Modulation of the stereoselectivity and reactivity of glycosylation via ( p -Tol) 2 SO/Tf 2 O preactivation strategy: From O -, C -sialylation to general O -, N -glycosylation

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

“…In the current work, it is worth noting that ( p -Tol) 2 SO was an important additive that can efficiently modulate reaction yields and stereoselectivities. Since our preactivation strategy was not affected by the β/α ratio of Kdo donors (Table S2), based on our previous works and similar glycosylations of the sialic acid series, a plausible mechanism was proposed to explain the results (Scheme ). Specifically, for thioglycoside 24 , the donor was first activated by Tf 2 O/( p -Tol) 2 SO to generate the widely accepted oxacarbenium ion 28 , and it could be further stabilized by excess ( p -Tol) 2 SO, resulting in an equilibrium between oxosulfonium salts 29 and oxosulfonium supramers 30 .…”

“…Unfortunately, the desired product 27c was not detected. Based on our experience with glycosylation, the amount of ( p -Tol) 2 SO and temperature were changed carefully. Surprisingly, glycosylation using 10.0 equiv of ( p -Tol) 2 SO at −40 °C for 6 h showed excellent stereoselectivity (Table , entry 3).…”

“…During the past decade, our group was committed to developing a facile and universal method based on the ( p -Tol) 2 SO/Tf 2 O preactivation strategy for O -, C -, and N -glycosylation reactions . By modulating the amount of ( p -Tol) 2 SO, various desired glycosides were obtained in high yields and with good stereoselectivities.…”

Chemical and chemoenzymatic stereoselective synthesis of β-nucleosides and their analogues

“…Furthermore, they also proposed a plausible mechanism (Scheme 16). 28 Initially, the diaryl sulfoxide bi(triflate) intermediate 77 was generated in situ from ( p -Tol) 2 SO/Tf 2 O, which reacted with the thioglycoside donor 74 to give the sulfonium ion 78 . The reaction then proceeded through three different paths based on the assisting group at C2′ and C3′.…”