Benzylic tellurides

Dibenzyl ditelluride, benzyl telluride and benzyl tellurocyanate generate benzyl bromide on treatment with excess bromine. 

It has been reported that sodium-, potassium- calcium- and magnesium-tellurium exchanges are achieved by similar procedures with alkyl, aryl, ethynyl, vinyl, allyl and benzyl tellurides. ... 

It was observed that in the case of bromo- or iodo-substituted benzylic tellurides the lithium-Br exchange and/or the halogen displacement by the n-butyllithium competes with the Te-Li exchange, resulting in lower yields of the desired products. This drawback is avoided by using ether as solvent. 

Dibenzyl ditelluride exhibits the peculiar lability of the tellurium-benzyl bond already mentioned for the corresponding tellurides. By heating the solid at 120°C, or by exposure in solution to ordinary incandescent lighting or to a Hanovia lamp, a rapid decomposition into elementary tellurium and dibenzyl telluride occurs. ... 

Dibenzyl telluride (typical procedure) Rongalite (18.0 g, 0.5 mol) is added under N2 at 80°C to a suspension of Te (2.56 g, 20 mmol) in a solution of NaOH (12 g, 0.3 mol) in 125 mL of H2O. After stirring for 1 h, a solution of benzyl chloride (1.26 g, 10 mmol) in a small volume of EtOH is added dropwise at room temperature to the almost colourless telluride solution. After stirring for an additional hour, the mixture is extracted with ether, and the ethereal solution dried (MgS04) and evaporated. The residue is recrystalUzed from petroleum ether (40-60°C) under red light, giving the telluride as yellow needles (1.09 g (70%) m.p. 49-57°C). 

The title reagent (prepared by the reaction of sodium hydrogen telluride with chlorotriph-enylstannane) reacts easily with the more active halides such as benzyl bromides whereas common halides need to be activated by cesium fluoride. 

Dibenzyl and arylbenzyl tellurides (like dibenzyl ditelluride, see Section 3.5.3) exhibit an unusual behaviour towards halogens, undergoing cleavage of the teUurium-benzyl... 

The known property of diorganyl tellurides of reducing metallic salts, applied to tita-nium(IV) chloride, generates a titanium(III) species which is a useful reagent for some selective reductions. By this method benzaldehyde is reduced to dihydrobenzoin, and benzyl to benzoin, and successively to desoxybenzoin. ... 

Common esters such as alkyl and benzyl carboxylates are easily dealkylated by sodium hydrogen telluride, sodium telluride and sodium ditelluride in DMF. In accordance with a typical S 2 displacement at the aUcoxy group carbon, methyl, ethyl and benzyl esters react smoothly. The nucleophilicity of the reagents is enhanced by the polar aprotic solvent, and the reactivity decreases with higher alkoxy chains due to steric hindrance (e.g. 

Alkyl, aryl, allyl, benzyl, vinyl, ethynyl tellurides, tellurobutadienes, divinyltellurides, tellurobutenines, telluro(thio)- and telluro(seleno)ketene acetals and j3-(phosphorovinyl) tellurides are susceptible to such exchange, giving the corresponding lithium compounds trapped in sequence with selected electrophiles. ... 

Reaction of organotellurium compounds with quinones (typical procedure, 2-benzyl-l, 4-benzoquinone) A solution of benzyl p-methylphenyl telluride (111 mg, 0.36 mmol) and 1,4-benzoquinone (78.0 mg, 0.72 mmol) in benzene (0.6 mL) in a Pyrex tube was irradiated with a 200 W high-pressure mercury lamp at 100°C for 1 h. After the solvent was removed under reduced pressure, the crude mixture was purified by flash chromatography (silica gel 6.4 g elution with 5% ethyl acetate in hexane) to give the product in 57% yield. 

Diphenyl benzyl tellurium bromide,1 (CeH5)2(C6H5.CH2)TeBr, from diphenyl telluride dissolved in benzyl bromide, forms a crystalline mass, M.pt. 90° to 91° C., converted by silver hydroxide into the corresponding hydroxide, a yellow oil, very soluble in water, and yielding a sparingly soluble picrate on treatment with picric acid. 

Tellurides 1129 prepared from a-bromo-o-toluylesters 1128 undergo lithium-tellurium exchange to give the corresponding benzylic anions 1130, which react with aldehydes or ketones to afford dihydroisocoumarins in high yield (Scheme 281) <1997SL1047>. 

The method is less successful with benzylic and allylic halides, and problems of selectivity with these substrates have been overcome in the past via an initial substitution with lithium butyltelluride the organolithium is then formed cleanly from the telluride 135 or 136 (which need not be isolated) by tellurium-lithium exchange.112... 

Some nucleophilic species of tellurium are used to regenerate a functional group from its protected form. For example, carboxylic acids 51 are regenerated in high yields from their alkyl and benzyl esters by using sodium hydrogen telluride or sodium telluride (Scheme 27).21,30,114,115... 

Dihydro-l//-2-benzotellurin, prepared from 2-(2 -bromoethyl)benzyl bromide and disodium telluride, has a much greater stability than the telluranes2. 

Sodium telluride, prepared from tellurium and sodium borohydride in aqueous medium, reacted with benzoyl chlorides using a phase transfer technique, to produce rather unstable 7e-benzyl tellurobenzoates (benzyl benzoyl telluriums)1 in low yields and not the expected dibenzoyl telluriums. Sodium telluride must reduce benzoyl groups to benzyl groups during these reactions. 

However, benzoyl chlorides and sodium telluride under these conditions gave benzoyl benzyl tellurium1 and not dibenzoyl tellurium (p. 560). 

Selenides (selenoethers)and tellurides can be prepared via RSe and RTe species, and selenium and borohydride exchange resin followed by the halide give the selenoether. The La/l2-catalyzed reaction of diphenyl diselenide with primary alkyl iodides gave arylalkyl selenides, and Inl has been used with benzyl halides. Diaryl selenides (Ar—Se—AF) have been prepared by couphng aryl iodides with tin reagents (ArSeSnR3) with a palladium(O) catalyst. ... 

The enantiomerically pure telluronium salts 81 can also be obtained in moderate to high (41-73%) yields by the reaction between tellurides 74 and benzyl bromide or bromoethylacetate (00TA3323) (Scheme 46). The reaction is highly diastereoselec-tive. Thus, the ratio of diastereomers of the salts 81 formed under treatment of telluride 74 (R = Me) with benzyl bromide is 6 1. According to the data of an X-ray study, the main product of this reaction possesses the (R) configuration at the pyramidal tricoordinated tellurium. 

Treatment of oestrone with tetraphenylbismuth monotrifluoroacetate gave oestrone phenyl ether and exemplified, in part, a new procedure for aryl ether formation.31 A detailed study was reported of the formation of benzyl ethers by sequential reaction of alcohols with chloro(phenylmethylene)dimethylammonium chloride and sodium hydrogen telluride.32 Steroidal alcohols, inter alia, were converted into hydrolytically stable silyl ethers by reaction with B N Sil or BulPh2I which were generated in situ from the selenosilane and iodine.33 The 5a-hydroxycholestane (21) was protected in this way. 

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