Disubstituted vinylic tellurides

The sequential treatment of 1-alkynes with n-BuLi, trialkyl borane and a tellurenyl bromide reaches the (Z)-borosubstituted vinyl telluride which is easily hydrolyzed to the disubstituted vinyl tellurides. The reaction proceeds with high regio- and stereocontrol. ... 

Disubstituted vinylic tellurides are converted into trisubstituted olefins by a similar reaction catalysed by Ni(O). ... 

Several vinylic tellurides are prepared starting from monosubstituted aryl alkynes.41,42,133-136 The yields are usually high and the reports in the literature mention that the stereochemistry of the product is 100% Z. In the same way, only the formation of 1,2-disubstituted vinylic tellurides is reported (Scheme 36). 

Alkynes conjugated to a triple bond are very reactive systems toward hydrotelluration. The reaction occurs in a shorter reaction time when compared to the reactions commented above. In this case, even disubstituted triple bonds give vinylic tellurides in good yields.41,42,139 140 In the case of non-symmetrical diynes, an order of reactivity is established for the hydrotelluration of triple bonds of the enyne systems (terminal > propargylic > alkyl substituted > aryl substituted).140 This order of reactivity is reflected in the preferential formation of the vinylic tellurides shown in Scheme 39. 

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