Vinyl Thianthrenium Tetrafluoroborate: A Practical and Versatile Vinylating Reagent Made from Ethylene

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.

Harnessing the Sulfur-for-Oxygen Shift: A Magic Bullet for Dynamic Photophysical and Anticancer Activities of Indole-Barbituric Acid Construct

The development of small molecule-based drugs emerged as a cornerstone of modern drug discovery. Structural activity relationship (SAR) studies in medicinal chemistry are crucial for lead optimization, where a subtle change in the substituent can significantly alter its binding affinity with the biological target. Herein, a highly efficient single-atom substitution (SAS) approach has been developed, where sulfur for oxygen strategy is utilized as a powerful molecular editing technique to identify N-vinyl Indole-thiobarbituric acid (6 a) as a novel small molecule-based scaffold with tunable photophysical and antiproliferative activities. A series of NIR-emitting indole-barbituric/thiobarbituric acid conjugates exhibiting aggregation-induced emission (AIE) were prepared, where the replacement of oxygen for sulfur strategy emerged as a magic bullet. On the evaluation of photophysical properties and chemopreventive efficacies, a significant improvement in the absorption and emission profile, cellular uptake, and antiproliferative activity was noted for sulfur counterparts. From the pool of the molecules, the lead molecule 6 a unveils a 55 nm emission shift, 142-fold increased anticancer profile, and ~4-fold elevated cellular uptake. Furthermore, the colocalization experiment unravels the nuclear localization of 6 a, where it causes severe DNA damage, arrests the cell cycle in the G2/M phase, and leads to the activation of p53-mediated apoptosis. Our experimental findings represent 6 a as a potential lead molecule possessing excellent anticancer potency in the HCT 116 cell line and HCT 116-derived 3D spheroid model.

Palladium-Catalyzed α-Arylation of Sulfoxonium Ylides with Aryl Thianthrenium Salts via C-S and C-H Bond Activation

Diverse α-aryl α-carbonyl sulfoxonium ylides were efficiently synthesized in yields ranging from moderate to high via a palladium-catalyzed α-arylation of sulfoxonium ylides with aryl thianthrenium salts. The reactions proceeded smoothly via C-S and C-H bond functionalization, exhibiting broad substrate scope and good compatibility to various functionalities. In addition, the scale-up synthesis could be achieved, and the one-pot protocol commencing from the use of simple arene as the precursor of aryl thianthrenium salt could also be accomplished.

Mechanochemical Palladium-Catalyzed Cross-Coupling of Thianthrenium Salts and Arylboronic Acids

Cross-coupling reactions are indispensable for the construction of complex molecular scaffolds. In this work, we developed a sustainable methodology for the cross-coupling reaction of arene thianthrenium salts with aryl boronic acids, which can be effectively realized under mechanochemical conditions. Liquid-assisted grinding (LAG) enabled fast and high-yielding synthesis of a range of biaryls via Pd/RuPhos-catalyzed cross-coupling. The transformation works under ambient temperature and on air. Environmentally friendly solvent 2-methyltetrahydrofurane (Me-THF) was used as a LAG additive. Moreover, the major by-product of the cross-coupling reaction, thianthrene, can be recovered and reused.

Copper-Catalyzed Difluoromethylation of Alkenyl Thianthrenium Salts

We have developed a novel and straightforward protocol that facilitates the transformation of alkenylsulfonium salts leading to the direct synthesis of E-difluoromethylated alkenes. The success of this method relies on the use of copper catalysis and Vicic-Mikami reagent (DMPU)2Zn(CF2H)2. These mild protocols offer the advantage of selectively synthesizing either aromatic or aliphatic difluoromethylated alkenes. Furthermore, our methodology extends to the perfluoroalkylation of alkenylsulfonium salts. Notably, this approach is conducive to large-scale synthesis and holds promise for diverse applications.

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.

