Lanthanum Trifluoromethane-sulfonate‐Catalyzed Facile Synthesis of Per‐O‐acetylated Sugars and Their One‐Pot Conversion to S‐Aryl and O‐Alkyl/Aryl Glycosides†

^†CDRI Communication No. 7157.

Lanthanum trifluoromethanesulfonate‐catalyzed solvent‐free per‐O‐acetylation with stoichiometric acetic anhydride proceeds in high yield (95%–99%) to afford exclusively pyranose products as anomeric mixtures. Subsequent anomeric substitution employing borontrifluoride etherate and thiols or alcohols furnished the corresponding 1,2‐trans‐linked thioglycosides and O‐glycosides, respectively, in good to excellent overall yield (75%–85%). Alternatively, reaction of free sugars in neat alcohol employing the same catalyst at elevated temperature gives the corresponding 1,2‐cis‐linked O‐glycosides (along with 1,2‐trans‐linked glycosides as minor product) in good yield (73%–80%). Anomeric mixtures of compounds thus produced were characterized as their per‐O‐acetylated derivatives.

Keywords:

• O‐Glycoside
• S‐Glycoside
• Per‐O‐acetylation
• La(OTf)₃

Acknowledgements

VKR, SD, and BR are thankful to CSIR, New Delhi, for providing fellowship. Instrumentation facilities from SAIF, CDRI are gratefully acknowledged. This work is funded by the Department of Science and Technology under Fast Track Grant SR/FTP/CS‐110/2005.

Notes

^†CDRI Communication No. 7157.

^‡Authors have made equal contribution.