Tunable stereoselectivity in the synthesis of α- and β-aryl glycosides using 1,2-α-anhydrosugars as glycosyl donors.

The stereochemical course of O-glycosidation of 1,2- α -d- anhydrosugars (glycal epoxides) with phenols can be tuned by varying the metal ion of the base. While the reaction of 1,2- α -d- anhydrosugars with phenols mediated by trimethylaluminium leads exclusively to 1,2- ci s- α - O -aryl glycosides, similar reaction mediated by caesium carbonate gives exclusively 1, 2-trans - β - O -aryl glycosides. In contrast, reaction with phenoxides generated from Grignard reagent and calcium salts affords mixture of the anomers. [ABSTRACT FROM AUTHOR]