Electro-Oxidative S-H/S-H Cross-Coupling with Hydrogen Evolution: Facile Access to Unsymmetrical Disulfides

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.

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.

Metal free cross-dehydrogenative N-N coupling of primary amides with Lewis basic amines

Hydrazides, N-N containing structural motifs, are important due to their presence in a wide variety of biologically significant compounds. While the homo N-N coupling of two NH moieties to form the hydrazide N-N bond is well developed, the cross-dehydrogenative hetero N-N coupling remains very unevolved. Here we present an efficient intermolecular N-N cross-coupling of a series of primary benzamides with broad range of Lewis basic primary and secondary amines using PhI(OAc)2 as both a terminal oxidant and a cross-coupling mediator, without the need for metal catalysts, high temperatures, and inert atmospheres, and with substantial potential for use in the late-stage functionalization of drugs.

Potassium xanthate-promoted reductive sulfuration reaction: from aldehydes to thiol, disulfide, and thioester derivatives

Herein, we developed a synthetic strategy for the direct construction of C-S bonds to obtain biologically active sulfur-containing compounds and a methodology involving the reductive sulfuration of aldehydes or ketones to obtain diverse substituted thiol, disulfide, and thioester derivatives. EtOCS2K is demonstrated as a potential substitute for the Berzelius reagent or Lawesson's reagent for the construction of C-S bonds.

Electrochemical Nickel-Catalyzed Selective Inter- and Intramolecular Arylations of Cysteine-Containing Peptides

Here we report a simple electrochemical route towards the synthesis of S-arylated peptides by a site selective coupling of peptides with aryl halides under base free conditions. This approach demonstrates the power of electrochemistry to access both highly complex peptide conjugates and cyclic peptides.

1,2-Fluorosulfenylation of unactivated alkenes with thiols and a fluoride source promoted by bromodimethylsulfonium bromide

A practical method that enables the fluorosulfenylation of unactivated alkenes processed directly with thiols and fluoride salts is presented. Good to excellent efficiencies and functional group tolerance are observed for both alkene substrates and thiols. The procedure also allows the use of gaseous ethylene as a two-carbon building block for β-fluoro thioether products.

Selective C(sp3)-S Bond Cleavage of Thioethers to Build Up Unsymmetrical Disulfides

The selective C(sp3)-S bond cleavage of thioethers was first developed to prepare unsymmetrical disulfides by using electrophilic halogenation reagents. In this strategy, NBS (N-bromosuccinimide) achieves selective furfuryl C(sp3)-S bond cleavage of furfuryl alkylthioethers at room temperature. Meanwhile, NFSI (N-fluorobenzenesulfonimide) enables selective methyl C(sp3)-S bond cleavage of aryl and alkyl methylthioethers at an elevated temperature. Notably, the substrate scope investigation indicates that the order of selectivity of the C-S bond cleavage is furfuryl C(sp3)-S > benzyl C(sp3)-S > alkyl C(sp3)-S > C(sp2)-S bond. Moreover, this practical and operationally simple strategy also provides an important complementary way to access various unsymmetrical disulfides with excellent functional group tolerances and moderate to good yields.

Regioselectively Electrochemical Synthesis of N2-Selective C-H Amination of Ethers with N-Tosyl 1,2,3-Triazole via Triazole Radical Cation

A regioselective electrochemical C-H amination method to synthesize N²-substituted 1,2,3-triazole using easily accessible ethers has been developed. Various substituents, including heterocycles, have a good tolerance, and 24 examples were obtained in moderate to good yields. Control experiments and DFT calculation investigations demonstrate that the electrochemical synthesis undergoes a N-tosyl 1,2,3-triazole radical cation process promoted by the single-electron transfer of the lone pair electrons of the aromatic N-heterocycle, and the desulfonation is responsible for the high N²-regioselectivity.

Visible-Light-Driven Iodine-Catalyzed Synthesis of Unsymmetrical Disulfides via Oxidative Coupling

Herein, a facile and environmentally friendly oxidative coupling reaction to obtain unsymmetrical disulfide compounds, without using metal or organic dyes as photocatalyst and only using a catalytic amount of iodine, was developed. Oxygen is used as oxidant in the reaction and the substrate scope is wide. A gram-scale synthesis also highlights the synthetic practicality of this photochemical strategy. Moreover, our mechanistic studies support the formation of disulfide products through free-radical coupling.

