The intriguing dual-directing effect of 2-cyanobenzyl ether for a highly stereospecific glycosylation reaction.

The diverse presence as well as their very specific bio-responses of glycoconjugates found in all living species requires scientists to synthesize the precise structure of these complex oligosaccharides for various studies on glycoscience. Very few approaches were able to offer the sole α- or β-glycosylated products, even at the cost of complicating the preparative route or usage of exotic chiral auxiliaries to drive the stereoselectivity. In this report, the unification of solvent assistance and neighbouring group participation concepts have led us to the use of 2-cyanobenzyl ether as the dual-directing auxiliary for stereospecific construction of α- and β-glycosidic bonds from a single starting material, and both isomers can be obtained in exclusive stereoselectivity. This work demonstrates the difference in reactivities of glycosyl acceptors can be employed to completely drive the stereoselectivity, drawing the parallel comparison with the arming/disarming concept, which has been exclusively confined to glycosyl donors.