Transition-Metal-Catalyzed C–S, C–Se, and C–Te Bond Formations via Cross-Coupling and Atom-Economic Addition Reactions. Achievements and Challenges

Metal-catalyzed methylthiolation of chloroarenes and diverse aryl electrophiles

In this study, we report the first development of metal catalyzed methylthiolation of chloroarenes and diverse aromatic electrophiles, addressing the persistent challenges of catalyst and intermediate deactivation in the functionalization of less reactive substrates. To overcome these issues, we designed a novel anion-shuttle-type methylthiolation agent, 4-((methylthio)methyl)morpholine, which enables the controlled in situ release of methylthiolate anions, thereby preventing catalyst poisoning and enhancing reactivity. This strategy allows efficient methylthiolation not only of chloroarenes but also of a broad range of aryl electrophiles, including bromoarenes, aryl triflates, aryl tosylates, aryl pivalates, aryl nitriles, and aryl carboxylic acids. The developed system exhibits excellent functional group compatibility, making it applicable to the derivatization of pharmaceuticals and natural products. Furthermore, detailed mechanistic investigations revealed key factors underlying the exceptional efficiency of this methylthiolation agent, providing new insights into C-S bond formation under practical conditions.

Palladium-catalyzed reductive cross-coupling reaction of carboxylic acids with thiols: an alternative strategy to access thioesters

A practical and alternative approach to access thioesters is presented, utilizing readily available starting precursors such as carboxylic acids and thiols via direct reductive C-S cross-coupling reactions under palladium catalysis. The present protocol features good atom economy, excellent yields, wide functional group tolerance, broad substrate scope, operational simplicity, and mild reaction conditions with no additional steps.

Photo- and Cerium-Mediated C─C Bond Cleavage for the Deconstructive Diversification of Cyclic Acids

The selective cleavage of inert carbon-carbon bonds in unstrained rings continues to pose a formidable challenge in chemical synthesis. Current methods for C(sp3) ─C(sp3) bond cleavage are highly limited, typically relying on transition-metal catalysis to facilitate ring-opening via small-ring strain or inducing β-fragmentation after generating radicals from oxygen or nitrogen atoms pre-installed in the substrate. Herein, we introduce an effective strategy for the decarboxylative ring-opening functionalization of α-trisubstituted carboxylic acids, mediated by both light and cerium. This method enables the ring-opening of carboxylic acids with ring sizes ranging from 3 to 12 members, allowing the construction of C─CN, C-halide, C─C, C─Se, and C─oxime bonds. Notably, this reaction does not require the pre-installation of an oxygen atom in the substrate, as the carbonyl group is derived from atmospheric oxygen. Furthermore, late-stage modification establishes distally functionalized carbonyl compounds, which serve as versatile synthons for accessing valuable building blocks.

Carbonyl and Carbonyl-N-Heterocyclic Carbine-Ligated Iron Complexes as Catalysts for Markovnikov-Selective Alkyne Hydrothiolation and Hydroselenation Reactions: A Mechanistic Study

In the present work, iron carbonyl-catalyzed hydrothiolation/hydroselenation of alkynes has been studied computationally. The catalytic efficiency of inexpensive iron carbonyls and three iron-N-heterocyclic carbene (NHC)-based complexes-Fe(NHC)ax(CO)4, Fe(NHC)eq(CO)4, and Fe(aNHC)ax(CO)4-is evaluated. The results demonstrate significantly reduced energy barriers for the catalytic reactions compared to uncatalyzed gas-phase reactions. A high degree of regioselectivity for the Markovnikov product is observed, validating the effectiveness of these complexes in producing Markovnikov vinyl sulfides/selenides. An alternative catalytic pathway involving alkyne insertion into the MS/Se and MH bonds is also explored, and it is found that the catalyst regio- and stereoselectively leads to the formation of Markovnikov product in MS/Se insertion pathway and Z-anti-Markovnikov product in MH insertion pathway, consistent with the existing literature reports.

Multicomponent Reaction Integrating Selenium(II)-Nitrogen Exchange (SeNEx) Chemistry and Copper-Catalyzed Azide-Alkyne Cycloaddition (CuAAC)

Multicomponent reactions (MCRs) are powerful tools for rapidly constructing compound libraries with sufficient molecular diversity and complexity. Herein, to fully leverage a third aspect of molecular diversity enabled by the selenium-nitrogen exchange (SeNEx) reaction between alkynes and benzoselenazolones, a novel CuI-catalyzed three-component reaction has been successfully developed. This reaction integrates SeNEx with CuAAC click chemistry, enabling rapid and regioselective synthesis of 1,4,5-trisubstituted 5-seleno-1,2,3-triazoles with high atom economy and good to excellent yields (65 examples, 50%-95%). Notably, this MCR demonstrates excellent functional group tolerance and features modular, predictable, robust, mild reaction conditions, and operational simplicity (air and water compatibility). Extensive mechanism studies have revealed that this reaction proceeds by a unique SeNEx-CuAAC tandem reaction pathway, distinguishing it from conventional copper(I)-catalyzed interrupted click reactions. Importantly, a mononuclear σ-bound copper(I)-acetylide Cu1 was synthesized and confirmed to be an efficient catalyst for the SeNEx reaction. This discovery provides crucial mechanistic insights into the preferential reactivity of alkynyl groups toward SeNEx over CuAAC. Furthermore, preliminary biological activity screening identified compound 14 as a potent inhibitor of Escherichia coli β $\upbeta$ -glucuronidase (EcGUS), with an IC50 value of 3.16 µM. These findings underscore the significant potential of this MCR in synthetic chemistry, medical chemistry, and chemical biology.

