Diarylation of chalcogen elements using arylboronic acids via copper- or palladium-catalyzed oxidative coupling

Exploring nickel-catalyzed organochalcogen synthesis via cross-coupling of benzonitrile and alkyl chalcogenols with computational tools

The preparation of organochalcogens has increased in recent times due to their promising biological activity properties. This work studies the reaction mechanism of a nickel(0)-catalyzed cross-coupling between benzonitrile and propanethiol to produce new C-S bonds by computational means. The proposed mechanism follows the classical oxidative addition/transmetalation/reductive elimination cross-coupling sequence, involving an unusual oxidative addition of a Ph-CN bond onto the active species. The computed catalytic cycle for thioether synthesis has been examined to determine whether the same protocol could be employed to build the analogous C-Se and C-Te bonds. The proposed mechanism for C-S coupling is validated by microkinetic modeling and shows a very good agreement with available experimental data. The extension of the proposed mechanism to C-Se and C-Te couplings indicates that these new reactions should be operative, although their reaction rates appear to be significantly slower.

Benzoimidazolyl Organoseleniums: Antioxidant Activity and Catalysts for Selective Iodination of Arenes and Nitro-Michael Reaction

Here, the synthesis and catalytic activities of benzoimidazole-derived organoselenium compounds have been explored. The synthesized bis(2-benzoimidazolyl) diselenide, having increased Lewis acidity on the selenium center, outperforms simple phenyl and N-phenyl benzamide-based diselenides when compared for thiol peroxidase hydrogen peroxide decomposing antioxidant activity with a reduction rate of 18.6 ± 1.9 μM/s. The synthesized diselenide also acted as an efficient catalyst for the activation of N-iodo-succinimide toward the regioselective, monoiodination of electron-rich arenes and activation of nitro-alkene for nitro-Michael reactions for the first time.

Nucleophilic Selenocyclization Reaction of Benzodiynes Promoted by Sodium Selenide: Synthesis of Isoselenochromenes

We describe here the synthesis of isoselenochromenes via a nucleophilic selenocyclization reaction of benzodiynes with sodium selenide. The central parameters that affect this cyclization reaction were studied, and the best reaction conditions were applied to different substrates to determine the scope of the method. The results indicated that isoselenochromenes were obtained in higher yields when the reactions were performed by the addition of NaBH4 (3 equiv), at room temperature, under nitrogen atmosphere, to a solution of elemental selenium (2 equiv) in dimethylformamide (2 mL). After 1 h, a benzodiynes (0.25 mmol) solution in EtOH (3 mL) was added at room temperature. The reaction was stirred at 75 °C until the starting material was consumed. The best conditions were applied to benzodiynes having electron-rich, electron poor aromatic rings, and alkyl groups directly bonded to the alkynes. The same reaction condition was extended to isothiochromene derivatives but failed to prepare isotelurochromenes. The isoselenochromenes were easily transformed into three new classes of organoselenium compounds using classical methods available in the literature. We also conducted several control experiments to propose a reaction mechanism.

Synthesis of Diaryl Tellurides with Sodium Aryltellurites under Mild Conditions

A highly efficient new protocol has been developed for the formation of C-Te bonds, leading to both symmetrical and unsymmetrical diaryl tellurides. This protocol utilizes sodium aryltellurites (4), which can be easily prepared from low-cost aryltelluride trichlorides and NaOH. The synthesis involves the use of 4 and arylazo sulfones as starting materials in the presence of (MeO)2P(O)H. A variety of diaryl tellurides are obtained in moderate to good yields using this method. Importantly, this innovative protocol eliminates the need for traditional, highly toxic aryltellurolating reagents such as diaryl ditellurides and elemental tellurium. This study will bring new vitality to the synthesis of tellurides.

Bidentate Ligand Driven Intramolecularly Te…O Bonded Organotellurium Cations from Synthesis, Stability to Catalysis

A new series of unsymmetrical phenyl tellurides derived from 2-N-(quinolin-8-yl) benzamide ligand has been synthesized in a practical manner by the copper-catalyzed method by using diaryl ditelluride and Mg as a reductant at room temperature. In order to augment the Lewis acidity of these newly formed unsymmetrical monotellurides, these have been transformed into corresponding unsymmetrical 2-N-(quinolin-8-yl)benzamide tellurium cations. Subsequently, these Lewis acidic tellurium cations were used as chalcogen bonding catalysts, enabling the synthesis of various substituted 1,2-dihydroquinolines by activating ketones with anilines under mild conditions. Moreover, the synthesized 2-N-(quinolin-8-yl)benzamide phenyl tellurium cation has also catalyzed the formation of β-amino alcohols in high regioselectivity by effectively activating epoxides at room temperature. Mechanistic insight by 1 H and 19 F NMR study, electrostatic surface potential (ESP map), control reaction in which tellurium cation reacted explosively with epoxide, suggested that the enhanced Lewis acidity of tellurium center seems responsible for efficient catalytic activities under mild conditions enabling β-amino alcohols with excellent regioselectivity and 1,2-dihydroquinolines with trifluoromethyl, nitro, and pyridylsubstitution, which were difficult to access.

