Zirconocene-mediated deoxygenative ring contractions of vinyl-substituted carbohydrates: An expedient route to enantiomerically pure, densely functionalized 4-to-8-membered carbocycles

The zirconocene reagent reacts with vinyl furanosides and pyranosides, readily available via established carbohydrate transformations, to furnish enantiopure cyclobutanols and cyclopentanols. These transformations proceed with predictable regioselectivity via chelated transition states, such that the hydroxyl and neighboring vinyl substituents are ultimately cis related. Some synthetic uses to which these products have been applied are briefly described.