Single-Atom Based Metal-Organic Frameworks for Efficient C-S Cross-Coupling

Single-atom-based Metal-Organic Frameworks (MOFs) hold great promising candidates for heterogeneous catalysis, demonstrating outstanding catalytic activity and exceptional product selectivity. This is attributed to their optimal atom utilization, high surface energy, and the presence of unsaturated coordination environments. Here in, we have developed a nickel single-atom catalyst (SAC) featuring Ni single atoms covalently attached to defect-engineered Zr-oxide clusters within the stable UiO-66 (Universitetet i Oslo) framework, synthesized via a straightforward solution impregnation method (denoted as UiO-66/Ni now onwards). The resulting UiO-66/Ni catalyst, with a uniform distribution of nickel single atoms, exhibits remarkable stability and demonstrates exceptional performance in C-S coupling reactions of various aryl thiols and aryl halides, yielding desired products with outstanding catalytic activity and selectivity, regardless of electron-donating or withdrawing substituents at room temperature and maintains robust stability even after six cycles. Advanced density functional theory calculations have been exploited to clarify the mechanism of C-S cross-coupling for examining the influence of substituents on the aromatic ring of aryl thiols through free energy profiles. The collaborative action of nickel single atoms and the defects of UiO-66 during the oxidative addition and reductive elimination steps facilitated the formation of energetically favorable C-S cross-coupling products. This study offers valuable insights for the development of enhanced single atom-based hybrid catalytic systems for heterogeneous coupling reactions.

Photoredox/Pyridine N-Oxide Catalyzed Carbohydroxylation and Aminohydroxylation of α-Olefins

Regioselective carbohydroxylation and aminohydroxylation of α-olefins were developed by a photoredox catalyst and pyridine N-oxide. This approach offers the catalytic and direct conversion of unactivated alkenes to a series of primary alcohols, including those bearing β-quaternary carbon centers and β-amino alcohols. The regioselective difunctionalization is enabled by the radical addition of α-olefin from the pyridine N-oxy radical, which is generated from readily available pyridine N-oxide via photoredox catalyzed single-electron oxidation. A combination of experimental and computational mechanistic studies was employed to lend support for the proposed reaction mechanism that proceeds via interwoven radical steps and polar substitution. The implications of this method for regioselective difunctionalization of α-olefins were further demonstrated by the examples of carboetherification, carboesterification, and lactone formation.

Pd-Catalyzed Coupling of Aryl Chloride, Isocyanides, and Thiocarboxylate To Synthesize Thioamides

Although aryl chlorides are among the most abundant and stable aromatic electrophiles, the coupling of aryl chlorides with isocyanides has remained an unsolved challenge. Herein, we report a general transformation of aryl chlorides, isocyanides, and thiocarboxylates to synthesize thioamides. The sterically hindered and electron-rich Josiphos ligand significantly facilitates the rate-determining oxidative addition step and reduces the toxicity of isocyanides toward the metal center. The combination of thiocarboxylate as the nucleophile and Josiphos as the ligands enabled the coupling-tolerated various 1°, 2°, and 3° isocyanides, which provides a rapid, efficient, and versatile method for the synthesis of large quantities of thioamides, including those of pharmaceutical relevance.

Are activation barriers of 50-70 kcal mol-1 accessible for transformations in organic synthesis in solution?

High-temperature organic chemistry represents a transformative approach for accessing reaction pathways previously considered unattainable under conventional conditions. This study focuses on a high-temperature synthesis as a powerful method for performing solution-phase organic reactions at temperatures up to 500 °C. Using the isomerization of N-substituted pyrazoles as a model reaction, we demonstrate the ability to overcome activation energy barriers of 50-70 kcal mol-1, achieving product yields up to 50% within reaction times as short as five minutes. The methodology is environmentally friendly, leveraging standard glass capillaries and p-xylene as a solvent. The significance of high-temperature synthesis lies in its simplicity, efficiency, and ability to address the limitations of traditional methods in solution chemistry. Kinetic studies and DFT calculations validate the experimental findings and provide insights into the reaction mechanism. The method holds broad appeal due to its potential to access diverse compounds relevant to pharmaceuticals, agrochemicals, and materials science. By expanding the scope of accessible reactions, this exploration of experimental possibilities opens a new frontier in synthetic chemistry, enabling the exploration of previously inaccessible transformations. This study establishes a new direction for further innovations in organic synthesis, fostering advancements in both fundamental research and practical applications.

Rapid C-S Coupling in Water via Ion-Pair-Catalyzed Dehydration

The C-S bond is of significant importance due to its unique properties and diverse roles in chemistry, biology, and materials science. In this work, we present an efficient synthetic protocol of a rapidly dehydrative C-S coupling reaction with alcohols and thiols in water catalyzed by a triaryl-carbenium ion pair. Under metal-free conditions, a wide range of thioethers were obtained in good yields (up to 99%) with excellent functional group tolerance, including the fast modification of amino acid derivatives and functional molecules. This method allowed reactions to be conducted with low catalyst loading, down to 1.0 mol %, and was practical for gram-scale synthesis. Furthermore, the reactions were performed under biocompatible conditions, making this approach highly suitable for potential bioconjugation.