Green Synthesis of Morpholines via Selective Monoalkylation of Amines

Morpholines are common heterocycles in pharmaceutical and agricultural products, yet methods to synthesize them from 1,2-amino alcohols are inefficient. We report the simple, high yielding, one or two-step, redox neutral protocol using inexpensive reagents (ethylene sulfate and tBuOK) for the conversion of 1,2-amino alcohols to morpholines. Key to this methodology is the identification of general conditions that allow for the clean isolation of monoalkylation products derived from a simple SN2 reaction between an amine and ethylene sulfate. Experiments suggest that the degree of selectivity is dependent upon the structure of reacting 1,2-amino alcohol as well as the unique properties of ethylene sulfate. This method can be used for the synthesis of a variety of morpholines containing substituents at various positions, including 28 examples derived from primary amines and multiple examples contained in known active pharmaceutical ingredients. We have conducted multiple examples on >50 g scale. We have also demonstrated the formal synthesis of a morpholine from a simple primary amine using ethylene sulfate. Overall, while this new methodology has many environmental and safety benefits relative to the traditional methods used to prepare morpholines from 1,2-amino alcohols, the most striking feature is the facile selective monoalkylation of a variety of primary amines. We have also explored various reactions beyond those related to the synthesis of morpholines, including obtaining proof-of-principle that ethylene sulfate can be used for the synthesis of piperazines and as a 2-carbon electrophile for fragment couplings.

Palladium-Catalyzed Cross-Electrophile Couplings of Aryl Thianthrenium Salts with Aryl Bromides via C-S Bond Activation

We report here a step-economic and cost-effective cross-electrophile coupling of aryl thianthrenium salts with widely available aryl bromides, which proceeded effectively via C-S bond activation at ambient temperature in THF in the presence of a palladium catalyst, magnesium turnings, and lithium chloride to enable the facile assembly of a wide array of structurally diverse biaryls in modest to good yields with good functional group compatibility. In addition, the gram-scale reaction could also be realized.

Thianthrene/TfOH-catalyzed electrophilic halogenations using N-halosuccinimides as the halogen source

Organohalides are vital organic building blocks with applications spanning various fields. However, direct halogenation of certain neutral or unreactive substrates by using solely the regular halogenating reagents has proven challenging. Although various halogenation approaches via activating halogenating reagents or substrates have emerged, a catalytic system enabling broad substrate applicability and diverse halogenation types remains relatively underexplored. Inspired by the halogenation of arenes via thianthrenation of arenes, here we report that thianthrene, in combined use with trifluoromethanesulfonic acid (TfOH), could work as an effective catalytic system to activate regular halogenating reagents (NXS). This new protocol could accomplish multiple types of halogenation of organic compounds including aromatics, olefins, alkynes and ketones. The mechanism study indicated that a highly reactive electrophilic halogen thianthrenium species, formed in situ from the reaction of NXS with thianthrene in the presence of TfOH, was crucial for the efficient halogenation process.

Palladium-Catalyzed Carbonylative Sonogashira Coupling of Aryl Thianthrenium Salts with Arylalkynes

Alkynones are valuable compounds with applications in various areas. In this work, we developed an efficient carbonylation procedure for the carbonylative cross-coupling of aryl thianthrenium salts with aromatic alkynes. Various useful alkynones were produced in moderate to excellent yields under mild conditions. Notably, among the various tolerated functional groups, the bromide group can be maintained, which is ready for further coupling reactions.

Thianthrenation-promoted photoinduced alkene difunctionalization and aryl allylation with Morita-Baylis-Hillman adducts

An organophotoredox-catalyzed alkoxyallylation of feed-stock olefins, through thianthrenation using a Morita-Baylis-Hillman adduct as an allylating agent, is described. Site-selective addition of MeOH to an alkene-thianthrenium salt and its subsequent conversion into a nucleophilic radical species forms the basis of this unique difunctionalization strategy. The scope is also expanded into radical aryl allylation.

Base-Mediated Divergent Synthesis of Spiro-heterocycles Using Pronucleophiles and Ethylene via Thianthrenation

Spirocyclic compounds are abundant in biologically active products. However, the divergent synthesis of spirocyclic compounds using low-cost and abundant available starting materials remains a challenge. Herein, we report an effective method for producing spirocyclic motifs using a cyclic β-carbonyl ester or amide and ethylene via thianthrenation. This strategy highlights the exciting possibility of utilizing abundant ethylene as a C-2 synthon and allows regulating the core structure of the spirocyclic compound by simply altering the base type.

