Kinetic studies for amination of ketenimines: change of rate-determining step by electron-withdrawing N-substituents through electronic effects
作者:Kuangsen Sung、Pin-Mei Huang、Shu-Min Chiang
DOI:10.1016/j.tet.2006.03.022
日期:2006.5
to Kk2 for the amination of 1a–d and the Hammett plot was a convex curve with ρD=ρ1=7.08 and ρA=ρK+ρ2=0.98, indicating change of the rate-determining step. The electron-withdrawing para-substituents on the N-phenyl group of ketenimines significantly stabilize the first transition state of CN addition, resulting in change of the rate-determining step to the second step of tautomerization. The N-substituent
通过紫外分光光度法对酮亚胺1a - d和2a - e用n -BuNH 2胺化的动力学进行了研究。哈米特方程应用于二阶速率常数(ķ 1)为的胺化2A - Ë和哈米特情节表现出与反应常数的线性自由能关系(ρ 1的2.87),这表明在第二阶速率常数(k 1)对应于速率确定CN加成的第一步。相反,将Hammett方程应用于Kk 2为的胺化1A - d和哈米特情节具有凸曲线ρ d = ρ 1 = 7.08和ρ甲= ρ ķ + ρ 2 = 0.98,表明速率决定步骤的变化。酮亚胺的N-苯基上的吸电子对位取代基显着稳定了CN加成的第一过渡态,导致速率确定步骤变为互变异构第二步骤。该ñ-取代电子效应对烯酮亚胺比在C中的取代基电子效应的胺化更显著影响β。