Study on the Preparation of Highly Strained Polycyclic Compounds and Their Transformation into Novel Chemical Species

1.[4]对环番及其衍生物是已知的对环番中最紧张的，但其极不稳定的热稳定性阻碍了对其物理和化学性质的探索。在这项研究中，通过引入空间要求很高的取代基来保护桥头碳原子不被其他试剂访问，成功地稳定了对环芳烃[4]。所制备的物种足够稳定，可以进行~1H核磁共振的测量，这表明尽管苯环发生了极大的扭曲，但仍存在显著的抗磁环电流。理论计算还表明，电子在[4]对环番分子的弯曲苯中的循环离域保留与实验观察一致。杜瓦苯是苯的一种高度应变价的异构体，因此前者向后者的热转化通常是无法实现的。理论计算表明，极端应变的对环番分子热异构化为相应的杜瓦苯在能量上是可行的。然而，到目前为止，由于[4]对环磷酰胺的极端热不稳定，这个过程还没有观察到。在本研究中，[4]对环番的成功的动力学稳定使得该过程首次得以观察到。三环[4.2.2.2^&lt；2，5&gt；]十二烷-1，3，5，7，9，11-己烯是一种新型的全不饱和、高应变碳氢化合物。

1. [4] Paracyclophane and its derivatives are the most strained of known paracyclophanes, but their extreme thermal instability has thwarted the exploration of physical and chemical properties. In this study, [4] paracyclophane was kinetically stabilized successfully by introducing sterically demanding substituents which specifically shield the bridgehead carbon atoms from the access of other reagents. The prepared species was sufficiently stable to permit the measurement of ^1H NMR,which suggested the sustenance of significant diamagnetic ring current despite the extreme distortion of the benzene ring. Theoretical calculations also indicated the retention of cyclic delocalization of electrons in the bent benzene of [4] paracyclophane in accord with the experimental observation.2. Dewar benzene is a highly strained valence isomer of benzene, hence the thermal transformation of the former to the latter is generally unattainable. Theoretical calculations suggest that thermal isomerization of extremely strained [4] paracyclophane to the corresponding Dewar benzene is energetically feasible. The process, however, has so far been unobservable owing to the extreme thermal instability of [4] paracyclophane. The successful kinetic stabilization of [4] paracyclophane in the present study allowed the obervation of the process for the first time.3. Tricyclo [4.2.2.2^<2,5>] dodeca-1,3,5,7,9,11-hexaene, a novel fully unsaturated, highly strained hydrocarbon, was successfully generated from a Dewar benzene derivative and chemically intercepted.