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.

Regioselective 1,4-/1,3-Difunctionalization of 1,3-Enynes with Selenosulfonates in Water

1,4-/1,3-Regioselective bifunctionalization of 1,3-enynes with selenosulfonates in water under catalyst-free conditions for the construction of sulfonyl allene and 1,3-disulfonyl-conjugated dienes respectively have been developed. The reactions feature mild reaction conditions in aqueous solution and remarkable regioselectivity controlled by substrates.

BF3·Et2O-assisted synthesis of sulfinylated spiro[5.5]trienones from biaryl ynones

Sulfinyls are valuable structural moieties used for developing synthetically new pharmaceuticals and agrochemicals. Herein, we disclose a straightforward synthesis of sulfinylated spiro[5.5]trienones proceeding via an unprecedented BF3·Et2O-promoted spirocyclization of biaryl ynones. The availability of relatively inexpensive BF3·Et2O to carry out transformations on a bulk scale along with its further application towards the synthesis of dibenzocyclohepten-5-ones delivers a unique opportunity to deploy it in various synthetic directions.

Iron-catalyzed benzylic C-H thiolation via photoinduced ligand-to-metal charge-transfer

Here, we describe an iron-catalyzed benzylic C-H thiolation of alkylarenes via photoinduced ligand-to-metal charge-transfer. The protocol features operational simplicity, mild reaction conditions, and the use of FeCl3 as catalyst and thiols/disulfides as sulfur sources, which enables the transformation of diverse benzylic C-H bonds into C-S bonds with a high efficiency.

Synthesis of (Furyl)Methyl Disulfides via Tandem Reaction of Conjugated Ene-Yne-Ketones with Acetyl-Masked Disulfide Nucleophiles

In this study, we outline a general method for the construction of various (furyl)methyl disulfides from acetyl-masked disulfide nucleophiles and ene-yne-ketones. This protocol is feathered by metal-free, simple experimental conditions, high efficiency, and scalable potential, which make it attractive and practical.

Visible-Light-Promoted Cascade Coupling of 2-Isocyanonaphthalenes with Elemental Sulfur and Amines to Construct Naphtho[2,1-d]thiazol-2-Amines

A visible-light-induced strategy has been explored for the synthesis of naphtho[2,1-d]thiazol-2-amines through ortho-C-H sulfuration of 2-isocyanonaphthalenes with elemental sulfur and amines under external photocatalyst-free conditions. This three-component reaction, which utilizes elemental sulfur as the odorless sulfur source, molecular oxygen as the clean oxidant, and visible light as the clean energy source, provides a mild and efficient approach to construct a series of naphtho[2,1-d]thiazol-2-amines. Preliminary mechanistic studies indicated that visible-light-promoted photoexcitation of reaction intermediates consisting of thioureas and DBU might be involved in this transformation.

C-H arylation of thiopyran derivatives with aryl halides

A C-H arylation of thiopyran derivatives with aryl halides has been developed. Under the catalysis of Pd(OAc)2/Ag2CO3, the C-H arylation takes place at the α-position of the thiopyran ring. When dibromo-substituted compounds are used as reactants, double C-H arylations may occur on the same thiopyran ring at its α- and β-positions.

Copper-Catalyzed Chemoselective Coupling of N-Dithiophthalimides and Alkyl Halides: Synthesis of Unsymmetrical Disulfides and Sulfides

In this paper, we report an unprecedented copper-catalyzed disulfides or sulfides coupling reaction involving unactivated alkyl halides and N-dithiophthalimides. This reaction can be conducted under mild conditions using low-cost metal catalysts and exhibits high chemical selectivity and functional group compatibility, enabling the efficient assembly of various sulfides and disulfides.

Direct C-H Sulfuration: Synthesis of Disulfides, Dithiocarbamates, Xanthates, Thiocarbamates and Thiocarbonates

In light of the important biological activities and widespread applications of organic disulfides, dithiocarbamates, xanthates, thiocarbamates and thiocarbonates, the continual persuit of efficient methods for their synthesis remains crucial. Traditionally, the preparation of such compounds heavily relied on intricate multi-step syntheses and the use of highly prefunctionalized starting materials. Over the past two decades, the direct sulfuration of C-H bonds has evolved into a straightforward, atom- and step-economical method for the preparation of organosulfur compounds. This review aims to provide an up-to-date discussion on direct C-H disulfuration, dithiocarbamation, xanthylation, thiocarbamation and thiocarbonation, with a special focus on describing scopes and mechanistic aspects. Moreover, the synthetic limitations and applications of some of these methodologies, along with the key unsolved challenges to be addressed in the future are also discussed. The majority of examples covered in this review are accomplished via metal-free, photochemical or electrochemical approaches, which are in alignment with the overraching objectives of green and sustainable chemistry. This comprehensive review aims to consolidate recent advancements, providing valuable insights into the dynamic landscape of efficient and sustainable synthetic strategies for these crucial classes of organosulfur compounds.

