enantiopure substituted 4 - deoxypentenosides and related dihydropyrans are prepared from common carbohydrates via a novel process . the 4 - dps and related dhps are amenable to a broad range of stereoselective transformations and are used as synthetic intermediates to prepare a variety of enantiopure tetrahydropyrans , including rare or exotic sugars and other complex thps of commercial or medicinal value . in one embodiment of the instant invention , 4 - dps are converted to l - sugars in a novel process that offers distinct advantages over known synthetic methods .