Novel stereocontrolled glycosidations using a solid acid, SO₄/ZrO₂, for direct syntheses of α- and β-mannopyranosides

Novel stereocontrolled glycosidations using an environmentally friendly solid acid, sulfated zirconia (SO₄/ZrO₂), for direct syntheses of α- and β-mannopyranosides have been developed. The glycosidations of the totally benzylated mannopyranosyl fluoride 1 and various alcohols using SO₄/ZrO₂ in CH₃CN at 40°C for 15 h exclusively gave the corresponding α-mannopyranosides. On the other hand, the corresponding β-mannopyranosides were selectively obtained by the glycosidations of 1 and various alcohols employing SO₄/ZrO₂ in the presence of molecular sieves 5Å in Et₂O at 25°C for 15 h.