Selenonium Salt as a Catalyst for Nucleophilic Substitution Reactions in Water: Synthesis of Thiocyanites and Selenocyanates.

Organothiocyanates and selenocyanates are valuable compounds, both in terms of functional group interconversion and due to their biological activities. In this contribution, we report the synthesis of a series of these important substances in a mixture of water and dimethyl carbonate (20/1 proportion) using potassium thio- or selenocyanates salts and organic bromides. The key to the effectiveness of the reaction is a chalcogen bond interaction between a selenonium salt catalyst and the organic substrate.

Synthetic application of chalcogenonium salts: beyond sulfonium.

The application of chalcogenonium salts in organic synthesis has grown enormously in the past decades since the discovery of the methyltransferase enzyme cofactor S-adenosyl-L-methionine (SAM), featuring a sulfonium center as the reactive functional group. Chalcogenonium salts can be employed as alkylating agents, sources of ylides and carbon-centered radicals, partners for metal-catalyzed cross-coupling reactions and organocatalysts. Herein, we will focus the discussion on heavier chalcogenonium salts (selenonium and telluronium), presenting their utility in synthetic organic transformations and, whenever possible, drawing comparisons in terms of reactivity and selectivity with the respective sulfonium analogues.

Xerogel-sequestered silanated organochalcogenide catalysts for bromination with hydrogen peroxide and sodium bromide.

While H2O2 is a powerful oxidant, decomposing into environmentally benign H2O and O2, a catalyst is often required for reactions with H2O2 to proceed at synthetically useful rates. Organotellurium and organoselenium compounds catalyze the oxidation of halide salts to hypohalous acids using H2O2. When sequestered into xerogel monoliths, the xerogel-chalcogenide combinations have demonstrated increased catalytic activity relative to the organochalcogen compound alone in solution for the oxidation of halide salts to hypohalous acids with H2O2. Diorganotellurides, diorganoselenides, and diorganodiselenides bearing triethoxysilane functionalities were sequestered into xerogel monoliths and their catalytic activity and longevity were investigated. The longevity of the catalyst-xerogel combinations was examined by isolating and recycling the catalyst-xerogel combination. It was found tellurium-containing catalyst 3 and selenium-containing catalyst 8 maintained their catalytic activity through three recycling trials and adding electron-donating substituents to catalyst 3 also increased the catalytic rate. The presence of organotellurium and organoselenium groups in the +4 oxidation state was determined by X-ray photoelectron spectroscopy.

Ephedrine-based diselenide: a promiscuous catalyst suitable to mimic the enzyme glutathione peroxidase (GPx) and to promote enantioselective C-C coupling reactions.

The ephedrine-based diselenide appears as a new promiscuous catalyst, able to generate optically active alcohols by addition of organozinc to aldehydes (up to 97% ee), and shows powerful GPx like activity, reducing H(2)O(2) to water in only 16.33 min (eleven times faster than PhSeSePh).

GPx-Like activity of selenides and selenoxides: experimental evidence for the involvement of hydroxy perhydroxy selenane as the active species.

The reaction mechanism of the GPx-like oxidation of PhSH with H(2)O(2) catalyzed by selenoxides proceeds via formation of the hydroxy perhydroxy selenane, which is a stronger oxidizing agent than selenoxide. A hydroxy perhydroxy selenane intermediate was observed by electrospray ionization mass spectrometry and (77)Se NMR spectroscopy in reactions of selenoxide 8 with H(2)O(2).The initial velocity of oxidation of PhSH by H(2)O(2) with selenoxide 8 is 4 orders of magnitude higher than that of 8 without peroxide. Selenoxide 8 is not reduced to selenide 6 by PhSH in the presence of H(2)O(2). While electronic substituent effects have minimal impact on the catalytic performance of selenoxides, chelating groups increase the rate of catalysis.

Evaluation of the biological effects of (S)-dimethyl 2-(3-(phenyltellanyl) propanamido) succinate, a new telluroamino acid derivative of aspartic acid.

(S)-dimethyl 2-(3-(phenyltellanyl) propanamido) succinate, a new telluroamino acid derivative, showed remarkable glutathione peroxidase (GPx)-like activity, attesting to its antioxidant potential. However, the stability and toxicity of this compound has not yet been investigated. The present study was designed to investigate the pharmacological/toxicological properties of this compound in vitro and in vivo. In vitro, this telluroamino acid derivative significantly blocked spontaneous and Fe(II)-induced TBARS formation in rat brain homogenates, demonstrating high antioxidant activity. In addition, it exhibited GPx-like and thiol oxidase activities. However, when subcutaneously administered to mice, (S)-dimethyl 2-(3-(phenyltellanyl) propanamido) succinate indicated genotoxic and mutagenic effect in adult male mice. Considering the differential effects of (S)-dimethyl 2-(3-(phenyltellanyl) propanamido) succinate in vitro and in vivo, additional experiments are needed to elucidate the mechanism(s) by which this compound displays its antioxidant/toxicological effects.

Imidazolium ionic liquids containing selenium: synthesis and antimicrobial activity.

The synthesis and antimicrobial profile of imidazolium ionic liquids containing selenium are described herein. Minimum inhibitory concentration revealed that these compounds are especially active against algae, and their activity is modulated by substituents attached to the selenium moiety as well as by the counterion.

Synthesis of diorganyl selenides mediated by zinc in ionic liquid.

A new approach for the synthesis of diorganyl selenides is described. By using economically attractive zinc dust in BMIM-BF(4), a series of diorganyl selenides were efficiently achieved in excellent yields, under neutral reaction conditions. Compared to the usual organic solvents, BMIM-BF(4) exhibited higher performance with the advantage to be reused up to five successive runs.

Ionic liquid: an efficient and recyclable medium for synthesis of unsymmetrical diorganyl selenides promoted by InI.

In an environmentally friendly protocol, InI was used as a reducing agent for the Se-Se bond to prepare unsymmetrical diorganyl selenides with very short reaction times, mild conditions and excellent yields using (bmim)BF(4) as a recyclable solvent.

Synthesis of telluroamino acid derivatives with remarkable GPx like activity.

A series of modular telluroamino acid derivatives with remarkable GPx-like behavior was prepared in an efficient and short two-step synthesis.