Trifluoromethyl Thianthrenium Triflate: A Readily Available Trifluoromethylating Reagent with Formal CF3+, CF3•, and CF3- Reactivity

Bichromophoric Ruthenium Complexes for Photocatalyzed Late-Stage Synthesis of Trifluoromethylated Indolizines

Indolizines are a promising class of biologically active compounds. However, photocatalytic methods for their selective derivatization are scarce in the literature. Herein, a mild, simple, and chemoselective protocol for the synthesis of 3-(trifluoromethyl)indolizine has been developed. The desired products were obtained in good to excellent yields and can be easily obtained on a gram scale. By tuning the redox properties of a Ru-based photocatalyst, it is possible to achieve competitive yields and further apply the optimized conditions to a broad variety of substrates. This method tolerates many functional groups and, therefore, can be used for late-stage functionalization. Our combined theoretical and spectroscopic findings revealed that the superior dyad-like ruthenium catalyst developed in this study has a completely different electronic nature of both key species that are crucial for efficient photoredox catalysis compared to commonly used homoleptic ruthenium complexes.

Photoactivation of Thianthrenium Salts: An Electron-Donor-Acceptor (EDA)-Complex Approach

Thianthrenium salts have emerged as one of the most versatile reagents, gaining significant popularity within the synthetic community for their utility in the construction of C-C and C-X (X = N, O, S, P, halogens) bonds. The use of photoredox and transition metal catalysis with thianthrenium salts for C-C and C-heteroatom bond formation is well established. However, most of these methods require elevated temperatures, expensive catalysts, and ligands under stringent conditions for effective execution. In contrast, the photocatalysis- and transition-metal-free approaches for constructing C-C and C-X bonds using thianthrenium salt derivatives have become increasingly sought after. In this regard, electron-donor-acceptor (EDA)-complex reactions have emerged as a powerful strategy in organic synthesis, eliminating the need for photocatalysts under visible light irradiation. EDA-complex photochemistry exploits the electron-acceptor properties of thianthrenium salts, facilitating the rapid generation of radical intermediates via the C-S bond cleavage. These radical intermediates play a pivotal role in enabling a variety of valuable C-C and C-X formations. In this Perspective, we highlight significant advances in the EDA-complex-mediated reactions involving thianthrenium salts with mechanisms, substrate scope, and limitations for constructing C-C and C-heteroatom bonds. For the sake of brevity, the article is organized into five main sections: (1) Nitrogen-based donor reactions, (2) Oxygen-based donor reactions, (3) Sulfur-based donor reactions, (4) Phosphorus-based donor reactions, and (5) π-based donor reactions, with a focus on C-C, C-S, C-B and C-P bond formations.

Triflic Anhydride-Mediated Synthesis of Anthraquinones and Anthrones via Unusual Intramolecular Rearrangement

Triflic anhydride (Tf2O) is a potent electrophilic activator for carbonyl groups, facilitating the formation of versatile triflate intermediates that undergo nucleophilic trapping to generate a broad array of valuable compounds. In this work, we have developed a novel method that utilizes Tf2O as a mediator for carbonyl activation and subsequent intramolecular rearrangement of 3,3-diarylbenzofuranones into anthraquinones 2 and anthrones 3. Both anthraquinones and anthrones are important molecules in the fields of natural products research, pharmaceuticals, and traditional Chinese medicines. A plausible reaction mechanism is proposed involving Tf2O-mediated activation, carbocation formation, nucleophilic addition, and intramolecular cyclization, ultimately leading to the formation of anthraquinones and anthrones. The developed methodology is both operationally simple and convenient, without the need for an inert atmosphere. This study broadens the scope of Tf2O utility and extends the practical application of intriguing intramolecular rearrangement to the synthesis of biologically active compounds, pharmaceuticals, and functional materials.

Single-Electron-Transfer-Mediated Carbonylation Reactions

ConspectusTransition-metal-catalyzed carbonylation coupling methods have been accepted as an essential tool for producing carbonylated products over the past few decades. Despite its long-standing history and widespread industrial applications, several challenges remain in carbonylation chemistry. These include reliance on precious metal catalysts, the need of high-energy radiation, difficulties in carbonylation of unactivated chemical bonds, etc. As an alternative to classic two-electron transfer process, single-electron-transfer (SET)-mediated carbonylation has emerged as a powerful tool to achieve elusive carbonylation transformations. Over the past few years, carbonylation of commonly available functional handles, such as alkenes and alkyl halides, via the single-electron pathway has emerged as a valuable area of research.Our team has been dedicated to developing new carbonylation reactions using bulk chemicals to construct high-value carbonylated products. These reactions have broad synthetic and industrial applications, motivating us to explore SET-mediated carbonylation transformations for two key classes of bulk chemicals: alkanes and alkyl halides. Specifically, our work has centered on two main approaches: (1) Single-electron reduction of C(sp3)-X bonds: this strategy leverages single-electron reduction to activate C(sp3)-X bonds, promoting the formation of carbon radicals, which in turn promotes subsequent addition to metals or CO. However, a significant challenge lies in the highly negative reduction potential of certain substrates [Ered < -2 V compared to the saturated calomel electrode (SCE) for unactivated alkyl iodides]. Despite these challenges, the intrinsic reducibility of CO and the reactivity of various carbonyl-metal intermediates facilitate smooth reaction progress. (2) Single-electron oxidative of C(sp3)-H bonds: this strategy emphasizes efficiency, high atomic utilization, and minimal waste by bypassing traditional preactivation methods. Using 3d metal catalysts, we have successfully performed aminocarbonylation and alkoxycarbonylation on a wide range of C(sp3)-H bonds (such as those in aliphatic alkanes, ethers, amines, etc.). The above two approaches also enabled radical relay carbonylation of alkenes, allowing precise control over reaction intermediates and pathways. Such control improves both reaction efficiency and selectivity. These advancements have enabled transition metal or photoredox catalysis to facilitate radical relay carbonylation of unactivated alkenes, resulting in transformations such as oxyalkylative carbonylation, aminoalkylative carbonylation, fluoroalkylative carbonylation, double carbonylation, and rearrangement carbonylation.SET-mediated carbonylation significantly enhances the sustainability and scalability of the carbonylation process by reducing reliance on precious metal catalysts and enabling milder reaction conditions. Additionally, by carefully controlling reaction intermediates, we have fine-tuned the process to produce a wide range of carbonylation products with high selectivity. This flexibility expands the applications of carbonylation in synthetic chemistry and industrial processes. Finally, we place particular emphasis on the application of carbonylation reactions in drug discovery, where they serve as powerful functional handles for the late-stage modification of bioactive molecules. The broad applicability of SET-mediated carbonylation methods to various chemical bonds significantly enriches the toolbox for drug synthesis, enabling the efficient functionalization of complex molecules. This versatile approach has the potential to accelerate the discovery of novel therapeutic agents, making it a critical tool in modern medicinal chemistry.

