Palladium-Catalyzed Oxidative Cross-Coupling of Arylhydrazines and Arenethiols with Molecular Oxygen as the Sole Oxidant

Cross-Electrophile Couplings of Benzyl Sulfonium Salts with Thiosulfonates via C-S Bond Activation

A zinc-mediated cross-electrophile coupling of benzyl sulfonium salts with thiosulfonates via C-S bond cleavage was achieved. The reductive thiolation proceeded well under transition metal-free conditions to afford the desired benzyl sulfides in good yields, exhibiting both broad substrate scope and good functionality tolerance. In addition, the reaction could be applied to the use of selenosulfonate as an effective selenylation agent and be subjected to scale-up synthesis.

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

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

Palladium-catalyzed C-C bond cleavage of N-cyclopropyl acylhydrazones

Despite their utility as directing groups, the C-C bond cleavage of cyclopropanes utilizing hydrazones has not been explored. Herein, Pd-catalyzed C-C bond cleavage reaction of N-cyclopropyl acylhydrazones, followed by cycloisomerization to yield pyrazoles, has been developed. The protocol enables the synthesis of various α-pyrazole carbonyl compounds, which have a potential of biological activity. Control experiments and DFT calculations suggest that β-carbon elimination of a stable 6-membered chelate palladium complex occurs, generating a conjugated azine as a reaction intermediate for the following cycloisomerization.

[IPr#-PEPPSI]: A Well-Defined, Highly Hindered and Broadly Applicable Pd(II)-NHC (NHC = N-Heterocyclic Carbene) Precatalyst for Cross-Coupling Reactions

In this Special Issue, "Featured Papers in Organometallic Chemistry", we report on the synthesis and characterization of [IPr#-PEPPSI], a new, well-defined, highly hindered Pd(II)-NHC precatalyst for cross-coupling reactions. This catalyst was commercialized in collaboration with MilliporeSigma, Burlington, ON, Canada (no. 925489) to provide academic and industrial researchers with broad access to reaction screening and optimization. The broad activity of [IPr#-PEPPSI] in cross-coupling reactions in a range of bond activations with C-N, C-O, C-Cl, C-Br, C-S and C-H cleavage is presented. A comprehensive evaluation of the steric and electronic properties is provided. Easy access to the [IPr#-PEPPSI] class of precatalysts based on modular pyridine ligands, together with the steric impact of the IPr# peralkylation framework, will facilitate the implementation of well-defined, air- and moisture-stable Pd(II)-NHC precatalysts in chemistry research.

Palladium-Catalyzed Oxidative Nonclassical Heck Reaction of Arylhydrazines with Allylic Alcohols via C-N Bond Cleavage: Access to β-Arylated Carbonyl Compounds

An efficient palladium-catalyzed oxidative nonclassical Heck reaction of arylhydrazines with allylic alcohols via C-N bond cleavage has been successfully developed. This method provides a series of β-arylated carbonyl compounds with broad functional group tolerance under base-free, simple, and mild open air reaction conditions. In the reaction, arylhydrazines with the smaller molecular weight of the leaving group were employed as the "green" arylation reagent, which released N₂ and water as the byproducts under air. Mechanistic studies suggested that an aryl radical process and Pd-H complex migration reinsertion were involved. Moreover, the synthesis of the antiarrhythmic drug propafenone was completed with this transformation as the key step.

Palladium-catalyzed bisthiolation of terminal alkynes for the assembly of diverse (Z)-1,2-bis(arylthio)alkene derivatives

An efficient and straightforward palladium-catalyzed three-component cascade bisthiolation of terminal alkynes and arylhydrazines with sodium thiosulfate (Na₂S₂O₃) as the sulfur source for the assembly of functionalized (Z)-1,2-bis(arylthio)alkene derivatives is described. Using 0.5 mol% IPr–Pd–Im–Cl₂ as the catalyst, a wide range of terminal alkynes and arylhydrazines are well tolerated, thus producing the desired products in good yields with good functional group tolerance and excellent regioselectivity. Moreover, this protocol could be readily scaled up, showing potential applications in organic synthesis and material science.

An efficient palladium-catalyzed bisthiolation of terminal alkynes and arylhydrazines with Na₂S₂O₃ as the sulfur source for the assembly of (Z)-1,2-bis(arylthio)alkene derivatives is described.

Recent Advances in the Pd-Catalyzed Coupling of Arylhydrazines and Ammonium Salts via C-N Bond Cleavage

Both arylhydrazines and quaternary ammonium salts are readily accessible or commercially available chemicals that show versatile reactivity in Pd-catalyzed coupling reactions via C-N bond cleavage. A tremendous array of coupling reactions involving reaction partners such as organoborons, aryl silanes, alkenes, alkynes, arylation or alkylation reagents in C-H functionalization and carbonylation reactions are summarized, in which arylhydrazines or quaternary ammonium salts function as aryl or alkyl donors. This account mainly focuses on recent advances in Pd-catalyzed coupling reactions with arylhydrazines or quaternary ammonium salts via C-N bond cleavage, including mechanistic elucidations.

