Pedersen Stephan K, Eriksen Kristina, Ågren Hans, Minaev Boris F, Karaush-Karmazin Nataliya N, Hammerich Ole, Baryshnikov Glib V, Pittelkow Michael
Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen Ø, Denmark.
Division of Theoretical Chemistry and Biology, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH, Royal Institute of Technology, 10691 Stockholm, Sweden.
J Am Chem Soc. 2020 Aug 19;142(33):14058-14063. doi: 10.1021/jacs.0c05898. Epub 2020 Aug 4.
Fully aromatic []circulenes have only been known to encompass up to eight aromatic rings ( = 8), with no reports of endeavors in the synthesis of higher-order analogues ( > 8). Herein we present the first [9]circulene, formally a diazatrioxa[9]circulene, along with a tetrahydro-diazatetraoxa[10]circulene. The key transformation, for construction of the macrocyclic framework, is a simple high-yielding dimerizing condensation between 3,6-dihydroxycarbazole and glyoxal. Single crystal X-ray analysis reveals the [9]circulene to be perfectly planar and containing elongated benzene rings, which is induced by strain to accommodate planarity. Alternating bond lengths in the solid state indicate contribution from a [9]radialene resonance structure in the [9]circulene π-system. The central nonaromatic rings of both circulenes have paratropic ring currents, as evident by nucleus independent chemical shift (NICS) and anisotropy of the induced current density (ACID) calculations, which can be attributed to induced paratropicity from the surrounding aromatic rings.
完全芳香性的[]轮烯仅已知包含多达八个芳香环（ = 8），尚无关于合成高阶类似物（ > 8）的研究报道。在此，我们展示了首个[9]轮烯，即形式上的二氮杂三氧杂[9]轮烯，以及一种四氢二氮杂四氧杂[10]轮烯。构建大环骨架的关键转化步骤是3,6 - 二羟基咔唑与乙二醛之间简单的高产率二聚缩合反应。单晶X射线分析表明[9]轮烯完全呈平面结构且包含伸长的苯环，这是由应变诱导以适应平面性。固态下交替的键长表明[9]轮烯π体系中[9]环亚甲基共振结构的贡献。两种轮烯的中心非芳香环都具有抗磁环流，这通过核独立化学位移（NICS）和感应电流密度各向异性（ACID）计算得以证明，这可归因于周围芳香环诱导的抗磁性。
