Mode Selectivity in the Intramolecular Cyclization of Ketenimines Bearing<i> N</i>-Acylimino Units: A Computational and Experimental Study
作者:Mateo Alajarín、Pilar Sánchez-Andrada、Angel Vidal、Fulgencio Tovar
DOI:10.1021/jo0482716
日期:2005.2.1
6π-electrocyclic ring closure leading to compounds enclosing a 1,3-oxazine ring. The [2+2] cycloaddition reaction takes place via a two-step process with formation of a zwitterionic intermediate, which has been characterized as a cross-conjugated mesomeric betaine. The 6π-electrocyclic ring closure occurs via a transition state whose pseudopericyclic character has been established on the basis of its magnetic
通过从头算和DFT计算,已经研究了特定种类的带有N-酰亚胺基酮胺的分子内环化中的模式选择性。在模型化合物中,羰基碳原子和烯键氮原子通过乙烯基或邻亚苯基系链连接。分析了两种环化模式:[2 + 2]环加成化合物与azeto [2,1- b]嘧啶酮部分和6π-电子环闭环导致化合物包围1,3-恶嗪环。[2 + 2]环加成反应是通过两步法进行的,形成了两性离子中间体,该两性离子中间体已被表征为交叉共轭的美索美甜菜碱。6π-电环闭环通过过渡态发生,该过渡态的伪周环特征是根据其磁性能,几何形状和NBO分析确定的。尽管[2 + 2]环加合物是热力学控制的产物,但在[2 + 2]环加成反应中,6π-电子环的闭环在能量上更受青睐。定量动力学分析预测,1,3-恶嗪将是动力学控制的产物,但它们应在室温下迅速且完全转化为[2 + 2]环加合物。从2-叠氮基苯甲酰氯开始,已在三个步骤中成功合成了其中两个反应性官能团都