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 whereb y 3-buten2-yl 2-deoxy-2-azidoglycosides and 3-buten-2-yl 2-deoxy-2-phthalim idoglycosides are used as building blocks for the preparation of amino suga r containing oligosaccharides. The allyl moieties of the latent substrates 5, 16 and 19 can be conveniently isomerised by treatment with a catalytic a mount of (Ph3P)(3)RhCl/BuLi to give the active vinyl glycosides 6, 17 and 2 0 in high yield. These glycosyl donors were successfully used in glycosylat ions with accepters 7, 9 and 11. In the case of glycosyl donor 6, the disac charides 8, 10 and 12 could be obtained as anomeric mixtures or with high a lpha-or beta-selectivities depending on the reaction conditions selected. G lycosylations with glycosyl donors 17 and 20 in each case gave solely the b eta-linked products only in high yields.