Room-temperature ionic liquids enhanced green synthesis of β-glycosyl 1-ester

• The yield of β-glycosyl aliphatic ester was highly improved using C6mim·OTf as solvent.
• Our approach was mild and compatible with a wide range from aliphatic to aromatic substrates.
• All products were isolated exclusively as the β-anomers.
• RTIL might be pivotal to the synergistic effect of C6mim·OTf, Ag2O and TBAI.
• Quaternary ammonium salts also displayed a special function in the system.

We herein report an efficient synthesis of β-glycosyl 1-ester in room-temperature ionic liquids (RTILs) promoted via silver salt and quaternary ammonium salt (PTC) with good or excellent yields. All products were isolated exclusively as the β-anomers. Four different RTILs, eight metal salts and four quaternary ammonium salts were screened in the glycosylation reaction. The synergistic effect of C6mim·OTf, Ag2O and tetrabutylammonium iodine gave the best results. Their promotion to the system was integral. Thorough study provided insight into the catalytic activity of ionic liquid structure, metal salts and quaternary ammonium salt to these reactions. It is worth mentioning that the yield of aliphatic compound 2,3,4,6-tetra-O-acetyl-β-d-galactopyranosyl butyrate (3l) was highly improved when using C6mim·OTf as solvent compared with the normal volatile solvents under the same catalysts. This green approach has been proved to be practical and compatible with a wide range from aliphatic to aromatic substrates.

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