Organosulfur Materials for Rechargeable Batteries: Structure, Mechanism, and Application

Lithium-ion batteries have received significant attention over the last decades due to the wide application of portable electronics and increasing deployment of electric vehicles. In order to further enhance the performance of the batteries and overcome the capacity limitations of inorganic electrode materials, it is imperative to explore new cathode and functional materials for rechargeable lithium batteries. Organosulfur materials containing sulfur-sulfur bonds as a kind of promising organic electrode materials have the advantages of high capacities, abundant resources, tunable structures, and environmental benignity. In addition, organosulfur materials have been widely used in almost every aspect of rechargeable batteries because of their multiple functionalities. This review aims to provide a comprehensive overview on the development of organosulfur materials including the synthesis and application as cathode materials, electrolyte additives, electrolytes, binders, active materials in lithium redox flow batteries, and other metal battery systems. We also give an in-depth analysis of structure-property-performance relationship of organosulfur materials, and guidance for the future development of organosulfur materials for next generation rechargeable lithium batteries and beyond.

Practical synthesis of unsymmetrical disulfides promoted by bromodimethylsulfonium bromide

Oxidative cross-coupling of two thiols is the most direct tool for the synthesis of unsymmetrical disulfides and highly desirable across academia and industry. However, the inevitable formation of significant amounts of the corresponding symmetrical by-products is a major issue. We herein present a method toward the synthesis of unsymmetrical disulfides in which the homo-coupling of the thiols is effectively inhibited by adding the two thiols sequentially, taking advantage of rapid oxidation of the thiol by bromodimethylsulfonium bromide.

Electrochemical Regioselective C(sp2)-H Selenylation and Sulfenylation of Substituted 2-Amino-1,4-naphthoquinones

A straightforward and efficient electrochemical method for regioselective C(sp²)-H selenylation and sulfenylation of substituted 2-amino-1,4-naphthoquinones has been unearthed. This oxidative cross-coupling reaction avoids using transition metal catalysts, oxidants, and high temperatures. The other notable advantages of this protocol are the tolerance of diverse functional groups, mild reaction conditions at ambient temperature, energy efficiency, good to excellent yields, short reaction times (in minutes), gram-scale applicability, and eco-friendliness.

Synthesis of N-acyl sulfenamides via copper catalysis and their use as S-sulfenylating reagents of thiols

Sulfur-heteroatom bonds such as S-S and S-N are found in a variety of natural products and often play important roles in biological processes. Despite their widespread applications, the synthesis of sulfenamides, which feature S-N bonds that may be cleaved under mild conditions, remains underdeveloped. Here, we report a method for synthesis of N-acyl sulfenamides via copper-catalyzed nitrene-mediated S-amidation reaction of thiols with dioxazolones. This method is efficient, convenient, and broadly applicable. Moreover, the resulting N-acetyl sulfenamides are highly effective S-sulfenylation reagents for the synthesis of unsymmetrical disulfides under mild conditions. The S-sulfenylation protocol enables facile access to sterically demanding disulfides that are difficult to synthesize by other means.

Decatungstate-catalyzed radical disulfuration through direct C-H functionalization for the preparation of unsymmetrical disulfides

Unsymmetrical disulfides are widely found in the areas of food chemistry, pharmaceutical industry, chemical biology and polymer science. Due the importance of such disulfides in various fields, general methods for the nondirected intermolecular disulfuration of C-H bonds are highly desirable. In this work, the conversion of aliphatic C(sp³)-H bonds and aldehydic C(sp²)-H bonds into the corresponding C-SS bonds with tetrasulfides (RSSSSR) as radical disulfuration reagents is reported. The decatungstate anion ([W₁₀O₃₂]⁴⁻) as photocatalyst is used for C-radical generation via intermolecular hydrogen atom transfer in combination with cheap sodium persulfate (Na₂S₂O₈) as oxidant. Herein a series of valuable acyl alkyl disulfides, important precursors for the generation of RSS-anions, and unsymmetrical dialkyl disulfides are synthesized using this direct approach. To demonstrate the potential of the method for late-stage functionalization, approved drugs and natural products were successfully C-H functionalized.

Despite the importance of unsymmetrical disulfides in various fields such as food chemistry, pharmaceutical industry, and polymer science, the nondirected intermolecular disulfuration of C-H bonds remains challenging. Here, the authors report the conversion of aliphatic C(sp³)-H bonds and aldehydic C(sp²)-H bonds into the corresponding C-SS bonds with tetrasulfides (RSSSSR) as radical disulfuration reagents.