Palladium-catalyzed aerobic oxyarylthiolation of alkynone O-methyloximes with arylhydrazines and elemental sulfur

A novel and practical palladium-catalyzed aerobic oxyarylthiolation of alkynone O-methyloximes for the assembly of 4-sulfenylisoxazole derivatives using S8 and arylhydrazines as the S-aryl sources is accomplished. In the presence of 0.1 mol% of IPr-Pd-allyl-Cl as the catalyst and O2 (1 atm) as the sole oxidant, both alkynone O-methyloximes and arylhydrazines are suitable substrates, delivering diverse 4-sulfenyl isoxazoles in moderate to good yields with good functional group tolerance. Notably, the phenyl diazonium salt and sodium phenyl sulfinate are also suitable arylation reagents, providing an alternative synthetic strategy to access structurally diverse 4-sulfenyl isoxazoles.

The synthesis of quinolines via denitrogenative palladium-catalyzed cascade reaction of o-aminocinnamonitriles with arylhydrazines

The first example of the palladium-catalyzed cascade reaction of o-aminocinnamonitriles with arylhydrazines has been achieved, providing an efficient synthetic pathway to access quinolines with moderate to good yields. Preliminary mechanistic experiments indicate that this cascade process involves sequential denitrogenative addition followed by an intramolecular cyclization.

Pd-catalyzed cascade denitrogenative addition and intramolecular cyclization of o-aminocinnamonitriles with arylhydrazine for the synthesis of quinolines.

Recent developments in palladium-catalyzed C–S bond formation

This review summarized the recent developments in palladium-catalyzed C–S bond formation involving sulfenylation and sulfonylation reactions.

A template free protocol for fabrication of a Ni(ii)-loaded magnetically separable nanoreactor scaffold for confined synthesis of unsymmetrical diaryl sulfides in water

In the present report, an environmentally benign magnetically recoverable nickel(ii)-based nanoreactor as a heterogeneous catalyst has been developed via a template free approach. The catalytic performance of the synthesized catalyst is assessed in the confined oxidative coupling of arenethiols with arylhydrazines to form unsymmetrical diaryl sulfides under aerobic conditions. The salient features of our protocol include oxidant- and ligand-free conditions, use of water as a green solvent, room temperature and formation of nitrogen and water as the only by-products. Moreover, a broad range of functional groups are tolerated well and provide the corresponding diaryl sulfides in moderate to good yields. Moreover, the heterogeneous nature of the catalyst permits facile magnetic recovery and reusability for up to seven runs, making the present protocol highly desirable from industrial and environmental standpoints.

An environmentally benign nickel(ii)-based magnetic nanoreactor has been developed for oxidative coupling of arenethiols with arylhydrazines to form unsymmetrical diaryl sulfides in water at room temperature.

Aryldithiocarbamates as thiol alternatives in Cu-catalyzed C(aryl)-S coupling reactions using aryldiazonium tetrafluoroborate salts

An efficient method for the synthesis of unsymmetrical diaryl sulfides has been developed by the C-S cross coupling of aryldithiocarbamates and aryldiazonium salts in the presence of CuI-2,2'-bipyridine and Zn. Aryldithiocarbamate compounds have been used here as thiol substitutes. The protocol shows wide substrate scope and good yields of the products.

Surfactant-Type Catalyst for Aerobic Oxidative Coupling of Hydrazine with Thiol in Water

A series of PEG-functionalized nitrogen ligands were developed to conduct an aerobic oxidative cross-coupling reaction between alkyl- or aryl-hydrazines with thiols in water. This surfactant-type catalyst enables high efficiencies and selectivities, while tolerating a large variety of functional groups. The mother liquor is still catalytically active after five runs.

Visible-light-promoted organic dye-catalyzed sulfidation and phosphorylation of arylhydrazines toward aromatic sulfides and diarylphosphoryl hydrazides

Visible-light-promoted sulfidation and phosphorylation of arylhydrazines for the synthesis of aromatic sulfides and diarylphosphoryl hydrazides were developed using the organic dyes rose bengal and Na₂-eosin Y as photocatalysts, respectively.

Facile synthesis of 1,2-thiobenzonitriles via Cu-catalyzed denitrogenative radical coupling reaction

The first example of denitrogenative radical coupling with 3-aminoindazoles is presented. A diverse array of 1,2-thiobenzonitriles were obtained in good yields with wide substrate scope via oxidative C–N cleavage of 3-aminoindazoles.

Arylhydrazines: novel and versatile electrophilic partners in cross-coupling reactions

Arylhydrazines are extremely valuable compounds in organic chemistry that are widely used for the synthesis of a variety of biologically active molecules such as indoles, indazoles, pyrazoles, aryltriazoles, β-lactams and quinazolines. These compounds have also been widely utilized as arylation agents in oxidative cross-coupling reactions. In this review, we will highlight the most important explorations and developments in the carbon-carbon and carbon-heteroatom (nitrogen, phosphorus, sulfur, and selenium) cross-coupling of arylhydrazines. The literature has been surveyed from 2001 to June 2018.