NBS-promoted regioselective thiocyanatothiolation of alkenes with free thiols and NH4SCN

An efficient NBS-promoted three-component thiocyanatothiolation of alkenes with free thiols and NH4SCN has been developed. This protocol avoids tedious preactivation of thiols and employs a diverse range of accessible thiols directly as sulfur sources. Moreover, the reaction exhibits regioselectivity and shows high compatibility with styrenes and unactivated alkenes. Preliminary mechanism studies revealed that both a radical pathway and thiol-oxidation-coupling were involved in this protocol.

Synthesis of Functionalized Thioimidates from Thioamides and Arylboronic Acids via Copper-Catalyzed Cross-Coupling Reaction at Room Temperature

Functionalized S-aryl thioimidates were synthesized from thioamides and arylboronic acids at room temperature under mild conditions. The reaction was catalyzed by copper(II) acetate in the presence of DBU under an open atmosphere. A wide range of functionalized aryl and alkyl boronic acids was chemo-selectively coupled with aryl and alkyl thioamides to obtain corresponding S-aryl and S-alkyl thioimidates in 64-80% yields. Room temperature reactions, easy operation, and broad substrate scope are the salient features of the developed methodology.

Sustainable catalysts in a short time: harnessing bacteria for swift palladium nanoparticle production

Adapting biological systems for nanoparticle synthesis opens an orthogonal Green direction in nanoscience by reducing the reliance on harsh chemicals and energy-intensive procedures. This study addresses the challenge of efficient catalyst preparation for organic synthesis, focusing on the rapid formation of palladium (Pd) nanoparticles using bacterial cells as a renewable and eco-friendly support. The preparation of catalytically active nanoparticles on the bacterium Paracoccus yeei VKM B-3302 represents a more suitable approach to increase the reaction efficiency due to its resistance to metal salts. We introduce an efficient method that significantly reduces the preparation time of Pd nanoparticles on Paracoccus yeei bacteria to only 7 min, greatly accelerating the process compared with traditional methods. Our findings reveal the major role of live bacterial cells in the formation and stabilization of Pd nanoparticles, which exhibit high catalytic activity in the Mizoroki-Heck reaction. This method not only ensures high yields of the desired product but also offers a greener and more sustainable alternative to conventional catalytic processes. The rapid preparation and high efficiency of this biohybrid catalyst opens new perspectives for the application of biosupported nanoparticles in organic synthesis and a transformative sustainable pathway for chemical production processes.

Disulfide-mediated ruthenium-catalyzed direct C-H thiolation in benzoxazinone systems: selective synthesis of ortho-thiolated 2-arylbenzoxazinones

2-Arylbenzoxazinone undergoes direct ortho-C-H thiolation by using diaryl disulfide in the presence of a Ru(II)-phosphine catalytic system and an Ag additive. The protocol has been generalized with benzoxazinone substrates having different substituents and a series of disulfides. ortho-Selenylation has also been performed successfully using diphenyl diselenide under similar catalytic conditions. Based on control experiments and reported literature studies, a probable mechanistic pathway has been suggested.

Exploring nickel-catalyzed organochalcogen synthesis via cross-coupling of benzonitrile and alkyl chalcogenols with computational tools

The preparation of organochalcogens has increased in recent times due to their promising biological activity properties. This work studies the reaction mechanism of a nickel(0)-catalyzed cross-coupling between benzonitrile and propanethiol to produce new C-S bonds by computational means. The proposed mechanism follows the classical oxidative addition/transmetalation/reductive elimination cross-coupling sequence, involving an unusual oxidative addition of a Ph-CN bond onto the active species. The computed catalytic cycle for thioether synthesis has been examined to determine whether the same protocol could be employed to build the analogous C-Se and C-Te bonds. The proposed mechanism for C-S coupling is validated by microkinetic modeling and shows a very good agreement with available experimental data. The extension of the proposed mechanism to C-Se and C-Te couplings indicates that these new reactions should be operative, although their reaction rates appear to be significantly slower.

Nickel-Catalyzed Electroreductive Sulfuration of Alkyl Alcohols with Pyridyl Thioesters

We demonstrate here an efficient and facile Ni-catalyzed electrochemical cross-electrophile thiolation approach for readily available alkyl alcohols with pyridyl thioesters. This C(sp3)-S bond-forming modular strategy displays extensive substrate adaptability and good functional group tolerance, which allows the production of a range of alkyl sulfides with specific chemoselectivity. Furthermore, the potential applications of this methodology are illustrated by last-stage modification of bioactive molecules and sulfinylative cross-couplings. Preliminary mechanistic experiments support a radical process.

