Transition-Metal-Free Aryl-Heteroatom Bond Formation via C-S Bond Cleavage

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.

Syntheses of Aryl Thioethers via Aromatic Substitution of Aryl Halides at 0 to 25 °C

In this study, we developed mild conditions for the synthesis of an aryl thioether via aromatic substitution using aryl halides, which is a process that has rarely been studied. Aromatic substrates such as aryl fluorides activated with a halogen substituent are difficult to use for substitution reactions, but by using 18-crown-6-ether as an additive, these were successfully converted to their corresponding thioether products. Under the conditions we established, in addition to a wide variety of thiols, less-toxic and odorless disulfides could be used directly as nucleophiles at 0 to 25 °C.

Construction of C(sp2)-Si Bonds via Ligand-Promoted C-C Bonds Cleavage of Unstrained Ketones

Herein, we report an efficient palladium-catalyzed silylation of aryl and alkenyl ketones via C-C bond cleavage and C-Si bond formation. This protocol features high efficiency and broad substrate scope. Further applications in the late-stage diversification of biologically important molecules demonstrate the synthetic utility of this method.

Transition-Metal-Free Cascade Approach for the Synthesis of Functionalized Biaryls by SNAr of Arylhydroxylamines with Arylsulfonium Salts

We report a transition-metal-free protocol for the synthesis of functionalized biaryls through nucleophilic aromatic substitution (S_NAr) of arylhydroxylamines to arylsulfonium salts. With this protocol, structurally diverse functionalized biaryls were obtained smoothly in moderate to good yields. Merits of this transformation include mild reaction conditions, broad substrate scope, great functional group tolerance, feasibility of a one-pot procedure, and ease of handing and scale-up.

Coupling of Thiols and Aryl Halides Mediated by Dicyclohexano-18-Crown-6 and Potassium Carbonate

AIMS

A simple, transition-metal-free C-S coupling protocol for the synthesis of aryl thioethers is reported Background: Sulfur-containing moieties are ubiquitous in pharmaceutical drugs and materials and therefore methods for their construction are of great importance. One approach entails the catalytic coupling of an aryl halohydrocarbon with a thiol, but the transition metal catalysts usually used are prone to poisoning by participating sulfur species and efficient catalysis is usually only achieved after complex ligand optimization.

OBJECTIVE

New transition-metal-free approaches to the synthesis of C-S bonds are urgently need Method: We screened the reaction conditions such as alkali, crown ether, solvent, temperature, etc., tested the compatibility of the reaction substrate, and analyzed the mechanism process.

RESULT

the optimized reaction conditions were determined to be 1.0 equiv of aryl halides and 1.2 equiv of thiols at 110 ℃ in toluene with K2CO3 (1.5 equiv) as a base, promoted by 10 mol% dicyclohexano-18-crown-6. Up to 33 examples of thioethers were synthesized under transition-metal-free conditions in good to excellent yields.

CONCLUSION

we have developed a simple and efficient method for the C-S cross-coupling of a wide variety of (hetero)aryl halides and thiols mediated by dicyclohexano-18-crown-6 and without the need for transition-metal catalyst. In addition, the preparation and gram-scale experiments of a variety of drug molecules further verify the practicability of our developed method.

Visible-Light-Initiated Catalyst-Free Trifluoromethylselenolation of Arylsulfonium Salts with [Me4N][SeCF3]

The redox potential gap between arylsulfonium salt and [Me4N][SeCF3] has been clearly disclosed by CV measurements. Construction of carbon-selenium bond by overcoming this gap without using catalysts and additives is...

Metal-free and Selectfluor-mediated diverse transformations of 2-alkylthiobenzamides to access 2,3-dihydrobenzothiazin-4-ones, benzoisothiazol-3-ones and 2-alkylthiobenzonitriles

Diverse transformations of 2-alkylthiobenzamides have been established to synthesize 2,3-dihydrobenzothiazin-4-ones, benzoisothiazol-3-ones and 2-alkylthiobenzonitriles in the presence of Selectfluor.