Electrochemical Sulfoxidation of Thiols and Alkyl Halides

Sulfoxides are actively engaged as versatile synthetic building blocks, chiral ligands, bioactive molecules, and function materials. However, their oxidative syntheses from thioethers are inevitably impeded by overoxidation, excess oxidants, and the tedious preparation of thioethers. To address these shortcomings, we report herein a highly selective electrochemical sulfoxidation reaction featuring the use of simple starting materials, i.e., thiols and alkyl halides, in a single operation.

Photochemical and Electrochemical Applications of Proton-Coupled Electron Transfer in Organic Synthesis

We present here a review of the photochemical and electrochemical applications of multi-site proton-coupled electron transfer (MS-PCET) in organic synthesis. MS-PCETs are redox mechanisms in which both an electron and a proton are exchanged together, often in a concerted elementary step. As such, MS-PCET can function as a non-classical mechanism for homolytic bond activation, providing opportunities to generate synthetically useful free radical intermediates directly from a wide variety of common organic functional groups. We present an introduction to MS-PCET and a practitioner's guide to reaction design, with an emphasis on the unique energetic and selectivity features that are characteristic of this reaction class. We then present chapters on oxidative N-H, O-H, S-H, and C-H bond homolysis methods, for the generation of the corresponding neutral radical species. Then, chapters for reductive PCET activations involving carbonyl, imine, other X═Y π-systems, and heteroarenes, where neutral ketyl, α-amino, and heteroarene-derived radicals can be generated. Finally, we present chapters on the applications of MS-PCET in asymmetric catalysis and in materials and device applications. Within each chapter, we subdivide by the functional group undergoing homolysis, and thereafter by the type of transformation being promoted. Methods published prior to the end of December 2020 are presented.

Smart Flow Electrosynthesis and Application of Organodisulfides in Redox Flow Batteries

Electrochemical techniques have been recognized as an environmentally friendly and sustainable synthetic way to form organodisulfides. However, searching for optimum conditions which suffers from time/material-consuming caused by the uncertainty of reactant consumption has hindered its rapid and large-scale development. Inspired by advanced nonaqueous redox flow batteries (NARFBs) technology, it is proposed a smart flow electrosynthesis (SFE) method of organodisulfides that the voltage curve of NARFBs can be utilized as a precise indicator to reflect the desired information about reactants and distinguish the end point of reaction automatically. This electrochemical method also exhibits certain universality and scalability. Additionally, organodisulfides generated in electrolytes can be used as active species for NARFBs without further purification, and their electrochemical properties are easily adjusted by changing raw materials, which effectively alleviate the waste in complex synthesis steps for optimizing and designing active materials separately. An organodisulfide dervied from isopropyl alcohol and carbon disulfide shows excellent cycling life (1000 cycles) with low capacity fade rate (0.024% per cycle). Taking advantages of the inherent NARFBs, this work not only proves a SFE strategy, but also supplies a green and low-cost molecular engineering scheme for designing electroactive materials for energy storage.

(NH4)2S2O8-Promoted cross-coupling of thiols/diselenides and sulfoxides for the synthesis of unsymmetrical disulfides/selenosulfides

(NH4)2S2O8-Promoted cross-coupling of thiols/diselenides and sulfoxides to construct unsymmetrical disulfides/selenosulfides is disclosed. Control experiments demonstrate that (NH4)2S2O8 acts as an acid and an oxidant while both ionic and radical routes...

Photochemical and electrochemical regioselective cross-dehydrogenative C(sp2)–H sulfenylation and selenylation of substituted benzo[a]phenazin-5-ols

The essence of photo- and electrochemistry: sulfenylation and selenylation of substituted benzo[a]phenazin-5-ols through cross-dehydrogenative C(sp2)–H functionalization.

Electrochemical Desaturative β-Acylation of Cyclic N-Aryl Amines

Herein, we disclose a straightforward, robust, and simple route to access β-substituted desaturated cyclic amines via an electrochemically driven desaturative β-functionalization of cyclic amines. This transformation is based on multiple single-electron oxidation processes using catalytic amounts of ferrocene. The reaction proceeds in the absence of stoichiometric amounts of electrolyte under mild conditions, affording the desired products with high chemo- and regioselectivity. The reaction was tolerant of a broad range of substrates and also enables late-stage β-C(sp³ )-H acylation of potentially valuable products. Preliminary mechanistic studies using cyclic voltammetry reveal the key role of ferrocene as a redox mediator in the reaction.