Low-coordinate bis-phosphine and monophosphine Ni(0) complexes: synthesis and reactivity in C-S cross-coupling

Preformed Ni(0) complexes are rarely used as precatalysts in cross-coupling reactions, although they can incorporate catalytically active nickel directly into the reaction. In this work, we focus on the preparation and the catalytic application of low-coordinate Ni(0) complexes supported by bulky monophosphine ligands in C-S cross-coupling reactions. We have prepared two families of Ni(0) complexes, bis-phosphine aducts of the type [Ni(PR2Ar')2] (Ar' = m-terphenyl group) and monophosphine derivatives of the type [Ni(PR2Ar')(DVDS)] (DVDS = divinyltetramethyldisiloxane). DFT calculations were used to account for the atypical bent structures displayed by the bis-phosphine Ni(0) complexes. Monophosphine-Ni(0) complexes display catalytic activity superior to bis-phosphine Ni(0) adducts, which suggests that the former facilitate the generation of highly reactive monoligated PNi(0) species. Furthermore, the reactivity of monophosphine-Ni(0) precatalysts outperform that observed with Ni(II) precatalysts with the same phosphine ligands, supporting a more facile activation step to the same catalytic species. This enhanced reactivity allows for the use of lower catalyst loadings (1-5 mol%) and for carrying out the challenging coupling between aryl chlorides and alkylthiols.

C2-Selective Palladium-Catalyzed C-S Cross-Coupling of 2,4-Dihalopyrimidines

Under most conditions, 2,4-dihalopyrimidines undergo substitution reactions at C4. Here we report that Pd(II) precatalysts supported by bulky N-heterocyclic carbene ligands uniquely effect C2-selective cross-coupling of 2,4-dichloropyrimidine with thiols. The regioselectivity of this reaction stands in stark contrast to ∼1500 previously reported Pd-catalyzed cross-couplings that favor C4 in the absence of other substituents on the pyrimidine ring. Selectivity in the catalytic system reported herein is extremely sensitive to the structure of the Pd(II) precatalyst, largely due to competing C4-selective nucleophilic aromatic substitution. C2-selectivity is high with most 1° thiols and thiophenols, and a range of substituted dichloropyrimidines can be used. The atypical selectivity of this transformation may facilitate diversity-oriented synthesis, as demonstrated for derivatives of an antiviral agent. Under these conditions, C2─Cl cleavage may not take place through a typical oxidative addition pathway.

Green-light-induced selective hydroselenation of olefins with diselenides

A selective green-light-induced hydroselenation of alkenes with diselenides using Hantzsch ester as the hydrogen donor has been developed. In the case of electron-neutral diaryl diselenides and diacyl ones, alkenes undergo anti-Markovnikov-selective hydroselenation. When switching to electron-deficient diaryl diselenides and dialkyl ones, Markovnikov-selective hydroselenation occurs.

Photoinduced Radical Relay Reaction of 2-Methylthiolated Phenylacetylenes/Alkynones Initiated by Electron Donor-Acceptor Complexes

A method was found to construct sulfur-containing five- and six-membered heterocyclic alkyl sulfonyl compounds by using visible light and free radicals activated and/or generated by EDA complexes/homolytic cleavage as initiators to stimulate the relay reaction of alkynes/alkynones. This method puts forward a new strategy to initiate alkyl sulfonation of alkynes/alkynones with only a catalytic amount of the initiator. This strategy of generating the initiator by EDA complex activation/homolytic cleavage provides a new idea for the following substances that must be excited.

Selenium(II)-Nitrogen Exchange (SeNEx) Chemistry: A Good Chemistry Suitable for Nanomole-Scale Parallel Synthesis, DNA-encoded Library Synthesis and Bioconjugation

The continuous development of click reactions with new connecting linkage is crucial for advancing the frontiers of click chemistry. Selenium-nitrogen exchange (SeNEx) chemistry, a versatile chemistry in click chemistry, represents an all-encompassing term for nucleophilic substitution events that replace nitrogen at an electrophilic selenium(II) center, enabling the flexible and efficient assembly of linkages around a Se(II) core. Several SeNEx chemistries have been developed inspired by the biochemical reaction between Ebselen and cysteine residue, and demonstrated significant potential in on-plate nanomole-scale parallel synthesis, selenium-containing DNA-encoded library (SeDEL) synthesis, as well as peptide and protein bioconjugation. This concept aims to present the origins, advancements, and applications of selenium(II)-nitrogen exchange (SeNEx) chemistry while also outlining the potential directions for future research in this field.

50 Years of Organoselenium Chemistry, Biochemistry and Reactivity: Mechanistic Understanding, Successful and Controversial Stories

In 1973, two major discoveries changed the face of selenium chemistry: the identification of the first mammal selenoenzyme, glutathione peroxidase 1, and the discovery of the synthetic utility of the so-called selenoxide elimination. While the chemical mechanism behind the catalytic activity of glutathione peroxidases appears to be mostly unveiled, little is known about the mechanisms of other selenoproteins and, for some of them, even the function lies in the dark. In chemistry, the capacity of organoselenides of catalyzing hydrogen peroxide activation for the practical manipulation of organic functional groups has been largely explored, and some mechanistic details have been clearly elucidated. As a paradox, despite the long-standing experience in the field, the nature of the active oxidant in various reactions still remains matter of debate. While many successes characterize these fields, the pharmacological use of organoselenides still lacks any true application, and while some organoselenides were found to be non-toxic and safe to use, to date no therapeutically approved use was granted. In this review, some fundamental and chronologically aligned topics spanning organoselenium biochemistry, chemistry and pharmacology are discussed, focusing on the current mechanistic picture describing their activity as either bioactive compounds or catalysts.

