Synthesis of 1,2-cis- and 1,2-trans-glycosides of 2-acetamido-4,6-O-benzylidene-2-deoxy-d-glucopyranose by anomeric O-alkylation

The reaction of a partially protected 1-hydroxy derivative of N-acetyl-d-glucosamine with benzyl bromide under conditions of anomeric O-alkylation was studied. It was found that the stereoselectivity of the reaction depended on the nature of the alkali metal cation constituent of a transient ion pair. The substitution of the Li+ cation for K+ or complexation with a crown ether allowed the steric outcome to be shifted from β- to α-selectivity.