2- Chloroalkyltellurium trichloride

Reaction of the appropriate alkene with 1 equiv of tellurium tetrachloride in chloroform or acetonitrile gives a 2-chloroalkyltellurium trichloride adduct in a high yield (see Section 3.5.1.2). Reduction of this adduct with aqueous sodium sulphide results in the instantaneous separation of elemental tellurium and formation of the starting alkenes which, in most cases, exhibit an inverted configuration (with relevant variations depending on the solvent and olefin used). The proposed mechanism involves an intermediate epitelluride. 

The addition of tellurium tetrachloride to alkenes produces chloroalkyltellurium trichlorides. Butenes, 1-decene, cycloalkenes, and 3-substituted 1-propenes give mixtures of syn and anti additions. ... 

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. 

Ketones react with 16 probably via the enol form to give a-trichlorotellurium ketones.61,62 Reaction of alkenes with 16 in an inert solvent gives chloroalkyltellurium trichlorides (e.g., 18).63 When an alcohol is present in the reaction medium, an oxyalkyltellurium trichloride (e.g., 19) is formed64 (Scheme 5). In some cases, tellurium tetrachloride is generated in situ from TeC>2 and HC1.65... 

The addition of aryltellurium trichlorides to alkenes occurs with a high stereospecificity, giving exclusively anfi-2-chloroalkyltellurium dichlorides, " in contrast to the addition of tellurium tetrachloride which gives mixtures of syn and anti adducts... 

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