Formation of δ-Lactones with <i>anti</i>
-Baeyer-Villiger Regiochemistry: Investigations into the Mechanism of the Cerium-Catalyzed Aerobic Coupling of β-Oxoesters with Enol Acetates
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 this case of an oxidative C-C coupling reaction the less substituted alkyl residue undergoes a 1,2-shift. An endoperoxidic oxycarbenium ion comparable to the Criegee intermediate
Formation of δ-lactones is observed when cyclopentanone-2-carboxylates are converted in a cerium-catalyzed reaction with α-aryl vinyl acetates under oxidative conditions. The products of this transformation possess a 1,4-dicarbonyl constitution together with a quaternary carbon center. Atmospheric oxygen is the oxidant in this process, which can be regarded as ideal from economic and ecological points
当环戊酮-2-羧酸酯在铈催化下与α-芳基乙酸乙烯酯在氧化条件下转化为铈时,可观察到δ-内酯的形成。该转化的产物具有1,4-二羰基结构以及季碳中心。大气中的氧气是该过程中的氧化剂,从经济和生态角度来看,这可以认为是理想的氧化剂。这种新的C–C偶联和氧化反应的其他优点是操作简便以及无毒廉价的CeCl 3 ·7 H 2的应用O作为前催化剂。提出了迄今为止前所未有的反应,它是通过1,2-二恶烷衍生物进行的,该衍生物在Baeyer-Villiger型途径中的氧碳正离子形成时分解。这种机理的观点得到了以下观察结果的支持:富电子的(供体取代的或杂芳族的)烯醇酯比缺电子的同类物具有更高的产率。除了作为副产物形成的1,4-二酮和α-羟基化的β-氧代酯外,δ-内酯的收率范围从中等到良(最高74%)。