Nucleophilic disulfurating reagents for unsymmetrical disulfides construction via copper-catalyzed oxidative cross coupling

Copper(0)-Catalyzed Reductive Coupling of Disulfurating Reagents and (Hetero)aryl/Alkyl Halides

Herein, we reported a copper(0)-catalyzed reductive coupling of disulfurating reagents and (hetero)aryl/alkyl halides. Copper(0) can be directly inserted into tetrasulfide and then undergoes reductive coupling with (hetero)aryl Iodides to construct disulfide. The method features the unprecedented use of copper(0)-catalyzed disulfurating reagents (tetrasulfides) in cross-coupling chemistry and is convenient with broad substrate scopes, even applicable to different halogenated hydrocarbons. It is worth noting that the methodology is practical with the late-stage modification of bioactive scaffolds of pharmaceuticals. In the meantime, the synthesis of disulfides is successfully achieved on a gram scale, indicating the approach is highly valuable.

Synthesis of unsymmetrical phosphorus disulfides

A sulfur-mediated umpolung strategy employing N-thiosuccinimides and (EtO)2P(O)SH has been developed to synthesize unsymmetrical organophosphorus disulfides (P(O)-S-S motif). A pronucleophile (EtO)2P(O)SH, Brønsted acid and phosphorothioate nucleophile, converts N-thiosuccinimides into unsymmetrical phosphorus disulfides. This protocol achieves catalyst- and additive-free reaction conditions, uses a renewable solvent (EtOH), and avoids harsh reagents.

Nickel-catalyzed selective disulfide formation by reductive cross-coupling of thiosulfonates

Developing innovative methodologies for disulfide preparation is of importance in contemporary organic chemistry. Despite significant advancements in nickel-catalyzed reductive cross-coupling reactions for forming carbon-carbon and carbon-heteroatom bonds, the synthesis of S-S bonds remains a considerable challenge. In this context, we present a novel approach utilizing nickel catalysts for the reductive cross-coupling of thiosulfonates. This method operates under mild conditions, offering a convenient and efficient pathway to synthesize a wide range of both symmetrical and unsymmetrical disulfides from readily available, bench-stable thiosulfonates with exceptional selectivity. Notably, this approach is highly versatile, allowing for the late-stage modification of pharmaceuticals and the preparation of various targeted compounds. A comprehensive mechanistic investigation has been conducted to substantiate the proposed hypothesis.

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.

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.

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.

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.

Radical approaches to C-S bonds

Organosulfur functionalities are ubiquitous in nature, pharmaceuticals, agrochemicals, materials and flavourants. Historically, these moieties were introduced almost exclusively using ionic chemistry; however, radical-based methods for the installation of sulfur-based functional groups have recently come to the fore. These radical methods have enabled their late-stage introduction into complex molecules, avoiding the need to preserve labile organosulfur moieties through multistep synthetic sequences. Here, we discuss homolytic C-S bond-forming processes, with a particular emphasis on radical substitution approaches to sulfide, disulfide and sulfinyl products, and the use of sulfur dioxide and its surrogates to build sulfonyl products. We also highlight the mechanistic considerations that we hope will guide further development of radical-based strategies compatible with the various organosulfur moieties that feature in modern chemistry.

Visible-light-induced synthesis of N-disulfanyl indoles, pyrroles or carbazoles via the construction of stable S-S-N bonds

A simple and efficient visible-light-induced approach for the formation of stable S-S-N bonds has been developed. Through these photocatalytic reactions, a series of N-disulfanyl indoles, pyrroles and carbazoles were afforded with good to excellent yields. Moreover, the gram-scale experiment has confirmed the practicability of this approach.

Photocatalytic C-H Disulfuration for the Preparation of Indolizine-3-disulfides

A photocatalytic C-H disulfuration of indolizines was developed, giving an approach to a wide variety of indolizine-3-disulfides with good yields. Trisulfide dioxides were explored as a high-efficient disulfuration reagent. This disulfuration reaction could be scaled up to grams. Mechanistic studies support a photoinduced pathway involving the generation of indolizine cationic radicals. A bulky alkyl substituent on terminal sulfur of trisulfide dioxide A was necessary for selective formation of disulfide over monosulfide.

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.

Nickel(ii)/TPMPP catalyzed reductive coupling of oxalates and tetrasulfides: synthesis of unsymmetric disulfides

A Ni(ii)/TPMPP-catalyzed reductive cross-coupling reaction of benzyl oxalates and tetrasulfides to synthesize unsymmetric disulfides is reported.

(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...

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.

A Divergent Strategy for Site-Selective Radical Disulfuration of Carboxylic Acids with Trisulfide-1,1-Dioxides

The direct conversion of carboxylic acids into disulfides is described. The approach employs oxidative photocatalysis for base-promoted decarboxylation of the substrate, which yields an alkyl radical that reacts with a trisulfide dioxide through homolytic substitution. The trisulfide dioxides are easily prepared by a newly described approach. 1°, 2°, and 3° carboxylic acids with varied substitution are good substrates, including amino acids and substrates with highly activated C-H bonds. Trisulfide dioxides are also used to achieve the γ-C(sp³ )-H disulfuration of amides through a radical relay sequence. In both reactions, the sulfonyl radical that results from substitution propagates the reaction. Factors governing the selectivity of substitution at S2 versus S3 of the trisulfide dioxides have been explored.

