P-Methoxyphenyl telluroxide

Bis(p-methoxyphenyl) telluroxides as a mild and selective oxidizing reagent... 

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 following compounds are unaffected by bis(p-methoxyphenyl) telluroxide dithi-olanes, enamines, aldehydes, ketones, alcohols, pyrroles, indoles, amino acids, aromatic amines, monohydroxyarenes, esters, hindered thiocarbonates, isonitriles, oximes, arylhy-drazones, sulphides, and selenides. ... 

A useful modification of the bis(p-methoxyphenyl) telluroxide reagent is its immobilization on a polymeric resin. This polymer-supported reagent, prepared from p-methoxyphenyl tellurocyanate and polylp-Uthiostyrene), exhibits several advantages over the monomeric reagent, such as easier product work-up and multiple recycle from the spent reagent. 

Bis(p-methoxyphenyl) telluroxide (118) and the corresponding tellurone (119) have recently been shown to exhibit mild oxidizing properties towards easily oxidizable substrates. Thus the telluroxide (118) oxidizes thiocarbonyl compounds RR C=S to the corresponding ketone RR C—O364,365 and 3,4-di-f-butylpyrocatechol to 3,4-di-f-butyl-o-quinone.364 The tellurone (119) oxidizes benzyl alcohols to the corresponding carbonyl compounds, a reaction. .which is not observed with (118).366... 

Oxidation. Bis(p-methoxyphenyl)telluroxide (1) is a mild and selective oxidant for conversion of xanthates, thiocarbamates, thioamides, and nonenolizable thiones into the corresponding oxo derivatives, and also of thiols into disulfides. Typically these reactions afford products in 70-100% yield. 1,2- and 1,4-Hydroquinones are oxidized by 1 to o- and p-quinones, respectively. Phenylhydroxylamine is oxidized to nitrosobenzene (90% yield). Phenols, amines, enamines, alcohols, oximes, dithiolanes, isonitriles, and 2,4-dinitrophenylhydrazones are unreactive. 

With the exception of a few examples of nucleophilic attack on the thiocarbonyl group, including a more recently published method using sodium hydroxide under phase transfer conditions,most conversions are carried out with oxidative reagents. Sodium peroxide, dimethyl sulfoxide with acid or iodine,selenium-derived reagents and bis(p-methoxyphenyl)telluroxide have been used. 

Like p-methoxyphenyl telluroxide, teUurinic anhydrides do not affect phenols but oxidize hydroquinones to the corresponding quinones, and oxidize thiols, thioesters, thioamides and phosphines to disulphides, esters, nitriles and phosphine oxides. 

Nitroso-dimers are also the products of the oxidation of primary or secondary amines, in essentially quantitative yields, by m-chloroperbenzoic acid, and similarly bis-(p-methoxyphenyl)telluroxide is a new mild and highly selective oxidizing agent capable of oxidizing arylhydroxylamines to nitrosobenzenes in high yield. ... 

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