Substitution of acyclic sugar acetals. Is the acid-catalyzed substitution of erythro and threo l,2,3,4,5-penta-O-acetyl-l-arabinose S-ethyl monothioacetals anchimerically assisted?

Abstract

The rate constants for the inversion and for the 14C-acetoxy exchange of the diastereomeric 1,2,3,4,5-penta-O-acetyl S-ethyl monothioacetals show that the substitution is not anchimerically assisted by the C2-acetoxy group. The substitution of acyclic poly-O-acetyl sugar monoacetals is best explained by the formation of the acyclic intermediate [Formula: see text] (X = S or O) in the rate-determining step.