potassium fluoride (KF) as a safe and inexpensive fluoride source has been developed. Both aryl carboxylic acids and cinnamyl carboxylic acids could be efficiently transformed into valuable acyl fluorides in moderate to high yields with good functional group tolerance. A scale-up reaction could be carried out smoothly under solvent-free conditions, which further demonstrated the practicality of this reaction in organic synthesis.

The perfluoroalkylthiolation/decarbonylation reaction of 1,3-diketones with perfluoroalkanesulfenic acids

The perfluoroalkylthiolation/decarbonylation reactions of 1,3-dicarbonyl compounds with in situ formed perfluoroalkanesulfenic acids were achieved. Using trifluoromethanesulfonic acid as an additive, a series of α-perfluoroalkylthiolated arylethanones were obtained in moderate to good yields. A possible mechanism was proposed based on the reaction results and control experiments.

Organophotocatalyzed Mono- and Bis-Alkyl/Difluoroalkylative Thio/Selenocyanation of Alkenes

Organophotocatalyzed three-component 1,2-difluoroacetyl/alkyl/perfluoroalkylative thio/selenocyanation of styrene derivatives under stoichiometric, transition metal-, oxidant-, and additive-free, and mild redox-neutral conditions is reported. Organophotocatalyst 4CzIPN operates the overall radical-polar-crossover mechanistic cycle via initial oxidative luminescence quenching, and the key intermediates were experimentally detected. Selective mono-alkylative thiocyanation of alkenes using dibromoalkanes is also demonstrated. This one-pot synthetic methodology is suitable for primary, secondary, and tertiary alkyl halides and also extended for double alkylative thiocyanation of the dibromoalkanes with excellent yields.

Umpolung trifluoromethylthiolation of alcohols

Herein we develop a metal-free umpolung dehydroxytrifluoromethylthiolation of alcohols with commercially available PPh3 and N-trifluoromethylthiophthalimide within 30 minutes. This protocol shows excellent functional group tolerance and high regioselectivity. The dehydroxytrifluoromethylthiolation of a series of natural products and drugs further demonstrates its practicality. Preliminary mechanistic studies suggest that PPh3 is responsible for deoxygenation and the key trifluoromethylthiophosphonium ion may be hydrolyzed by H2O in solvent.

Copper-Catalyzed Aryne Insertion into the Carbon-Iodine Bond of Heteroaryl Iodides

Aryne insertions into the carbon-iodine bond of heteroaryl iodides has been achieved for the first time. This novel reaction provides an efficient pathway for the synthesis of valuable building blocks 2-iodoheterobiaryls from heteroaryl iodides and o-silylaryl triflates in excellent regioselectivity. The copper(I) catalyst, which bears a N-heterocyclic carbene (NHC) ligand, is essential to accomplish the reaction. Control reactions and DFT calculations indicate that the coordination of copper, as a Lewis acid, with nitrogen atoms of heteroaryl iodides mediates the insertion of arynes into heteroaryl carbon-iodine bonds.

Radical-mediated sulfonylative/thiolative cyclization of biaryl enones to phenanthrone derivatives

An approach for the assembly of phenanthrone derivatives bearing all carbon quaternary centres has been developed through visible light-promoted tandem sulfonylation/intramolecular-arylation of biaryl enones with sulfonyl chlorides. A series of sulfonylated 10,10-dialkylphenanthrones were obtained in good yields. In addition, the approach has been extended to thiotrifluoromethyl (SCF3) and thiocyanato (SCN) radicals to obtain the corresponding phenanthrones under oxidative conditions. The synthetic utility was also illustrated by the scalability and further transformations of the product.

Trifluoromethylthiolation of Tryptophan and Tyrosine Derivatives: A Tool for Enhancing the Local Hydrophobicity of Peptides

The incorporation of fluorinated groups into peptides significantly affects their biophysical properties. We report herein the synthesis of Fmoc-protected trifluoromethylthiolated tyrosine (CF3S-Tyr) and tryptophan (CF3S-Trp) analogues on a gram scale (77-93% yield) and demonstrate their use as highly hydrophobic fluorinated building blocks for peptide chemistry. The developed methodology was successfully applied to the late-stage regioselective trifluoromethylthiolation of Trp residues in short peptides (66-80% yield) and the synthesis of various CF3S-analogues of biologically active monoamines. To prove the concept, Fmoc-(CF3S)Tyr and -Trp were incorporated into the endomorphin-1 chain (EM-1) and into model tripeptides by solid-phase peptide synthesis. A remarkable enhancement of the local hydrophobicity of the trifluoromethylthiolated peptides was quantified by the chromatographic hydrophobicity index determination method, demonstrating the high potential of CF3S-containing amino acids for the rational design of bioactive peptides.