Silver-Mediated Acetoxyselenylation of Alkynes: Mild Stereoselective Access to Bifunctional Alkenes

Herein, we report a AgF-mediated regio- and stereoselective acetoxyselenylation of terminal/internal alkynes from iodobenzene dicarboxylate [PhI(OCOR)2] and diorganyl diselenides via multiple-site functionalization to afford β-selenyl enol esters in good yields. Alkynes derived from bioactive molecules, such as l(-)-borneol, l-menthol, and acyne oxalate, are also suitable for this transformation and afford the expected compounds.

Metal-catalyzed divergent synthesis from ylides with 3-arylbenzo[d][1,2,3]triazin-4(3H)-ones

The present work reveals a new metal-catalyzed synthetic reaction involving 1,2,3-benzotriazinones with carbonyl sulfoxonium ylide and iodonium ylide, resulting in divergent products. Within this catalytic system, 3-phenylbenzo[d][1,2,3]triazin-4(3H)-one derivatives undergo C-H alkylation processes facilitated by a Cp*Rh(III) catalyst when combined with a carbonyl sulfoxonium ylide. On the other hand, when iodonium ylide substrates are used, they undergo an alkenylation reaction facilitated by a Cp*Ir(III) catalyst. In addition, hydrazone products are produced by synthesizing iodonium ylide substrates with the use of a copper catalyst. These transformations demonstrate mild reaction conditions, a wide range of substrates, and excellent compatibility with various functional groups. The strategy and tactics utilized have been effectively implemented on a significant scale.

Sulfur-based fluorescent probes for biological analysis: A review

The widespread adoption of small-molecule fluorescence detection methodologies in scientific research and industrial contexts can be ascribed to their inherent merits, including elevated sensitivity, exceptional selectivity, real-time detection capabilities, and non-destructive characteristics. In recent years, there has been a growing focus on small-molecule fluorescent probes engineered with sulfur elements, aiming to detect a diverse array of biologically active species. This review presents a comprehensive survey of sulfur-based fluorescent probes published from 2017 to 2023. The diverse repertoire of recognition sites, including but not limited to N, N-dimethylthiocarbamyl, disulfides, thioether, sulfonyls and sulfoxides, thiourea, thioester, thioacetal and thioketal, sulfhydryl, phenothiazine, thioamide, and others, inherent in these sulfur-based probes markedly amplifies their capacity for detecting a broad spectrum of analytes, such as metal ions, reactive oxygen species, reactive sulfur species, reactive nitrogen species, proteins, and beyond. Owing to the individual disparities in the molecular structures of the probes, analogous recognition units may be employed to discern diverse substrates. Subsequent to this classification, the review provides a concise summary and introduction to the design and biological applications of these probe molecules. Lastly, drawing upon a synthesis of published works, the review engages in a discussion regarding the merits and drawbacks of these fluorescent probes, offering guidance for future endeavors.

Ru(II)-Catalyzed C7 Trifluoromethylthiolation and Thioarylation of Indolines Using Bench-Stable Reagents

A Ru(II)-catalyzed C(sp2)-H trifluoromethylthiolation and thioarylation of indolines using bench-stable reagents have been explored. Diversely substituted indolines were functionalized at C7 position in good to excellent yields. Radical quenching, deuterium labeling, KIE, and reaction order determination experiments were performed to support the proposed reaction pathway. Gram-scale synthesis and post-transformation of the synthesized products have also been carried out to demonstrate the applicability of the developed catalytic protocol.

Visible-light-driven synthesis of alkenyl thiocyanates: novel building blocks for assembly of diverse sulfur-containing molecules

The first visible-light-induced protocol for the general preparation of alkenyl thiocyanates from alkenyl bromides is presented. The reaction is simple, proceeds under very mild conditions and demonstrates broad functional group tolerance. Additionally, a flow protocol was developed to enable efficient scale-up of alkenyl thiocyanate synthesis, further enhancing the practicality and value of the method. Importantly, these alkenyl thiocyanates serve as valuable building blocks for the construction of diverse families of sulfur-containing molecules through trifluoromethylations, cycloadditions, oxidations, and C-S or P-S bond forming reactions.

Facile Synthesis of β-trifluoromethyl thioethers via DBN-catalyzed Hydrothiolation of α-(Trifluoromethyl)styrenes with Thiols

A very simple and atom-economical method for the synthesis of vicinal trifluoromethyl thioethers via DBN-catalyzed hydrothiolation of α-(trifluoromethyl)styrenes with thiols was reported. The reaction proceeded smoothly under mild reaction conditions and provided the β-CF3-thioethers in moderate to good yields in an anti-Markovnikov manner. Furthermore, this method features several remarkable advantages, such as the use of a catalytic amount of DBN, broad substrate scope, excellent functional group compatibility, and easy scalability.

Nickel-Catalyzed Cross-Coupling of Aziridines with Thioesters toward Atom-Economic Synthesis of β-Sulfanyl Amides

Thioesters have been recognized as a class of powerful bifunctional reagents, namely, great donors of acyl and sulfide moieties. However, such application in value-added synthesis is still very limited to date. Herein, a nickel-catalyzed cross-coupling reaction system of aziridines with thioesters was developed under redox-neutral and mild conditions. This catalytic method provides an atom-economic route for the synthesis of diverse β-sulfanyl amide derivatives with wide substrate scope (43 examples), good functional group tolerance, and regioselectivity.