2-Benzamide Tellurenyl Iodides: Synthesis and Their Catalytic Role in CO2 Mitigation

Benzamide-derived organochalcogens (chalcogen=S, Se, and Te) have shown promising interest in biological and synthetic chemistry. Ebselen molecule derived from benzamide moiety is the most studied organoselenium. However, its heavier congener organotellurium is under-explored. Here, an efficient copper-catalyzed atom economical synthetic method has been developed to synthesize 2-phenyl-benzamide tellurenyl iodides by inserting a tellurium atom into carbon-iodine bond of 2-iodobenzamides in one pot with 78-95 % yields. Further, the Lewis acidic nature of Te center and Lewis basic nature of nitrogen of the synthesized 2-Iodo-N-(quinolin-8-yl)benzamide tellurenyl iodides enabled them as pre-catalyst for the activation of epoxide with CO2 at 1 atm for the preparation of cyclic carbonates with TOF and TON values of 1447 h-1 and 4343, respectively, under solvent-free conditions. In addition, 2-iodo-N-(quinolin-8-yl)benzamide tellurenyl iodides have also been used as pre-catalyst for activating anilines and CO2 to form a variety of 1,3-diaryl ureas up to 95 % yield. The mechanistic investigation for CO2 mitigation is done by 125 Te NMR and HRMS studies. It seems that the reaction proceeds via formation of catalytically active Te-N heterocycle, an ebtellur intermediate which is isolated and structurally characterized.

Silver-catalyzed synthesis of symmetrical diaryl tellurides from arylboronic acids and tellurium

The synthesis of symmetrical tellurides from different arylboronic acids and elemental tellurium using AgNO3 as a catalyst was performed.

A Base-Free Copper-Assisted Synthesis of C2-Symmetric Spirotelluranes and Biaryls Based on Divergent Stoichiometry of Na2Te

A one pot Cu(I)-assisted synthetic methodology has been developed for the preparation of biologically important C2-symmetric spirodiaza, benzyloxy, benzoxytelluranes from 2-bromo-N-aryl benzamides, benzyl alcohols, and benzoic acid by using tellurium...

Stability of di-butyl-dichalcogenide-capped gold nanoparticles: experimental data and theoretical insights

Metals capped with organochalcogenides have attracted considerable interest due to their practical applications, which include catalysis, sensing, and biosensing, due to their optical, magnetic, electrochemical, adhesive, lubrication, and antibacterial properties. There are numerous reports of metals capped with organothiol molecules; however, there are few studies on metals capped with organoselenium or organotellurium. Thus, there is a gap to be filled regarding the properties of organochalcogenide systems which can be improved by replacing sulfur with selenium or tellurium. In the last decade, there has been significant development in the synthesis of selenium and tellurium compounds; however, it is difficult to find commercial applications of these compounds because there are few studies showing the feasibility of their synthesis and their advantages compared to organothiol compounds. Stability against oxidation by molecular oxygen under ambient conditions is one of the properties which can be improved by choosing the correct organochalcogenide; this can confer important advantages for many more suitable applications. This paper reports the successful synthesis and characterization of gold nanoparticles functionalized with organochalcogenide molecules (dibutyl-disulfide, dibutyl-diselenide and dibutyl-ditelluride) and evaluates the oxidation stability of the organochalcogenides. Spherical gold nanoparticles with diameters of 24 nm were capped with organochalcogenides and were investigated using X-ray photoelectron spectroscopy (XPS) to show the improved stability of organoselenium compared with organothiol and organotellurium. The results suggest that the organoselenium is a promising candidate to replace organothiol because of its enhanced stability towards oxidation by molecular oxygen under ambient conditions and its slow oxidation rate. The observed difference in the oxidation processes, as discussed, is also in agreement with theoretical calculations.

Advances in Cu and Ni-catalyzed Chan–Lam-type coupling: synthesis of diarylchalcogenides, Ar2–X (X = S, Se, Te)

Advances in the Cu and Ni-catalyzed Chan–Lam-type coupling of aryl/heteroarylboronic acids with various chalcogen sources for diarylsulfide, diarylselenide and diaryltelluride synthesis are covered in this review.

Lewis Acid-Catalyzed Asymmetric Selenocyanation of β-Ketoesters with N-Selenocyanatosaccharin

The first electrophilic asymmetric selenocyanation has been achieved in the presence of Ni(OTf)₂ and (R,R)-DBFOX/Ph using N-selenocyanatosaccharin as the new selenocyanation reagent. Thus, a series of α-selenocyanato-β-keto esters were synthesized with high yields (up to 99%) and good ee values (up to 92% ee). The readily preparation of the reagent and high enantioselectivity make this methodology much practical for the synthesis of chiral selenocyanates.

DNA Junction Ligands Trigger DNA Damage and Are Synthetic Lethal with DNA Repair Inhibitors in Cancer Cells

Translocation of DNA and RNA polymerases along their duplex substrates results in DNA supercoiling. This torsional stress promotes the formation of plectonemic structures, including three-way DNA junction (TWJ), which can block DNA transactions and lead to DNA damage. While cells have evolved multiple mechanisms to prevent the accumulation of such structures, stabilizing TWJ through ad hoc ligands offer an opportunity to trigger DNA damage in cells with high levels of transcription and replication, such as cancer cells. Here, we develop a series of azacryptand-based TWJ ligands, we thoroughly characterize their TWJ-interacting properties in vitro and demonstrate their capacity to trigger DNA damage in rapidly dividing human cancer cells. We also demonstrate that TWJ ligands are amenable to chemically induced synthetic lethality strategies upon association with inhibitors of DNA repair, thus paving the way toward innovative drug combinations to fight cancers.

Copper-Catalyzed Synthesis of Unsymmetrical Diorganyl Chalcogenides (Te/Se/S) from Boronic Acids under Solvent-Free Conditions

The efficient and mild copper-catalyzed synthesis of unsymmetrical diorganyl chalcogenides under ligand- and solvent-free conditions is described. The cross-coupling reaction was performed using aryl boric acids and 0.5 equiv. of diorganyl dichalcogenides (Te/Se/S) in the presence of 3 mol % of CuI and 3 equiv. of DMSO, under microwave irradiation. This new protocol allowed the preparation of several unsymmetrical diorganyl chalcogenides in good to excellent yields.