Novel N-(3-(1-(4-sulfamoylphenyl)triazol-4-yl)phenyl)benzamide Derivatives as Potent Carbonic Anhydrase Inhibitors with Broad-Spectrum Anticancer Activity: Leveraging Tail and Dual-Tail Approaches

Carbonic anhydrases (CAs) IX and XII are crucial for the survival and metastasis of solid tumors under hypoxic conditions. We designed compounds 7a-s, integrating triazole and benzenesulfonamide scaffolds known for inhibiting tumor-associated CAs IX/XII. Initial synthesis included compounds 7a-e, followed by diversification with small hydrophobic groups (7f-m) and hydrophilic heterocyclic secondary amines (7n-s). Compounds were evaluated against CA II, IX, and XII to assess activity and selectivity. Chlorinated derivative 7l exhibited the highest efficacy against CA IX (KI = 0.317 μM) and ditrifluoromethylated 7j against CA XII (KI = 0.081 μM). Subsequent testing on 60 cancer cell lines at 10 μM revealed promising anticancer activity, especially for dimethylated derivative 7h (CA IX, KI = 1.324 μM; CA XII, KI = 0.435 μM), with GI50 values ranging from 0.361 to 9.21 μM. Molecular docking analyses elucidated binding mechanisms, highlighting potential inhibitory actions of compound 7h on CAs IX and XII.

Diversified Fluoroalkylation of Alkenes Using Quaternary Fluoroalkyl Alcohols as the Fluoroalkylating Reagents

Given the widespread presence of fluoroalkyl functionalities in bioactive molecules, the development of fluoroalkylation reactions with bench-stable and easy-to-use fluoroalkylating reagents is highly desirable. In addition, realization of mono-, di-, tri-, or polyfluoroalkyation usually requires distinct types of fluoroalkylating reagents under different or even harsh reaction conditions, and a universal method to accomplish different hydrofluoroalkylation of alkenes is lacking. Herein, the use of quaternary fluoroalkyl alcohols is reported as the universal fluoroalkylating reagents to readily facilitate mono-, di-, tri-, or polyfluoroalkylation of a wide range of alkene substrates in high yields. Moreover, a cascade reaction of hydrofluoroalkylation followed by intramolecular fluoroalkylation facilitates the construction of a variety of high-value complex heterocycles bearing diverse fluoroalkyl functionalities from alkenes. Mechanistic studies suggest that a proton-coupled electron transfer (PCET) process may be involved through a radical-generating pathway. The utility of this method is showcased by the late-stage fluoroalkylation of various high-value complex molecules derived from either natural products or drug-like compounds. Of note is that a continuous-flow system is amenable to this homogeneous photoredox conditions, thereby opening up a possibility of using this protocol to realize large-scale manufacturing of fluoroalkyl products with industrial interests.

Ground-state flavin-dependent enzymes catalyzed enantioselective radical trifluoromethylation

The introduction of fluoroalkyl groups into pharmaceutical compounds has the potential to enhance their therapeutic properties. Nevertheless, the synthesis of enantiomerically pure C(sp³)-CF₃ compounds poses a significant challenge. Biocatalysis offers precise stereochemical control, however, the scarcity of fluorine-containing natural products makes it difficult to find enzymes capable of incorporating fluoroalkyl groups. Herein, we develop a ground-state flavin-dependent enzyme-catalyzed strategy for the radical-mediated enantioselective trifluoromethylation. Two engineered flavin-dependent enzymes are successfully developed to catalyze stereoselective hydrotrifluoromethylation and trifluoromethyl-alkyl cross-electrophile coupling reactions using trifluoromethyl thianthrenium triflate as a radical donor. Experimental investigations and computational simulations demonstrate that the reaction is initiated through single-electron transfer from the ground state flavin hydroquinone (FMNhq) and quenched through hydrogen atom transfer by flavin semiquinone (FMNsq). This strategy provides an opportunity to bridge the gap between biocatalysis and organic fluorides but also introduces an alternative approach to address challenging stereoselective fluoroalkylation reactions in organic synthesis.

