Anomeric Xanthates: A New Activation of the Anomeric Center for Rapid Glycosylation

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Abstract
In recent years, glycosides, especially di- and oligosaccharides, have become substances of interest owing to their biochemical and pharmacological importance as antibiotics and antigens and many reports have appeared concerning the synthesis of these complex molecules1. Synthesis generally involved the preparation of two poly - functional partners; the hydroxyl component, prepared by selective blocking of a monosaccharide unit and the electrophilic partner, generated from an activated species. Various methods of activation of the anomeric center have been devised giving generally very good results. Oligosaccharides have been obtained from halogenoses, orthoesters2, imidates3, acetates4 in the presence of acidic catalysts or heavy metal salts5, as well as from thiomethyl glycosides as a glycosyl donor and methyl triflate or dimethyl-(methylthio)-sulfonium triflate as a promoter6. More complex heteroatomic activating groups have been developed such as N,N-dialkyldithiocarbamates7, phosphorodithioates8 and 2-benzothiazolyl9 derivatives, the latter providing an efficient glucosylation method.