Bimodal Glycosyl Donors Protected by 2- O-( ortho-Tosylamido)benzyl Group.

A glucosyl donor equipped with C2- o-TsNHbenzyl ether was shown to provide both α- and β-glycosides stereoselectivity, by changing the reaction conditions. Namely, β-glycosides were selectively obtained when the trichloroacetimidate was activated by Tf2NH. On the other hand, activation by TfOH in Et2O provided α-glycosides as major products. This "single donor" approach was employed to assemble naturally occurring trisaccharide α-d-Glc-(1→2)-α-d-Glc-(1→6)-d-Glc and its anomers.