A General Hydrotrifluoromethylation of Unactivated Olefins Enabled by Voltage-Gated Electrosynthesis

Here we present the first successful hydrotrifluoromethylation of unactivated olefins under electrochemical conditions. Commercially available trifluoromethyl thianthrenium salt (TT+-CF3BF4 -, Ep/2=-0.85 V vs Fc/Fc+) undergoes electrochemical reduction to generate CF3 radicals which add to olefins with exclusive chemoselectivity. The resulting carbon centered radical undergoes a second cathodic reduction, instead of a classical HAT process, to generate a carbanion that can be terminated by protonation from solvent. The use of MgBr2 (+0.20 V onset oxidation potential) plays a key role as an enabling sacrificial reductant for the reaction to operate in an undivided cell. Guided by cyclic voltammetry (CV) studies, fine-tuning the solvent system, trifluoromethylating reagent's counteranion and careful selection of redox processes, this work led to the development of a voltage-gated electrosynthesis by pairing two redox processes with a narrow potential difference (ΔE≈1.00 V) allowing the reaction to proceed with two important advances: (a) high reactivity and selectivity towards hydrotrifluoromethylation over undesired dibromination, and (b) an unprecedented functional group tolerance, including aniline, phenols, unprotected alcohol, epoxide, trialkyl amine, and several redox sensitive heterocycles.

Visible Light-Driven Metal- and Photocatalyst-Free Synthesis of β-Trifluoromethylated Enamines via Trifluoromethyl Thianthrenium Salts

A novel protocol for the visible-light-driven synthesis of β-trifluoromethylated enamines has been developed, which operates without the use of transition metals or any photocatalysts, utilizing trifluoromethylthiosulfonium salts as the source of trifluoromethyl groups under mild conditions. According to this new protocol, more than 40 products have been prepared in moderate to good yields. In addition to eliminating the need for expensive or toxic transition metals and photocatalysts, this new methodology proves its potential scalability through air-stability, the use of safe and readily available reagents, a two-step one-pot procedure, and effective gram-scale reactions. This innovative approach not only demonstrates promise for green chemical synthesis but also offers a new pathway for the advancement of fluorine chemistry in sustainable organic synthesis.

Silver-Catalyzed Thio-Claisen Rearrangement of Aryl Sulfoxides with AIBN

The Pummerer reaction represents a well-known transformation of sulfoxides. Mechanistically, this reaction is initiated by the generation of the thionium ion, whereas forming such intermediates typically requires the use of a stoichiometric amount of activating reagent. In this regard, we report the activator-free Pummerer-type transformation, a silver-catalyzed thio-Claisen rearrangement of aryl sulfoxides with AIBN. Facilitated by silver catalyst, AIBN is transformed into highly reactive ketenimine in situ, which directly captures the sulfoxides to generate thionium ion intermediates.

Recent Applications of Sulfonium Salts in Synthesis and Catalysis

The use of sulfonium salts in organic synthesis has experienced a dramatic increase during the last years that can arguably be attributed to three main factors; the development of more direct and efficient synthetic methods that make easily available sulfonium reagents of a wide structural variety, their intrinsic thermal stability, which facilitates their structural modification, handling and purification even on large scale, and the recognition that their reactivity resembles that of hypervalent iodine compounds and therefore, they can be used as replacement of such reagents for most of their uses. This renewed interest has led to the improvement of already existing reactions, as well as to the discovery of unprecedented transformations; in particular, by the implementation of photocatalytic protocols. This review aims to summarize the most recent advancements on the area focusing on the work published during and after 2020. The scope of the methods developed will be highlighted and their limitations critically evaluated.

C-S-Selective Stille-Coupling Enables Stereodefined Alkene Synthesis

A palladium-catalyzed highly C-S-selective Stille cross-coupling between aryl thianthrenium salts and tri- or tetrasubstituted alkenyl stannanes is described. Herein, critical challenges including site- and chemoselectivity control are well addressed through C-H thianthrenation and C-S alkenylation, thereby providing an expedient access to stereodefined tri- and tetrasubstituted alkenes in a stereoretentive fashion. Indeed, the palladium-catalyzed Stille-alkenylation of poly(pseudo)halogenated arenes displays privileged capability to differentiate C-S over C-I, C-Br, C-Cl bonds, as well as oxygen-based triflates (C-OTf), tosylates (C-OTs), carbamates and sulfamates under mild reaction conditions. Sequential and multiple cross-couplings via selective C-X functionalization should be widely applicable for increasing functional molecular complexity. Modular installation of stereospecific alkene motifs into pharmaceuticals illustrated the synthetic application of the present protocol in drug discovery.

One-Pot Telescoping S-Transfer and Trifluoromethylation for the Synthesis of 2-CF3S-Imidazoles with N-Oxides as Convenient Precursors

Readily available 2-unsubstituted imidazole N-oxides were examined as starting materials for the preparation of fully substituted 1,4,5-aryl/alkyl 2-trifluoromethylsulfanyl-imidazoles. Whereas activation of the N-oxide function followed by attempted nucleophilic addition of the -SCF3 was in vain, the alternative approach involving "sulfur transfer reaction" and subsequent electrophilic trifluoromethylation with Togni reagent provided target products in high yield via a one-pot procedure. The structure of representative enantiomerically pure imidazol-2-yl trifluoromethyl sulfide was confirmed by X-ray analysis.

Polar-Effect-Directed Control in Site-Selectivity of Radical Substitution Enables C-H Perfluoroalkylation of Coumarins

A novel Ru-catalyzed protocol for C-7 selective C-H trifluoromethylation of coumarins in the presence of light is presented. This reaction undergoes a radical type nucleophilic substitution instead of a radical type electrophilic substitution owing to the benzocore activation as a result of lowering the lowest unoccupied molecular orbital (LUMO).

Metal-Free Synthesis of 2-(per)Fluoroalkyl-3-nitro Indoles via Intramolecular Cyclization of Amides

A metal-free intramolecular cyclization of N-acyl amides for the synthesis of 3-nitro-2-(per)fluoroalkyl indoles is reported. Good functional group tolerance and a broad range of substrates are the features of this approach. The developed method is easy to operate and is suitable for the preparation of 2-difluoromethyl/trifluoromethyl/perfluoroethyl/perfluoropropyl indoles in yields of 84 to 99%. Also, the application of this protocol in the gram scale is shown.

