Tellurinates

Kinetic studies on racemization, oxygen exchange reaction using H2lsO, and theoretical studies clarified the mechanism for racemization of optically active chalcogenic acids.34,37 The mechanism of racemization of tellurinic acids is different from that of the corresponding seleninic acids. In fact, the mechanism for racemization of optically active tellurinic acids was found to involve an... 

Diorgano diselenides have been used extensively as precursors to seleninic acids in the presence of hydrogen peroxide.The catalytic activity of preformed seleninic acids and seleninic acids generated in situ are identical. Diorgano ditellurides have also been used as catalysts in thiolperoxidase-like reactions for the oxidation of thiols with various peroxides. However, tellurinic acids are not thought to be involved even though RTe(=0)SPh types of structures are proposed as intermediates. 

Diaryl ditellurides, like diaryl disulphides and diselenides, undergo disproportionation into arene tellurolates and tellurinates by alkaline treatment. 

The tellurolate anion formed can be alkylated in situ, giving alkyl aryl tellurides, if the above reaction is effected in the presence of a phase transfer catalyst. Otherwise, performing the reaction in the presence of the reducing agent TUDO a telluride yield near to quantitative is generated, owing to the reduction of the aryl tellurinate anion to aryl tellurolate. ... 

Mixed anhydrides are prepared by reacting tellurinic anhydrides with carboxylic acids or anhydrides. ... 

Pyrrohdine, indoline, phthaloylhydrazide and 4-phenylurazole are unaffected by tellurinic anhydrides. 

Like p-methoxyphenyl teUuroxide, tellurinic 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. 

Epoxidation of olefins catalysed by polystyrene-supported tellurinic acid... 

The catalytic activity is dependent on the polymeric structure of the reagent, no epoxidation being observed with free tellurinic acids. 

The acmal reactive species which adds to the C=C bond is a reduction product of the tellurinic anhydride, formed at the expense of the ditelluride produced as the reaction proceeds. Two successive anft -acetolyses (a) of the formed teUuronium intermediate and (b) of the resulting acetoxytelluride (which is acid catalysed), give the final diacetate with an... 

As shown for the preceding method employing phenyltellurinic anhydride, the diacetoxylation prefers a yyn-stereochemistry, especially for cyclic aUcenes and dy-linear aUcenes, whereas for frany-alkenes the preference for the yyn-stereochemistry is decreased. In accordance with the mechanism proposed in the case of the tellurinic anhydride, the reaction can be rationalized as involving the intermediacy of a frany-adduct followed by an SN2-type detellurative acetolysis. 

The observation that the previously described diacetoxylation of olefins by means of tel-lurinic anhydrides produces quantitative yields of the corresponding ditellurides suggested the oxidative functionalization of olefins employing diphenyl diteUuride combined with an oxidizing agent instead of the tellurinic anhydride. ... 

Aryltellnrinyl acetates, generated as previously described from the corresponding tellurinic anhydrides and acetic acid, add to hydroxy olefins, giving tellurinylated cyclic ethers. The reaction is performed in refluxing acetic acid or in chloroform in the presence of BFj EtjO. Owing to their hygroscopicity and intractable nature, the products are reduced with hydrazine hydrate, and isolated as tellurides (as for the aminotellurinylation reactions). 

TELLURIN AND DERIVATIVES OF 4-H-TELLURINS AND 4-OXO-4-H-TELLURINS (TELLUROPYRAN-4-ONES)... 

Disubstituted tellurins were obtained by reduction (with DIBAL-Fl) of the the 4-oxo-4//-tellurins, prepared by the addition of alkali metal tellurides to... 

Di-tert-butyl-4H-tellurin A solution of 1.60 g (5.0 mmol) of 2,6-di-ferf-butyl-4-oxo /7-tellurin in 15 mL dry tetrahydrofuran is placed into a flame-dried, 50 mL, two-necked flask equipped with a rubber septum cap and a dry-argon inlet. The flask is cooled to 0°C 7.5 mL of a 1.5 M solution (10.5 mmol) of diisobutyl aluminium hydride in toluene are dropped to the cold solution with the help of a syringe. The reaction is quenched by addition of 10 mL of moist diethyl ether. The resulting solution is poured into 100 mL diethyl ether. The organic phase is washed with three 25 mL portions of 5% hydrochloric acid and then with two 50 mL portions of brine, dried with anhydrous sodium sulphate, filtered and the filtrate concentrated. Cold pentane (5 mL) is added to the residual oil and the mixture is cooled to -20°C. The pentane is decanted from the yellow aystals. The decantate is chromatographed on sihca gel with dichloromethane as the mobile phase to give a yellow oil. Yield 62%. 

By treatment with halogens, the 4-oxo-4H tellurins are converted into the corresponding dihalides. ... 

During the second method of preparation a by-product is produced which after reduction consists of a compound of one molecule of phenox-tellurine with one molecule of 2( )-chloro-8( )-methylphenoxtellurine. This results from the presence of a small proportion of phenyl p( )-tolyl ether in the diphenyl ether.1... 

Electrophilic addition reactions of tetravalent tellurium compounds have been reviewed.64 2-Naph-thyltellurium trichloride (ArTeCb) adds to alkenes in an anti stereospecific manner (equation 11), whereas tellurium tetrachloride gives mixtures of 2 1 adducts with both syn and anti addition.72 A one-pot alkene inversion procedure has been developed, based upon TeCU addition to alkenes followed by treatment of the (3-chloroalkyltellurium trichloride adduct with aqueous Na2S (Scheme 37).73 Tellurium compounds such as tellurinyl acetates, ArTe(0)0Ac, prepared in situ through reaction of tellurinic acid anhydrides with acetic acid, can be employed in oxytelluration and aminotelluration procedures (Schemes 38 and 39).74 In the oxytelluration reaction intermediate triacetates of the type RCH2Te(OAc)2Ph are reduced with hydrazine to the corresponding tellurides. 

A direct synthetic route to 4//-7-hydroxybcnzo[ ]tellurin-4-ones 138 involves acid-promoted dehydration of the corresponding (Z)-unsaturated carboxylic acid derivatives 137 (Scheme 14) <19980M3588>. These precursors can be readily prepared by a metallation-telluration sequence. Previous attempts to prepare molecules of this type, particularly the telluroflavones (R = Ph), were unsuccessful due to the unexpected reactivity of the C-Te bond relative to the C-Se and C-S bonds. 

As expected, similar cycloaddition reactions have been used to prepare analogous tellurium-containing heterocycles. In ///-generated tellurocarbonyl difluoride 156 can be trapped as the difluorodihydro-2//-tellurin 157 using 2,3-dimethylbutadiene (Equation 63) <1993JCD2547>. 

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