甲酰基硫代双烯酮与甲亚胺4+2及2+2环加成反应的比较理论研究

Compared theoretical studies on the 4+2 and 2+2 cycloaddition reactions between formylthioketene and methylenimine

用量子化学从头算方法 ,研究了甲酰基硫代双烯酮与甲亚胺间的 4+2及 2 +2环加成反应 .结果表明 :生成六员环产物的 4+2反应 (1 )为非同步的协同过程 ,且活化势垒较低 .而两种生成四员环产物的 2 +2反应 (2 )和 (3)均为各经过一个两性离子中间体的分步过程 ,其中第二步为速率控制步骤 ,且活化势垒均比反应 (1 )的高 .所得结果与实验一致 .

The 4+2 and 2+2 cycloaddition reactions of formylthioketen e and methylenimine have been studied by using ab initio method at HF/6?31G  l evel.All the geometries of the stationary points on the reaction path have been o ptimized with the energy gradient technique.The single point energy calculations of the stationary points have been performed by MP2/6?31G  method.All the t r ansition states were characterized by vibration frequency analysis.The 4+2 react ion (1) formatting six?membered heterocyclic product is a asynchronous concerte d process and this reaction is easy to proceed.In the case of 2+2 reactions (2) a nd (3) formatting two different fourmembered heterocyclic products,two paral lel reactions are stepwise,proceeding via a zwitterionic intermediate respective ly;the second step is the rate controlling one.The activation barrier of the rat e?determining steps of reactions (2) and (3) are higher than that of reaction ( 1).This is consistent with experimental fact.