Mechanochemical synthesis of organoselenium compounds

We disclose herein a strategy for the rapid synthesis of versatile organoselenium compounds under mild conditions. In this work, magnesium-based selenium nucleophiles are formed in situ from easily available organic halides, magnesium metal, and elemental selenium via mechanical stimulation. This process occurs under liquid-assisted grinding (LAG) conditions, requires no complicated pre-activation procedures, and operates broadly across a diverse range of aryl, heteroaryl, and alkyl substrates. In this work, symmetrical diselenides are efficiently obtained after work-up in the air, while one-pot nucleophilic addition reactions with various electrophiles allow the comprehensive synthesis of unsymmetrical monoselenides with high functional group tolerance. Notably, the method is applied to regioselective selenylation reactions of diiodoarenes and polyaromatic aryl halides that are difficult to operate via solution approaches. Besides selenium, elemental sulfur and tellurium are also competent in this process, which showcases the potential of the methodology for the facile synthesis of organochalcogen compounds.

Asymmetric Allenylation of Alkynes mediated by Chiral Organoselenated Reagents under Oxidative Conditions

The reactivity of novel chiral lactamide-substituted diselenide-based reagents under oxidative conditions was exploited to develop a metal-free method for the preparation of enantioenriched allenylamides from simple alkynes in good yields, and with enantiomeric excesses up to 99 %. The key of the success in this method is attributed to the hydrogen-bonded lactamide appendages that ensure configurational stability of chiral vinyl selenoxide intermediates for an optimal enantiotopic β-syn-elimination step.

Copper-Catalyzed Cascade Multicomponent Reaction of Azides, Alkynes, and Selenium: Synthesis of Ditriazolyl Diselenides

A copper-catalyzed cascade multicomponent reaction for synthesizing ditriazolyl diselenides from azides, terminal alkynes, and elemental selenium has been developed. The present reaction features utilizing readily available and stable reagents, high atom-economy, and mild reaction conditions. A possible mechanism is proposed.

Homocouplings of Sodium Arenesulfinates: Selective Access to Symmetric Diaryl Sulfides and Diaryl Disulfides

Symmetrical diaryl sulfides and diaryl disulfides have been efficiently and selectively constructed via the homocoupling of sodium arenesulfinates. The selectivity of products relied on the different reaction systems: symmetrical diaryl sulfides were predominately obtained under the Pd(OAc)2 catalysis, whereas symmetrical diaryl sulfides were exclusively yielded in the presence of the reductive Fe/HCl system.

Visible-Light-Driven Thioesterification of Aryl Halides with Potassium Thiocarboxylates: Transition-Metal Catalyst-Free Incorporation of Sulfur Functionalities into an Aromatic Ring

Reactions of acceptor-substituted aryl iodides and bromides with potassium thiocarboxylates under white light irradiation allow for the preparation of S-aryl thioesters including synthetically versatile S-aryl thioacetates. This transition-metal and external photocatalyst-free method features extremely mild reaction conditions compared with those used in transition-metal-catalyzed protocols. Reactions proceed via the initial formation of an electron donor-acceptor (EDA) complex in the ground state, which was supported by UV-vis spectra. Electron paramagnetic resonance (EPR) spin-trapping experiments using phenyl-N-tert-butylnitrone (PBN) have revealed the radical nature of the reaction.

Highly efficient synthesis of diselenides and ditellurides catalyzed by polyoxomolybdate-based copper

A polyoxomolybdate-based copper-catalyzed synthesis of diselenides and ditellurides from organic iodides and elemental selenium or tellurium in moderate to excellent yields is developed.

Copper catalyzed reaction of alcohols, alkyl halides and Na2S2O3: An odorless and ligand-free rout to unsymmetrical thioether synthesis

A CuI-catalyzed condensation reaction between alcohols, alkyl halides, and Na2S2O3 leading to structurally diverse thioethers is reported. A variety of alkyl halides and electron-rich benzyl alcohols were employed successfully in...

Transition Metal Catalyst, Solvent, Base Free Synthesis of Diaryl Diselenides under Mechanical Ball Milling

A convenient, efficient, and general procedure for the synthesis of diaryl diselenides has been developed by the reaction of aryl diazonium tetrafluoroborates and Potassium Selenocyanate on the surface of alumina under ball-milling in absence of any solvent, transition metal catalyst and base in room temperature. A wide range of functionalized diaryl diselenides are obtained in high purity and high yield by this procedure.