Palladium-catalyzed phosphorylation of arylsulfonium salts with P(O)H compounds via C–S bond cleavage

Herein we report a novel palladium-catalyzed phosphorylation of arylsulfonium salts with P(O)H compounds via C–S bond cleavage under mild conditions.

Construction of α-Amino Azines via Thianthrenation-Enabled Photocatalyzed Hydroarylation of Azine-Substituted Enamides with Arenes

α-Amino azines are widely found in pharmaceuticals and ligands. Herein, we report a practical method for accessing this class of compounds via photocatalyzed hydroarylation of azine-substituted enamides with the in situ-generated aryl thianthrenium salts as the radical precursor. This reaction features a broad substrate scope, good functional group tolerance, and mild conditions and is suitable for the late-stage installation of α-amino azines in complex structures.

Pd/Cu-Catalyzed Vinylation of Terminal Alkynes with (2-Bromoethyl)diphenylsulfonium Triflate

The potential of (2-bromoethyl)diphenylsulfonium triflate to be a powerful vinylation reagent was determined by the Sonogashira cross-coupling reactions with terminal alkynes. The vinylation proceeded smoothly at 25 °C under Pd/Cu catalysis to afford a variety of 1- and 2-unsubstituted 1,3-enynes in moderate to excellent yields. This protocol represents the first application of (2-haloethyl)diphenylsulfonium triflate as a CH═CH₂ transfer source in organic synthesis.

Peri-Selective Direct Acylmethylation and Amidation of Naphthalene Derivatives Using Iridium and Rhodium Catalysts

An iridium-catalyzed acylmethylation and a rhodium-catalyzed amidation of naphthalene derivatives are reported, adopting sulfoxonium ylides and dioxazolones as carbene and nitrene transfer agents, respectively. The use of SMe group as a directing group was key to ensure the peri-selective functionalization, and it can be easily removed or diversely transformed to other synthetically useful functionalities after the catalysis.

A nickel-catalyzed silylation reaction of alkyl aryl sulfoxides with silylzinc reagents

Ni(PEt3)Cl2-catalyzed silylation of alkyl aryl sulfoxides with silylzinc reagents was carried out. This protocol allows alkyl aryl sulfoxides to convert to arylsilicon compounds under mild reaction conditions, tolerates a range of functional groups and is suitable for a wide scope of substrates.

Pd/Cu-Catalyzed C-H/C-H Cross Coupling of (Hetero)Arenes with Azoles through Arylsulfonium Intermediates

A highly efficient method for the selective formal C-H/C-H cross-coupling of azoles and (hetero)arenes was established through arylsulfonium intermediates under transition-metal catalysis, which produced a variety of 2-(hetero)aryl azoles in good to excellent yields. Advantages of the reaction included mildness, a good functional group tolerance, a wide range of substrates, a high regio- and chemoselectivity, one-pot procedures, and the late-stage functionalization of complex molecules without the use of oxidants, offering a promising strategy for the transition-metal-catalyzed C-H arylation of azoles.

Illuminating Stannylation

We have developed photoboosted stannylation reactions of terminal alkynes (linear-selective hydrostannylation) and fluoroarenes (defluorostannylation), in which the stannyl anion is photoexcited to an excited triplet (T₁) stannyl diradical species. This unprecedented T₁-stannyl diradical species shows completely different reactivity and selectivity from those of stannyl anions and stannyl radicals. This methodology is operationally simple, has broad functional group tolerance, and proceeds in high yield without the need for any catalyst.

