Ring Expansion, Ring Contraction, and Annulation Reactions of Allylic Phosphonates under Oxidative Cleavage Conditions.

Abstract

Oxidative cleavage of cycloalkenylalkylphosphonates 1 followed by treatment with base gives rise to homologated cycloalkenones 2 in good to excellent yields. Subjecting cycloalk-2-enylphosphonates 3 to identical conditions provides the one-carbon ring-contracted compounds 4 in excellent yields. Oxidative cleavage of γ,δ-unsaturated ketophosphonates 6 followed by treatment with base affords 2-cyclopenten-1-ones 7 in good overall yields. This method may offer a practical alternative to existing methods for effecting one-carbon ring expansion, ring contraction, and annulation reactions.