Epimerisation of Carbohydrates and Cyclitols, 17.¹ 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-galacto) were epimerised in a one-pot procedure by heating with chloral/DCC/1,2-dichloroethane 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) configuration. Compound 8, directly generated or obtained by deformylation of its 6-O-formyl derivative 9, was used as the key intermediate for further syntheses. Besides the acetylation of 8 to 10, and decarbamoylation to the 4,6-dihydroxy derivative 11, the latter 11 was acetylated to 12 and benzylated to 13. Moreover, the azide function of 8 was converted into an amino group using tributyltin hydride/AIBN or Staudinger conditions. The amino derivatives were isolated in the form of their N-acetyl derivatives 14 and 15, respectively. 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.

carbohydrates - azides - acetals - amides - stereoselectivity