Cascade [1,3]-Sigmatropic Rearrangements of Ketene <i>O</i>,<i>O</i>-Acetals: Kinetic and DFT Level Mechanistic Studies
作者:Perla Y. López-Camacho、Pedro Joseph-Nathan、Bárbara Gordillo-Román、Oscar R. Suárez-Castillo、Martha S. Morales-Ríos
DOI:10.1021/jo902520z
日期:2010.3.19
The regioisomeric α-cyano ketene-O,O-dialkyl acetals 2a−e and 4a−e, sequential intermediates in the diazomethane induced conversion of indole α-cyano-γ-lactones 1a−e to 2-indolyl cyanomalonates 5a−e, were isolated and characterized. Formation of the steady-state intermediate cycloprop[b]indoles 3a−e was evidenced by means of NMR and confirmed by the X-ray structure of 3c, demonstrating that the formation
区域异构的α氰基二硫缩烯酮ø,ö二烷基缩醛2A - ë和4A - ë,顺序中间体吲哚α氰基γ内酯的重氮甲烷诱导的转换1A - ë到2-吲哚基cyanomalonates 5A - ë,分别为隔离和表征。NMR证实了稳态中间体环丙[ b ]吲哚3a - e的形成,并由3c的X射线结构证实了这一点,表明从中形成了5a - e图2a - e通过两个连续且平行的单分子步骤进行,其中中间体3a - e以可逆过程形成。提供了可逆反应通过[1,3]重排进行的证据。应用于中间体3的稳态动力学方法允许执行最小的两个连续步骤2 → 4 → 5动力学模型,其中烷基取代基的空间体积极大地影响了相关的速率常数k 1和k 2,倒转速率确定步骤。溶剂化作用增强了这些骨架重排的可行性,因为它们在很大程度上稳定了过渡态。实验确定的热力学参数和DFT计算表明,这些级联重排是通过[1,3]-σ机制发生的,其中通过四元伪外环过渡态进行的异步键重组过程是非常有利的。