Stereoselective epoxidation of alkenylidene acetals derived from carbohydrates with d-allo, d-altro, d-galacto, d-gluco and d-xylo configurations

The synthesis of 2,3-epoxypropylidene acetals of sugar derivatives from N-acetyl-2-amino-2-deoxy-d-allopyranose, d-altropyranose, d-galactopyranose, N-acetyl-d-glucosamine, d-glucofuranose and d-xylofuranose is described. The epoxidation with m-CPBA of the corresponding alkenylidene derivatives took place with different stereoselectivities depending upon the sugar configuration, the protecting group of the hydroxyl groups of the sugar, and the substitution of the unsaturated system. The analysis of the ring-opening reaction of these oxiranes by hydrogenolysis enabled the assignation of their configuration at the new stereogenic centres.