The Chan-Lam-type synthesis of thioimidazolium salts for thiol-(hetero)arene conjugation

The design of stable and variable aryl linkers for conjugating drug moieties to the metabolism-related thiols is of importance in drug discovery. We disclosed that thioimidazolium groups are unique scaffolds for the thiol-(hetero)arene conjugation under mild conditions. The drug bound thioimidazolium salts, which are easily accessible via a copper-mediated Chan-Lam process in gram-scale, could be successfully applied to the late-stage coupling of bioactive thiols to construct a broad array of drug-like molecules.

Electrochemical selective divergent C-H chalcogenocyanation of N-heterocyclic scaffolds

An electrochemical direct selective C-H chalcogenocyanation approach for indolizine derivatives under mild conditions has been described. Cyclic enone-fused, chromone-fused and 2-substituted indolizines possessing EDGs (electron donating groups) and EWGs (electron withdrawing groups) were successfully reacted with NH4SCN and KSeCN under electrochemical conditions to provide a wide array of mono and bis-chalcogenocyanate-indolizines in 75-94% yields. In addition, 1-substituted imidazo[1,5-a]quinolines were also successfully chalcogenocyanated under the optimized reaction conditions providing a platform for the synthesis of pharmaceutically privileged molecules. By switching the reaction conditions, the developed protocol offers selective synthesis of C-3 thiocyanate and 1,3 bis-thiocyanate indolizines in good to excellent yields under catalyst-free conditions. On the basis of control experiments and cyclic voltammetry data, a plausible reaction pathway is also presented.

Visible-Light-Induced Radical Sulfonylative-Cyclization Cascade of 1,6-Enynol Derivatives with Sulfinic Acids: A Sustainable Approach for the Synthesis of 2,3-Disubstituted Benzoheteroles

Benzoheteroles are promising structural scaffolds in the realm of medicinal chemistry, but sustainable synthesis of 2,3-difunctionalized benzoheterole derivatives is still in high demand. Indeed, we have conceptually rationalized the intrinsic reactivity of propargylic-enyne systems for the flexible construction of 2,3-disubstituted benzoheteroles through radical sulfonylative-cyclization cascade under organophotoredox catalysis. We hereby report an efficient visible-light-induced sulfonyl radical-triggered cyclization of 1,6-enynols with sulfinic acids under the dual catalytic influence of 4CzIPN and NiBr2⋅DME, which led to the formation of 2,3-disubstituted benzoheteroles in good to high yields. Additionally, the Rose Bengal (RB)-catalyzed radical sulfonylative-cycloannulation of acetyl-derived 1,6-enynols with sulfinic acids under blue LED irradiation allowed to access 3-(E-styryl)-derived benzofurans and benzothiophenes in moderate to good yields. The scope and limitations of the present strategies were successfully established using different classes of 1,6-enynols and sulfinic acids bearing various sensitive functional groups, yielding the desired products in a highly stereoselective fashion. Plausible mechanistic pathways were also proposed based on the current experimental and control experiments.

Lead-free Cs2AgBiBr6 double perovskite microcrystals for effective visible-light photocatalytic thio/selenocyanation

Lead-free perovskite microcrystals (MCs) have been regarded as promising potential photocatalysts, owing to their high molar extinction coefficient, low economic cost, adjustable light absorption range, and ample surface-active sites. Herein, C-3 thio/selenocyanation of indoles is demonstrated in high selectivity and yield by using lead-free double perovskite Cs2AgBiBr6 MCs under visible light irradiation. Moreover, the photocatalyst can be recycled at least 5 times without a significant decrease in catalytic activity.

Catalyst-Free Synthesis of Thiosulfonates and 3-Sulfenylindoles from Sodium Sulfinates in Water

This paper presents a green and efficient aqueous-phase method for the synthesis of thiosulfonates, which has the benefits of no need for catalysts or redox reagents and a short reaction time, providing a method with great economic value for synthesizing thiosulfonates. Furthermore, 3-Sulfenylindoles can be easily synthesized using this method, which expands the potential applications of this reaction.

Modulating the Catalytic Properties of Polyoxovanadates with Transition-Metal-Complex Units for Selective Oxidation of Sulfides

