Chang Dongdong, Zhu Jiangyu, Sun Yutao, Chi Kai, Qiao Yanjun, Wang Teng, Zhao Yan, Liu Yunqi, Lu Xuefeng
Department of Materials Science, State Key Laboratory of Molecular Engineering of Polymers, Fudan University Shanghai 200433 China
Chem Sci. 2023 May 15;14(22):6087-6094. doi: 10.1039/d3sc01295f. eCollection 2023 Jun 7.
The precise synthesis of cycloarenes remains a challenging topic in both organic chemistry and materials science due to their unique fully fused macrocyclic π-conjugated structure. Herein, a series of alkoxyl- and aryl-cosubstituted cycloarenes (kekulene and edge-extended kekulene derivatives, K1-K3) were conveniently synthesized and an unexpected transformation of the anthryl-containing cycloarene K3 into a carbonylated cycloarene derivative K3-R was disclosed by controlling the temperature and gas atmosphere of the Bi(OTf)-catalyzed cyclization reaction. All their molecular structures were confirmed by single-crystal X-ray analysis. The crystallographic data, NMR measurements, and theoretical calculations reveal their rigid quasi-planar skeletons, dominant local aromaticities, and decreasing intermolecular π-π stacking distance with extension of the two opposite edges. The much lower oxidation potential for K3 by cyclic voltammetry explains its unique reactivity. Moreover, carbonylated cycloarene derivative K3-R shows a remarkable stability, large diradical character, a small singlet-triplet energy gap (Δ = -1.81 kcal mol), and weak intramolecular spin-spin coupling. Most importantly, it represents the first example of carbonylated cycloarene diradicaloids as well as the first example of radical-acceptor cycloarenes and will shed some light on synthesis of extended kekulenes and conjugated macrocyclic diradicaloids and polyradicaloids.
由于其独特的全稠合大环π共轭结构，环芳烃的精确合成在有机化学和材料科学领域仍然是一个具有挑战性的课题。在此，我们便捷地合成了一系列烷氧基和芳基共取代的环芳烃（凯库勒烯和边缘扩展的凯库勒烯衍生物，K1 - K3），并且通过控制Bi(OTf)催化环化反应的温度和气体氛围，揭示了含蒽基的环芳烃K3意外地转化为羰基化环芳烃衍生物K3 - R。它们的所有分子结构均通过单晶X射线分析得到证实。晶体学数据、核磁共振测量以及理论计算揭示了它们刚性的准平面骨架、占主导地位的局部芳香性，以及随着两个相对边缘的延伸分子间π - π堆积距离减小。循环伏安法测得K3的氧化电位低得多，这解释了其独特的反应性。此外，羰基化环芳烃衍生物K3 - R表现出显著的稳定性、较大的双自由基特征、较小的单重态 - 三重态能隙（Δ = -1.81 kcal/mol）以及较弱的分子内自旋 - 自旋耦合。最重要的是，它代表了羰基化环芳烃双自由基oid的首个实例以及自由基受体环芳烃的首个实例，将为扩展凯库勒烯以及共轭大环双自由基oid和多自由基oid的合成提供一些启示。
