H₂SO₄-Silica-Promoted One-Pot Protection of Sugars

Significance

A silica gel supported sulfuric acid (H₂SO₄-silica) was used for one-pot acetalation and subsequent acetylation of glycosides. Thus, when methyl-β-d-glucopyranoside (1: 1 mmol) was treated with benzaldehyde, dimethylacetal and H₂SO₄-silica in acetonitrile, 4,6-O-benzyli­dene acetal was formed within 25 minutes. After complete conversion into the acetal, acetic anhydride was added to the reaction mixture to afford methyl 2,3-di-O-acetyl-4,6-O-benzylidene-β-d-glucopyranoside (2) in 93% yield. This one-pot strategy was applied to the protection of 11 different pyranosides to afford the corresponding products in 75-95% yield.