Selective oxidation of sulfides to sulfoxides is of great significance in the synthesis of pharmaceuticals, desulfurization of fuels, and detoxification of sulfur mustard chemical warfare agents. Designing selective catalysts to achieve the efficient transformation of sulfides to sulfoxides is thus highly desired. Herein, we report three transition metal-complex-functionalized polyoxovanadates, [Zn2(BPB)2][V4O12]·0.5BPB·H2O (1), [Ni(BPB)(H2O)][V2O6]·2H2O (2), and [Co(HBPB)2][V4O12] (3) (BPB = 1,4-bis(pyrid-4-yl)benzene)), and explore their applications for selective oxidation of sulfides using H2O2 as an oxidant. All three compounds were catalytically effective for the oxidation of methyl phenyl sulfide to methyl phenyl sulfoxide, with 1 being best-performing with complete conversion and a selectivity of 96.7%. In the selective oxidation of a series of aromatic and aliphatic sulfides to corresponding sulfoxides, 1 also showed satisfactory performance; in particular, the chemical warfare agent stimulant 2-chloroethyl ethyl sulfide can be completely and selectively oxidized to the nontoxic 2-chloroethyl ethyl sulfoxide within 20 min at room temperature. Catalyst 1 can be recycled and reused at least six times with uncompromised performance. The perfect performance of 1 is attributed to the synergistic effect of coordinatively unsaturated V and Zn sites in bimetallic oxide, as revealed by comparative structural and catalytic studies.

Photodriven Radical Perfluoroalkylation-Thiolation of Unactivated Alkenes Enabled by Electron Donor-Acceptor Complex

A clean and direct three-component radical 1,2-difunctionalization of various alkenes with perfluoroalkyl iodides and thiosulfonates enabled by the electron donor-acceptor complex has been developed under light illumination at room temperature. The approach offers a convenient and environmentally friendly route for the simultaneous incorporation of Csp3-Rf and Csp3-S bonds, affording valuable polyfunctionalized alkane derivatives containing fluorine and sulfur in satisfactory yields. Consequently, this methodology holds significant value and practicality in the field of organic synthesis.

Exploring Tunable Properties, Solvent-Modulated Dynamics, and Novel C(sp3)-H Activation Mechanisms in Electron Donor-Acceptor Complexes

Electron donor-acceptor (EDA) complex photochemistry has emerged as a vibrant area in visible-light-mediated synthetic radical chemistry. However, theoretical insights into the reaction mechanisms remain limited. Our study investigates the influence of solvent polarity and halogen atom types on radical reaction pathways in EDA complexes. We demonstrate that solvent polarity modulates the charge transfer and spatial arrangement within EDA complexes, thereby influencing their stability and reaction kinetics. Iodide ions play a crucial role in facilitating free radical generation and stabilizing reaction intermediates. Different halogen atom types exhibit distinct effects on radical reactions. Variations in radical concentration and solvent environment further affect the pathway selectivity. Additionally, light conditions influence the free radical generation and pathway selectivity. Our findings enhance the understanding of EDA complex photochemistry and radical reactions, offering insights for organic synthesis and photochemistry applications.

Formation of Bridged Disulfide in Epidithiodioxopiperazines

Epidithiodioxopiperazine (ETP) alkaloids, featuring a 2,5-diketopiperazine core and transannular disulfide bridge, exhibit a broad spectrum of biological activities. However, the structural complexity has prevented efficient chemical synthesis and further clinical research. In the past few decades, many achievements have been made in the biosynthesis of ETPs. Here, we discuss the biosynthetic progress and summarize them as two comprehensible metabolic principles for better understanding the complex pathways of α, α'- and α, β'-disulfide bridged ETPs. Specifically, we systematically outline the catalytic machineries to install α, α'- and α, β'-disulfide by flavin-containing oxygenases. This concept would contribute to the medical and industrial applications of ETPs.

Chemoselective Heterogeneous Hydrogenation of Sulfur Containing Quinolines under Mild Conditions

Sulfur, alongside oxygen and nitrogen, holds a prominent position as one of the key heteroatoms in nature and medicinal chemistry. Its significance stems from its ability to adopt different oxidation states, rendering it valuable as both a polarity handle and a hydrogen bond donor/acceptor. Nevertheless, the poisonous nature of its free electron pairs makes sulfur containing substrates inaccessible for many catalytic protocols. Strong and (at low temperatures) irreversible chemisorption to the catalyst's surface is in particular detrimental for heterogeneous catalysts, possessing only few catalytically active sites. Herein, we present a novel heterogeneous Ru-S catalyst that tolerates multiple sulfur functionalities, including thioethers, thiophenes, sulfoxides, sulfones, sulfonamides, and sulfoximines, in the hydrogenation of quinolines. The utility of the products was further demonstrated by subsequent diversifications of the sulfur functionalities.