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.

Mechanism of Z-Selective Allylic Functionalization via Thianthrenium Salts

A detailed mechanistic study of the Z-selective allylic functionalization via thianthrenium salts is presented. Kinetic analyses, deuterium labeling experiments, and computational methods are used to rationalize the observed reactivity and selectivity. We find that the reaction proceeds via a rate-determining and stereodetermining allylic deprotonation of an alkenylthianthrenium species. The Z-configuration of the resultant allylic ylide is translated into the Z-allylic amine product through a sequence of subsequent fast and irreversible steps: protonation to form a Z-allylic thianthrenium electrophile and then regioselective substitution by the nucleophile. In the stereodetermining deprotonation step, computational studies identified a series of stabilizing nonbonding interactions in the Z-alkene-forming transition state that contribute to the stereoselectivity.

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).

Photocatalytic Functionalization of Dehydroalanine-Derived Peptides in Batch and Flow

Unnatural amino acids, and their synthesis by the late-stage functionalization (LSF) of peptides, play a crucial role in areas such as drug design and discovery. Historically, the LSF of biomolecules has predominantly utilized traditional synthetic methodologies that exploit nucleophilic residues, such as cysteine, lysine or tyrosine. Herein, we present a photocatalytic hydroarylation process targeting the electrophilic residue dehydroalanine (Dha). This residue possesses an α,β-unsaturated moiety and can be combined with various arylthianthrenium salts, both in batch and flow reactors. Notably, the flow setup proved instrumental for efficient scale-up, paving the way for the synthesis of unnatural amino acids and peptides in substantial quantities. Our photocatalytic approach, being inherently mild, permits the diversification of peptides even when they contain sensitive functional groups. The readily available arylthianthrenium salts facilitate the seamless integration of Dha-containing peptides with a wide range of arenes, drug blueprints, and natural products, culminating in the creation of unconventional phenylalanine derivatives. The synergistic effect of the high functional group tolerance and the modular characteristic of the aryl electrophile enables efficient peptide conjugation and ligation in both batch and flow conditions.

Stereospecific syn-dihalogenations and regiodivergent syn-interhalogenation of alkenes via vicinal double electrophilic activation strategy

Whereas the conventional anti-dihalogenation of alkenes is a valuable synthetic tool with highly predictable stereospecificity, the restricted reaction mechanism makes it challenging to alter the diastereochemical course into the complementary syn-dihalogenation process. Only a few notable achievements were made recently by inverting one of the stereocenters after anti-addition using a carefully designed reagent system. Here, we report a conceptually distinctive strategy for the simultaneous double electrophilic activation of the two alkene carbons from the same side. Then, the resulting vicinal leaving groups can be displaced iteratively by nucleophilic halides to complete the syn-dihalogenation. For this purpose, thianthrenium dication is employed, and all possible combinations of chlorine and bromine are added onto internal alkenes successfully, particularly resulting in the syn-dibromination and the regiodivergent syn-bromochlorination.

Reactivity of α-diazo sulfonium salts: rhodium-catalysed ring expansion of indenes to naphthalenes

In the presence of catalytic amounts of the paddlewheel dirhodium complex Rh2(esp)2, α-diazo dibenzothiophenium salts generate highly electrophilic Rh-coordinated carbenes, which evolve differently depending on their substitution pattern. Keto-moieties directly attached to the azomethinic carbon promote carbene insertion into one of the adjacent C-S bonds, giving rise to highly electrophilic dibenzothiopyrilium salts. This intramolecular pathway is not operative when the carbene carbon bears ester or trifluoromethyl substituents; in fact, these species react with olefins delivering easy to handle cyclopropyl-substituted sulfonium salts. When indenes are the olefins of choice, the initially formed cyclopropyl rings smoothly open with concomitant departure of dibenzothiophene, enabling access to a series of 2-functionalized naphthalenes.

