Intramolecular DielsâAlder reactions of ester-linked 1,3,8-nonatrienes carrying a diphenylcyclopropyl substituent attached to C1 proceed with high levels of stereoselectivity. The stereochemical outcomes of these reactions are explained by reference to B3LYP/6-31G(d) transition structures. Experimentally, the diphenylcyclopropane rings remain intact through these IMDA reactions, notwithstanding their predicted extremely high degree of asynchronicity (the B3LYP-computed lengths in the IMDA transition structures differ by as much as 1.1 Ã
), providing support to the notion that these reactions are concerted processes.
C1 上带有二苯基环丙基取代基的酯链式 1,3,8-nonatrienes 分子内 DielsâAlder 反应具有高度的立体选择性。参考 B3LYP/6-31G(d) 过渡结构解释了这些反应的立体
化学结果。从实验上看,二苯基
环丙烷环在这些 I
MDA 反应中保持完好无损,尽管预测它们具有极高的异步性(I
MDA 过渡结构中 B3LYP 计算的长度相差达 1.1 Ã),这为这些反应是协同过程的观点提供了支持。