From Tellurolates

Lithium tellurolate reacted exothermically with an equimolar amount of elemental sulfur in tetrahydrofuran. The organotellurothiolates were identified as the products by Te-NMR 

The butyl derivative - but not the phenyl derivative - undergoes an internal redox reaction below 20 to form dihutyl ditellurium and disulfide anion.  

Piperidinium 2-methoxy(tellurolobenzoate) condensed with 2,4-dinitrobenzenesulfenyl chloride in dichloromethane at — 30 . The product was 2-methoxybenzoyl 2,4-dinitrobenzenesulfenyl tellurium isolated in 32% yield as a yellow, crystalline solid that melted at 108-110° with decomposition.  

Benzenesulfonyl chloride oxidized the piperidinum tellurolate to the bis[2-methoxybenzoyl ditellurium.  

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Additional advantages are the possibility of generating the reducing agents in situ as well in catalytic amounts in the presence of an inexpensive co-reductant, and recovery of the tellurium material (for example, elemental tellurium from the above inorganic reagents and ditellurides from tellurols). 

Table 10 Unsymmetrical Diorgano Tellurium Compounds from Tellurolates and Alkyl Halides... 

Table 12 Ethenyl Organo Tellurium Compounds from Tellurolates and Acetylenes...

Alkoxycarbonylalkyl organo telluriums are conveniently prepared from tellurolates and alkoxycarbonylalkyl halides. The esters can be saponified in refluxing aqueous ethanol containing potassium hydroxide or sodium hydroxide. 

A large number of stable /e-organo tellurocarboxylates were prepared from tellurolates and aliphatic1,2 or aromatic2 carboxylic acid chlorides or aliphatic carboxylic acid anhydrides . The tellurolates were obtained by reduction of diorgano ditelluriums with sodium borohydride. 

Te-Esters of tellurocarboxylic acids were prepared from tellurolates and carboxylic acid chlorides or anhydrides, and from sodium telluride and aroyl chlorides". The following types of 7e-organo tellurocarboxylates have thus far been synthesized ... 

Carboxylic acids were obtained in good yields from tellurol esters in the presence of copper(II) chloride dihydrate in acetone at room temperature for 5 min (Eq.64) [122]. 

The chemistry of alkaline-earth chacogenolates have been developed from the nineties with the structural characterization of the first magnesium thiolate in 1990,69 magnesium and calcium tellurolates in 1992,70,71 and the first magnesium and strontium selenolates in 1994.72... 

Trimethylsylilmethyl telluride generated in situ from methyllithium and trimethyl-chlorosilane can be used instead of the tellurolate in the latter reaction. ... 

Organyl tellurols are very unstable compounds owing to their extreme sensitivity to oxygen, giving the corresponding ditellurides. The first short-chain alkyltellurols (C1-C4) have been isolated as yellow liquids with an obnoxious odour, from the reaction of aluminium telluride and hydrogen telluride, respectively, with alcohols and aUcyl bromides. Aryltellurols seem not to have been isolated. As shown in Sections 3.1.3.2 and 3.2.2, aryl tellurolates are... 

From organyl tellurols or tellurolates and terminal acetylenes... 

From organyl tellurolate (and telluride) anions and vinyl bromides... 

From vinylic tellurolate anions and alkyl halides... 

Important remarks are that starting from mixtures of ElZ enol derivatives, only the (Z)-vinylic tellurides are obtained, and comparative experiments demonstrate that alkyl tellurolates ( -,. t- and f-BuLi) react faster than the aromatic (PhMgBr, 2-ThLi), and that the reaction time is not influenced by the nature of the leaving group (phosphate, acetate, tosylate and triflate). 

Addition of aryl tellurolates to acetylenic ketones (general procedure) NaBH4 (0.55 g, 15 mmol) is added in small portions, under N2, to a solution of the diaryl ditelluride (5 mmol) in EtOH (20 mL) at room temperature. A solution of the acetylenic ketone (10 mmol) in EtOH (10 mL) is then added to the reaction mixture, with stirring. The resulting precipitate of the 2-carbonylvinyl telluride is filtered off and recrystallized from EtOH. 

Methyl phenylethynyl telluride (typical procedure). To NaNH2 (from 6.0 g, 0.26 mol Na) in liquid NHj (250 mL) is added phenylacetylene (25 g, 0.25 mol) dropwise, and then Te powder (30 g, 0.24 mol) in small portions, stirring well for 30 min. Methyl iodide (36 g, 0.25 mol) is added over 20 min to the tellurolate solution. The NHj is then evaporated, the residue extracted with ether and the ether solntion washed with HjO and dried (MgS04). The residue is distilled under vacnum, giving the product (28 g (46%) b.p. 122-124°C/2 torr). 

Method G. ° A catalytic cycle is also involved in this method. Sodium thienyl tellurolate, generated from the ditelluride and NaBH4, attacks a bromine atom and the formed tel-lurenyl bromide reacts with another tellurolate molecule regenerating the starting ditelluride. 

The tellurolate-promoted anfi -debromination by method G is extended to the preparation of conjugated dienes, starting from 1,2,3,4-tetrabromoalkanes and cycloalkanes, 1, 4-dibromo-2-aIkenes and aUylic dibromides. ... 

Typical procedure Phenylcinnamyl telluride (prepared from sodium phenyl tellurolate, 1 mmol, and cinnamyl bromide, 1 mmol in EtOH, 10 mL) was treated with Phl=NTS (1.5 mmol) and the mixture was stirred at 25°C for 20 h. After removal of the solvent, the product was purified by column chromatography on Si02 (eluent hexane/AcOEt). 

Since the starting tellurides are easily prepared from alkyl hahdes or epoxides by displacement with tellurolate anions (see Section 3.1.3.2), the overall sequence constitutes a mild reduction of these substrates and is advantageous over the analogous reductions of selenides, which require more severe conditions (a temperature of 120°C is necessary). 

Since the starting tellurides are easily prepared (see Section 3.1.3.2) from the corresponding alkyl bromides and tellurolate ions, and -hydroxyalkyl tellurides by the opening of epoxides with the same reagents, the combined procedures furnish a method for the dehydrobromination of alkyl bromides and for the conversion of epoxides into allylic alcohols. Moreover, combining the telluroxide elimination with the methoxytelluration of olefins (see Sections 3.9.3.2 and 4.4.8.3), allylic and vinylic ethers are easily prepared. 

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