Telluride-ion-promoted coupling of allylic halides

The first reported radical reaction promoted by tellurium reagent was probably the conversion of allylic halides into the coupled 1,5-dienes by treatment with telluride anions. The reaction, which gives the best results when employing the reagent prepared in situ from elemental tellurium and lithium triethylborohydride, proceeds through the intermediacy of the thermally unstable bis-allylic telluride followed by extrusion of tellurium and coupling of the formed allylic radicals. 

Substituted allylic bromides furnish mixtures of the expected and rearranged products. The same mixture of products is formed independently from the geometry of the double bond (e.g. l-bromo-2-hexenes). 

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