Imidazole Promoted Efficient Anomerization of β-D-Glucose Pentaacetate in Solid State and Reaction Mechanism

Graphical An unprecedent “mixing and stand” anomerization of D-glucose pentaacetate in solid state was discovered after simple premixing in solvent and then removal of solvent, and the reaction proceeded continuously to full conversion without stirring or mechanomixing. Gram scale reaction was demonstrated and a new mechanism was also proposed. Anomerization of glycosides was rarely performed under basic condition. Here, an imidazole promoted anomerization of β-D-glucose pentaacetate in solid state at room temperature was discovered. This unprecedent anomerization occurred after simple premixing and reaction proceeded continuously in solid state to full conversion without stirring or mechanomixing. Full conversion of all β-forms in the mixture (α:β=2.2 : 1) into α-forms only was demonstrated at 1 gram scale. A proposed mechanism involved with inter/intramolecular acyl transfer promoted by imidazoles in a concerted manner may promote the discovery of more new transformations in solid state.