BACKGROUND

Synthesis of diaryl diselenides was restricted into only few Cu-catalyzed C-Se Cross coupling protocol where use of ligands, high reaction temp, long reaction time were required.

OBJECTIVE

To achieve a sustainable protocol for the synthesis of diaryl diselenides Method: Reaction of aryl diazonium fluoroborate with KSeCN was successfully performed under ball milling in absence of any ransition metal catalyst, ligands, base and external heating to get diaryl diselenides.

RESULTS

A library of diaryl diselenides were obtained in good yields with different functional groups.

CONCLUSION

First transition metal free protocol for the synthesis of diaryl diselenides has been developed successfully.

Application of Bulky NHC-Rhodium Complexes in Efficient S-Si and S-S Bond Forming Reactions

The efficient and straightforward syntheses of silylthioethers and disulfides are presented. The synthetic methodologies are based on new rhodium complexes containing bulky N-heterocyclic carbene (NHC) ligands that turned out to be efficient catalysts in thiol and thiol-silane coupling reactions. These green protocols, which use easily accessible reagents, allow obtaining compounds containing S-Si and S-S bonds in solvent-free conditions. Additionally, preliminary tests on coupling of mono- and octahydro-substituted spherosilicates with selected thiols have proved to be very promising and showed that these catalytic systems can be used for the synthesis of a novel class of functionalized silsesquioxane derivatives.

Unusual Deoxidative Coupling Reaction of β-Sulfinyl Esters with Benzylic Trimethylammonium Salts

A KOH-promoted unusual deoxidative coupling reaction of β-sulfinyl esters with benzylic trimethylammonium salts to produce thioethers is discovered for the first time. If quaternary ammonium salts synthesized from enantiomerically enriched amines are adopted, highly enantiomerically enriched benzyl thioethers (>95-99% ee) with configurations opposite to those of the enantiomerically enriched amines are obtained.

Visible-Light Mediated Diarylselenylative Cyclization of 1,6-Enynes

We herein described a selenylative cyclization reaction of enynes by the utilization of diselenides as radical sources. The visible-light irradiation of the reaction mixture enables the generation of the selenium atom radical to trigger the radical addition/cyclization/selenation sequences. Both terminal alkyne and internal alkyne derived 1,6-enynes were tested and suitable for the current synthetic protocol, delivering various kinds of selenium-containing cycles in good yields.

Polyselenonium salts: synthesis through sequential selenium-epoxy 'click' chemistry and Se-alkylation

With the help of amphiphilic homopolymers, this work explores three new avenues in polymer chemistry: (i) the 'click' nature of the selenium-epoxy reaction, (ii) alkylation of the seleno-ethers as a means to prepare cationic polyelectrolytes, and (iii) the antibacterial activity of polyselenonium salts.

Selenium and Tellurium Derivatives of Corannulene: Serendipitous Discovery of a One-Dimensional Stereoregular Coordination Polymer Crystal Based on Te-O Backbone and Side-Chain Aromatic Array

Monobromo-, tetrabromo-, and pentachloro-corannulene are subjected to nucleophilic substitution reactions with tolyl selenide and phenyl telluride-based nucleophiles generated in situ from the corresponding dichalcogenides. In the case of selenium nucleophile, the reaction provides moderate yields (52-77 %) of the targeted corannulene selenoethers. A subsequent oxidation of the selenium atoms proceeds smoothly to furnish corannulene selenones in 81-93 % yield. In the case of tellurides, only monosubstitution of the corannulene scaffold could be achieved albeit with concomitant oxidation of the tellerium atom. Unexpectedly, this monotelluroxide derivative of corannulene (RR'Te=O, R=Ph, R'=corannulene) is observed to form a linear coordination polymer chain in the crystalline state. In this chain, Te-O constitutes the polymer backbone around which the aromatic groups (R and R') arrange as polymer side-chains. The polymer crystal is stabilized through intramolecular π-π stacking interactions of the side-chains and intermolecular hydrogen and halogen bonding interactions with the solvent (chloroform) molecules. Interestingly, each diad of the polymer chain is racemic. Therefore, in terms of stereoregularity, the polymer chain can be described as syndiotactic.

