title: Formation of δ-Lactones with anti-Baeyer-Villiger Regiochemistry: Investigations into the Mechanism of the Cerium-Catalyzed Aerobic Coupling of β-Oxoesters with Enol Acetates.
abstract: The cerium-catalyzed, aerobic coupling of β-oxoesters with enol acetates and dioxygen yields δ-lactones with a 1,4-diketone moiety. In contrast to the Baeyer-Villiger oxidation (BVO), where the higher substituted residue migrates; in the case of this oxidative C-C coupling reaction, the less substituted alkyl residue undergoes a 1,2-shift. An endoperoxidic oxycarbenium ion comparable to the Criegee intermediate in the BVO is proposed as a reaction intermediate and submitted to conformational analysis by computational methods. As a result, the inverse regiochemistry is explained by a primary stereoelectronic effect. A Hammett analysis using different donor- and acceptor-substituted enol esters provides support for the oxycarbenium ion being the crucial intermediate in the rate determining step of the conversion. An overall mechanism is suggested with a radical chain reaction for the formation of endoperoxides from β-oxoesters, enol acetates and dioxygen with a cerium(IV) species as initiating reagent.
authors.affiliation: Institut für Chemie, Carl von Ossietzky Universität Oldenburg, 26111, Oldenburg, Germany.
authors.forename: Irina
authors.initials: I
authors.lastname: Geibel
authors.affiliation: Institut für Chemie, Carl von Ossietzky Universität Oldenburg, 26111, Oldenburg, Germany.
authors.forename: Anna
authors.initials: A
authors.lastname: Dierks
authors.affiliation: Institut für Chemie, Carl von Ossietzky Universität Oldenburg, 26111, Oldenburg, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Müller
authors.affiliation: Institut für Chemie, Carl von Ossietzky Universität Oldenburg, 26111, Oldenburg, Germany.
authors.forename: Jens
authors.initials: J
authors.lastname: Christoffers
mesh_terms: D000085:Acetates / Q000138:chemical synthesis / Q000737:chemistry*; D002384:Catalysis; D002563:Cerium / Q000737:chemistry*; D004951:Esterification; D004952:Esters / Q000138:chemical synthesis / Q000737:chemistry; D007783:Lactones / Q000138:chemical synthesis / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry; D013237:Stereoisomerism
chemical_list: D000085:Acetates; D004952:Esters; D007783:Lactones; D002563:Cerium; D010100:Oxygen
keywords: Baeyer-Villiger oxidation; density functional calculations; enol esters; lactones; stereoelectronic effects