A sequential one-pot per-O-acetylation–S-/O-glycosidation of native mono and disaccharides under solvent free conditions using 0.5 mole% of Mg(OTf)2 as a non-hygroscopic, recyclable catalyst is reported. Regioselective 4,6-O-arylidenation of glycosides and thioglycosides with benzaldehyde or p-methoxybenzaldehyde dimethyl acetal is catalyzed by 10 mole% of Mg(OTf)2 to produce the corresponding 4,6-O-arylidenated product in high yields. Mg(OTf)2 can also mediate sequential one-pot benzylidenation–acetylation of mono and disaccharide based glycosides and thioglycosides in high yield.
