Development of Novel Qumoid Compounds by Taking Advantage of the Molccular Cavities as a Steric Protection Environment

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Novel bowl-type molecular cavities have been applied to synthesis of a variety of quinoid compounds including highly reactive ones. A bridged calix[6]arene, where a 1,4-benzoquinone moiety is covalently anchored in the cavity of the calix[6]arene macrocycle with a rigid cone conformation, was synthesized and its structure was determined by X-ray analysis. The cyclic voltammogram showed 'that :its reduction potential is negatively shifted in comparison with the reference compounds without the calixarene macrocode. A stable N- unsubstituted quinoneimine was successfully synthesized by thermolysis of the corresponding p-azidophenol under basic conditions. Its crystal structure was established by X-ray analysis, presenting the first example of the crystallographic analysis of an N-unsubstituted quinoneimine. It was revealed that the imine moiety is effectively protected by the calix[6]arene macrocycle. The cyclic voltammogram indicated that the quinoneimine is subject to two-electron reduction in one step in contrast to the corresponding quinone, which is reduced by two steps. Stabilization of other reactive quinoid species such as thioquinones was also investigated.