N-4-戊烯基硝酮的分子内环加成反应的区域选择性的理论研究

A Theoretical Study on the Regiochemistry of Intramolecular N-4-Alkenylnitrone Addition

用MINDO/3方法求出了N-4-戊烯基硝酮分子内环加成反应的过渡态和反应途径.两个环加成区域异构体是由N-4-戊烯基硝酮的两个不同的构象经过各自的过渡态得到的.理论分析满意地解释了实验结果.

The geometries of three conformers of N-4-alkeny]nitrone(Ra,Rb and Rc)wereoptimized with the aid of energy gradient technique.The geometries of two transitionstates(Ta and Tb)were obtained by Komornieki’s method.The reaotion paths were alsofound out.The conformers Ra,Rb and Rc are all stable,but only the first two are activein the intramolecular cycloaddition,generating regioisomer Pa and Pb via transitionstate Ta and Tb respectively.Actually intramolecular cyoloaddition of N-4-alkenylni-trone consists of two parallel reactions.Beoause the activation barrier of the reactionfrom Rb to Pb JS lower than that from Ra to Pa,the higher yield of the former is pre-dieted.This is in good consistence with experiments.The mechanism of the tworeactions are similar.All the caloulations were performed on semiempirical MINDO/3molecular orbital method.