Synthesis and structural data of tetrabenzo[8]circulene.
Synthesis and structural data of tetrabenzo[8]circulene.
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DOI：
10.1002/chem.201304657
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发表时间：
2014-03-24
影响因子：
4.3
通讯作者：
Whalley, Adam C.
中科院分区：
文献类型：
--
作者：
Miller, Robert W.;Duncan, Alexandra K.;Schneebeli, Severin T.;Gray, Danielle L.;Whalley, Adam C.
在1976年，第一次尝试合成鞍形分子[8]环烯被报道。在接下来的37年里，这种复杂分子的构建没有取得任何进展。然而，值得注意的是，在过去的六个月里，两个研究小组报告了合成[8]环烯衍生物的独立和截然不同的策略，取得了一系列进展。在此，我们提出了第三种合成方法，其中我们靶向四苯并[8]环烯。我们的方法采用Diels-Alder反应和钯催化的芳基化反应作为关键步骤。尽管计算描述了[8]环烯的不稳定性，加上母体分子的合成衍生物的不稳定性，但在分子外围添加四个稠合的苯环提供了高度稳定的结构。这种相对于母体[8]环烯的增加的稳定性是使用Clar的芳香六联体理论预测的，并且是化合物在并入这些额外的环后变得完全苯型的结果。合成的化合物在环境条件下表现出显着的稳定性-即使在高温下-在几个月内没有分解的迹象。与计算结构相比，该化合物的固态结构显著扭曲，主要是由于固态中的晶体堆积力。尽管这种扭曲从最低的能量结构，一系列的结构数据，确认存在本地化的芳香性在这个大的多环芳烃。
In 1976, the first attempted synthesis of the saddle-shaped molecule [8]circulene was reported. The next 37 years produced no advancement towards the construction of this complicated molecule. Remarkably, however, over the last six months a flurry of progress has been made with two groups reporting independent and strikingly different strategies for the synthesis of [8]circulene derivatives. Herein, we present a third synthetic method in which we target tetrabenzo[8]circulene. Our approach employs a Diels-Alder reaction and a palladium-catalyzed arylation reaction as the key steps. Despite calculations describing the instability of [8]circulene, coupled with the reported instability of synthesized derivatives of the parent molecule, the addition of four fused benzenoid rings around the periphery of the molecule provides a highly stable structure. This increased stability over the parent [8]circulene was predicted using Clar’s theory of aromatic sextets and is a result of the compound becoming fully benzenoid upon incorporation of these additional rings. The synthesized compound exhibits remarkable stability under ambient conditions – even at elevated temperatures – with no signs of decomposition over several months. The solid-state structure of this compound is significantly twisted compared to the calculated structure primarily as a result of crystal packing forces in the solid state. Despite this contortion from the lowest energy structure, a range of structural data is presented confirming the presence of localized aromaticity in this large polycyclic aromatic hydrocarbon.
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