Osmium-catalyzed tethered aminohydroxylation of glycals: a stereodirected access to 2- and 3-aminosugars.

The osmium-catalyzed aminohydroxylation of glycals has been achieved with complete regio- and stereocontrol by taking advantage of the Donohoe tethering approach. Glucals and galactals showed complementary reactivity in dependence of the stage at which the reaction was performed, i.e., directly or after double-bond shift consequent to a Ferrier rearrangement (that is, on the 1,2 or 2,3-unsaturated sugar), allowing access to both classes of 2-amino (mannosamine) and 3-amino (talosamine) sugar derivatives, respectively.