Elucidation of Biradical Character in pi-Conjugated Hydrocarbons Caused by Annelation with Strained Bicycloalkene Frameworks

(1)合成了最重要的芳香烃苯(1)和环多烯环己烯（COT, 2），并与高应变双环体系双[2.1.1]己烯（BCH）相连。通过理论计算、光谱和电化学测量对其芳香性和抗芳香性进行了研究。(2)发现苯1与SbCl_5的单电子氧化导致1重排为与1,2-和3,4位的BCH单元相连的新型萘衍生物3。3的x射线结构分析表明，由于键长平衡，bch - annated的6元环比其他环更芳香。它可以被氧化成一个稳定的自由基阳离子，因为HOMO能级大大提高。(3)苯1表现出多烯而非芳香族化合物的典型反应性。因此，它被m-CPBA氧化，并进行simmons - smith反应，得到相应的全顺式三环氧化物和三环丙烷衍生物，收率高。(4)由于萘- 3与张力BCH体系的亲和作用，在室内光照射下，萘- 3很容易与空气氧化，生成具有两个羰基和两个顺式环丁烷-1,4-二基的新型大环炔。这是由内过氧化物首先在bch -环合萘的1,4位形成的反向[2+2+2]裂解反应形成的。这是由于萘3的高双基性。(5)合成了一系列由双环[2.2.2]辛烯单元完全包围的低硫噻吩（2-、3-、4-、6-和8-m），并转化为稳定的自由基阳离子盐或阳离子盐，通过x射线晶体学测定了其精确结构。这些被认为是有关的模型极化子或双极化子的p掺杂状态的寡硫吩。

(1)The most essential aromatic hydrocarbon, benzene (1), and cyclic polyene, cyclooctatetraene (COT, 2), annelated with a highly strained bicyclic system, bicyclo[2.1.1]hexene (BCH), were synthesized. Their aromaticity and antiaromaticity were examined by the use of theoretical calculations and spectral and electrochemical measurements.(2) One-electron oxidation of benzene 1 with SbCl_5 was found to cause rearrangement of 1 to a novel naphthalene derivative 3 annelated with the BCH units at 1,2- and 3,4-positions. The X-ray structural analysis of 3 demonstrated that the BCH-annelated 6-membered ring is more aromatic than the other ring owing to bond-length equalization. It can be oxidized to a stable radical cation because of the considerably raised HOMO energy levels.(3) Benzene 1 exhibited the reactivity typical for the polyene rather than an aromatic compound. Thus, it was oxidized by m-CPBA and underwent Symmons-Smith reactions to give the corresponding all-cis tri-epoxide and tri-cyclopropane derivatives in high yields.(4) Because of the annelation with strained BCH systems, naphthalene 3 readily underwent oxidation with air under irradiation of room light to give a novel macrocyclic alkyne having a two carbonyl groups and two cis-cyclobutane-1,4-diyl units. This was shown to be formed by retro[2+2+2] cleavage reaction of the endoperoxide first formed at the 1,4-positions of the BCH-annelated naphthalene. This is due to the high biradical character of naphthalene 3.(5) A series of oligothiophenes (2-,3-,4-,6-, and 8-mers) completely surrounded by bicyclo[2.2.2]octene units were synthesized, and were converted to stable radical cation salts or dication salts, whose precise structures were determined by X-ray crystallography. These are considered as pertinent models for polaron or bipolaron of the p-doped states of oligothiophenes.