Fluoroalkylations and Fluoroalkenylations with Iodonium Salts

Synthesis and applications of fluoroalkyl and fluoroalkenyliodonium salts are summarized in this account article, focusing preferably to the reagents designed in our laboratory in the last decade. Among these reagents trifluoroethyl(aryl)iodonium salts have been used most frequently to build carbon-carbon and carbon-heteroatom bonds in simple nucleophilic substitutions and through transition metal catalyzed coupling reactions. Iodonium salts equipped with unsaturated fluorinated function showed diverse reactivity due to their electron deficient character, and these molecular motifs enable cycloadditions and nucleophilic additions to prepare fluorinated carbo- and heterocyclic molecules. Beyond the overview of existing transformations, with the presented collection, we aim to inspire future developments of iodonium reagents and their application in organic synthesis.

Recent Advances in Visible Light-Mediated Radical Fluoro-alkylation, -alkoxylation, -alkylthiolation, -alkylselenolation, and -alkylamination

In the last few years, many reagents and protocols have been developed to allow for the efficient fluorofunctionalization of a diverse set of scaffolds ranging from alkanes, alkenes, alkynes, and (hetero)arenes. The concomitant rise of organofluorine chemistry and visible light-mediated synthesis have synergistically expanded the fields and have mutually benefitted from developments in both fields. In this context, visible light driven formations of radicals containing fluorine have been a major focus for the discovery of new bioactive compounds. This review details the recent advances and progress made in visible light-mediated fluoroalkylation and heteroatom centered radical generation.

Recent Advances in the Synthesis and Transformation of Carbamoyl Fluorides, Fluoroformates, and Their Analogues

Carbamoyl fluorides, fluoroformates, and their analogues are a class of important compounds and have been evidenced as versatile building blocks for the preparation of useful molecules in organic chemistry. While major achievements were made in the synthesis of carbamoyl fluorides, fluoroformates, and their analogues in the last half of 20th century, an increasing number of reports have focused on using O/S/Se=CF2 species or their equivalents as the fluorocarbonylation reagents for the direct construction of these compounds from the parent heteroatom-nucleophiles in recent years. This review mainly summarizes the advances in the synthesis and typical application of carbamoyl fluorides, fluoroformates, and their analogues by the halide exchanges and fluorocarbonylation reactions since 1980.

Chemistry and Pharmacology of Fluorinated Drugs Approved by the FDA (2016-2022)

Fluorine is characterized by high electronegativity and small atomic size, which provide this molecule with the unique property of augmenting the potency, selectivity, metabolic stability, and pharmacokinetics of drugs. Fluorine (F) substitution has been extensively explored in drug research as a means of improving biological activity and enhancing chemical or metabolic stability. Selective F substitution onto a therapeutic or diagnostic drug candidate can enhance several pharmacokinetic and physicochemical properties such as metabolic stability and membrane permeation. The increased binding ability of fluorinated drug target proteins has also been reported in some cases. An emerging line of research on F substitution has been addressed by using 18F as a radiolabel tracer atom in the extremely sensitive methodology of positron emission tomography (PET) imaging. This review aims to report on the fluorinated drugs approved by the US Food and Drug Administration (FDA) from 2016 to 2022. It cites selected examples from a variety of therapeutic and diagnostic drugs. FDA-approved drugs in this period have a variety of heterocyclic cores, including pyrrole, pyrazole, imidazole, triazole, pyridine, pyridone, pyridazine, pyrazine, pyrimidine, triazine, purine, indole, benzimidazole, isoquinoline, and quinoline appended with either F-18 or F-19. Some fluorinated oligonucleotides were also authorized by the FDA between 2019 and 2022.

Trifluoromethyl-Functionalized 2D Covalent Organic Framework for High-Resolution Separation of Isomers

Development of novel functional materials for effective isomer separation is of great significance in environmental science, chemical industry, and life science due to the different functions of isomers. However, the similar physicochemical properties of isomers make their separation greatly challenging. Here, we report the fabrication of trifluoromethyl-functionalized 2D covalent organic framework (COF) TpTFMB with 2,2'-bis(trifluoromethyl)benzidine (TFMB) and 1,3,5-triformylphloroglucinol (Tp) for the separation of isomers. TpTFMB was in situ-grown on the inner surface of a capillary for the high-resolution separation of isomers. The introduction of hydroxyl and trifluoromethyl functional groups with uniform distribution in 2D COFs is a powerful tactic to endow TpTFMB with various functions such as hydrogen bonding, dipole interaction, and steric effect. The prepared TpTFMB capillary column enabled the baseline separation of positional isomers such as ethylbenzene and xylene, chlorotoluene, carbon chain isomers such as butylbenzene and ethyl butanoate, and cis-trans isomers 1,3-dichloropropene. The hydrogen-bonding, dipole, and π-π interactions as well as the structure of COF significantly contribute to the isomer separation. This work provides a new strategy for designing functional 2D COFs for the efficient separation of isomers.

