C-GLYCOSIDATIONS USING UNPROTECTED SUGARS AND ITS APPLICATION TO SYNTHESIS OF BIOACTIVE NATURAL-PRODUCTS

Practical and highly stereoselective aryl and allyl C-glycosidations u sing 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 trifluorom ethanesulfonate (TMSOTf)-AgClO4 or TMSOTf exclusively gave the corresp onding unprotected o-hydroxyaryl beta-C-glycosides which appear in man y biologically attractive aryl C-glycoside antibiotics as the key subu nit. On the other hand, allyl C-glycosidations of several unprotected glycals with allyltrimethylsilane by TMSOTf afforded the corresponding unprotected and 2,3-unsaturated allyl alpha-C-glycosides in high yiel ds which are versatile synthetic intermediates for the syntheses of op tically active natural products. Furthermore, the total synthesis of u rdamycinone B, a prototypical member of the C-glycosyl angucycline ant ibiotics, was accomplished by the successful application of the presen t aryl C-glycosidation of unprotected sugar as the key step.