Multiscale Study on the Intramolecular C-S Bond Formation Catalyzed by P450 Monooxygenase CxnD Involved in the Biosynthesis of Chuangxinmycin: The Critical Roles of Noncrystal Water Molecule and Conformational Change

Cytochrome P450 monooxygenase CxnD catalyzes intramolecular C-S bond formation in the biosynthesis of chuangxinmycin, which is representative of the synthesis of sulfur-containing natural heterocyclic compounds. The intramolecular cyclization usually requires the activation of two reaction sites and a large conformational change; thus, illuminating its detailed reaction mechanism remains challengeable. Here, the reaction pathway of CxnD-catalyzed C-S bond formation was clarified by a series of calculations, including Gaussian accelerated molecular dynamics simulations and quantum mechanical-molecular mechanical calculations. Our results revealed that the C-S formation follows a diradical coupling mechanism. CxnD first employs Cpd I to abstract the hydrogen atom from the imino group of the indole ring, and then, the resulted Cpd II further extracts another hydrogen atom from the thiol group of the side chain to afford a diradical intermediate, in which a noncrystal water molecule entering into the active site after the formation of Cpd I was proved to play an indispensable role. Moreover, the diradical intermediate cannot directly perform the coupling reaction. It should first undergo a series of conformational changes leading to the proximity of two reaction sites. It is the flexibility of the active site of the enzyme and the side chain of the substrate that makes the diradical coupling to be successful.

4-Fluoro-benzyl (Z)-2-(2-oxoindolin-3-yl-idene)hydrazine-1-carbodi-thio-ate

The title compound, C16H12FN3OS, a fluorinated di-thio-carbazate imine derivative, was synthesized by the one-pot, multi-component condensation reaction of hydrazine hydrate, carbon di-sulfide, 4-fluoro-benzyl chloride and isatin. The compound demonstrates near-planarity across much of the mol-ecule in the solid state and a Z configuration for the azomethine C=N bond. The Z form is further stabilized by the presence of an intra-molecular N-H⋯O hydrogen bond. In the extended structure, mol-ecules are linked into dimers by N-H⋯O hydrogen bonds and further connected into chains along either [20] or [100] by weak C-H⋯S and C-H⋯F hydrogen bonds, which further link into corrugated sheets and in combination form the overall three-dimensional network.

Transition-Metal-Free Disulfuration of Amides with Trisulfide Dioxides via Formation of Unaccessible S-S-N Bonds

Under transition-metal-free conditions, trisulfide dioxides were used as disulfurating reagents to react with a wide range of amides, affording various substituted N-disulfanyl amides in good yields. Furthermore, the gram-scale experiment has confirmed the practicability of this approach.

A general copper-catalysed enantioconvergent C(sp3)-S cross-coupling via biomimetic radical homolytic substitution

Although α-chiral C(sp3)-S bonds are of enormous importance in organic synthesis and related areas, the transition-metal-catalysed enantioselective C(sp3)-S bond construction still represents an underdeveloped domain probably due to the difficult heterolytic metal-sulfur bond cleavage and notorious catalyst-poisoning capability of sulfur nucleophiles. Here we demonstrate the use of chiral tridentate anionic ligands in combination with Cu(I) catalysts to enable a biomimetic enantioconvergent radical C(sp3)-S cross-coupling reaction of both racemic secondary and tertiary alkyl halides with highly transformable sulfur nucleophiles. This protocol not only exhibits a broad substrate scope with high enantioselectivity but also provides universal access to a range of useful α-chiral alkyl organosulfur compounds with different sulfur oxidation states, thus providing a complementary approach to known asymmetric C(sp3)-S bond formation methods. Mechanistic results support a biomimetic radical homolytic substitution pathway for the critical C(sp3)-S bond formation step.

Electrochemical desulfurative formation of C-N bonds through selective activation of inert C(sp3)-S bonds

In this study, we introduce an efficient, metal-free electrocatalytic desulfurative protocol for forming C-N bonds by selectively activating inert C(sp3)-S bonds of alkyl thioethers. This method offers a straightforward and environmentally friendly approach for modification of heterocyclic compounds from readily accessible thioethers. Preliminary mechanistic investigations suggest that the reaction proceeds via a carbocation intermediate. Furthermore, successful synthesis on a 10-gram scale was achieved in a continuous flow electrochemical reactor.

Construction of C-S and C-Se Bonds from Unstrained Ketone Precursors under Photoredox Catalysis

A mild photoredox catalyzed construction of sulfides, disulfides, selenides, sulfoxides and sulfones from unstrained ketone precursors is introduced. Combination of this deacylative process with SN 2 or coupling reactions provides novel and convenient modular strategies toward unsymmetrical or symmetric disulfides. Reactivity studies favor a bromine radical that initiates a HAT (Hydrogen Atom Transfer) from the aminal intermediate resulting in expulsion of a C-centered radical that is intercepted to make C-S and C-Se bonds. Gram scale reactions, broad substrate scope and tolerance towards various functional groups render this method appealing for future applications in the synthesis of organosulfur and selenium complexes.

