A Lewis Acid Mediated StereoselectiveRemoval of an Anomeric Urea Substituent

The first Lewis acid mediated stereoselective removal of an anomeric chiral urea group or an electron deficient nitrogen substituent is described here. The ability to remove this urea group which had served as a chiral auxiliary, along with stereoselective hydroboration-oxidation of the endocyclic olefin renders the pyranyl cycloadduct from hetero [4+2] cycloadditions of chiral allenamides a useful chiral template. This represents a new approach to synthesis of complex pyranyl heterocycles or C-glycoside derivatives.