The role of sugar configuration in the acetolysis of 6-deoxyhexose methyl glycosides

The acetolysis of several perbenzylated 6-deoxyhexose methyl glycosides under two mild conditions (10 equiv ZnCl₂ in 2:1 v/v Ac₂O-AcOH at 5 °C; 10:10:1 v/v/v Ac₂O-AcOH-TFA at 70 °C) was studied. We focused on the effect of sugar configuration on the competition between mechanisms with activation at exocyclic or endocyclic oxygen site. No effect was detected in acetolysis using the TFA protocol promoting an exo-activation mechanism, which affords 1-O-Ac-pyranosides regardless of sugar configuration. On the contrary, it has a primary role in determining the endo- versus exo-product distribution on ZnCl₂-promoted acetolysis.