Microwave-assisted group-transfer cyclization of organotellurium compounds

Primary- and secondary-alkyl aryl tellurides, prepared by arenetellurolate ring-opening of epoxides/O-allylation, were found to undergo rapid (3 - 10 min) group-transfer cyclization to afford tetrahydrofuran derivatives in 60-74% yield when heated in a microwave cavity at 250 degreesC in ethylene glycol or at 180 degreesC in water. To go to completion, similar transformations had previously required extended photolysis in refluxing benzene containing a substantial amount of hexabutylditin. The only drawback of the microwave-assisted process was the loss in diastereoselectivity which is a consequence of the higher reaction temperature. Substitution in the Te-aryl moiety of the secondary-alkyl aryl tellurides (4-OMe, 4-H, 4-CF3) did not affect the outcome of the group-transfer reaction in ethylene glycol. However, at lower temperature, using water as a solvent, the CF3 derivative failed to react. The microwave-assisted group-transfer cyclization was extended to benzylic but not to primary- and secondary-alkyl phenyl selenides.