-Stereoselective 3-Deoxy-d-manno-oct-2-ulosonoic Acid (Kdo) O-Glycosylation with a p-Toluenethioglycoside Donor by the (p-Tol)₂SO/Tf₂O Preactivation Strategy

A convenient and efficient approach was developed tosynthesize alpha-Kdo O-glycosides based on the Tf2O/(p-Tol)(2)SO preactivation strategy usingperacetylated Kdo thioglycoside as a donor. Under the optimized reactionconditions, several O-glycoside products, including alpha-(2 -> 1)-, alpha-(2 -> 2)-, alpha-(2 -> 3)-, and alpha-(2 -> 6)-Kdo products, were stereoselectivelysynthesized in high yields. Remarkably, a series of aromatic alpha-Kdo O-glycosides were first and successfully constructed inhigh yields. An S(N)2-like mechanism was revealed by DFTcalculations and experimental results.