α-Elimination of organic halides from organotellurium(IV) halides

Three types of α-elimination (oxidative, photolytic, and thermal) of organotellurium(IV) halides to give organic halides have been disclosed. Treatment of organotellurium(IV) halides with some oxidants, preferably t-butyl hydroperoxide, in 1,4-dioxane, acetic acid, or acetonitrile affords the corresponding organic halides in good yields with retention of configuration and by ipso-replacement. The reactivity order of this α-elimination is roughly as follows: alkyl > aryl > alkenyl. The main reaction course seems to be a 1,2-tellurium halogen shift in unstable organotellurium(VI) compounds formed in situ by oxidation. Similar α-elimination also occurs by photolysis of these compounds with a high-pressure mercury lamp in benzene as the solvent. Here, a cross-coupling of the organic moiety with benzene scarcely occurs except for the cases of diaryltellurium(IV) dihalides. Neat pyrolysis of some alkyl(phenyl)tellurium(IV) dibromides at 200–250 °C (Kugelrohr distillation apparatus) again results in α-elimination to produce the corresponding alkyl bromides almost quantitatively.