Syntheses and Peculiar Behavior in Solutions of Optically Active Telluronium Salts

A diastereomeric (epimeric) mixture of ethylmethylphenyltelluronium (1S)-(+)-camphor-10-sulfonate (dia.-1) was optically resolved by fractional recrystallization into the diastereomerically pure isomers (R)(Te)-1 and (S)(Te)-1. The absolute configurations of the isomers were determined by the X-ray crystallographic analysis of (R)(Te)-1. Enantiomerically pure (R)-ethylmethylphenyltelluronium perchlorate, tetrafluoroborate, p-chlorobenzenesulfonate, bornane-10-sulfonate, tetraphenylborate, and picrylsulfonate (R)-2-7 were isolated, respectively, by anion-exchange reactions of diastereomerically pure (R)(Te)-1. The optically active telluronium salts were found to show peculiar optical properties on their specific rotations and circular dichroism spectra in solutions compared with those of the corresponding sulfonium and selenonium salts. On the basis of NMR studies, the behavior on the optical properties of the optically active telluronium salts was found to be caused by a strong solvation in polar solvents.