VINYL GLYCOSIDES IN OLIGOSACCHARIDE SYNTHESIS .2. THE USE OF ALLYL AND VINYL GLYCOSIDES IN OLIGOSACCHARIDE SYNTHESIS

A novel latent-active glycosylation strategy has been described that r elies on the isomerization of substituted allyl glycosides to give the corresponding vinyl glycosides, which can subsequently be used in Lew is acid-mediated glycosylations. The isomerization reaction was perfor med by a rhodium catalyst obtained by treating tris(triphenylphosphine )rhodium(I) chloride with n-butyllithium. This catalyst has many advan tageous properties over the use of conventional Wilkinson's catalyst. The glycosylation reactions gave high yields for both primary and seco ndary sugar alcohols, and the anomeric selectivity could be controlled by the constitution of the glycosyl donor and reaction conditions. Th e new isomerization and glycosylation approach enables complex oligosa ccharides of biological importance to be prepared in a highly converge nt manner.