Three-component N-alkenylation of azoles with alkynes and iodine(III) electrophile: synthesis of multisubstituted N-vinylazoles

A stereoselective N-alkenylation of azoles with alkynes and iodine(III) electrophile is reported. The reaction between various azoles and internal alkynes is mediated by benziodoxole triflate as the electrophile in a trans-fashion, affording azole-bearing vinylbenziodoxoles in moderate to good yields. The tolerable azole nuclei include pyrazole, indazole, 1,2,3-triazole, benzotriazole, and tetrazole. The iodanyl group in the product can be leveraged as a versatile synthetic handle, allowing for the preparation of hitherto inaccessible types of densely functionalized N-vinylazoles.

Alkene Thianthrenation Unlocks Diverse Cation Synthons: Recent Progress and New Opportunities

Oxidative alkene functionalization reactions are a fundamental class of complexity-building organic transformations. However, the majority of established approaches rely on electrophilic reagents that limit the diversity of groups that can be installed. Recent advances have established a new approach that instead relies on the transformation of alkenes into thianthrene-derived cationic electrophiles. These linchpin intermediates can be generated selectively and undergo a diverse array of mechanistically distinct reactions with abundant nucleophiles. Taken together, this unlocks a suite of net oxidative alkene transformations that have been elusive using conventional strategies. This Minireview describes these advances and is organized around the three distinct synthons formally accessible from alkenes via thianthrenation: 1) alkenyl cations; 2) vicinal dications; 3) allyl cations. Throughout the Minireview, we illustrate how thianthrenium salts address key limitations endemic to classic alkene-derived electrophiles and highlight the mechanistic origins of these distinctions wherever possible.

Desulfurative Functionalization of β-Acyl Allylic Sulfides with N-H Free Indoles Highly Regioselective at C3 and N1 Positions: Rapid Access to α-Branched Enones

A regiodivergent allylation of 1H-indoles highly selectively at the C3 and N1 positions with β-acyl allylic sulfides through desulfurative C-C/C-N bond-forming reactions has been developed under mild conditions. Notably, the remarkable site-selective switch can be achieved by a delicate choice of solvents and bases. This cost-efficient method displays a broad substrate scope, good functional compatibility, and excellent site-selectivity, thus offering a divergent synthesis of indole substituted α-branched enones, which possess diverse potential opportunities for further applications and derivatization.

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.

Piperazine-Fused Cyclic Disulfides Unlock High-Performance Bioreductive Probes of Thioredoxins and Bifunctional Reagents for Thiol Redox Biology

We report piperazine-fused six-membered-cyclic disulfides as redox substrates that unlock best-in-class bioreduction probes for live cell biology, since their self-immolation after reduction is unprecedentedly rapid. We develop scalable, diastereomerically pure, six-step syntheses that access four key cis- and trans-piperazine-fused cyclic dichalcogenides without chromatography. Fluorogenic redox probes using the disulfide piperazines are activated >100-fold faster than the prior art monoamines, allowing us to deconvolute reduction and cyclization rates during activation. The cis- and trans-fused diastereomers have remarkably different reductant specificities, which we trace back to piperazine boat/chair conformation effects: the cis-fused disulfide C-DiThia is activated only by strong vicinal dithiol reductants, but the trans-disulfide T-DiThia is activated even by moderate concentrations of monothiols such as GSH. Thus, in cellular applications, cis-disulfide probes selectively report on the reductive activity of the powerful thioredoxin proteins, while trans-disulfides are rapidly but promiscuously reactive. Finally, we showcase late-stage diversifications of the piperazine-disulfides, promising their broad applicability as redox-cleavable cores for probes and prodrugs that interface powerfully with cellular thiol/disulfide redox biology, for solid phase synthesis and purification, and for stimulus-responsive linkers in bifunctional reagents and antibody-drug conjugates - in addition to their dithiols' potential as high-performance reducing agents.

Nucleophilic functionalization of thianthrenium salts under basic conditions

In recent years, S-(alkyl)thianthrenium salts have become an important means of functionalizing alcohol compounds. However, additional transition metal catalysts and/or visible light are required. Herein, a direct thioetherification/amination reaction of thianthrenium salts is realized under metal-free conditions. This strategy exhibits good functional-group tolerance, operational simplicity, and an extensive range of compatible substrates.

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.

