Mechanistic Insights into the Formation of δ‐Lactones by Cerium‐Catalyzed Aerobic Coupling of β‐Oxoesters with Enol Acetates

Abstract δ‐Valerolactone derivatives are formed by the cerium‐catalyzed, aerobic coupling of β‐oxoesters with enol acetates and dioxygen. The products possess a 1,4‐diketone moiety, thus, conversion can be regarded as an Umpolung since oxidized to electrophilic α‐radicals. transformation has similarities Baeyer‐Villiger oxidation (BVO) where higher substituted residue migrates. An endoperoxidic oxycarbenium ion comparable Criegee intermediate in BVO is proposed reaction this case oxidative C−C reaction, but contrast BVO, less alkyl It was demonstrated two stereocenters that 1,2‐alkyl shift proceeds retention configuration. A radical chain mechanism furthermore evidenced cyclopropyl substituents. Isolation characterization opened cyclopropane rings established constitution intermediates.