Mild synthesis of disaccharidic 2,3-enopyranosyl cyanides and 2-C-2-deoxy pyranosyl cyanides with Hg(CN)2/HgBr2/TMSCN

Lewis acid-catalyzed dimerization of mono- and disaccharidic per-O-acetylated glycals gave di- and tetrasaccharidic O-acetylated C-glycosides, respectively. 2,3-Enopyranosyl cyanides were obtained from per-O-acetylated glycals by a new, mild anomeric S-N'-acetoxy displacement with Hg(CN)(2)/HgBr2/TMSCN. Per-O-acetylated 2-C-2-deoxy-pyranoses were converted into pyranosyl cyanides by the same reagent. An unprecedented acetic acid elimination from dimers with D-galacto- and L-fuco-configurations accompanied the S-N-displacement under those conditions. A new set of H-1 NMR coupling constants for 2,3-enopyranosyl systems was used for configurational assignment of complicated tetrasaccharide mimics.