Diastereoselective synthesis of glycopyrans 1,2-annulated with dioxazinanes from 1,2-anhydrosugars and -substituted nitrones.

1,2-Annulated pyranose sugars fused with six membered rings have emerged as an important class of carbohydrates with wide biological and synthetic utility. We now describe zinc chloride catalyzed one pot diastereoselective synthesis of sugar fused dioxazinanes from 1,2-anhydro sugars and -substituted aromatic nitrones. Various aromatic nitrones with different substituents undergo the reaction smoothly. The developed strategy works well with both ester and ether protection on the sugar and proceeds under mild reaction conditions. The mechanism seems to involve activation of the anhydrosugar by ZnCl for nucleophilic attack by the nitrone followed by cyclization.