Rigidochromism of tetranuclear Cu(I)-pyrazolate macrocycles: steric crowding with trifluoromethyl groups

Macrocyclic Cu(I)-pyrazolate tetramers (Cu4pz4) can fold into compact structures with luminescent Cu4 cores whose emission wavelengths are sensitive to steric effects along the periphery of the macrocycle. Introducing CF3 at the C4 position of 3,5-di-tBu-pyrazolate increases steric crowding that modifies the conformational behavior of the Cu4pz4 complex, highlighted by a low-temperature martensitic transition. Variable-temperature analysis of solid-state luminescence reveal an unexpected blueshifting of emission with rising temperature.

Photocatalytic synthesis of polyfluoroalkylated dihydropyrazoles and tetrahydropyridazines

A photocatalytic trifluoromethylation/cyclization reaction of N-allyl and N-homoallyl aldehyde hydrazones with trifluoromethyl thianthrenium triflate was developed for the synthesis of trifluoromethylated dihydropyrazoles and tetrahydropyridazines. Besides, PhI(O2CCHF2)2 was employed to realize the construction of difluoromethylated dihydropyrazoles and tetrahydropyridazines. These protocols exhibit a broad substrate scope and good functional group tolerance.

Nickel-Mediated Divergent Trifluoromethylation of Chlorinated and Brominated Phenol Derivatives through Chemoselective Cleavage of Ar-O and Ar-Cl(Br) Bonds

We report herein that nickel-mediated trifluoromethylation of chlorinated and brominated phenol derivatives ClArOTs and BrArOTf gave chloro(bromo)trifluoromethylarenes through the chemoselective cleavage of Ar-O bonds. Furthermore, under similar reaction conditions, the chemoselective trifluoromethylation of Ar-Cl and Ar-Br bonds of ClArOPiv and BrArOTs was achieved to give trifluoromethylated phenol derivatives.

Radical Cascade Cyclization of N-(o-Cyanobiaryl)acrylamides with Sulfonium Salts via Synergetic Photoredox and Copper Catalysis

As the magic methyl effect is well acknowledged in pharmaceutical molecules, the development of simple and efficient methods for the installment of methyl groups on complex molecules is highly coveted. Hence, we provide a general strategy for radical cascade cyclization of N-(o-cyanobiaryl)acrylamides by utilizing sulfonium salts as the sources of methyl radical and merging photoredox and copper catalysis. This novel protocol can access a wide variety of methylation or remote thioether-substituted benzo-fused N-heterocycle derivatives, which can be easily transformed into diverse highly valuable sulfone and sulfoximine compounds via late-stage diversification. Moreover, to further demonstrate the synthetic utility of this conversion, the methyl(phenyl)sulfide, which serves as both raw material and byproduct, can be recovered and reused in this transformation. The scale-up experiment for the one-pot two-step process directly offers the target product in good yield under the standard conditions.

Photocatalytic fluoroalkylation by ligand-to-metal charge transfer

Trifluoromethyl (CF3) and other fluoroalkyl groups are of great significance in the fields of pharmaceutical chemistry and agricultural chemicals. Fluoroalkyl acids, especially trifluoroacetic acid (TFA) is considered the most ideal fluoroalkylation reagent due to its low cost and easy availability. However, the extremely high oxidation potential requirement of TFA limits its wide application. In recent years, since visible-light-induced fluoroalkylation through the ligand-to-metal charge transfer (LMCT) process can overcome the above limitations, it has become an effective synthetic tool for the construction of fluorinated compounds with complex molecules and structures. In this review, according to the classification of different metal catalysts, we summarize the trifluoromethylation and fluoroalkylation of olefins, heteroaromatics, and terminal alkynes in different metal catalytic systems and their corresponding reaction mechanisms. The photocatalytic fluoroalkylation via LMCT is believed to expedite the development of fluoro-containing drugs, and more novel fluoroalkylation methologies using this strategy will be disclosed.

Direct Synthesis of 2-Hydroxytrifluoroethylacetophenones via Organophotoredox-Mediated Net-Neutral Radical/Polar Crossover

Alkene difunctionalization is a very attractive tool in synthetic organic chemistry. Herein, we disclose an operationally and practically simple method to access 2-hydroxytrifluoroethylacetophenones from styrene derivatives via photoredox catalysis. This light-mediated transformation promotes the generation of the 1-hydroxy-2,2,2-trifluoroethyl carbon-centered radical as key synthon, which undergoes Giese addition with styrenes followed by a Kornblum oxidation process. The presented method is not only mild and cost-effective, but also utilizes an organic photocatalyst and DMSO as oxidant. Experimental investigations support the operative mechanism via net-neutral radical/polar crossover.

Orthogonal bioconjugation targeting cysteine-containing peptides and proteins using alkyl thianthrenium salts

Late-stage specific and selective diversifications of peptides and proteins performed at target residues under ambient conditions are recognized to be the most facile route to various and abundant conjugates. Herein, we report an orthogonal modification of cysteine residues using alkyl thianthreium salts, which proceeds with excellent chemoselectivity and compatibility under mild conditions, introducing a diverse array of functional structures. Crucially, multifaceted bioconjugation is achieved through clickable handles to incorporate structurally diverse functional molecules. This "two steps, one pot" bioconjugation method is successfully applied to label bovine serum albumin. Therefore, our technique is a versatile and powerful tool for late-stage orthogonal bioconjugation.