Electrochemical Trifluoromethylation of Thiophenols with Sodium Trifluoromethanesulfinate

We developed an electrochemical trifluoromethylation of thiophenols without the use of metal catalysts and oxidants. This reaction features mild reaction conditions, readily available substrate, as well as moderate to good yields. In addition, this protocol can be easily scaled up with moderate efficiency.

Electrochemical Oxidative Cross-Coupling between Vinyl Azides and Thiophenols: Synthesis of gem-Bisarylthio Enamines

An electrochemical radical strategy involving alkene substrates provides a powerful approach for alkene functionalization. Herein, we described the first electrochemical synthesis of gem-bisarylthio enamines from vinyl azides and thiophenols through the C-H/S-H cross-coupling. This electrochemical oxidative cross-coupling is characterized by good functional group tolerance, affording a series of gem-bisarylthio enamines in excellent yields, and was carried out at room temperature without additional oxidant, transition-metal catalyst, or base. Notably, the reaction could be easily performed on a gram scale with good efficiency.

Oxidative electro-organic synthesis of dimeric hexahydropyrrolo-[2,3-b]indole alkaloids involving PCET: total synthesis of (±)-folicanthine

An efficient electrochemical oxidation strategy for the total synthesis of a dimeric hexahydropyrrolo[2,3-b]indole alkaloid, (±)-folicanthine (1b), has been envisioned. Control experiments suggest that a PCET pathway involving stepwise electron transfer followed by proton transfer (ET-PT) was involved in the key oxidative dimerization process.

Electrochemically selective double C(sp2)-X (X = S/Se, N) bond formation of isocyanides

The construction of C(sp²)-X (X = B, N, O, Si, P, S, Se, etc.) bonds has drawn growing attention since heteroatomic compounds play a prominent role from biological to pharmaceutical sciences. The current study demonstrates the C(sp²)-S/Se and C(sp²)-N bond formation of one carbon of isocyanides with thiophenols or disulfides or diselenides and azazoles simultaneously. The reported findings could provide access to novel multiple isothioureas, especially hitherto rarely reported selenoureas. The protocol showed good atom-economy and step-economy with only hydrogen evolution and theoretical calculations accounted for the stereoselectivity of the products. Importantly, the electrochemical reaction could exclusively occur at the isocyano part regardless of the presence of susceptible radical acceptors, such as a broad range of arenes and alkynyl moieties, even alkenyl moieties.

Sandmeyer-Type Reductive Disulfuration of Anilines

A transition metal/ligand-free disulfuration of anilines with disulfur transfer reagents (dithiosulfonate or tetrasulfide) is reported herein. The reaction, which can be considered as a reductive disulfuration variation of the classic Sandmeyer reaction, is performed under mild conditions and exhibits broad scope across the aniline substrate and disulfur transfer reagent classes. The gram-scale synthesis of disulfides is successfully achieved through this method, rendering the approach highly valuable.

Electrochemical Heteroatom-Heteroatom Bond Construction

Heteroatom-heteroatom linkage, with S-S bond as a presentative motif, served a crucial role in biochemicals, pharmaceuticals, pesticides, and material sciences. Thus, preparation of the privileged scaffold has always been attracting tremendous attention from the synthetic community. However, classic protocols suffered from several drawbacks, such as toxic and unstable agents, poor functional group tolerance, multiple steps, and explosive oxidizing regents as well as the transitional metal catalysts. Electrochemical organic synthesis exhibited a promising alternative to the traditional chemical reaction due to the sustainable electricity can be employed as the traceless redox agents. Hence, toxic and explosive oxidants and/or transitional metals could be discarded under mild reaction with high efficiency. In this context, a series of electrochemical approaches for the construction of heteroatom-heteroatom bond were reviewed. Notably, most of the cases illustrated the dehydrogenative feature with the clean energy molecules hydrogen as the sole by-product.

