Oxidative Cyclization of Some γ- and δ-Hydroxy Olefins Induced by Tellurium Dioxide

Article abstract of DOI:10.1021/ja00407a041

TeO2 reacted with 2 equiv of a γ- or δ-hydroxy olefin in acetic acid containing LiCl.The resulting dialkyltellurium dichlorides are derivatives of furan, tetrahydrofuran, and 2,3-dihydrobenzofuran, formed via an internal cyclization.The dialkyltellurium dichlorides were reduced to their corresponding dialkyltellurides with use of Na2S2O5 or hydrazine hydrate.A mechanism is postulated involving an electrophilic attack by a solubilized tellurium species followed by an intramolecular nucleophilic attack by a hydroxy group.An analysis of the vicinal proton coupling constants indicated one preferred conformation of the dialkyltellurium dichlorides, where the oxygen atoms of the furan rings are coordinated to tellurium.