Detelluration

Refluxing a toluene solution of 2-methylbenzotellurazole 12b with Fc3(CO)l2 leads to detelluration of the heterocycle and formation of the iron clusters (97MI1). 

Organoiron chemistry offers the C-coordination mode, carbene series, ring opening and detelluration. Organoruthenium and especially organoosmium species are sometimes peculiar along with the classical cases of N-coordination and carbene formation, C,N- and S,N-cases can be traced. 

Dipolar cycloaddition reactions occur with mesitonitrile oxide and tellones to afford oxatellurazole in good yield,25,245,248 while a triazene is formed with phenyl azide25 probably via detelluration of a telluratriazoline ring (Scheme 44). 

The first stable 1-germaallene 89 was obtained either from the detelluration of 78 or alternatively from the dechlorination of the chlorovinylchlorogermane 90 (Scheme 27).200 The identity 89 was confirmed via trapping... 

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. 

If the dichlorotellurolactones are reduced previously to the parent tellurolactones by treatment with NaBH4, the successive detelluration saves 2 equiv of TBTH, and the... 

Reductive detelluration of aryldichlorotellurolactones (general procedure) f To a solution of the dichloroteUurolactone (1 mmol) in deoxygenated toluene, (10 mL), under reflux and N2, is added dropwise BujSuH (4 mmol). The reaction is monitored by TLC. After 4 h the solvent is evaporated and the residue chromatographed on Si02 (eluted first with petroleum ether to remove Te and Sn by-products, and then with petroleum ether/EtOAc, 1 5), giving the tellurium-free lactone. 

The synthetic utility of the described reactions is clearly illustrated by the reductive detel-luration of telluroethers with BujSnH, the entire telluration/detelluration process providing a cyclization under mild conditions for unsaturated alcohols. 

Reductive detelluration of cyclic dichlorotelluroethers (general procedure) This procedure is identical to that described for dichlorotellurolactones (see Section 4.5.1.5). 

Reductive detelluration of cyclic telluroethers (typical procedure) To a solution of 2,3-diliydro-2-[(phenylteUuro)methyl]benzofuran (0.338 g, 1 mmol) in toluene (6 ml.) is injected TBTH (0.67 ml, 2.5 mmol) at room temperamre, and the resulting solution is stirred under reflux for 1 h. The solution is evaporated under vacuum and the residual yellowish oil subjected to Si02 column chromatography (eluting with benzene/hexane, 3 1) to give pure 2,3-dihydro-2-methylbenzofuran as a colourless oil (0.128 g (95%) b.p. 93-94°C/23 torr). 

Detelluration of organotellurium compounds with the formation of new C-C bonds (carbodetelluration)... 

Diaryltellurium dichlorides are detellurated by heating with Raney nickel in appropriate solvents, giving the corresponding biaryls. ... 

In the absence of the olefin, the corresponding biaryls are formed in moderate yields (like the Raney nickel-promoted detellurations (see Section 4.6.1.1)). 

Detellurative carbonylation of organotellurium compounds preparation of carboxylic acids... 

Detellurative carbonylation of aryltellurium trichloride NiiCO) method (typical procedure). Ni(CO)4 (2.6 mL, 20 mmol) is added to p-methoxyphenyltellurium trichloride (2.0 g,... 

Detellurative carbonylation of diary It ellurium dichlorides (typical procedure) Following the above procednre, Ni(CO)4 (1.5 mL, 11.5 mmol) and di-p-methoxyphenyl-tellurium dichloride (2.0 g, 4.8 mmol) furnish p-Me0CgH4C02H (1.05 g (71%)), (p-MeOCgH4)2Te (0.25 g (15%)) and a trace amount of (p-MeOCgH4)2CO. 

Carboxylic acids are also produced through the detellurative carbonylation of several types of telluride by treatment with carbon monoxide at atmospheric pressure and room temperature in the presence of Pd(ll) salts, in various solvents. ... 

The detellurative methoxylation of the telluroxides also proceeds in high yields by treatment with trifluoroperoxyacetic acid (generated in situ from TFA and (method C). 

Detellurative methoxylation of alkyl phenyl tellurides (typical procedure)2-Methoxy 3-phenyltelluro-l,2,3,4-tetrahydronaphthalene (1.85 g, 5 mmol) is treated with MCPBA (3.3 g, 15 mmol) in MeOH (30 mL) at 25°C with stirring. After 1 h the mixture is treated with aqueous Na2S203 followed by aqueous NaHCOj and extracted with ether (3x30 mL). The extract is dried (MgS04) and evaporated, to leave a residue which is purified by Si02 TLC (eluting with hexane/EtOAc, 4 1) to afford pure tranx-2,3-dimethoxy-l,2,3,4-tetrahy-dronaphthalene (0.37 g, 1.94 mmol) and the c/x-isomer (0.15 g, 1.76 mmol (54%)). 

The title compounds, important anti-inflammatory pharmaceuticals, can be synthesized starting from aromatic ketones, as depicted in the accompanying scheme, involving the above-described detellurative methoxylation in the key step. - ... 

Further examples of reductive detelluration of tellurium compounds have been shown in connection with tellurolactonization and telluroetherification reactions (see Section 4.5). 

Styryl tellurides are also detellurated on treatment with lithium chloropalladate (2 equiv), giving stereoisomeric mixtures of the homocoupled 1,3-butadienes. 

Alternatively, if tellurium dioxide is the product desired, the sodium tellurite solution can be neutralized in a controlled fashion with sulfuric acid. As the pH is lowered, precipitates containing impurities such as lead and silica that form are filtered off. At pH 5.6 the solubility of tellurous acid reaches a minimum and essentially all of the tellurium precipitates (>98%). After filtration and drying, commercial tellurium dioxide is obtained. A diagram for the process of detellurizing of slimes and recovering tellurium products is shown in Figure 1. 

The interaction of that same ligand, type 521 (R = Me), this time with Fe3(CO)12, leads to some complexes amongst which a detellurized metal-cyclic compound 523 is found [916]. At the same time [reaction (2.14)], benzoisotelluroazole 524 forms, together with Fe3(CO)12, the azomethinic compound 525 [916] ... 

Vinylic tellurides (e.g., 183) are reacted with diethylzinc to give the corresponding vinylzincs, which are captured with H20 or D20 to give the detellurated olefin (e.g., 184) in variable isomeric ratios (Scheme 103).262 In one case, the intermediate vinylzinc was coupled with para-MeC6H4l under Pd(PPh3)4 catalysis, leading to the trisubstituted olefin 185 in 72% yield with retention of the double-bond geometry (Scheme 103).262... 

Diaryl ditellurium compounds are detellurated when refluxed in bis[methoxyethyl] ether over degassed Raney nickel4. The aryl groups are coupled to form biaryls in yields ranging from 50 to 80%. Bis[3-methyl-4-methoxyphenyl] ditellurium reacted similarly4. 

The yields vary with the solvent and the oxidizing agent employed12. Photolytic detelluration in benzene solution produces the same organic halides but in most cases in lower yield1. 

Chloroethyl tellurium trichlorides heated with sodium sulfide nonahydrate to 100° formed ethenes2,4. The detelluration step is a slereospecific /rani-elimination, which, together with the syn-addition of tellurium tetrachloride to the olefin, results in an inversion of the olefin4. 

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