Glycosylation with glycosyl bromides

Thioglycosides containing free OH groups readily tolerate silver triflate-pro-moted glycosylations with glycosyl bromides and chlorides, and also tin(II) chloride-silver perchlorate-activated glycosylation, and several examples have... 

Glycosidic thiol groups can be introduced into glycosyl bromides by successive reactions with thiourea and aqueous sodium disulfite (D. Horton, 1963 M. Cemy, 1961, 1963). Such thiols are excellent nucleophiles in weakly basic media and add to electrophilic double bonds, e.g., of maleic esters, to give Michael adducts in high yields. Several chiral amphiphiles have thus been prepared without any need for chromatography (J.-H. Fuhrhop, 1986 A). 

This ether, developed for the protection of a pyranoside anomeric hydroxyl, is prepared via a Konigs-Knorr reaction from the glycosyl bromide and 2-(ben-zylthio)ethanol in the presence of DIPEA. It is cleaved, after oxidation with dimethyldioxirane, by treatment with LDA or MeONa. ... 

These compounds are made by allowing the salt made from piperidine and sodium hydride to react with CS2 and then with an acetylated glycosyl bromide.56... 

Fluorination with Silver Fluoride from Glycosyl Bromide [17] A mixture of 2,3,4,6-tetra- O-acetyl-a-D-glucopyranosyl bromide (5 g) and anhydrous silver fluoride (5 g) in dry acetonitrile (25 ml) was shaken under argon overnight. The resulting solution was filtered and aqueous sodium chloride was added to precipitate any silver ions from the solution. The mixture was filtered and concentrated to a syrup that was... 

Very recently, direct displacement of acylated glycosyl bromides (D-Man and l-Fuc) with nucleotide 5 -diphosphates has been shown to proceed stereoselectively... 

Also works well with glycosyl bromides... 

Several other examples have been reported in which thioglycosides were used as glycosyl acceptors. Thus, thioglycosides containing free hydroxyls can be coupled chemoselectively with glycosyl bromides and chlorides in the presence of silver triflate or tin(II) chloride-silver perchlorate as the promoter system [12,53,56,162,218-221]. 

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... 

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