Glycosyl bromides and chlorides

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... 

As generally expressed in Section I, derivatives of a-D-glucopyranose are thermodynamically more stable than the /3-d anomers, whereas, for the D-glucofuranoses, the opposite stability of the anomers is observed. This regularity also applies to the respective glycosyl bromides and chlorides. 

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]. 

Glycosyl bromides and chlorides are effectively produced using bromine [44, 45] (also I-Br [46]) or chlorine [47] (also I-Cl [46]), nowadays often with CH2CI2 as solvent. Under these mild conditions even unstable glycosyl halides can be produced, as e.g. furanosyl [48, 49] and alkylated oligosaccharide bromides [50], and various acid-labile protecting groups are allowed as well. 

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