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'.

Convenient Synthesis of Functionalized Unsymmetrical Vinyl Disulfides and Their Inverse Electron-Demand Hetero-Diels-Alder Reaction

The simple, convenient, and efficient methods for the preparation of unsymmetrical vinyl disulfides with additional functional groups under mild conditions with moderate to high yields were designed. The developed methods include the reaction of S-vinyl phosphorodithioate with thiotosylates or S-vinyl thiotosylate with thiols. The designed methods allow for the synthesis of unsymmetrical vinyl disulfides with additional functionalities such as hydroxy, carboxy, protected amino, or ester groups. Vinyl disulfides reacted with the generated transient o-iminothioquinones in an inverse electron-demand [4+2] cycloaddition to produce benzo[b][1,4]thiazine derivatives.

Elemental-Sulfur-Enabled Divergent Synthesis of Disulfides, Diselenides, and Polythiophenes from β-CF3 -1,3-Enynes

Divergent synthesis for precise constructions of cyclic unsymmetrical diaryl disulfides or diselenides and polythiophenes from CF₃ -containing 1,3-enynes and S₈ was developed when the ortho group is F, Cl, Br, and NO₂ on aromatic rings. Meanwhile, disulfides (diselenides) were also quickly constructed when the ortho group is H. These transformations undergo cascade thiophene construction/selective C3-position thiolation process, featuring simple operations, divergent synthesis, broad substrate scope, readily available starting materials, and valuable products. A novel plausible radical annulation process was proposed and validated by DFT calculations for the first time. A series of derivatizations about the thiophene (TBT) and disulfides were also well-represented.

Polysulfuration via a Bilateral Thiamine Disulfurating Reagent

An efficient moduling disulfuration was developed for polysulfide construction via a bilateral six-membered thiamine disulfurating reagent. Under the control of energy release of ring strain, diverse unsymmetrical trisulfides and tetrasulfides were generated through the assembly of nucleophiles on both sides of the sulfur-sulfur motif. This strategy exhibits features of high efficiency, mild conditions, and general scope.

Radical Substitution Provides a Unique Route to Disulfides

Radical substitution on tetrasulfides is demonstrated to be a highly effective means to prepare unsymmetric disulfides. Alkyl and aryl radicals generated thermally or photochemically underwent substitution on readily prepared dialkyl, diaryl, and diacyl tetrasulfides to yield the corresponding disulfides in good to excellent yields. Classic and contemporary thermal and photochemical radical sources could be employed; while photoredox catalysis approaches led to either oxidation or reduction of the tetrasulfide, energy transfer photocatalysis was particularly useful. The success of the approach is driven by the thermodynamic stability of the perthiyl radicals formed upon substitution on the tetrasulfide; they simply combine under the reaction conditions to provide the starting tetrasulfide. Competition kinetic experiments reveal that alkyl radical substitution on tetrasulfides is a rapid reaction (6 × 10⁵ M^-1 s^-1) that is enhanced at least 6-fold upon moving from dialkyl tetrasulfide to diacyl tetrasulfide due to favorable polar effects. This unique and versatile reaction enables introduction of disulfide moieties from a variety of radical precursors and straightforward access to hydropersulfides.

Synthesis of unsymmetrical disulfides via PPh3-mediated reductive coupling of thiophenols with sulfonyl chlorides

A facile and rapid synthesis of unsymmetrical aryl disulfides using PPh3-mediated reductive coupling of thiophenols with aryl sulfonyl chlorides was described. Good functional group tolerance and scalability were achieved in this strategy. More importantly, the approach enables the introduction of sulfonyl chlorides into the synthesis of asymmetric organic disulfides under catalyst- and base-free conditions. Using this method, unsymmetrical aromatic disulfides could be prepared from inexpensive and readily available starting materials in moderate to excellent isolated yields, through a nucleophilic substitution pathway.

Phenylboronic acid-catalyzed tandem construction of S-S and C-S bonds: a new method for the synthesis of benzyl disulfanylsulfone derivatives from S-benzyl thiosulfonates

A unique phenylboronic acid-catalyzed dimerization-sulfonylation of S-benzyl thiosulfonates has been disclosed. A metal-free tandem construction of S-S and C-S bonds is an operationally simple method to access a wide range of benzyl disulfanylsulfone derivatives in high to excellent yields. Moreover, the robustness of this tandem transformation has been demonstrated by gram-scale reactions, and a plausible mechanism is also proposed.

Unsymmetrical Organotrisulfide Formation via Low-Temperature Disulfanyl Anion Transfer to an Organothiosulfonate

New methodology is presented for the formation of unsymmetrical organotrisulfides in a high yield and purity, relatively free of polysulfide byproducts. The highlight of the method is the low-temperature (-78 °C) deprotection of a disulfanyl acetate with sodium methoxide in THF to form a disulfanyl anion, which reacts rapidly in situ with an organothiosulfonate ( S-aryl or S-alkyl) within 30 seconds followed by quenching. The discovery of these new reaction conditions together with the relative greenness of the chemistry overall makes for an efficient protocol, from which a range of organotrisulfides covering aliphatic, aromatic, as well as cysteine and sugar groups can be accessed in a high yield and purity.