Metal- versus ligand-centered reactivity of a cobalt-phenylenediamide complex with electrophiles

A new series of [CoIII-CF3]n+ complexes supported by a bidentate redox-active ligand is presented. The cationic [Co-CF3]+ complex was first obtained by reacting [CpCo(tBuUreaopda)] (Cp = cyclopentadienyl, opda = o-phenylenediamide) with an electrophilic trifluoromethyl source, for which the redox-active phenylenediamide ligand serves as a 2e- reservoir to generate [CpCp(tBuUreabqdi)(CF3)]+ (bqdi = benzoquinonediimine). Electrochemical studies of [Co-CF3]+ revealed two reversible 1e- reductions. Chemical reduction with 1 or 2 equiv. reducing agent enabled isolation of the neutral and anionic complexes, respectively, where the [CoIII-CF3] bond remains intact in all three oxidation states (n = +1, 0, -1). Structural analysis shows systematic changes to the redox-active ligand backbone upon reduction, consistent with sequential ligand-centered electron transfer in the series [bqdi]0 to [s-bqdi]˙- to [opda]2-. In contrast, the reaction of [CpCo(tBuUreaopda)] with alkyl triflates resulted in ligand-centered alkylation at the ureayl groups instead of the targeted Co-alkyl bond formation, suggesting less favorable bond formation at cobalt and greater nucleophilic accessibility of the ligand compared to the metal center.

C-H Bond Sulfonylation from Thianthrenium Salts and DABCO·(SO2)2: Synthesis of 2-Sulfonylindoles

A three-component reaction of 1-(1H-indol-1-yl)isoquinolines or 1-(pyridin-2-yl)-1H-indoles, DABCO·(SO2)2, and thianthrenium salts under synergistic photoredox and palladium catalysis is accomplished. This direct C-H bond sulfonylation of indoles with the insertion of sulfur dioxide under mild conditions works efficiently, giving rise to a wide range of 2-sulfonated indoles in moderate to good yields under mild conditions. In this protocol, the generality of aryl/alkyl thianthrenium salts is demonstrated as well. A photoredox radical process combined with palladium catalysis is proposed.

Site-selective S-gem-difluoroallylation of unprotected peptides with 3,3-difluoroallyl sulfonium salts

Bench-stable 3,3-difluoroallyl sulfonium salts (DFASs), featuring tunable activity and their editable C-β and gem-difluoroallyl group, proved to be versatile fluoroalkylating reagents for site-selective S-gem-difluoroallylation of cysteine residues in unprotected peptides. The reaction proceeds with high efficiency under mild conditions (ambient temperature and aqueous and weak basic conditions). Various protected/unprotected peptides, especially bioactive peptides, are site-selectively S-gem-difluoroallylated. The newly added gem-difluoroallyl group and other functional groups derived from C-β of DFASs are poised for ligation with bio-functional groups through click and radical chemistry. This stepwise "doubly orthogonal" modification of peptides enables the construction of bioconjugates with enhanced complexity and functionality. This proof of principle is successfully applied to construct a peptide-saccharide-biotin chimeric bioconjugate, indicating its great potential application in medicinal chemistry and chemical biology.

Redox Reactions of Organic Molecules Using Rotating Magnetic Field and Metal Rods

In recent years, redox reactions have harnessed light or mechanical energy to enable the formation of chemical bonds. We postulated a complementary approach that electromagnetic induction could promote the redox reaction of organic molecules using a rotating magnetic field and metal rods. Here, we report that electromotive force activates the redox-active trifluoromethylating reagents. This magnetoredox system can be applied to the trifluoromethylation of heteroarenes with high regioselectivity and hydrotrifluoromethylation of alkenes without the need for catalysts and organic additives.

Organic Photoredox-Catalyzed S-Trifluoromethylation of Aromatic and Heteroaromatic Thiols

A visible-light-mediated trifluoromethylation protocol was developed for the conversion of (hetero)aromatic thiols to their respective S-trifluoromethylated derivatives employing trifluoromethanesulfonyl chloride (CF3SO2Cl) as a cost-effective source of trifluoromethyl radical (CF3·) and a highly reducing organophotocatalyst, 3DPA2FBN. The developed methodology is operationally simple, providing access to a diverse range of products in up to 92% yield. A plausible mechanism has been postulated based on preliminary mechanistic studies, including irradiation on/off, UV-vis studies, and radical trapping experiments.

Creation of a Chiral All-Carbon Quaternary Center Induced by CF3 and CH3 Substituents via Cu-Catalyzed Asymmetric Conjugate Addition

Cu-catalyzed asymmetric construction of a chiral quaternary center bearing CH3 and CF3 groups was achieved with high to excellent enantioselectivity using our originally developed ligands. The asymmetric conjugate addition of Me3Al to β-CF3-substituted enones and unsaturated ketoesters proceeded efficiently. The use of unsaturated ketoesters gives optically active furanones in high yields with high enantioselectivities. The perfluoroalkyl-substituted enone does not seem to be favorable in the present reaction.

Red-light-mediated copper-catalyzed photoredox catalysis promotes regioselectivity switch in the difunctionalization of alkenes

Controlling regioselectivity during difunctionalization of alkenes remains a significant challenge, particularly when the installation of both functional groups involves radical processes. In this aspect, methodologies to install trifluoromethane (-CF3) via difunctionalization have been explored, due to the importance of this moiety in the pharmaceutical sectors; however, these existing reports are limited, most of which affording only the corresponding β-trifluoromethylated products. The main reason for this limitation arises from the fact that -CF3 group served as an initiator in those reactions and predominantly preferred to be installed at the terminal (β) position of an alkene. On the contrary, functionalization of the -CF3 group at the internal (α) position of alkenes would provide valuable products, but a meticulous approach is necessary to win this regioselectivity switch. Intrigued by this challenge, we here develop an efficient and regioselective strategy where the -CF3 group is installed at the α-position of an alkene. Molecular complexity is achieved via the simultaneous insertion of a sulfonyl fragment (-SO2R) at the β-position. A precisely regulated sequence of radical generation using red light-mediated photocatalysis facilitates this regioselective switch from the terminal (β) position to the internal (α) position. Furthermore, this approach demonstrates broad substrate scope and industrial potential for the synthesis of pharmaceuticals under mild reaction conditions.

