Isolation of stable enantiomerically pure telluroxides and their stereochemistry

Optical resolution of kinetically and thermodynamically stabilized diaryl t elluroxides possessing bulky substituents (rac-1a-d) and amino group (rac-2 a-c), respectively, by liquid chromatography using optically active columns yielded stable enantiomerically pure telluroxides. The absolute configurat ions of the optically active telluroxides were determined by comparing thei r specific rotations and CD spectra with those of sulfur or selenium analog ues. The kinetics for the racemization of optically active telluroxides in solution was studied, and it was found that kinetic and thermodynamic stabi lization were very effective preventing the racemization of telluroxides. T he stabilization energy of telluroxides by intramolecular coordination of t he amino group to the tellurium atom was estimated to be ca. 5 kcal mol(-1) by variable temperature H-1 NMR measurement. The mechanism for the racemiz ation of optically active telluroxides was studied by an isotope experiment using (H2O)-O-18 and the results indicated that optically active telluroxi des underwent racemization via an achiral tetracoordinated hydrate.