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-cis-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.