Efficient Trifluoromethylation of Halogenated Hydrocarbons Using Novel [(bpy)Cu(O2CCF2SO2F)2] Reagent

This study introduces a novel trifluoromethylating reagent, [(bpy)Cu(O2CCF2SO2F)2], notable for not only its practical synthesis from cost-effective starting materials and scalability but also its nonhygroscopic nature. The reagent demonstrates high efficiency in facilitating trifluoromethylation reactions with various halogenated hydrocarbons, yielding products in good yields and exhibiting broad functional group compatibility. The development of [(bpy)Cu(O2CCF2SO2F)2] represents an advancement in the field of organic synthesis, potentially serving as a valuable addition to the arsenal of existing trifluoromethylating agents.

Trifluoromethylation of 2D Transition Metal Dichalcogenides: A Mild Functionalization and Tunable p-Type Doping Method

Chemical modification is a powerful strategy for tuning the electronic properties of 2D semiconductors. Here we report the electrophilic trifluoromethylation of 2D WSe2 and MoS2 under mild conditions using the reagent trifluoromethyl thianthrenium triflate (TTT). Chemical characterization and density functional theory calculations reveal that the trifluoromethyl groups bind covalently to surface chalcogen atoms as well as oxygen substitution sites. Trifluoromethylation induces p-type doping in the underlying 2D material, enabling the modulation of charge transport and optical emission properties in WSe2. This work introduces a versatile and efficient method for tailoring the optical and electronic properties of 2D transition metal dichalcogenides.

Photoinduced Regioselective Fluorination and Vinylation of Remote C(sp3)-H Bonds Using Thianthrenium Salts

Herein, a photoredox-driven practical protocol for fluorinated alkene synthesis using easily accessible and modular thianthrenium salts with electron-withdrawing alkynes or propargyl alcohols is reported. Vinyl radical intermediates, formed by the reaction between the alkyl or trifluoromethyl thianthrenium salts and electronically diverse alkynes, can mediate the key 1,5-HAT process of regioselective C(sp3)-H fluorination and vinylation. This protocol provides straightforward access to structurally diverse trifluoromethyl- or distally fluoro-functionalized alkene products in 21-79% yields with a broad substrate range under mild photocatalytic conditions.

Organohypervalent heterocycles

This review summarizes the structural and synthetic aspects of heterocyclic molecules incorporating an atom of a hypervalent main-group element. The term "hypervalent" has been suggested for derivatives of main-group elements with more than eight valence electrons, and the concept of hypervalency is commonly used despite some criticism from theoretical chemists. The significantly higher thermal stability of hypervalent heterocycles compared to their acyclic analogs adds special features to their chemistry, particularly for bromine and iodine. Heterocyclic compounds of elements with double bonds are not categorized as hypervalent molecules owing to the zwitterionic nature of these bonds, resulting in the conventional 8-electron species. This review is focused on hypervalent heterocyclic derivatives of nonmetal main-group elements, such as boron, silicon, nitrogen, carbon, phosphorus, sulfur, selenium, bromine, chlorine, iodine(III) and iodine(V).

Palladium-Catalyzed Carbonylation Reaction of Indole/Pyrrole Involving HCFO-1233zd (E)

3-Indole-3-one is a key intermediate in the synthesis of many drugs and plays an important role in synthetic chemistry and biochemistry. A new method for synthesizing trifluoromethylated 3-indoleketones by Pd(0)-catalyzed carbonylation was introduced. In the absence of additives, 1-chloro-3,3,3-trifluoropropyl (an inexpensive and environmentally friendly synthetic block of trifluoromethyl) reacts with indole and carbon monoxide to generate trifluoromethylindole ketones with good yields, regioselectivity, and chemical selectivity; furthermore, the products exhibit strong resistance to basic functional groups, such as alkynes, aldehydes, and esters. In addition to the conversion of indole compounds into corresponding products, pyrrole and heteroindole may be suitable for corresponding chemical transformations. This study provides a synthetic method for the further construction of trifluoromethylated 3-indole ketones.

nBu4N+[AgI(CF3)2]-: Trifluoromethylated Argentate Derived from Fluoroform and Its Reaction with (Hetero)Aryl Diazonium Salts

The preparation of a well-defined trifluoromethylated argentate nBu4N+[Ag(CF3)2]- 1 from fluoroform was described. The complex was stable in the solid state and in solution under an inert atmosphere. Treatment of a variety of (hetero)aryl diazonium tetrafluoroborates with nBu4N+[Ag(CF3)2]- 1 generated trifluoromethylated (hetero)arenes in good to excellent yields. Preliminary experiments were conducted, and a reasonable mechanism of the reaction was proposed.

Photoredox-Catalyzed Acylchlorination of α-CF3 Alkenes with Acyl Chloride and Application as Masked Access to β-CF3-enones

We disclose a photocatalytic strategy that simultaneously addresses the construction of trifluoromethylated quaternary carbon centers and the preparation of β-CF3-enones through radical difunctionalization of α-CF3 alkenes with acyl chlorides. This method is characterized by its broad functional group compatibility, high efficiency, and atom economy. The versatility of this transformation is poised to broaden the applications of α-CF3 alkenes, providing new pathways for the rapid assembly of structurally diverse fluorinated compounds.

Access to All-Carbon Quaternary Centers by Photocatalytic Fluoroalkylation of α-Halo Carbonyl Compounds

Perfluoroalkyl groups have become significantly important in pharmaceutical and agrochemical applications. In this study, we present a visible light-mediated photoredox neutral strategy for the fluoroalkylation of tertiary alkyl chlorides under transition-metal-free conditions. This method allows for the facile synthesis of fluoroalkylated all-carbon quaternary centers, exhibiting excellent functional group compatibility. Mechanistic studies reveal the involvement of two reactive radical intermediates and the in situ formation of metal enolates in a radical-polar crossover manner. The versatility of this methodology is demonstrated through synthetic transformations based on the carbonyl group, showcasing its potential for the rapid assembly of diverse organic molecules bearing fluoroalkyl all-carbon quaternary centers.