N-Vinylthio Phthalimides (N-VTPs): Modular Reagents for Vinylthio AIEgen Transfer

Novel sulfur reagents N-vinylthio phthalimides (N-VTPs) have been employed as modular reagents for vinylthiolation, enabling the construction of aggregation-induced emission (AIE)-active tetraaryldivinyl sulfides (TADVSs) and diarylvinyl sulfides (DAVSs). Notably, TADVSs with sulfur insertion to ethene stators are reported as AIE luminogens (AIEgens) for the first time, and the corresponding photophysical properties and aggregated confirmation have been detailed for the demonstration of the AIE effect. A water-soluble TADVS with a quinolinium salt was prepared for cell imaging.

Reductive Cross-Coupling of a Vinyl Thianthrenium Salt and Secondary Alkyl Iodides

We report the first reductive vinylation of alkyl iodides. The reaction uses a vinyl thianthrenium salt, a palladium catalyst, and an alkyl zinc intermediate formed in situ to trap the Ln PdII (vinyl) complex formed after oxidative addition before it undergoes undesired homocoupling to form butadiene.

Dithiolation of Alkenyl Sulfonium Salts with Arylthiols to Access 1,2-Dithioalkanes

A dithiolation of alkenyl sulfonium salts with arylthiols is described, affording a series of 1,2-dithioalkanes in high yields. This protocol features mild and catalyst-free conditions and involves the formation of two C-S bonds sequentially via the regioselective addition of an arylthiol to the unsaturated C═C bonds, followed by the attack of another arylthiol to form 1,2-dithioalkanes exclusively.

Regioselective Synthesis of N-Vinyl Pyrazoles from Vinyl Sulfonium Salts with Diazo Compounds

Herein, we develop a base-promoted regioselective synthesis of N-vinyl pyrazoles from vinyl sulfonium salts with diazo compounds. This metal-free synthetic protocol provides an efficient and practical approach to diverse N-vinyl pyrazoles in good to excellent yields under mild conditions. The reaction appears to experience a [3 + 2] annulation of vinyl sulfonium salts and diazo anions rather than diazo compounds, followed by N-vinylation.

Fluorinated Vinyl Sulfonium Salts and Their Synthetic Utilization

The fluorinated building block strategy and the direct fluorination strategy are of great importance for the synthesis of new fluorinated molecules. These strategies complement each other and can be combined to develop a new methodology for the construction of a wide variety of fascinating organofluorine compounds. In our opinion, the versatile building blocks used in this method should satisfy the following conditions: 1) readily prepared from commercially available reagents; 2) easy to handle; 3) storage under ordinary conditions without noticeable decomposition; 4) wide applicability. Based on the aforementioned requirements, we focused on the use of vinyl sulfonium salts. This brief review describes the synthesis of five types of fluorinated vinyl sulfonium salts and their reactions. Especially, we featured typical fluorinated groups containing trifluoromethyl (CF3 ), difluoromethyl (CF2 H), monofluoromethyl (CFH2 ), monofluoro (F) or β-bromotetrafluoroethyl (BrCF2 CF2 ) moieties in combination with vinyl sulfonium salts.

Oxetane Synthesis via Alcohol C-H Functionalization

Oxetanes are strained heterocycles with unique properties that have triggered significant advances in medicinal chemistry. However, their synthesis still presents significant challenges that limit the use of this class of compounds in practical applications. In this Letter, we present a methodology that introduces a new synthetic disconnection to access oxetanes from native alcohol substrates. The generality of the approach is demonstrated by the application in late-stage functionalization chemistry, which is further exploited to develop a single-step synthesis of a known bioactive synthetic steroid derivative that previously required at least four synthetic steps from available precursors.

Highly Regioselective Dichalcogenation of Alkenyl Sulfonium Salts to Access 1,1-Dichalcogenalkenes

An unprecedented geminal olefinic dichalcogenation of alkenyl sulfonium salts with dichalcogenides ArYYAr (Y = S, Se, Te) is reported, providing various trisubstituted 1,1-dichalcogenalkenes [Ar¹CH = C(YAr²)₂] in a highly selective manner under mild and catalyst-free conditions. The key process involves the formation of two geminal olefinic C-Y bonds via sequential C-Y cross-coupling and C-H chalcogenation. A mechanistic rationale is further supported by control experiments and density functional theory calculations.

