The stereochemistry of a 2-S-ethyl-2-thioaldohexose: ready epimerization of a 2-thioaldose

Abstract

The acid-catalysed replacement of the C-2 hydroxy-group in 3,4,5,6-tetra-O-benzoyl-D-glucose diethyl dithioacetal (1) by an ethylthio-group proceeds with inversion of configuration, probably through an episulphonium-ion intermediate, to give the diethyl dithioacetal (2) of 2-S-ethyl-2-thio-D-mannose (9), the free sugar (9) being exceptionally readily epimerized, at pH 8, to give the gluco-analogue (8).