Photocatalytic Keto- and Amino-Trifluoromethylation of Alkenes

Efforts to develop alternatives to triflic anhydride (Tf2O) as a trifluoromethylation reagent continue due to its limitations, including volatility, corrosiveness, and moisture sensitivity. Described herein is the use of a trifluoromethylsulfonylpyridinium salt (TFSP), easily obtained by a one-step reaction of Tf2O with 4-dimethylaminopyridine, as a reagent for the trifluoromethylative difunctionalization of alkenes by photoredox catalysis. DMSO and CH3CN are suitable solvents for achieving keto- and amino-trifluoromethylation of alkenes, respectively, with good functional group tolerance.

Chemoselective umpolung of thiols to episulfoniums for cysteine bioconjugation

Cysteine conjugation is an important tool in protein research and relies on fast, mild and chemoselective reactions. Cysteinyl thiols can either be modified with prefunctionalized electrophiles, or converted into electrophiles themselves for functionalization with selected nucleophiles in an independent step. Here we report a bioconjugation strategy that uses a vinyl thianthrenium salt to transform cysteine into a highly reactive electrophilic episulfonium intermediate in situ, to enable conjugation with a diverse set of bioorthogonal nucleophiles in a single step. The reactivity profile can connect several nucleophiles to biomolecules through a short and stable ethylene linker, ideal for introduction of infrared labels, post-translational modifications or NMR probes. In the absence of reactive exogenous nucleophiles, nucleophilic amino acids can react with the episulfonium intermediate for native peptide stapling and protein-protein ligation. Ready synthetic access to isotopologues of vinyl thianthrenium salts enables applications in quantitative proteomics. Such diverse applications demonstrate the utility of vinyl-thianthrenium-based bioconjugation as a fast, selective and broadly applicable tool for chemical biology.

Base-Promoted Ring-Opening Hydroxylation of Cyclic Sulfonium Salts

Herein, we reported a general strategy for the synthesis of sulfur-containing primary alcohol derivatives by base-promoted ring-opening hydroxylation of cyclic sulfonium salts. A variety of sulfonium salts were successfully transformed into the desired hydroxylated products in moderate to excellent yields with good functional group tolerance. Moreover, the one-pot synthesis, scale-up reaction, and late-stage functionalization of complex molecules demonstrated the practicability of this synthetic protocol in the field of synthetic chemistry.

Automated self-optimization, intensification, and scale-up of photocatalysis in flow

The optimization, intensification, and scale-up of photochemical processes constitute a particular challenge in a manufacturing environment geared primarily toward thermal chemistry. In this work, we present a versatile flow-based robotic platform to address these challenges through the integration of readily available hardware and custom software. Our open-source platform combines a liquid handler, syringe pumps, a tunable continuous-flow photoreactor, inexpensive Internet of Things devices, and an in-line benchtop nuclear magnetic resonance spectrometer to enable automated, data-rich optimization with a closed-loop Bayesian optimization strategy. A user-friendly graphical interface allows chemists without programming or machine learning expertise to easily monitor, analyze, and improve photocatalytic reactions with respect to both continuous and discrete variables. The system's effectiveness was demonstrated by increasing overall reaction yields and improving space-time yields compared with those of previously reported processes.

Favipiravir Analogues as Inhibitors of SARS-CoV-2 RNA-Dependent RNA Polymerase, Combined Quantum Chemical Modeling, Quantitative Structure-Property Relationship, and Molecular Docking Study

Our study was motivated by the urgent need to develop or improve antivirals for effective therapy targeting RNA viruses. We hypothesized that analogues of favipiravir (FVP), an inhibitor of RNA-dependent RNA polymerase (RdRp), could provide more effective nucleic acid recognition and binding processes while reducing side effects such as cardiotoxicity, hepatotoxicity, teratogenicity, and embryotoxicity. We proposed a set of FVP analogues together with their forms of triphosphate as new SARS-CoV-2 RdRp inhibitors. The main aim of our study was to investigate changes in the mechanism and binding capacity resulting from these modifications. Using three different approaches, QTAIM, QSPR, and MD, the differences in the reactivity, toxicity, binding efficiency, and ability to be incorporated by RdRp were assessed. Two new quantum chemical reactivity descriptors, the relative electro-donating and electro-accepting power, were defined and successfully applied. Moreover, a new quantitative method for comparing binding modes was developed based on mathematical metrics and an atypical radar plot. These methods provide deep insight into the set of desirable properties responsible for inhibiting RdRp, allowing ligands to be conveniently screened. The proposed modification of the FVP structure seems to improve its binding ability and enhance the productive mode of binding. In particular, two of the FVP analogues (the trifluoro- and cyano-) bind very strongly to the RNA template, RNA primer, cofactors, and RdRp, and thus may constitute a very good alternative to FVP.

Unified metal-free intermolecular Heck-type sulfonylation, cyanation, amination, amidation of alkenes by thianthrenation

Direct and site-selective C-H functionalization of alkenes under environmentally benign conditions represents a useful and attractive yet challenging transformation to access value-added molecules. Herein, a unified protocol for a variety of intermolecular Heck-type functionalizations of Csp2-H bond of alkenes has been developed by thianthrenation. The reaction features metal-free and operationally simple conditions for exclusive cine-selective C-H functionalization of aliphatic and aryl alkenes to forge C-C, C-N, C-P, and C-S bonds at room temperature, providing a general protocol for intermolecular Heck-type reaction of alkenes with nucleophiles (Nu = sulfinates, cyanides, amines, amides). Alkenes undergo cine-sulfonylation, cyanation, amination to afford alkenyl sulfones, alkenyl nitriles and enamines.

