Practical and highly stereoselective aryl and allyl
C-glycosidations 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) -AgClO
4 or TMSOTf exclusively gave the corresponding unprotected ο-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. Furthermore, the total synthesis of urdamycinone B, a prototypical member of the
C-glycosyl angucycline antibiotics, was accomplished by the successful application of the present aryl
C-glycosidation of unprotected sugar as the key step.
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