Synthesis and stereochemistry of optically active telluronium ylides

Abstract

Diastereoisomeric mixtures of 1-{4-[(–)-menthyloxycarbonyl]phenyl(methyl)telluroniumyl}-4,4-dimethyl-2,6-dioxocyclohexan-1-ide dia.-5a, b and 1-{4[(–)-menthyloxycarbonyl]phenyl(2,4,6-triisopropylphenyl)-telluroniumyl}-4,4-dimethyl-2,6-dioxocyclohexan-1-ide dia.-12a, b have been synthesized. Optical resolution by the fractional recrystallization of dia.-5a, b and dia.-12a, b from hexane–dichloromethane gave the optically active (+)_Te-telluronium ylides (+)_Te-5a and (+)_Te-12a as stable crystals, respectively. The absolute configuration of (+)_Te-5a has been determined to be R based on the CD spectrum. The kinetics for the epimerization by pyramidal inversion of the optically active telluronium ylide (+)_Te-12a have been studied.