5-(Diarylimino)- and 5-(sulfoximido)dibenzothiophenium triflates: syntheses and applications as electrophilic aminating reagents

The one-pot synthesis of well-defined 5-(diarylimino) and 5-(sulfoximido)dibenzothiophenium triflates, respectively from diarylimines or sulfoximines, is reported and the structures of a series of these compounds are elucidated by X-ray crystallography. In analogy to their hypervalent I(iii) analogues, the iminoyl and sulfoximidoyl groups of these compounds can be selectively transferred to organic substrates. Specifically, the uncatalyzed imination of thiols or sulfinates proceeds with good yields, while under the mild reaction conditions offered by visible light photoredox catalysis, the radical amination of hydrazones or the sulfoximidation of benzylic, allylic and propargylic C-H bonds takes place satisfactorily.

Arylation of ortho-Hydroxyarylenaminones by Sulfonium Salts and Arenesulfonyl Chlorides: An Access to Isoflavones

Herein we disclose three new methods for the straightforward and efficient synthesis of 3-arylchromones following the arylation of ortho-hydroxyarylenaminones by vast diversities of bench-stable and easy-to-use sulfonium salts and arenesulfonyl chlorides. Both developed methods, namely the light-mediated photoredox and electrophilic arylation, showed good efficiency, and are feasible for the preparation of 3-arylchromones in good-to-excellent yields. This work showcases the first described attempt where the sulfonium salts and arenesulfonyl chlorides were successfully utilized for the construction of the chromone heterocycle system.

Preparation of Sulfamates and Sulfamides Using a Selective Sulfamoylation Agent

Sulfamates and sulfamides are prevalent in biological molecules, but their universal synthetic methods are limited. We herein report a sulfamoylation agent with high solubility and shelf stability. Various sulfamates and sulfamides can be synthesized directly from alcohols or amines by employing this agent with high selectivity and high yields. This protocol was also successfully used for late-stage sulfamoylation of pharmaceuticals containing a hydroxyl or amino group.

α-Diazo Sulfonium Triflates: Synthesis, Structure, and Application to the Synthesis of 1-(Dialkylamino)-1,2,3-triazoles

The one-pot synthesis of a series of sulfonium salts containing transferable diazomethyl groups is described, and the structure of these compounds is elucidated by X-ray crystallography. Under photochemical conditions, reaction of these salts with N,N-dialkyl hydrazones affords 1-(dialkylamino)-1,2,3-triazoles via diazomethyl radical addition to the azomethine carbon followed by intramolecular ring closure. The straightforward transformation of the structures thus obtained into mesoionic carbene-metal complexes is also reported and the donor properties of these new ligands characterized.

Synthetic strategies for aryl/heterocyclic selenides and tellurides under transition-metal-catalyst free conditions

Aryl and heteroaryl selenides and tellurides are found to have broad applications in the diverse fields such as medicine, biology, materials science, pharmaceutical etc. and thus their synthesis remains a challenging field for synthetic chemists in last decade. Although a large no of methodologies have been developed based on metal catalyzed C-Se/Te coupling, a large number of researches has been focused on developing metal catalyst free protocols due to their sustainability in recent times. This review covers all the recent developments in last decade on their synthesis under metal catalyst free conditions by using different sustainable techniques e.g. greener reagents and solvents, ball milling, visible light photocatalysis, microwave, ultrasound etc.

Cu-Catalyzed highly selective silylation and borylation of alkenylsulfonium salts

A Cu-catalyzed highly selective silylation and borylation of alkenylsulfonium salts under mild conditions is reported providing various alkenylsilanes and alkenylboranes.

Synthetic Applications of Sulfonium Salts

This minireview aims to cover the developments over the past two decades in the chemistry of sulfonium salts. Specifically, insight is provided into the synthetic strategies available for the preparation of these compounds, the different reactivity patterns that are expected depending on their structural features or the reaction conditions applied, and the diversity of organic scaffolds that can thereby be synthesized. Additionally, the pros and cons derived from the use of sulfonium salts are presented and critically compared, when possible, in relation to reagents not based on sulfur but depicting similar reactivity.