Selenylated Analogs of Tacrine: Synthesis, In Silico and In Vitro Studies of Toxicology and Antioxidant Properties

We present our results on the synthesis and preliminary in silico and in vitro studies of the toxicology and antioxidant properties of selenylated analogs of Tacrine. Initially, we synthesized 2-aminobenzonitriles containing an organic selenium moiety, resulting in sixteen compounds with various substituents linked to the portion derived from diorganyl diselenide. These compounds were then used as substrates in reactions with cyclic ketones, in the presence of 1.4 equivalents of trifluoroboroetherate as a Lewis acid, to synthesize selenylated analogs of Tacrine with yields ranging from 20 % to 87 %. In silico studies explored computational parameters related to antioxidant activity and hepatotoxicity. In vitro studies elucidated the antioxidant effects of Tacrine and its selenium hybrid (TSe) in neutralizing ABTS radicals, scavenging DPPH radicals, and reducing iron ions. Additionally, the acute oral toxicity of one synthesized compound was evaluated.

Precision Propargylic Substitution Reaction: Pd-Catalyzed Suzuki-Miyaura Coupling of Nonactivated Propargylamines with Boronic Acids

Palladium-catalyzed Suzuki-Miyaura cross-coupling is an efficient approach for C-C bond construction. Here we report a deaminative Suzuki-Miyaura reaction to achieve chemo- and regioselectivity in the cross-coupling of nonactivated propargylamines with boronic acids, in which methyl propiolate is introduced to promote the cleavage of the C-N bond to form the C-C bond. This method features a wide range of substrates, good functional group tolerance, and ease of operation, providing an alternative approach to accessing valuable propargylated aromatic compounds.

Hydrazone-Linked Donor-Acceptor Covalent Organic Polymer as a Heterogeneous Photocatalyst for C-S Bond Formation

In the realm of solar energy utilization, there is a growing focus on designing and implementing effective photocatalytic systems, for the conversion of solar energy into valuable chemical fuels. The potential of Covalent Organic Polymers (COPs) as photocatalysts for visible-light-driven organic transformation has been widely investigated, positioning them as promising candidates in this field. In the design of COPs, introducing a donor-acceptor arrangement facilitates the transfer of electrons from the donor to the acceptor, creating a charge transfer complex and leading to enhanced conductivity and improved charge separation. Here we present a novel hydrazone-linked covalent organic polymer ETBC-PyHz containing TPE donor and pyridine acceptor. Utilizing this, an efficient method has been developed for an oxidative cross-coupling reaction involving C-S bond formation. This process involves arylhydrazines and arenethiols, and results in the production of unsymmetrical diaryl sulfides via the formation of aryl and thioarene radicals. This conversion holds significant importance because the byproducts produced during the process are nitrogen and water, making it environmentally benign.

Cobalt-catalyzed hydrothiolation of alkynes for the diverse synthesis of branched alkenyl sulfides

Alkenyl sulfides have gained increasing prominence in medicinal chemistry and materials. Hydrothiolation of alkynes for the diverse synthesis of alkenyl sulfides is an appealing method. Herein, we report a cobalt-catalyzed Markovnikov hydromethylthiolation of alkynes to afford branched alkenyl methylsulfanes with good yields and high regioselectivity. This method also enables the diverse synthesis of branched alkenyl sulfides. The reaction shows good functional group tolerance and could be scaled up. The mechanistic studies including control experiments, deuterium-labeling experiments, and Hammett plot indicated alkynes insertion followed by electrophilic thiolation pathway.

Enantioselective Arylation of Sulfenamides to Access Sulfilimines Enabled by Palladium Catalysis

Sulfur-containing functional groups have garnered considerable attention due to their common occurrence in ligands, pharmaceuticals, and insecticides. Nevertheless, enantioselective synthesis of sulfilimines, particularly diaryl sulfilimines remains a challenging and persistent goal. Herein we report a highly enantio- and chemoselective cross-coupling of sulfenamides with aryl diazonium salt to construct diverse S(IV) stereocenters by Pd catalysis. Bisphosphine ligands bearing sulfinamide groups play a crucial role in achieving high reactivity and selectivity. This approach provides a general, modular and divergent framework for quickly synthesizing chiral sulfilimines and sulfoximines that are otherwise challenging to access. In addition, the origins of the high chemoselectivity and enantioselectivity were extensively investigated using density functional theory calculations.

Access to Valuable Chalcogen-Containing Biaryl Derivatives via Regioselective 2,2'-Dichalcogenation of 2-Bromobiaryls

The regioselective installation of chalcogen atoms into biaryl scaffolds is an important synthetic task due to the great value of chalcogen-containing biaryl derivatives in many fields. Here we undertake this task by developing a regioselective 2,2'-dichalcogenation of 2-bromobiaryls with common chalcogen sources using an organolanthanum-mediated one-pot, two-step protocol. This strategy features high regioselectivity, readily available substrates, transition-metal-free conditions, and performance superior to those of previous methods, thereby demonstrating the unique advantages of organolanthanum reagents in organic synthesis.

Asymmetric Synthesis and Applications of Chiral Organoselenium Compounds: A Review

The synthesis and application of organoselenium compounds have developed rapidly, and chiral organoselenium compounds have become an important intermediate in the field of medicine, materials, organic synthesis. The strategy of developing a green economy is still a challenge in the synthesis of chiral organoselenium compounds with enantioselective properties. This review covers in detail the synthesis of chiral organoselenium compounds from 1979 to 2024 and their application in the fields of asymmetric synthesis and catalysis.

