Tellurium in organic synthesis : V. X-ray structure of 8-ethoxy-4-cyclooctenyltellurium trichloride and its relevance to the TeO2-oxidation of alkenes

The molecular structure of 8-ethoxy-4-cyclooctenyltellurium trichloride has been determined from three-dimensional X-ray diffraction data. The crystal belongs to the monoclinic system, space group P2₁/n, with four formula units in a cell of dimensions: a 7.712(1), b 13.406(3), c 13.820(2) Å and β 95.18(1)°. The structure was solved by the conventional heavy atom method, and refined by the least-squares procedure to R = 0.025 for 2199 reflections.The compound is formed from the corresponding β-chloroalkyltellurium tri-chloride, obtained from TeCl₄ and cis, cis-1,5-cyclooctadiene, by an unusually mild solvolytic substitution reaction in ethanol. Similar β-chloroalkyltellurium compounds are postulated as intermediates in the TeO₂ oxidation of alkenes to alkanediol diacetates and alkanediol monoacetates in HOAc containing a lithium halide, LiX. Oxidation of cis-2-butene and trans-2-butene with TeO₂/HOAc/LiBr gave a high preference for cis-stereochemistry in the products while 1-decene showed no stereospecificity.