Selenoglycosidation

VIII. Glycosyl Sulfoxides, Sulfones, and Selenoglycosides as Glycosyl Donors. 198... 

Although the aim of this chapter is specifically to survey the use of thioglycosides in glycosylation reactions, the presentation is incomplete without some information concerning glycosyl sulfoxides and selenoglycosides in glycosylation... 

Selenoglycosides have also emerged as valuable intermediates in oligosaccharide synthesis. Thus, the following has been described for phenyl selenoglycosides189 ... 

Disarmed as well as armed (see Section V and Scheme 9) phenyl selenoglycosides are reported to be activated by silver triflate in the presence of potassium or silver carbonate in the presence of armed ethyl thioglycoside acceptors, to produce ethyl thiodisaccharides in excellent yields. 

Glycosyl trichloroacetimidate donors in the presence of selenoglycoside acceptors can be used with triethylsilyl triflate as promoter. 

Such a synthesis is shown in Scheme 4.18a, in which a glycosyl bromide is coupled with the thioglycosyl acceptor to afford a thioglycosyl disaccharide. The glycosyl bromide was obtained from the corresponding 1-thioglycoside by treatment with Br2. It was shown [222-224] that phenyl selenoglycosides can be selectively activated in the... 

Selenoglycosides of sialic acid have been successfully prepared in excellent yields from the corresponding peracetylated glycosyl chloride with phenylselenol in the presence of N,N-di-isopropylethylamine [519]. This reagent combination succeeded where others were less effective or failed (Scheme 4.98 [520]. 

Scheme 4.102 Cation and radical-cation pathways for selenoglycoside glycosylation.

Selenoglycosides are attractive donor species owing to the wide range of reagents that can promote cation- and radical-cation-based processes for their activation and subsequent O-glycosylation (Scheme 4.102) [223,512],... 

Cation-Based Activation Pinto s works not only described Ag0Tf/K2C03 as the promoter of choice for the activation of phenyl selenoglycosides but also indicated... 

Scheme 4.103 Transformation of selenoglycosides to other potential donor species.

Scheme 4.104 Ag0Tf/K2C03 and MeOTf promoters for selenoglycoside glycosylation.

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