Paired Electrolysis Enabled Trifluoromethylheteroaromatization of Alkenes and Alkyne with Trifluoromethyl Thianthrenium Triflate (TT-CF3+OTf-) as a Bifunctional Reagent

We report a strategic exploitation of trifluoromethyl thianthrenium triflate (TT-CF3+OTf-) as both electromediator and CF3 radical precursors for paired electrolysis. Enabled by this strategy, the three-component trifluoromethylheteroaromatization of alkenes and alkynes was realized. The superiority of TT-CF3+OTf- to other electrophilic CF3 reagents is attributed to the cathodic generation of thianthrene (TT) as a mediator, which shifts the heterogeneous oxidation of interest to a homogeneous one.

Hydroxytrifluoroethylation and Trifluoroacetylation Reactions via SET Processes

Hydroxytrifluoroethyl and trifluoroacetyl groups are of utmost importance in biologically active compounds, but methods to tether these motifs to organic architectures have been limited. Typically, the preparation of these compounds relied on the use of strong bases or multistep routes. The renaissance of radical chemistry in photocatalytic, transition metal mediated, and hydrogen atom transfer (HAT) processes have allowed the installation of these medicinally relevant fluorinated motifs. This review provides an overview of the methods available for the direct synthesis of hydroxytrifluoroethyl- and trifluoroacetyl-derived compounds governed by single-electron transfer processes.

Direct Decarboxylation of Trifluoroacetates Enabled by Iron Photocatalysis

Trifluoroacetates are the most abundant and accessible sources of trifluoromethyl groups, which are key components in pharmaceuticals and agrochemicals. The generation of trifluoromethyl reactive radicals from trifluoroacetates requires their decarboxylation, which is hampered by their high oxidation potential. This constitutes a major challenge for redox-based methods, because of the need to pair the redox potentials with trifluoroacetate. Here we report a strategy based on iron photocatalysis to promote the direct photodecarboxylation of trifluoroacetates that displays reactivity features that escape from redox limitations. Our synthetic design has enabled the use of trifluoroacetates for the trifluoromethylation of more easily oxidizable organic substrates, offering new opportunities for late-stage derivatization campaigns using chemical feedstocks, Earth-abundant catalysts, and visible-light.

Photocatalytic hydrofluoroalkylation of alkenes with carboxylic acids

Incorporation of fluoroalkyl motifs in pharmaceuticals can enhance the therapeutic profiles of the parent molecules. The hydrofluoroalkylation of alkenes has emerged as a promising route to diverse fluoroalkylated compounds; however, current methods require superstoichiometric oxidants, expensive/oxidative fluoroalkylating reagents and precious metals, and often exhibit limited scope, making a universal protocol that addresses these limitations highly desirable. Here we report the hydrofluoroalkylation of alkenes with cheap, abundant and available fluoroalkyl carboxylic acids as the sole reagents. Hydrotrifluoro-, difluoro-, monofluoro- and perfluoroalkylation are all demonstrated, with broad scope, mild conditions (redox neutral) and potential for late-stage modification of bioactive molecules. Critical to success is overcoming the exceedingly high redox potential of feedstock fluoroalkyl carboxylic acids such as trifluoroacetic acid by leveraging cooperative earth-abundant, inexpensive iron and redox-active thiol catalysis, enabling these reagents to be directly used as hydroperfluoroalkylation donors without pre-activation. Preliminary mechanistic studies support the radical nature of this cooperative process.

Hydroxy- and Hydro-Perfluoroalkylation of Styrenes by Controlling the Quenching Cycle of Eosin Y

Fluoroalkyl compounds are widely used, underscoring a pressing need for the development of methods for their synthesis. However, reports on perfluoroalkylation to styrenes have been sparse. In this study, both hydroxy- and hydro-perfluoroalkylation of styrene were achieved using visible light reactions, catalyzed by eosin Y, by selecting appropriate additives and controlling the eosin Y quenching cycle. These reactions are heavy-metal free, use water as the hydroxyl or hydrogen source, and employ inexpensive and readily available reagents.

Sulfonium-based precise alkyl transposition reactions

S-adenosyl-L-methionine (SAM), a sulfonium-based cofactor, plays an important role in numerous biological processes as methyl donor. Inspired by the function of sulfonium motif in this nature's synthetic toolkit, we here present an aryne-activation strategy that the sulfonium intermediates in situ generated from thioethers display unique reactivity toward alkyl group transposition. Experimental and theoretical studies indicate that the reaction occurs in an intermolecular fashion where the TfO--incorporated [K(18-crown-6)] complex acts as a key promoter for this thermodynamically favored process. Next, a series of robust, easy-to-prepare sulfonium salts are designed and developed as electrophilic alkylation reagents accordingly. Both systems feature for broad scope, excellent selectivity, and simple operation. Moreover, we highlight the synthetic value through molecular editing and late-stage modification of complex scaffolds or even active pharmaceutical ingredients.

Chemo-divergent Cyano Group Migration: Involving Elimination and Substitution of the Key α-Thianthrenium Cyano Species

Herein, we report a light-driven, radical-type cyano migration in the absence of a photocatalyst, enabling a chemo-divergent synthesis of (Z)-alkenyl nitriles and ketones. Trifluoromethyl thianthrenium salt (TT-CF3+OTf-) plays multiple roles: (a) absorbing light to generate trifluoromethyl radicals to initiate the reaction and (b) forming α-thianthrenium cyano species by in situ capture of TT• +. (Z)-Alkenyl nitriles were formed through the elimination of thianthrenium salts, and aryl ketones were obtained via the nucleophilic substitution of thianthrenium salts.