Aryl and Allyl C-Glycosidation Methods Using Unprotected Sugars

Practical and highly stereoselective aryl and allyl C-glycosidation methods using unprotected sugars as glycosyl donors have been developed. Aryl C-glycosidations of several unprotected 2-deoxy sugars with phenol and naphthol derivatives by the combined use of trimethylsilyl trifluoromethanesulfonate (TMSOTf)-AgClO₄ or TMSOTf exclusively gave the corresponding unprotected o-hydroxyaryl β-C-glycosides which appear in many biologically attractive aryl C-glycoside antibiotics as the key subunit. On the other hand, allyl C-glycosidations of several unprotected glycals with allyltrimethylsilane by TMSOTf afforded the corresponding unprotected and 2,3-unsaturated allyl α-C-glycosides in high yields which are versatile synthetic intermediates for the syntheses of optically active natural products.