Benzisoselenazoles as Selenophenolate Anion Surrogates for the Formation of Carbon-Selenium Bonds via the Selena-Kemp Reaction

The in situ base-promoted generation of unstable selenophenolate anions from 1,2-benzisoselenazoles via a variant of the Kemp elimination has been developed. 2-Cyano-substituted selenophenolate anions obtained by this methodology were engaged in nucleophilic substitution, aromatic nucleophilic substitution, and Pd-catalyzed cross-coupling reactions to give functionalized arylalkyl and diaryl selenides in moderate to excellent yields.

Synthesis of Halogenated Dibenzo[1,2,6]triazonines and Late-Stage Functionalization of the Triazonine Ring

Dibenzotriazonine represent a new class of nine-membered cyclic azobenzenes with a nitrogen atom embedded in the bridging chain. To enable future applications of this photoactive backbone, we propose in this study the synthesis of mono- and dihalogenated triazonines, that allow the late-stage introduction of different functionalized aryl groups and heteroatoms (N, O, and P) via palladium-catalyzed reactions. Indeed, different diphenylphosphoryl-triazonines were synthesized with functional groups such as aniline or phenol. Bis(diphenylphosphoryl)phenyl mono- and bis-carbamate-triazonines were also isolated in good yields.

Zinc Promoted Cross-Electrophile Sulfonylation to Access Alkyl-Alkyl Sulfones

The transition metal-catalyzed multi-component cross-electrophile sulfonylation, which incorporates SO2 as a linker within organic frameworks, has proven to be a powerful, efficient, and cost-effective means of synthesizing challenging alkyl-alkyl sulfones. Transition metal catalysts play a crucial role in this method by transferring electrons from reductants to electrophilic organohalides, thereby causing undesirable side reactions such as homocoupling, protodehalogenation, β-hydride elimination, etc. It is worth noting that tertiary alkyl halides have rarely been demonstrated to be compatible with current methods owing to various undesired side reactions. In this work, a zinc-promoted cross-electrophile sulfonylation is developed through a radical-polar crossover pathway. This approach enables the synthesis of various alkyl-alkyl sulfones, including 1°-1°, 2°-1°, 3°-1°, 2°-2°, and 3°-2° types, from inexpensive and readily available alkyl halides. Various functional groups are well tolerated in the work, resulting in yields of up to 93%. Additionally, this protocol has been successfully applied to intramolecular sulfonylation and homo-sulfonylation reactions. The insights gained from this work shall be useful for the further development of cross-electrophile sulfonylation to access alkyl-alkyl sulfones.

Expedient, regioselective C-H chalcogenation of 3,4-dihydro-1,4-benzoxazines using a palladium-copper catalyst

The palladium-catalysed regioselective C-H chalcogenation of benzoxazines with disulfides and diselenides in air has been described. In this protocol, palladium acetate serves as the catalyst in conjunction with copper as an oxidizing agent. Through this approach, a wide array of sulfenylation and selenylation reactions of benzomorpholines have been effected, yielding results ranging from good to excellent. Thus, the established procedure demonstrates superb regioselectivity and a strong tolerance towards various functional groups and is suitable for gram-scale synthesis. Additionally, this synthetic approach offers a practical and convenient pathway for late-stage functionalization leading to the Rosenmund-von Braun reaction.

Bismuth(III)-Catalyzed Regioselective Selenation of Indoles with Diaryl Diselenides: Synthesis of 3-Selanylindoles

Heterocyclic aryl selenides have recently attracted considerable research interest owing to their applications in biological and pharmaceutical fields. Herein, we describe a simple and general synthesis of 3-selanylindoles via a novel regioselective C-H selenation of indoles using a bismuth reagent as a catalyst. The reactions of indoles with diselenides in the presence of 10 mol% BiI3 at 100 °C in DMF afforded the corresponding 3-selanylindoles in moderate-to-excellent yields. The reaction proceeded efficiently under aerobic conditions by adding only a catalytic amount of BiI3, which was non-hygroscopic and less toxic, and both selanyl groups of the diselenide were transferred to the desired products.

Visible-Light-Promoted Thiolation of Benzyl Chlorides with Thiosulfonates via a Photoactive Electron Donor-Acceptor Complex

Visible-light-promoted thiolation of benzyl chlorides with thiosulfonates is disclosed via an electron donor-acceptor complex strategy. In addition to efficiently delivering a series of arylbenzylsulfide compounds, versatile thioglycosides were also successfully constructed by applying the metal- and photocatalyst-free protocol. Preliminary mechanistic studies suggest that a radical-radical coupling process was involved in this transformation.

Nucleophilic Aromatic Substitution of Heteroaryl Halides with Thiols

The nucleophilic aromatic substitution (SNAr) between heteroaryl halides (Cl, Br) and thiols proceeds smoothly in DMAc under the action of K2CO3 at rt-100 °C. For most electron-deficient heteroarenes, reaction takes place without introducing an additional electron-withdrawing group. For electron-rich heteroarenes, an additional electron-withdrawing group such as a simple ester, keto, cyano, and nitro group is required to ensure the reaction completes. The reactivity trend of heteroaryl halides is highly dependent on the electronic nature of the heteroarenes and orientation of halogens. Besides thiols, a couple of functionalized thioureas and thioamides are compatible with these conditions, providing the corresponding heteroaryl thioethers in good yields.

