| Research Abstract |
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.
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