Investigation of the Scope of a Co-Mediated O → C Ring-Contraction

A series of dihydropyrans bearing a dicobalthexacarbonyl moiety have been found to undergo an efficient Al-promoted O → C ring-contraction process. This rearrangement reaction operates successfully for a broad range of substrates. Moreover, the potential of this approach for generating cyclopropanes from the corresponding dihydrofurans has been demonstrated.