Intramolecular Heterocyclization/Fluoromethylthiolation of Alkynes Enabled by a Multicomponent Reagent System

The BnSR_f (R_f = CF₂H or CF₃)/mCPBA/Tf₂O system was found to be an effective multicomponent reagent system for the one-pot synthesis of di/trifluoromethylthiolated heterocycles from alkynes. The reaction was postulated to proceed via a cascade sequence involving the oxidation of BnSR_f by mCPBA, activation of the in situ-generated sulfoxide by Tf₂O, and intramolecular cyclization/fluoromethylthiolation of the alkyne substrates enabled by the formed electrophilic sulfonium salt to give di/trifluoromethylthiolated heterocycles.

Straightforward Synthesis of Bis[(trifluoromethyl)sulfonyl]ethylated Isocoumarins from 2-Ethynylbenzoates

Herein, we report a facile isocoumarin and isoquinolone preparation by taking advantage of an initial bis(triflyl)ethylation [triflyl = (trifluoromethyl)sulfonyl] reaction, followed by heterocyclization, which contrasts with our previous results on cyclobutene formation. The efficiency of the catalyst- and irradiation-free heterocyclization/bis(triflyl)ethylation sequence showed exquisite dependence on the electronic nature of the substituents at the 2-ethynylbenzoate(benzamide) precursors. Molecular docking of model bis(triflyl)ethylated isocoumarins on human acetylcholinesterase (hAChE) revealed promising biological activities through selective coordination on both the catalytic active site and peripheral active site.

Copper-catalyzed ring-opening trifluoromethylthiolation/trifluoromethylselenolation of cyclopropanols with TsSCF3 or Se-(trifluoromethyl) 4-methoxybenzenesulfonoselenoate

We report a ring-opening trifluoromethylthiolation of cyclopropanols with TsSCF₃ by using Cu(OAc)₂ as the catalyst. Moreover, by using this strategy, the trifluoromethylselenolation of cyclopropanols with Se-(trifluoromethyl) 4-methoxybenzenesulfonoselenoate to access β-SeCF₃-substituted carbonyl compounds is achieved for the first time. The broad substrate scope, readily accessible reagents and cheap catalyst make this protocol an alternative and efficient method for the synthesis of β-SCF₃-substituted or β-SeCF₃-substituted carbonyl compounds.

Cascade Oxidative Trifluoromethylthiolation and Cyclization of 3-Alkyl-1-(2-(alkynyl)phenyl)indoles

Persulfate-promoted radical cascade trifluoromethylthiolation and cyclization of 3-alkyl-1-(2-(alkynyl)phenyl)indoles with AgSCF₃ were investigated. This protocol provides a novel route to CF₃S-substituted indolo[1,2-a]quinoline-7-carbaldehydes and CF₃S-substituted indolo[1,2-a]quinoline-7-methanone derivatives via the formation of the C-SCF₃ bond and C-C bond and benzylic carbon oxidation in a single step. This reaction can accommodate a broad range of functional groups. The single-crystal X-ray diffraction data confirm the chemical structure of the product. A scale-up experiment and radical inhibition experiments were operated in the reaction system. Photophysical properties of some selected 5-((trifluoromethyl)thio)indolo[1,2-a]quinoline-7-carbaldehydes were studied by UV-visible and fluorescence spectroscopy.

Synthesis of Indole-Substituted Trifluoromethyl Sulfonium Ylides by Cp*Rh(III)-Catalyzed Diazo-carbenoid Addition to Trifluoromethylthioether

The indole-substituted trifluoromethyl sulfonium ylide has been developed via Cp*Rh(III)-catalyzed diazo-carbenoid addition to trifluoromethylthioether and is the first example of an Rh(III)-catalyzed diazo-carbenoid addition reaction with trifluoromethylthioether. Several kinds of indole-substituted trifluoromethyl sulfonium ylide were constructed under mild reaction conditions. The reported method exhibited high functional group compatibility and broad substrate scope. In addition, the protocol was found to be complementary to the method disclosed by a Rh(II) catalyst.

