Ketone Formation from Carboxylic Acids by Ketonic Decarboxylation: The Exceptional Case of the Tertiary Carboxylic Acids
作者:Borja Oliver-Tomas、Michael Renz、Avelino Corma
DOI:10.1002/chem.201702680
日期:2017.9.18
For the reaction mechanism of the ketonic decarboxylation of two carboxylic acids, a β‐keto acid is favored as key intermediate in many experimental and theoretical studies. Hydrogen atoms in the α‐position are an indispensable requirement for the substrates to react by following this mechanism. However, isolated observations with tertiary carboxylic acids are not consistent with it and these are revisited
对于两种羧酸的酮基脱羧反应机理,在许多实验和理论研究中,β-酮酸均被认为是关键中间体。通过这种机理,α位上的氢原子是底物反应的必不可少的条件。但是,使用叔羧酸的孤立观测值与其不一致,因此本文将对此进行重新讨论。用新戊酸获得的实验结果表明该底物不会发生酮脱羧。取而代之的是,它在替代反应中被消耗,例如分解成异丁烯,一氧化碳和水(复古-库奇反应)。此外,羧酸被异构化或失去碳原子,这会将叔羧酸转化为带有α-质子原子的羧酸。因此,后者适合于通过β-酮酸途径进行反应。第二种底物2,2,5,5-四甲基己二酸,通过遵循相同的RetroKoch途径进行反应。主要产物是一元羧酸2,2,5-三甲基-4-己烯酸(及其双键异构体),可以进一步转化为环状烯酮或内酯。痕量观察到酮类脱羧产物2,2,5,5-四甲基环戊酮(<0.2%收率)。因此,可以得出结论,观察到的实验结果进一步支持了所提出的经由β-酮酸中间体进行酮基脱羧的机理。主要产物是一元羧酸2