Recent Developments and Perspectives in the C-Se Cross Coupling Reactions

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The C-Se bond forming reactions are attractive synthetic strategies for biochemists and synthetic chemists alike for the synthesis of various molecules that are of biological, pharmaceutical and material interest. Therefore, the design and synthesis of organoselenium compounds currently constitute engaging fundamental problems in applied chemistry both in pharmaceutical and academic laboratories. This review discusses the recent works reported in carbon–selenium cross-coupling reactions with the emphasis on the mechanistic aspects of the reactions. The reacting species, the addition of ligands, selection of catalysts, use of suitable solvents, proper setting of reaction time, are well discussed to understand the detailed mechanism. Various simple, economical and environmentally friendly protocols are demonstrated, which ensured product stability, low toxicity, environmentally benign and excellent reactivity for the synthesis of organoselenium compounds. This review covers the scientific literature from 2010 to 2019.

Synthesis and nano-Pd catalyzed chemoselective oxidation of symmetrical and unsymmetrical sulfides

A highly chemoselective, efficient and nano-Pd catalyzed protocol for the rapid construction of sulfoxides and sulfones via the oxidation of symmetrical and unsymmetrical sulfides using H2O2 as an oxidant has been developed, respectively. The ready availability of starting materials, easy recovery and reutilization of the catalyst, wide substrate scope, and high yields make this protocol an attractive alternative. The process also involves the metal-free and microwave-promoted synthesis of symmetrical diarylsulfides, and FeCl3-mediated preparation of symmetrical diaryldisulfides through the reaction of arenediazonium tetrafluoroborates with Na2S·9H2O as a sulfur source. In addition, unsymmetrical sulfides were generated via the K2CO3-mediated reaction of arenediazonium tetrafluoroborates with symmetrical disulfides.

Synthesis of C 3-symmetric star-shaped molecules containing α-amino acids and dipeptides via Negishi coupling as a key step

We demonstrate a new synthetic strategy toward star-shaped C₃-symmetric molecules containing α-amino acid (AAA) derivatives and dipeptides. In this regard, trimerization and Negishi cross-coupling reactions are used as the key steps starting from readily available 4’-iodoacetophenone and L-serine. These C₃-symmetric molecules containing AAA moieties are useful to design new ligands suitable for asymmetric synthesis and peptide dendrimers.

Iron(III)-Catalyzed Highly Regioselective Halogenation of 8-Amidoquinolines in Water

A simple protocol of iron(III)-catalyzed halogenation of 8-amidoquinolines in water under mild conditions was developed, affording the 5-halogenlated products in good to excellent yields up to 98%. The reaction mechanism most likely involves a single-electron transfer (SET) process.

Trifluoromethylthiolative 1,2-difunctionalization of alkenes with diselenides and AgSCF3

An efficient regioselective difunctionalization of alkenes via trifluoromethylthiolation has been accomplished employing diaryl diselenide and AgSCF₃ in the presence of BF₃·OEt₂.

In situ synthesis of CuO nanoparticles over functionalized mesoporous silica and their application in catalytic syntheses of symmetrical diselenides

A versatile and novel mesoporous silica supported CuO nanoparticle catalyst (nCuO-FMS) and its application in the syntheses of symmetrical diselenides.

Thermal conversion of primary alcohols to disulfidesviaxanthate intermediates: an extension to the Chugaev elimination

Heating primaryO-alkylS-difluoro(ethoxycarbonyl)methyl xanthates yields disulfides. This extends to the Chugaev elimination.

Elemental sulfur as a sulfuration agent in the copper-catalyzed C-H bond thiolation of electron-deficient arenes

By utilizing elemental sulfur as the thiolation agent and oxidant, a copper-catalyzed direct C-H bond thiolation of electron-deficient arenes was demonstrated. Various electron-deficient arenes were proved to be suitable for this transformation. Preliminary mechanistic studies indicated that this reaction underwent a radical pathway, in which the trisulfur radical anion (S₃˙^-) might play a vital role. Meanwhile, KIE experiments suggested that C-H bond cleavage was not involved in the rate-determining step.

Water and Aqueous Mixtures as Convenient Alternative Media for Organoselenium Chemistry

Even if water is the natural environment for bioorganic reactions, its use in organic chemistry is often severely limited by the high insolubility of the organic derivatives. In this review, we introduce some examples of the use of water to perform organoselenium chemistry. We mainly discuss the advantages of this medium when the recyclability is demonstrated and when the water can control the selectivity of a reaction or enhance the reaction rate.