Epimerisation of carbohydrates and cyclitols, 17. Synthesis of glycosyl azides and N-acetyl glycosyl amines of rare monosaccharides

The glycosyl azides 1 (D-arabino), 3 (L-fuco), 5 (D-manno), and 7 (D-galact o) were epimerised in a one-pot procedure by heating with chloral/DCC/1,2-d ichloroethane in good yields. The respective products, epimerised at the C- 3 atom, have D-lyxo (2), L-gulo (4), D-altro (6), and D-gulo (8, 9) configu ration. Compound 8, directly generated or obtained by deformylation of its 6-O-formyl derivative 9, was used as the key intermediate for further synth eses. Besides the acetylation of 8 to 10, and decarbamoylation to the 4,6-d ihydroxy derivative 11, the latter 11 was acetylated to 12 and benzylated t o 13. Moreover, the azide function of 8 was converted into an amino group u sing tributyltin hydride/ AIBN or Staudinger conditions. The amino derivati ves were isolated in the form of their N-acetyl derivatives 14 and 15, resp ectively. Finally, the dichloroethylidene (14) and the trichloroethylidene (15) groups were hydrodechlorinated forming the same ethylidene derivative 16. Crystal structures are given for the gulopyranoses 4 and 12.