Selenium, thiol derivatives

Oxidation with bis(p-methoxyphenyl) telluroxide (general procedure All the reactions are performed at room temperature under Nj in CHCI3 or CHjClj. Approximately 10 mL of solvent is used for every 100 mg of substrate. For thiocarbonyl derivatives, 1.1 equiv of the reagent is used, for thiols 0.55 equiv. The mixtures are concentrated by evaporation and submitted to thin layer or column chromatography to isolate the products. An2Te is always recovered in a yield of 64-96%, while sulphur or selenium is always recovered in near quantitative yields from reaction with thio- or selenocarbonyl derivatives. 

The use of hypervalent iodine reagents for heteroatom-heteroatom bond forming reactions is well established in the context of classical oxidation chemistry [1-11]. For example, oxidations of anilines to azobenzenes, thiols to disulfides, and sulfides to sulfoxides with aryl-A3-iodanes were documented decades ago [1-5]. During the last ten years, particular attention has also been given to oxidative transformations of compounds derived from heavier elements, including the interception of reaction intermediates or initially formed products with external nucleophiles. A second important development is the utilization of sulfonyliminoiodanes, ArI = NS02R, for heteroatom-nitrogen bond formation, especially for imidations of sulfur, selenium, phosphorus and arsenic com-... 

Carbonsulfur bonds can be formed by the reaction of elemental sulfur with a lithio derivative, as illustrated by the preparation of thiophene-2-thiol 446. If dialkyl or diaryl disulfides are used as reagents to introduce sulfur, then alkyl or aryl sulfides are formed sulfinic acids are available by reaction of lithium derivatives with sulfur dioxide. In the pyrrole series, a 2-thiol and the corresponding selenol can be prepared via reaction of 2-lithio-l-methylpyrrole with sulfur or selenium, then trapping with Me3SiCl leading to the 2-Me3SiX-substituted derivatives <1997T13079>. 

As well as thiol esters, selenol esters (1) frequently exhibit a high and selective reactivity toward nucleophiles, which is enhanced even further by activation with heavy ions or oxidizing agents. These properties make selenol esters valuable acyl transfer agents. This review deals with general methods for the synthesis of selenol esters and their reactivity as acyl transfer agents. Furthermore, selenoesters (2), isomeric compounds of selenol esters, and their derivatives selenoamides (3) are also described. These compounds show the characteristic reactivity based on the carbon-selenium double bond. 

Selenol esters are expected to be a more reactive species than the corresponding thiol esters or 0x0 esters due to the comparatively weak bonding between carbon and selenium. The ability of the selenol esters to serve as active acyl transfer agents has been readily demonstrated by the easy conversion of the selenol ester (34 equation 15) to its corresponding acid (35), ester (36) or amide (37). This acyl-selenium bond cleavage has also been promoted by Cu and Cu" salts. - The isopropylidene derivative (38 equation 16) of ribofuranosylacetate has been converted to a lactone (40) in good yield via the selenol ester (39). 

The oxygen attached to the selenium atom of ebselen derivatives can cause oxidation of a sulfide or phosphine to the sulfoxide or phosphine oxide, respectively (Scheme 12). Thiols are converted to... 

Among the most important volatile sulfur compounds are hydrogen sulfide (sulfan), various thiols, sulfides, isothiocyanates and heterocyclic sulfur compounds. Precursors of volatile sulfur compounds are usually non-volatile, sensory indifferent sulfur compounds, especially sulfur-containing amino acids cysteine, cystine, methionine and their derivatives, such as S-alk(en)yl cysteine sulfoxides, glucosinolates, thiamine and other compounds. An important sulfur compound is also sulfur dioxide, which is used as a preservative and an inhibitor of enzymatic browning reactions or the Maillard reaction. It also occurs in a small amount as a metabolite in fermentation processes. Sulfur compounds may be accompanied by their selenium analogues at very low concentrations. 

Sulfur, selenium and tellurium derivatives have also been synthesized. From thiols and alkylcyclopentanedienyl lanthanides (Stults et al. 1990b) dimeric compounds have been obtained according to the equation... 

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