Absolute configuration of ethylmethylpropylsulphonium ion determined by chemical correlation with (4S,6S)-4-ethyl-6-methyl-2-oxo-1,4-oxa-thianium ion

Abstract

The (4S,6S)- and (4R,6S)-4-ethyl-6-methyl-2-oxo-1,4-oxathianium ions (6) and (7) have been synthesized from ethyl (S)-lactate (1) and the trans-isomer (6) has been chemically degraded to (+)-methylethylpropylsulphonium ion (16). Control experiments served to ascertain that the sulphur centre retains its chirality virtually unimpaired under the reaction conditions employed. Consequently, dextrorotatory (16) possesses (S)-configuration. The optical rotation and thermodynamic parameters for pyramidal inversion of (S)-(16), produced by resolution of racemic (16), compared satisfactorily with those of (S)-(16) resulting from chemical degradation of (6).