α‑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 to synthesize α-Kdo O-glycosides based on the Tf2O/(p-Tol)2SO preactivation strategy using peracetylated Kdo thioglycoside as a donor. Under the optimized reaction conditions, several O-glycoside products, including α-(2 → 1)-, α-(2 → 2)-, α-(2 → 3)-, and α-(2 → 6)-Kdo products, were stereoselectively synthesized in high yields. Remarkably, a series of aromatic α-Kdo O-glycosides were first and successfully constructed in high yields. An SN2-like mechanism was revealed by DFT calculations and experimental results.