Tellurinyl Acetate

Aryltellurium trichlorides are suitable reagents for the telluroetherification of olefinic alcohols and allylphenols, exhibiting the advantages of stability and easy separability of the formed crystalline dichloroteUuro derivatives compared to the preceding tellurinyl acetate method. 

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. 

When the olefin has a hydroxyl group in a y- or exposition to the double bond, the addition of the tellurinyl acetate is accompanied by the formation of cyclic ethers5. The cyclization reactions compete with the formation of the linear addition products shown in the preceding equation. 

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). 

Ethoxyphenyl Tellurium Trichloride3 To a vigorously boiling suspension of 9.0 g (30 mmol) 4-ethoxybeiizcne tellurinyl chloride in 50 ml anhydrous carbon tetrachloride is added a solution of 6.4 g (60 mmol) butyryl chloride in 5 ml carbon tetrachloride. The refluxing mixture is stirred for 1 h. On cooling, 4-ethoxypheny] tellurium trichloride precipitates. The precipitate is collected by filtration and recrystallized from acetic acid. The filtrate is stripped of the solvent and the residue distilled at atmospheric pressure. Butyric anhydride boiled at 198° yield 89%. 

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