THE MERCAPTOLYSIS OF GLUCOSE AND GALACTOSE PENTAACETATES

Abstract

The mercaptolysis of the α-and β-pentaacetyl derivatives of glucopyranose and galactopyranose at 0 °C. with zinc chloride catalyst was studied. The β-pentaacetates were rapidly transformed to the corresponding ethyl tetraacetyl-1-thio-β-D-glycosides in excellent yields; however, the α-anomers were highly resistant to the mercaptolytic conditions. The results are interpreted on the basis of a participation by the C2-acetoxy group in the replacements at the lactol carbon atom of the β-pentaacetates with the intermediate formation of a resonance stabilized cyclic carbonium ion.