Vinyl glycosides in oligosaccharide synthesis (part 6): 3-Buten-2-YL 2-azido-2-deoxy glycosides and 3-buten-2-YL 2-phthalimido-2-deoxy glycosides as novel glycosyl donors

An extension of the latent-active glycosylation strategy is reported whereby 3-buten-2-yl 2-deoxy-2-azidoglycosides and 3-buten-2-yl 2-deoxy-2-phthalimidoglycosides are used as building blocks for the preparation of amino sugar containing oligosaccharides. The allyl moieties of the latent substrates 5, 16 and 19 can be conveniently isomerised by treatment with a catalytic amount of (Ph₃P)₃RhCl/BuLi to give the active vinyl glycosides 6, 17 and 20 in high yield. These glycosyl donors were successfully used in glycosylations with acceptors 7, 9 and 11. In the case of glycosyl donor 6, the disaccharides 8, 10 and 12 could be obtained as anomeric mixtures or with high α-or β-selectivities depending on the reaction conditions selected. Glycosylations with glycosyl donors 17 and 20 in each case gave solely the β-linked products only in high yields.