Electrosynthesis of 1,4-bis(diphenylphosphanyl) tetrasulfide via sulfur radical addition as cathode material for rechargeable lithium battery

Organic electrodes are promising as next generation energy storage materials originating from their enormous chemical diversity and electrochemical specificity. Although organic synthesis methods have been extended to a broad range, facile and selective methods are still needed to expose the corners of chemical space. Herein, we report the organopolysulfide, 1,4-bis(diphenylphosphanyl)tetrasulfide, which is synthesized by electrochemical oxidation of diphenyl dithiophosphinic acid featuring the cleavage of a P-S single bond and a sulfur radical addition reaction. Density functional theory proves that the external electric field triggers the intramolecular rearrangement of diphenyl dithiophosphinic acid through dehydrogenation and sulfur migration along the P-S bond axis. Impressively, the Li/bis(diphenylphosphanyl)tetrasulfide cell exhibits the high discharge voltage of 2.9 V and stable cycling performance of 500 cycles with the capacity retention of 74.8%. Detailed characterizations confirm the reversible lithiation/delithiation process. This work demonstrates that electrochemical synthesis offers the approach for the preparation of advanced functional materials.

Cross-Dehydrogenative N-N Coupling of Aromatic and Aliphatic Methoxyamides with Benzotriazoles

Nitrogen-nitrogen bond containing motifs are ubiquitous in bioactive compounds and organic materials. However, intermolecular hetero-selective N-H/N-H oxidative coupling reactions remain very challenging and largely unexplored. Here, we report an unprecedented, simple and hetero-selective cross-dehydrogenative N-N coupling of amides and benzotriazoles, utilizing only a hypervalent iodine species as the terminal oxidant. The scope and mechanistic investigations are discussed.

Recent Advances in the Electrochemical Synthesis of Organosulfur Compounds

Organosulfur compounds are being widely used in medicinal chemistry, as well as in organic transformations and in synthetic applications. Because of their interest in many areas, the development of sustainable and green synthetic methods to access various organosulfur compounds has a high influence on the chemistry community. Electroorganic synthesis has become a very valuable methodology for the synthesis of organosulfur compounds during the last decade. The use of electrochemical technology offers a green, sustainable and safe alternative to prepare and modify such compounds. This review summarises recent developments in the preparation of organosulfur compounds such as sulfoxides, sulfones, sulfinic esters, sulfonamides, thiosulfonates, sulfonyl fluorides and sulfoximines under electrochemical reaction conditions.

PdCl2/DMSO-Catalyzed Thiol-Disulfide Exchange: Synthesis of Unsymmetrical Disulfide

Unsymmetrical disulfides have been effectively prepared through thiol exchange with symmetrical disulfides employing a simple PdCl₂/DMSO catalytic system. The given method features excellent functional group tolerance, a broad substrate scope, and operational simplicity. This reaction is especially useful for late-stage functionalization of bioactive scaffolds such as peptides and pharmaceuticals. Disulfide-containing organic dyes have also been prepared. This transformation could be extended to thiol-diselenide or thiol-ditelluride exchange affording RS-SeR' or RS-TeR'.

A Review of Heterolytic Synthesis Methodologies for Organotri- and Organotetrasulfane Synthesis

It has been ten years since the last comprehensive review on polysulfanes, and during the intervening period, organodi-, organotri- and organotetrasulfanes have featured prominently in both the chemistry and biology literature. This timely update presents both a mechanistic and historical account of synthesis methodology available for organotri- and organotetrasulfanes involving heterolytic S–S bond formation.

Electrochemical Oxidative Carbon-Atom Difunctionalization: Towards Multisubstituted Imino Sulfide Ethers

Ethers (C-O/S) are ubiquitously found in a wide array of functional molecules and natural products. Nonetheless, the synthesis of imino sulfide ethers, containing an N(sp² )=C(sp² )-O/S fragment, still remains a challenge because of its sensitivity to acid. Developed here in is an unprecedented electrochemical oxidative carbon-atom difunctionalization of isocyanides, providing a series of novel multisubstituted imino sulfide ethers. Under metal-free and external oxidant-free conditions, isocyanides react smoothly with simple and readily available mercaptans and alcohols. Importantly, the procedure exhibited high stereoselectivities, excellent functional-group tolerance, and good efficiency on large-scale synthesis, as well as further derivatization of the products.

Continuous-flow electrosynthesis of selenium-substituted iminoisobenzofuran via oxidative cyclization of olefinic amides and diselenides

A novel method for the continuous synthesis of selenated iminoisobenzofurans by cyclization of olefinic amides with diselenides through electrochemical oxidation under metal-free and oxidant-free conditions has been developed.