Synthesis and Stability of Optically Active Benzylmethylphenyltelluronium Salts

Abstract

Diastereomeric benzylmethylphenyltelluronium salt was synthesized and optically resolved into the respective optical isomers. The absolute configurations of the isomers were determined by X-ray analysis of the (−)-isomer. Enantiomeric telluronium salts were also obtained by anion-exchange reactions of the diastereomeric isomers. Optically active telluronium bromide was found to racemize in solution and the racemization was indicated to occur through the elimination of benzyl bromide.

Isolation and Racemization Mechanism of Optically Active Benzylmethylphenyltelluronium Salts

“…[11] The diastereomeric mixture was separated roughly into acetone-soluble and -insoluble fractions. Repeated recrystallization (four times) of the acetonesoluble fraction from acetone/hexane afforded the diastereomerically pure (+)-telluronium salt (+)-1 as colorless needles.…”

“…[11] Therefore, the absolute configuration of (+)-1 was assigned to be R around the tellurium atom. The tellurium atom of (S)-(-)-1 was also found to interact with two oxygen atoms of the different sulfonate anions in the crystalline state, and the distances between the tellurium atom and the oxygen atoms were 2.84 and 3.01 Å, respectively (Figure 1).…”

“…We report herein the isolation, stereochemistry, and racemization of optically active benzylmethylphenyltelluronium salts, and clarify the racemization mechanism. [11] [a] Department of Chemistry, Graduate School of Science and Engineering, Tokyo Metropolitan University, Minami-ohsawa, Hachioji, Tokyo 192-0397, Japan Fax: +81-42-677-2525 E-mail: shimizu-toshio@tmu.ac.jp rated diastereomers. The optically active telluronium salts possessing counteranions with a high nucleophilicity, such as bromide and iodide, were found to racemize in solution.…”