Iron-catalyzed fluoroalkylative alkylsulfonylation of alkenes via radical-anion relay

Transition metal-catalyzed reductive difunctionalization of alkenes with alkyl halides is a powerful method for upgrading commodity chemicals into densely functionalized molecules. However, super stoichiometric amounts of metal reductant and the requirement of installing a directing group into alkenes to suppress the inherent β-H elimination bring great limitations to this type of reaction. We demonstrate herein that the difunctionalization of alkenes with two different alkyl halides is accessible via a radical-anion relay with Na2S2O4 as both reductant and sulfone-source. The Na2S2O4 together with the electron-shuttle catalyst is crucial to divert the mechanistic pathway toward the formation of alkyl sulfone anion instead of the previously reported alkylmetal intermediates. Mechanistic studies allow the identification of carbon-centered alkyl radical and sulfur-centered alkyl sulfone radical, which are in equilibrium via capture or extrusion of SO2 and could be converted to alkyl sulfone anion accelerated by iron electron-shuttle catalysis, leading to the observed high chemoselectivity.

KF-catalyzed direct thiomethylation of carboxylic acids with DMSO to access methyl thioesters

With dimethyl sulfoxide (DMSO) as the methylthio source, a KF-catalyzed strategy was employed for the direct thiomethylation of carboxylic acids with DMSO for the preparation of methyl thioesters. In this process, a wide range of methyl thioesters were obtained in moderate to excellent yields. This novel strategy features the first use of DMSO as a methylthiolating agent for the construction of methyl thioesters, transition metal-free conditions, inexpensive reagents, easy workup, broad substrate scope and sustainability. Additionally, this procedure can be readily scaled up to a gram scale.

Enzymatic Resolution and Decarboxylative Functionalization of α-Sulfinyl Esters

α-Sulfinyl esters can be readily prepared through thiol substitution of α-bromo esters followed by oxidation to the sulfoxide. Enzymatic resolution with lipoprotein lipase provides both the unreacted esters and corresponding α-sulfinyl carboxylic acids in high yields and enantiomeric ratios. Subsequent decarboxylative halogenation, dihalogenation, trihalogenation and cross-coupling gives rise to functionalized sulfoxides. The method has been applied to the asymmetric synthesis of a potent inhibitor of 15-prostaglandin dehydrogenase.

Recent advances in selective mono-/dichalcogenation and exclusive dichalcogenation of C(sp2)-H and C(sp3)-H bonds

Organochalcogen compounds are prevalent in numerous natural products, pharmaceuticals, agrochemicals, polymers, biological molecules and synthetic intermediates. Direct chalcogenation of C-H bonds has evolved as a step- and atom-economical method for the synthesis of chalcogen-bearing compounds. Nevertheless, direct C-H chalcogenation severely lags behind C-C, C-N and C-O bond formations. Moreover, compared with the C-H monochalcogenation, reports of selective mono-/dichalcogenation and exclusive dichalcogenation of C-H bonds are relatively scarce. The past decade has witnessed significant advancements in selective mono-/dichalcogenation and exclusive dichalcogenation of various C(sp2)-H and C(sp3)-H bonds via transition-metal-catalyzed/mediated, photocatalytic, electrochemical or metal-free approaches. In light of the significance of both mono- and dichalcogen-containing compounds in various fields of chemical science and the critical issue of chemoselectivity in organic synthesis, the present review systematically summarizes the advances in these research fields, with a special focus on elucidating scopes and mechanistic aspects. Moreover, the synthetic limitations, applications of some of these processes, the current challenges and our own perspectives on these highly active research fields are also discussed. Based on the substrate types and C-H bonds being chalcogenated, the present review is organized into four sections: (1) transition-metal-catalyzed/mediated chelation-assisted selective C-H mono-/dichalcogenation or exclusive dichalcogenation of (hetero)arenes; (2) directing group-free selective C-H mono-/dichalcogenation or exclusive dichalcogenation of electron-rich (hetero)arenes; (3) C(sp3)-H dichalcogenation; (4) dichalcogenation of both C(sp2)-H and C(sp3)-H bonds. We believe the present review will serve as an invaluable resource for future innovations and drug discovery.

Electro-oxidative quinylation of sulfides to sulfur ylides in batch and continuous flow

An unprecedented strategy for preparing a series of sulfur ylides through electro-oxidative quinylation of sulfides in batch and continuous flow has been developed. Good to excellent yields were obtained with excellent functional group compatibility and good concentration tolerance under exogenous oxidant- and transition metal-free conditions. Advantageously, this electrosynthesis methodology was scalable with higher daily production and steady production was achieved attributing to the use of micro-flow cells.

Synergistic Photoredox and Iron Catalyzed 1,2-Thiosulfonylation of Alkenes with Thiophenols and Sulfonyl Chlorides

Herein, a three-component 1,2-thiosulfonylation of alkenes with thiophenols and sulfonyl chlorides via synergistic photoredox and iron catalysis is described. Compared with previous studies, this protocol avoids tedious pre-synthesis of thiosulfonates and employs more readily accessible sulfonyl chlorides as a sulfonation reagent. Moreover, the reaction exhibits high compatibility with styrenes and unactivated alkenes as well as diverse sulfonyl chlorides, especially sulfamoyl chlorides. Preliminary mechanism investigations reveal that a radical pathway is involved in the catalytic cycle.