Tunable [3+2] and [4+2] annulations for pyrrolidine and piperidine synthesis

N-heterocycles are privileged pharmaceutical scaffolds in drug discovery and development. We disclose here divergent intermolecular coupling strategies that can access diverse N-heterocycles directly from olefins. The radical-to-polar mechanistic switching is key for the divergent cyclization processes. These distinctive annulations result in the coupling of alkenes with simple bifunctional reagents for divergent N-heterocycle syntheses.

Diastereoselective Synthesis of Cyclopropanes from Carbon Pronucleophiles and Alkenes

Cyclopropanes are desirable structural motifs with valuable applications in drug discovery and beyond. Established alkene cyclopropanation methods give rise to cyclopropanes with a limited array of substituents, are difficult to scale, or both. Herein, we disclose a new cyclopropane synthesis through the formal coupling of abundant carbon pronucleophiles and unactivated alkenes. This strategy exploits dicationic adducts derived from electrolysis of thianthrene in the presence of alkene substrates. We find that these dielectrophiles undergo cyclopropanation with methylene pronucleophiles via alkenyl thianthrenium intermediates. This protocol is scalable, proceeds with high diastereoselectivity, and tolerates diverse functional groups on both the alkene and pronucleophile coupling partners. To validate the utility of this new procedure, we prepared an array of substituted analogs of an established cyclopropane that is en route to multiple pharmaceuticals.

Syntheses of 2- and 3-Substituted Morpholine Congeners via Ring Opening of 2-Tosyl-1,2-Oxazetidine

Diastereoselective and diastereoconvergent syntheses of 2- and 3-substituted morpholine congeners are reported. Starting from tosyl-oxazatedine 1 and α-formyl carboxylates 2, base catalysis is utilized to yield morpholine hemiaminals. Their further synthetic elaborations allowed the concise constructions of conformationally rigid morpholines. The observed diastereoselectivities and the unusual diastereoconvergence in the photoredox radical processes seem to be the direct consequence of the avoidance of pseudo A^1,3 strain between the C-3 substituent and the N-tosyl group and the anomeric effect of oxygen atoms.

Regiospecific Alkene Aminofunctionalization via an Electrogenerated Dielectrophile

Modular strategies to rapidly increase molecular complexity have proven immensely synthetically valuable. In principle, transformation of an alkene into a dielectrophile presents an opportunity to deliver two unique nucleophiles across an alkene. Unfortunately, the selectivity profiles of known dielectrophiles have largely precluded this deceptively simple synthetic approach. Herein, we demonstrate that dicationic adducts generated through electrolysis of alkenes and thianthrene possess a unique selectivity profile relative to more conventional dielectrophiles. Specifically, these species undergo a single and perfectly regioselective substitution reaction with phthalimide salts. This observation unlocks an appealing new platform for aminofunctionalization reactions. As an illustrative example, we implement this new reactivity paradigm to address a longstanding synthetic challenge: alkene diamination with two distinct nitrogen nucleophiles. Studies into the mechanism of this process reveal a key alkenyl thianthrenium salt intermediate that controls the exquisite regioselectivity of the process and highlight the importance of proton sources in controlling the reactivity of alkenyl sulfonium salt electrophiles.

Palladium-Catalyzed Carbonylative Synthesis of Diaryl Ketones from Arenes and Arylboronic Acids through C(sp2)-H Thianthrenation

The development of mild methodology for converting inert C-H bonds to value-added molecules has been an attractive research topic during the last few decades as it offers efficient preparation. Meanwhile, diaryl ketones hold potent applications in antitumor drugs, the agrochemical industry, and synthetic chemistry. Herein, we report versatile palladium-catalyzed carbonylative cross-coupling reactions of aryl thianthrenium salts with arylboronic acids. Arenes were transformed site selectively via C(sp²)-H thianthrenation, and various desired diaryl ketones were produced in good to excellent yields.

CuF2/DMAP-Catalyzed N-Vinylation: Scope and Mechanistic Study

CuF₂/DMAP has been established as an excellent catalytic system for vinylsilane-promoted N-vinylation of amides and azoles at room temperature without an external fluoride source. A mechanism has been proposed on the basis of the isolation of reactive intermediate [Cu(DMAP)₄Cl₂], fluoride ion-assisted transmetalation, and ultraviolet-visible spectroscopic studies. The catalytic efficiency of the synthesized and structurally characterized [Cu(DMAP)₄Cl₂] complex has been demonstrated. The valuable monomers for water-soluble polymers, viz., NVP, NVC, and NVIBA, were synthesized on a gram scale.

