Copper-catalyzed desymmetrization of prochiral 4,4-disubstituted cyclopentenes via a site-selective allylic oxidation: a concise total synthesis of untenone A.

The desymmetrization of prochiral 4,4-disubstituted cyclopentenes via a site-selective copper-catalyzed allylic oxidation is described. This study provides a direct comparison of a series of known methods for allylic oxidation, and thus identifies ligand-free copper(i) iodide as the optimal catalyst for this particular process. Notably, this work offers a convenient approach to the preparation of γ-quaternary α,β-unsaturated cyclopentenones, which permits an efficient three-step total synthesis of (±)-untenone A.