Unexpected Noremestrin with a Sulfur-Bearing 15-Membered Macrocyclic Lactone from Emericella sp. 1454

Two previous unreported epipolythiodioxopiperazines of the emestrin family, namely, noremestrin A (1) and secoemestrin E (2), were successfully isolated from the fungal source Emericella sp. 1454. Employing comprehensive spectroscopic techniques, such as high-resolution electrospray ionization mass spectrometry, infrared, and nuclear magnetic resonance (NMR), along with NMR and electronic circular dichroism calculations, the chemical structures of compounds 1 and 2 were elucidated. Particularly noteworthy is the distinctive nature of noremestrin A, representing the inaugural instance of a noremestrin variant incorporating a sulfur-bearing 15-membered macrocyclic lactone moiety. Compounds 1 and 2 exhibited weak cytotoxic activities against the human chronic myelocytic leukemia cell lines MEG-01 and K562.

Construction of β-Acetoxy or β-Hydroxyl Disulfides via Highly Regioselective Ring-Opening of Epoxides with Acetyl Masked Disulfide Nucleophiles

In the organic or water phase, acetyl masked disulfide nucleophiles were used as the disulfide source to react with a wide range of epoxides, affording various β-acetoxy or β-hydroxyl disulfides in good yields with high regioselectivity. This method features transition-metal-free, simple experimental conditions, high atom economy, and scalable potential, which make it attractive and practical.

Visible-Light-Mediated Annulation/Thiolation of 2-Isocyanobiaryls with Disulfides to Organoylthiophenanthridines Derivatives

A visible-light-induced annulation/thiolation of 2-isocyanobiaryls with dialkyl(aryl)disulfides has been established, delivering a sustainable and atom-economic route to 6-organoylthiophenanthridines with wild functional group tolerance and good to excellent yields under oxidant-, base-, and transition-metal-free conditions.

Base-Induced Decarboxylative 1,1-Alkoxy Thiolation via Hydrothiolation of Vinylene Carbonate

A base-mediated 1,1-difunctionalization of vinylene carbonate has been achieved using two different nucleophiles, namely, thiol and alcohol, with the assistance of air (O2). In alcoholic solvents, decarboxylation occurs at room temperature to provide a 1,1-difunctionalized product, where vinylene carbonate serves as an ethynol (C2) synthon in this three-component reaction. On the other hand, in acetonitrile, exclusive hydrothiolation occurs under the basic conditions at room temperature. This method offers a one-pot decarboxylative regioselective difunctionalization of vinylene carbonate at room temperature for the construction of α-alkoxy-β-hydroxy sulfide.

Photocatalytic C(sp3)-H thiolation by a double SH2 strategy using thiosulfonates

Site-selective C(sp3)-H thiolation using thiosulfonates has been achieved using the decatungstate anion as a photocatalyst. Using the protocol, a variety of thiolated compounds were synthesized in good yields. The transformation consists of a cascade of double SH2 reactions, HAT and ArS group transfer, and PCET (proton-coupled electron transfer) of the leaving arylsulfonyl radical to arylsulfinic acid thus allowing the catalyst, W10O324-, to be recovered.

Glyoxylic Acid Monohydrate-Promoted Formation of the C-SO2 Bond Starting from Maleimides/Quinones and Sodium Sulfinates

By using glyoxylic acid monohydrate as a promoter, a wide range of substances containing a C-SO2 bond could be obtained from N-substituted maleimides or quinones and sodium sulfinates. The protocol features mild reaction conditions, short reaction time, and good atomic economics, which provides an alternative protocol for the α-sulfonylation of α,β-unsaturated ketones.

Photocatalytic Phosphine-Mediated Thioesterification of Carboxylic Acids with Disulfides

Herein, a practical and effective synthesis of thioesters from readily available carboxylic acids and odorless disulfides was developed under photocatalytic conditions. This approach involves phosphoranyl radical-mediated fragmentation to generate acyl radicals and allows for incorporation of both S atoms of the disulfides into the desired products. In addition to batch reactions, a continuous-flow reactor was employed, enabling rapid thioester synthesis on a gram scale. Preliminary experimental mechanistic studies and the rapid synthesis of dalcetrapib are also demonstrated.