Synthesis of Sulfur-Containing Oxindoles by Photoinduced Alkene Difunctionalization via Sulfur 1,2-Relocation

Organosulfur compounds are prevalent in various natural products, which have been widely applied in agrochemicals and pharmaceuticals. Herein, a new approach for the efficient construction of sulfur-containing oxindoles by photoinduced alkene difunctionalization via sulfur 1,2-relocation is developed. The method exhibited a high functional group tolerance and broad substrate compatibility. A library of sulfur-containing oxindole derivatives were synthesized under mild conditions (metal-, photocatalyst-, and additive-free). Mechanistic investigations revealed this photochemical process was triggered by the formation of an EDA complex of oxindole enolates with a redox-active ester, and the in situ generation of alkenes from the C-S bond cleavage of β-sulfanyl radicals was a key step in this transformation.

Polarity Transduction Enables the Formal Electronically Mismatched Radical Addition to Alkenes

The formation of carbon-carbon bonds via the intermolecular addition of alkyl radicals to alkenes is a cornerstone of organic chemistry and plays a central role in synthesis. However, unless specific electrophilic radicals are involved, polarity matching requirements restrict the alkene component to be electron deficient. This limits the scope of a fundamentally important carbon-carbon bond forming process that could otherwise be more universally applied. Herein, we introduce a polarity transduction strategy that formally overcomes this electronic limitation. Vinyl sulfonium ions are demonstrated to react with carbon-centered radicals, giving adducts that undergo in situ or sequential nucleophilic displacement to provide products that would be inaccessible via traditional methods. The broad generality of this strategy is demonstrated through the derivatization of unmodified complex bioactive molecules.

Intertwining Olefin Thianthrenation with Kornblum/Ganem Oxidations: Ene-type Oxidation to Furnish α,β-Unsaturated Carbonyls

A widely applicable, practical, and scalable synthetic method for efficient ene-type double oxidation of alkenes is reported via a two-step alkenyl thianthrenium umpolung/Kornblum-Ganem oxidation strategy. This chemo- and stereoselective procedure allows easy access to various α,β-unsaturated carbonyls that may be otherwise difficult or cumbersome to synthesize by conventional methods. For α-olefins, this metal-free transformation can be tuned according to synthetic needs to produce either the elusive (Z)-unsaturated aldehydes or their (E) counterparts. Moreover, this strategy has enabled streamlined synthesis of distinct butadienyl pheromones and kairomones.

Organothianthrenium salts: synthesis and utilization

Organothianthrenium salts are a class of compounds containing a positively charged sulfur atom and a neutral sulfur atom. Over the past years, organothianthrenium salts have been emerging as attractive precursors for a myriad of transformations to forge new C-C and C-X bonds due to their unique structural characteristics and chemical behaviors. The use of the thianthrenation strategy selectively transforms C-H, C-O, and other chemical bonds into organothianthrenium salts in a predictable manner, providing a straightforward alternative for regioselective functionalizations for arenes, alkenes, alkanes, alcohols, amines and so on through diverse reaction mechanisms under mild conditions. In this review, the preparation of different organothianthrenium salts is summarized, including aryl, alkenyl and alkyl thianthrenium salts. Moreover, the utilization of organothianthrenium salts in different catalytic processes and their synthetic potentials are also discussed.

N-Trifluoropropylation of Azoles through N-Vinylation and Sequential Hydrogenation

Installing a fluoroalkyl group onto the nitrogen atom of azoles represents a potential strategy for lead optimization in medicinal chemistry. Herein, we describe a method for the N-trifluoropropylation of azoles. This process is accomplished using a combination of regioselective N-vinylation and sequential hydrogenation. The two-step sequence is applicable to a diverse set of azoles and tolerates a wide range of functionalities. In addition, we showcase its practicability and utility through the gram-scale synthesis and the late-stage modification of a complex molecule.