The stereoselective synthesis of ketoside-typeanalogues of trehalose is described. O-Glycosidation of hept-2-ulopyranose with trimethylsilyl α-pyranoside promoted by trimethylsilyl trifluoromethanesulfonate afforded α-ketopyranosyl α-aldopyranosides exclusively. α-Ketopyranosyl β-aldooyranosides and α-ketopyranosyl α-ketopyranosides were also synthesized in a similar manner. The benzyl protecting