Deacylative Thiolation by Redox-Neutral Aromatization-Driven C-C Fragmentation of Ketones

Herein we report the development of deacylative thiolation of diverse methyl ketones. The reaction is redox-neutral, and heavy-metal-free, which provides a new way to introduce thioether groups site-specifically to unactivated aliphatic positions. It also features excellent functional group tolerance and broad substrate scope, thus allowing late-stage derivatization. The process benefits from efficient condensation between the activation reagent and ketone substrates, which triggers aromatization-driven C-C fragmentation and rapid radical coupling with thiosulfonates. Experimental and computational mechanistic studies suggest the involvement of a radical chain pathway.

Visible-Light-Induced Trifluoromethylsulfonylation Reaction of Diazo Compounds Enabled by Manganese Catalysis

A visible-light-induced trifluoromethylsulfonylation reaction of diazo compounds is herein reported. This developed synthetic method captures the relatively rare trifluoromethyl sulfone radicals via coordination to the Mn(acac)₃ catalyst, delivering the corresponding α-trifluoromethyl sulfone esters in good to moderate yields (up to 82%). This protocol exhibits broad substrate scope and is easily carried out under mild reaction conditions. Furthermore, a plausible mechanism of the reaction was investigated through DFT calculations.

Investigating the mechanism of Ni-mediated trifluoromethylthiolation of aryl halides using AgSCF3

The mechanism of the Ni-catalysed trifluoromethylthiolation of aryl chlorides using AgSCF₃ is studied herein. A variety of IPr Ni^II complexes were synthesized via oxidative addition of Ni⁰ to 2-(2-chloro)phenylpyridines. Their reactivity with AgSCF₃ was tested by performing stoichiometric experiments, cyclic voltammetry, and NMR spectroscopic studies. CuSCF₃ was shown to behave similarly to AgSCF₃, while reactions with NMe₄SCF₃ revealed a major stoichiometric side reaction that forms a nickel fluoride complex. NMR kinetic studies revealed there is little correlation between the electron-withdrawing/donating nature of the para substituents on either the phenyl or pyridyl groups with the formation of the corresponding products. Cyclic voltammetry (CV) indicated the feasibilty of Ni^I/Ni^III transitions, and an increased rate of formation of product was observed with increased solvent polarity. Evidence suggests that the mechanism proceeds via inner-sphere electron transfer (ET) from AgSCF₃ to Ni^II, ultimately leading to the formation of the trifluoromethylthiolated product.

A Toolbox of Reagents for Trifluoromethylthiolation: From Serendipitous Findings to Rational Design

Two types of electrophilic trifluoromethylthiolating reagents were developed in the past 10 years in our laboratory. The development of the first type of reagent, trifluoromethanesulfenate I, which is highly reactive toward a variety of nucleophiles, was based on an unexpected discovery in the initial design for the development of an electrophilic trifluoromethylthiolating reagent with a hypervalent iodine skeleton. A structure-activity study disclosed that α-cumyl trifluoromethanesulfenate (reagent II) without the iodo substituent is equally effective. Subsequent derivatization let us develop an α-cumyl bromodifluoromethanesulfenate III that could be used for the preparation of [¹⁸F]ArSCF₃. To remediate the low reactivity of the type I electrophilic trifluoromethylthiolating reagent for Friedel-Crafts trifluoromethylthiolation of electron-rich (hetero)arenes, we designed and prepared N-trifluoromethylthiosaccharin IV, which exhibits broad reactivity toward various nucleophiles, including electron-rich arenes. A comparison of the structure of N-trifluoromethylthiosaccharin IV with that of N-trifluoromethylthiophthalimide showed that the replacement of one carbonyl group in N-trifluoromethylthiophthalimide with a sulfonyl group made N-trifluoromethylthiosaccharin IV much more electrophilic. Thus, the replacement of both carbonyls with two sulfonyl groups would further increase the electrophilicity. Such a rationale prompted us to design and develop the current most electrophilic trifluoromethylthiolating reagent, N-trifluoromethylthiodibenzenesulfonimide V, and its reactivity was much higher than that of N-trifluoromethylthiosaccharin IV. We further developed an optically pure electrophilic trifluoromethylthiolating reagent, (1S)-(-)-N-trifluoromethylthio-2,10-camphorsultam VI, for the preparation of optically active trifluoromethylthio-substituted carbon stereogenic centers. Reagents I-VI now constitute a powerful toolbox for the introduction of the trifluoromethylthio group into the target molecules.

