We therefore proposed the mechanism for the β-mannosylation and the origin of the β-directing effect: the electron-withdrawing groups would stabilize the α-mannosyl triflate intermediate, and the subsequent reaction of the α-triflate (or its contact ion pair) with the acceptor would afford ...
The α-directing effect is partly considered to remote participation of the acyl groups, whereas the β-directing effect is somewhat attributed to the SN2-like reaction of the acceptor with the glycosyl triflate or the contact ion pair, which is stabilized by remote electron-withdrawing groups. ...