Glycosylation stannous triflate

Stannous triflate in acetonitrile as solvent at -40 °C catalyzes the glycosylation of the phosphite donor 7 with the acceptor 10. As result an tt-selective linkage takes place. 

Starting with phosphite 59 stannous triflate catalyzes the formation of an oxenium ion 60, which is stabilized by the solvent (61). The complex 61 is more favored than 63, justified by the reverse anomeric effect until now. But as it is shown there is no possibility for 61 to react in an SN2 reaction to 62. The intermediate 63 can be attacked by the alcohol functionality of the glycosyl acceptor, and with MeCN as leaving group you get 64. Ultimately the equilibrium between 61 and 63 shifts completely to 63. This kind of stereocontrol during a glycosylation is known as the nitrile effect.28... 

---

See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ ]

---