Recent Applications of Trifluoromethanesulfonic Anhydride in Organic Synthesis

Trifluoromethanesulfonic anhydride has been widely used in synthetic organic chemistry, not only for the conversion of various oxygen-containing compounds to the triflates, but also for the electrophilic activation and further conversion of amides, sulfoxides, and phosphorus oxides. In recent years, the utilization of Tf₂ O as an activator for nitrogen-containing heterocycles, nitriles and nitro groups has become a promising tool for the development of new valuable methods with considerable success. In addition, Tf₂ O has been used as an efficient radical trifluoromethylation and trifluoromethylthiolation reagent due to the contained SO₂ CF₃ fragment, and significant progress has been made in this area. This review summarizes the recent progress in the applications of Tf₂ O in the above two aspects, and aims to illustrate the role and potential application of this reagent in organic synthesis.

Organocatalytic Synthesis of Triflones Bearing Two Non-Adjacent Stereogenic Centers

Trifluoromethylsulfones (triflones) are useful compounds for synthesis and beyond. Yet, methods to access chiral triflones are scarce. Here, we present a mild and efficient organocatalytic method for the stereoselective synthesis of chiral triflones using α-aryl vinyl triflones, building blocks previously unexplored in asymmetric synthesis. The peptide-catalyzed reaction gives rise to a broad range of γ-triflylaldehydes with two non-adjacent stereogenic centers in high yields and stereoselectivities. A catalyst-controlled stereoselective protonation following a C-C bond formation is key to control over the absolute and relative configuration. Straightforward derivatization of the products into, e.g., disubstituted δ-sultones, γ-lactones, and pyrrolidine heterocycles highlights the synthetic versatility of the products.

Transition State Stabilization by SCF2 -H⋅⋅⋅O Bifurcated Hydrogen Bond

The difluoromethylthio group (SCF₂ H), which is generally considered a highly lipophilic weak hydrogen bonding donor, has attracted special interest from the pharmaceutical and agrochemical industry. Remarkably, there have been relatively few literature investigations of SCF₂ H hydrogen bonding interactions. Here, we report the determination of the hydrogen bond acidity parameter A of the SCF₂ H in the most popularly used electrophilic difluoromethylthiolating reagent. We present kinetic and computational evidence of the RSCF₂ -H⋅⋅⋅O2 bifurcated hydrogen bond for stabilizing the SCF₂ H-transferring transition state, which could cause a reversal of apparent electrophilic reactivity of difluoromethylthiolating and trifluoromethylthiolating reagents. Solvent effects on the RSCF₂ -H⋅⋅⋅O2 bifurcated hydrogen bonds will also be discussed.

Visible-Light-Promoted Trifluoromethylthiolation and Trifluoromethylselenolation of 1,4-Dihydropyridines

We report a metal-free trifluoromethylthiolation and trifluoromethylselenolation of 1,4-dihydropyridines with S-(trifluoromethyl) 4-methylbenzenesulfonothioate and Se-(trifluoromethyl) 4-methylbenzenesulfonoselenoate under visible light irradiation. This transformation was tolerated with a wide range of functional groups and provided an alternative and green strategy for the synthesis of trifluoromethylthioesters and trifluoromethylselenoesters.

β-Trifluorosulfinylesters: tuneable reagents for switchable trifluoromethylsulfinylation and C–H trifluoromethylthiolation

β-Trifluorosulfinylesters, a family of novel reagents from commercially available starting materials for direct trifluoromethylthiolation and trifluoromethylsulfinylation were developed.

Transition-metal-catalyzed C-H bond activation as a sustainable strategy for the synthesis of fluorinated molecules: an overview

The last decade has witnessed the emergence of innovative synthetic tools for the synthesis of fluorinated molecules. Among these approaches, the transition-metal-catalyzed functionalization of various scaffolds with a panel of fluorinated groups (XR_F, X = S, Se, O) offered straightforward access to high value-added compounds. This review will highlight the main advances made in the field with the transition-metal-catalyzed functionalization of C(sp²) and C(sp³) centers with SCF₃, SeCF₃, or OCH₂CF₃ groups among others, by C-H bond activation. The scope and limitations of these transformations are discussed in this review.

Direct fluoroalkylthiolation of indoles with iodofluoroethane enabled by Na2S2O4

In this paper, we report an efficient approach for the direct fluoroalkylthiolation of indoles with iodofluoroethane in the presence of Na₂S₂O₄. In this work, we employed readily available iodofluoroethane and Na₂S₂O₄ as fluoroalkylthiolation reagents, featuring mild conditions and a wide range of indole substrates. In addition, fluoroalkylthiolated 2,3'-biindole derivatives can also be prepared by this method.