Chemistry of Oxo-Sugars. III. Transformations of 2- and 3-Oxoglycosides in a Pyridine Solution

Methyl arabino-hexopyranosid-2-uloses rearranged, in pyridine, into arabino-hexopyranosid-3-uloses through an intramolecular hydride shift. The product further isomerized, through enolization, to the most stable ribo-hexopyranosid-3-uloses, which, on prolonged standing in the same solvent, gradually liberated methanol giving rise to dioxo derivatives. The last change was particularly evident for 3-oxoglycosides carrying a 4-axial hydroxyl group.