de Castro Pedro P, Batista Gabriel M F, Dos Santos Hélio F, Amarante Giovanni W
Chemistry Department, Federal University of Juiz de Fora, Campus Martelos, Juiz de Fora, Minas Gerais 36036-900, Brazil.
ACS Omega. 2018 Mar 26;3(3):3507-3512. doi: 10.1021/acsomega.8b00060. eCollection 2018 Mar 31.
Azlactones are versatile heterocycles employed in a diversity of transformations; the main drawback of these cycles consists in the epimerization of the α-carbonyl stereocenter during its preparation. We hereby present a theoretical study to explain how the racemization occurs. Two hypotheses were investigated: the keto-enol tautomerism and the base-mediated racemization, through an enolate intermediate. The results showed that the latter is consistent with the experimental data and can spontaneously occur at room temperature. The same pathway was evaluated for 2-alcoxy azlactone, showing a slower epimerization ratio, consistent with the literature data.
氮杂内酯是用于多种转化反应的多功能杂环化合物；这些环的主要缺点在于其α-羰基立体中心在制备过程中会发生差向异构化。我们在此进行一项理论研究，以解释外消旋化是如何发生的。研究了两种假设：酮-烯醇互变异构和通过烯醇负离子中间体进行的碱介导外消旋化。结果表明，后者与实验数据一致，并且在室温下可自发发生。对2-烷氧基氮杂内酯评估了相同的途径，结果显示差向异构化比率较慢，这与文献数据一致。