Copper-promoted S-arylation reactions with triarylbismuths for the synthesis of diaryl sulfides

A simple approach for copper-promoted S-arylation reactions utilizing triarylbismuths or triarylantimonys as arylating reagents has been described. These reactions can be performed under mild conditions and exhibit remarkable functional group tolerance and chemoselectivity. The corresponding 2-arylthiopyridine 1-oxide derivatives and arylthioanilines/phenols have been successfully synthesized, achieving good to excellent yields across over 49 examples.

syn-Selective Difunctionalization of Bicyclobutanes Enabled by Photoredox-Mediated C-S σ-Bond Scission

Given the importance of cyclic frameworks in molecular scaffolds and drug discovery, it is intriguing to precisely forge and manipulate ring systems in synthetic chemistry. In this field, the intermolecular synthesis of densely substituted cyclobutanes with precise diastereocontrol under simple reaction conditions remains a challenge. Herein, a photoredox strategy for the difunctionalization of bicyclo[1.1.0]butanes (BCBs) under high regio- and syn-selectivity is disclosed. C-S σ-bond cleavage of partially unsaturated sulfur-containing bifunctional reagents in an overall strain-release-driven process enables the thio-alkynylation, -alkenylation, and -allylation of BCBs under mild conditions and demonstrates the generality of this protocol. Mechanistic studies suggest that the intermediacy of cyclic distonic radical cations might be key for the efficient scission of C-S σ-bonds and the origin of diastereoselectivity.

Comprehensive genomic and metabolomic analysis revealed the physiological characteristics and pickle like odor compounds metabolic pathways of Bacillus amyloliquefaciens ZZ7 isolated from fermented grains of Maotai-flavor baijiu

Pickle like odor (PLO) is one of the main defective flavors of Maotai flavor baijiu (MFB). Understanding and controlling the PLO compounds producing strains not only solves the problem of PLO from the source, but also ensures the high-quality production of MFB. However, the relevant research on PLO compounds producing strains has not been reported in MFB. In this study, we identified a Bacillus amyloliquefaciens ZZ7 with high yield of PLO compounds in the fermented grains of MFB, and measured its physiological characteristics. It produces 627 volatile compounds and 1,507 non-volatile compounds. There are 7 volatile sulfur compounds that cause the PLO, the content of dimethyl disulfide, dimethyl trisulfide, and dimethyl sulfur is relatively high, accounting for 89.43% of the total volatile sulfur compounds. The genome size of B. amyloliquefaciens ZZ7 is 3,902,720 bp with a GC content of 46.09%, and a total of 3,948 protein coding genes were predicted. Moreover, the functional annotation of coding genes and an assessment of the metabolic pathways were performed by genome annotation, showing it has strong ability to transport and metabolize amino acids and carbohydrates. Comprehensive genomic and metabolomic analysis, the metabolic pathway of PLO compounds of B. amyloliquefaciens ZZ7 was revealed, which mainly involves 12 enzymes including sulfate adenylyltransferase, cysteine synthase, cystathionine γ-synthase, etc. This work provides biological information support at both genetic and metabolic levels for the mechanism of B. amyloliquefaciens ZZ7 to synthesize PLO compounds, and provides a direction for the subsequent genetic modification of ZZ7 to solve PLO from the source in the MFB.

Visible Light-Accelerated Palladium-Catalyzed Thiocarbonylation Using Oxalic Acid Monothioester with Aryl/Alkenyl Sulfonium Salts

Herein, we present a decarboxylative thiocarbonylation of aryl and alkenyl sulfonium salts with oxalic acid monothioethers (OAMs), which can be achieved by visible light-accelerated palladium catalysis. Sulfonium salts are widely available, and OAM is an easily accessible and stored reagent; this mild reaction method can also be used for the synthesis of different types of thioester compounds. The reaction represents a new application of visible light-accelerated palladium catalysis in catalytic decarboxylative cross-couplings.

Dimethyl Sulfoxide Provides Three Different Units in Synthesis of Chroman-4-ones Containing Sulfur and a Quaternary Carbon Center under HOAc Conditions

HOAc-promoted construction of chroman-4-ones with a sulfur atom and an α-carbonyl quaternary carbon center directly from ortho-hydroxyacetophenones and DMSO is described. In these unique reactions, DMSO is activated by HOAc and provides three different units (CH2, CH2OH, and CH2SMe) in the target molecules. This reaction displays good substrate scope and reaction yields with a series of substitutes. The mechanism showed that the three units were formed in sequential order.

1,2-Silyl Shift-Induced Heterocyclization of Propargyl Silanes: Synthesis of Five-Membered Heterocycles Containing a Functionalized Olefin Side Chain

Propargyl silanes with a terminal alkyne moiety undergo a 1,2-silyl shift when activated with electrophiles such as H+, Br+, I+, and PhSe+. A method was developed to trap 1,3-transposed electrophilic centers with various internal O-, N-, and S-nucleophiles in a 5-exo manner. This synthetic procedure provided five-membered heterocycles containing a trisubstituted olefin side chain. The scope of the method includes access to tetrahydrofuran, γ-butyrolactone, 2-isooxazoline, pyrrolidine, and thiolane derivatives in yields ranging from 25 to 85% (23 examples in total). Reactions with TsNBr2 ensured complete (E)-selectivity of the newly formed olefins. Further functionalization of the obtained 1-trialkylsilyl-2-bromovinyl side chain was demonstrated by double-bond geometry-preserving electrophilic substitution and cross-coupling reactions that provided heterocycles with a trisubstituted vinyl moiety.

