Tellurium-Carbon Bond

The vinylic carbon-tellurium bond in 3-129 can easily be cleaved by a tributyltin radical to afford vinyl radical 3-131, which can undergo further transformations as hydrogenation or C-C-bond formation, for example with dimethylfumarate in a (Z)-selective mode. 

The transformation of a carbon-tellurium bond into a carbon-halogen bond has been achieved in several types of organotellurium compound. 

A r/i3-carbon-tellurium bond can be homolyticaly cleaved either by action of a radical initiator (process A) or by light irradiation or heat (process B) (Scheme 82). The radical species formed interact with organic substrates through radical mechanistic pathways leading to the products with or without incorporation of tellurium in the final structure. 

One carbon-tellurium bond in divinyl tellurium is cleaved when the compound is treated in liquid ammonia with two molar equivalents of lithium5 7 or sodium8. The alkali ethenetellurolate was subsequently alkylated. 

The precipitation of black tellurium frequently encountered in reactions carried out with tellurols or tellurolates indicates that the carbon-tellurium bond is prone to cleavage under rather mild conditions. Alkanetellurols and -tellurolates appear to be less stable than the aromatic compounds. Exposure of tellurolates to air and water causes at least partial decomposition of arenetellurolates7 and ethynetellurolates8 to elemental tellurium. 

When sodium benzenetellurolate was treated with sodium in liquid ammonia, the carbon-tellurium bond was cleaved. Benzene was isolated after work-up2. 

The carbon-tellurium bond linking tellurium to the perfluoroalkyl groups in perfluoroalkyl telluriums is cleaved by potassium hydroxide liberating fluorohydrocarbons3. 

Formation of Carbon-Sulfur, Carbon-Selenium and Carbon-Tellurium Bonds via Organomagnesium Compounds... 

The following scheme provides a general survey of the known types of organic tellurium compounds with at least one carbon-tellurium bond. 

Because sp carbon-tellurium bonds are often unstable under photoirradiation conditions, carbotelluration producing sp -carbon-tellurium bonds occurs preferentially. Successful telluro group transfer cyclization has also been reported [119g]. Carbonyl tellurides are useful precursors for carbonyl radicals, which are employed for cyclization and addition reactions [127]. The reaction of diorganyl tellurides wifh isocyanides leads to fhe formation of imidoyl tellurides in high yields [128]. The carbotelluration system has also recenfly been applied to living radical polymerization (Scheme 15.52) [129]. 

The transformation of a carbon-tellurium bond into a carbon-halogen bond can be performed with several types of organotellurium trihalide or diorganotellurium dihalide compounds, in which the organic group is an alkyl, an alkenyl or an aryl substituent. A variety of reaction conditions have been described to realize these transformations, which belong to three main types ... 

Treatment of acetylenic tellurides (79) with three molecular equivalents of bromine or iodine leads to trihalovinylic derivatives (80). The reactions involve the oxidative halogenolysis of the carbon-tellurium bond followed by addition of the halide to the acetylenic bond. ... 

Activation of the carbon-tellurium bond is also possible under palladium catalysis, but requires stoichiometric amounts of copper iodide. Vinyl tellurides react with arylzincs in THF at rt in the presence of PdCl2 (20mol%) and Cul (1 equiv.) (Scheme 4.40) [149, 150]. Aryl tellurides react similarly, but require reflux temperature [151]. 

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