A suitably fabricated ternary nanocomposite (Cu-CuO@rGO-SiO2) as a sustainable and common heterogeneous catalyst for C-S, C-O and C-N coupling reactions

A hybrid composite based on π-electron rich reduced graphene oxide (rGO) and mesoporous silica (SiO2) was prepared and decorated with copper species to afford a ternary nanocomposite material (Cu-CuO@rGO-SiO2). This copper-based nanocomposite was successfully used as a robust and multi-tasking heterogeneous catalyst for most common cross-coupling reactions (e.g. C-S, C-O and C-N coupling). A broad range of catalytic activities are believed to be originated from the synergism of different co-existing copper species (Cu(0) and CuO) and facile charge transfer from the metal ions towards rGO-SiO2 matrices, as established from XPS and other studies.

t-BuOLi promoted regioselective N-thiolation of indoles with N-arylthio phthalimide

The selective N-thiolation of indole substrates poses a challenge due to their diminished nucleophilicity at nitrogen. Herein, we present a novel method for the thiolation of the NH group in indole derivatives by using N-arylthio phthalimide as the sulfur source, t-BuOLi as the base and MeCN as the solvent. The process was successfully conducted under transition metal catalyst-free and room temperature conditions with a high product yield and a short reaction time. The developed protocol exhibited excellent regioselectivity and broad substrate tolerance in the preparation of N-thioindoles with diverse functional groups.

Generation and Application of Aryl Radicals Under Photoinduced Conditions

Photoinduced aryl radical generation is a powerful strategy in organic synthesis that facilitates the formation of diverse carbon-carbon and carbon-heteroatom bonds. The synthetic applications of photoinduced aryl radical formation in the synthesis of complex organic compounds, including natural products, physiologically significant molecules, and functional materials, have received immense attention. An overview of current developments in photoinduced aryl radical production methods and their uses in organic synthesis is given in this article. A generalized idea of how to choose the reagents and approach for the generation of aryl radicals is described, along with photoinduced techniques and associated mechanistic insights. Overall, this article offers a critical assessment of the mechanistic results as well as the selection of reaction parameters for specific reagents in the context of radical cascades, cross-coupling reactions, aryl radical functionalization, and selective C-H functionalization of aryl substrates.

Aminoselenation and Dehydroaromatization of Cyclohexanones with Anilines and Diselenides

A three-component cascade reaction involving cyclohexanones, anilines, and diaryl diselenides under metal-free conditions is reported. The ortho-selenation of cyclohexanones with diaryl diselenides, followed by sequential dehydroaromatization with anilines, enables the preparation of a variety of o-selanyl anilines in moderate to excellent yields. This innovative transformation is notable for its excellent tolerance of functional groups and is suitable for the late-stage modification of complex pharmaceuticals.

Efficient synthesis of SCF3-containing 3-alkenylquinoxalinones via three-component radical cascade reaction

An efficient and practical method for the synthesis of 3-alkenylquinoxalinones containing the SCF3 group has been readily developed through a three-component radical cascade reaction involving quinoxalinones, alkynes and AgSCF3. The reaction was found to be compatible with a variety of substrates and exhibited a high functional group tolerance and complete E-selectivity. The preliminary study suggests the involvement of a SCF3 radical in the transformation.

Micropores in Hollow Organic Cage Nanocapsule as a Size Exclusion Gate: Cage Entrapped Pd(II)-Catalyst for Efficient Cross-Coupling Reaction

Hollow porous organic capsules (HPOCs) with an entrapped active catalyst have nanosized cavities, providing the benefits of a nanoreactor, as well as separation of the catalysts from the reaction medium via pores acting as a size-exclusion gate. Such purpose-built HPOCs with desired molecular weight cutoffs offer the advantages of semipermeable membrane separation and a sustainable chemical process that excludes energy-extensive separation. Here, we report a newly synthesized HPOC with an entrapped Pd(PPh3)2Cl2 as the catalyst for demonstrating a Suzuki-Miyaura coupling reaction as a proof of concept.

Sulfur in Waste-Free Sustainable Synthesis: Advancing Carbon-Carbon Coupling Techniques

This review explores the pivotal role of sulfur in advancing sustainable carbon-carbon (C-C) coupling reactions. The unique electronic properties of sulfur, as a soft Lewis base with significant mesomeric effect make it an excellent candidate for initiating radical transformations, directing C-H-activation, and facilitating cycloaddition and C-S bond dissociation reactions. These attributes are crucial for developing waste-free methodologies in green chemistry. Our mini-review is focused on existing sulfur-directed C-C coupling techniques, emphasizing their sustainability and comparing state-of-the-art methods with traditional approaches. The review highlights the importance of this research in addressing current challenges in organic synthesis and catalysis. The innovative use of sulfur in photocatalytic, electrochemical and metal-catalyzed processes not only exemplifies significant advancements in the field but also opens new avenues for environmentally friendly chemical processes. By focusing on atom economy and waste minimization, the analysis provides broad appeal and potential for future developments in sustainable organic chemistry.