How nature incorporates sulfur and selenium into bioactive natural products

Living organisms have evolved various strategies to incorporate sulfur and selenium into bioactive natural products. These chalcogen-containing compounds serve important and diverse biological functions for their producers and many of them are essential medicines against infectious diseases and cancer. We review recent advances in the biosynthesis of some sulfur/selenium-containing natural products with a focus on the formation or cleavage of C-S/C-Se bonds. We highlight unusual enzymes that catalyze these transformations, describe their proposed mechanisms, and discuss how understanding these enzymes may facilitate the discovery and synthesis of novel natural products containing sulfur or selenium.

Electroreductive Desulfurative Transformations with Thioethers as Alkyl Radical Precursors

Thioethers are highly prevalent functional groups in organic compounds of natural and synthetic origin but remain remarkably underexplored as starting materials in desulfurative transformations. As such, new synthetic methods are highly desirable to unlock the potential of the compound class. In this vein, electrochemistry is an ideal tool to enable new reactivity and selectivity under mild conditions. Herein, we demonstrate the efficient use of aryl alkyl thioethers as alkyl radical precursors in electroreductive transformations, along with mechanistic details. The transformations proceed with complete selectivity for C(sp3 )-S bond cleavage, orthogonal to that of established transition metal-catalyzed two-electron routes. We showcase a hydrodesulfurization protocol with broad functional group tolerance, the first example of desulfurative C(sp3 )-C(sp3 ) bond formation in Giese-type cross-coupling and the first protocol for electrocarboxylation of synthetic relevance with thioethers as starting materials. Finally, the compound class is shown to outcompete their well-established sulfone analogues as alkyl radical precursors, demonstrating their synthetic potential for future desulfurative transformations in a one-electron manifold.

Photo-induced 1,2-thiohydroxylation of maleimide involving disulfide and singlet oxygen

A visible light-driven di-functionalization of maleimide with disulfide and in situ-generated singlet oxygen offers selective 1,2-thiohydroxylation under additive-free conditions. Here the disulfide plays the dual role of photosensitizer and the coupling reagent. Notably, the hydroxyl functionality originates from the in situ generated singlet oxygen followed by HAT from H2O (moisture).

PPh3/I2 Promoted Synthesis of Unsymmetrical Disulfides from Sodium Sulfites and 2-Mercaptobenzo Heterocyclics

A simple and efficient method for the synthesis of unsymmetrical disulfides is reported. Using sodium sulfites and 2-mercaptobenzo heterocyclic compounds as starting materials, the unsymmetrical sulfur-sulfur bonds could be quickly constructed in the PPh3/I2 reaction system under transition-metal-free conditions. This protocol has the advantages of mild reaction conditions, easily available starting materials, and wide substrate scope, showing potential synthetic value for the synthesis of a diversity of biologically or pharmaceutically active compounds.

Visible light-driven photocatalytic thiol-ene/yne reactions using anisotropic 1D Bi2S3 nanorods: a green synthetic approach

Thiol-ene/yne click reactions play a significant role in creating carbon-sulfur (C-S) bonds, and there has been a growing interest in using visible-light photoredox catalysis for their formation. In this study, anisotropic 1D Bi2S3 nanorods were prepared using a simple polyol-assisted reflux method, and they were used as catalysts for the thiol-ene/yne click reactions under visible light irradiation. The developed protocol is highly compatible and tolerant to various substrates with excellent product yields. Also, thiol-ene and -yne reactions achieved maximum TONs of 93 and 95, respectively. Detailed mechanistic studies were conducted and supported by NMR studies, radical trapping utilizing TEMPO, and ESI-MS product analysis. The ability of Bi2S3 nanorods to catalyze thiol-ene/yne reactions is primarily due to the creation of photoexcited holes, which aid in the formation of thiyl radicals. This method can be scaled up to the gram-scale synthesis of benzyl styryl sulfide with an excellent chemical yield of 90%. The 1D Bi2S3 nanorods also demonstrated structural and morphological stability throughout five reaction cycles while maintaining a favorable photocatalytic activity. The developed methodology had the advantages of broad substrate scope, mild reaction conditions, scaled-up synthesis, and nonrequirement of free radical initiators.

Mechanistic Investigation of the Degradation Pathways of α-β/α-α Bridged Epipolythiodioxopiperazines (ETPs)

Epipolythiodioxopiperazines (ETPs) make up a class of biologically active fungal metabolites with a transannular disulfide bridge. In this work, we used DFT calculations to examine in detail the degradation (desulfurization) pathways of α-β/α-α bridged ETPs. The chemical stability of ETPs is influenced by the type of sulfur bridge, the structural features, and the storage conditions. Our results suggest appropriate protection of the phenolic OH of ETPs would improve various pharmaceutically relevant properties, including bioavailability.