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

The recent finding that the powerfully electrophilic zirconocene equivalent known as “Cp2Zr” is capable of transforming vinyl furanosides and pyranosides into enantiomerically pure, highly functionalized cis-2-vinyl cyclobutanols and cyclopentanols has been extended in a number of directions. The synthetic potential of this methodology is illustrated by the variety of carbocycles that can be produced, ranging from cyclobutanones, a carbacyclic nucleoside, cyclooctane polyols, and medium-ring carbohydrate mimics. Many of the key transformations are evaluated in terms of transition state energetics.