Design, Synthesis and Aromaticity of an Alternating Cyclo[4]Thiophene[4]Furan
Design, Synthesis and Aromaticity of an Alternating Cyclo[4]Thiophene[4]Furan
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DOI：
10.1002/chem.202300477
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发表时间：
2023-05-16
影响因子：
4.3
通讯作者：
Noonan，Kevin J. T.
中科院分区：
文献类型：
--
作者：
Kawakami，Manami;Sharma，Dhruv;Noonan，Kevin J. T.
报道了一类新的共轭大环--环[4]噻吩基[4]呋喃己酯(C4TE4FE)。该环由交替的α连接的噻吩3-酯和呋喃-3-酯重复单元组成，由2-(噻吩基-2-基)呋喃单体的铃木-宫浦交叉偶联一步合成。酯侧基有助于促进杂环的非同步构象，从而使大环的形成成为可能。循环伏安研究表明，C4TE4Fe可以发生多次氧化，因此SbCl5处理导致了[C4TE4Fe]2+离子的形成。计算工作与该产物的1H 核磁共振谱相结合，揭示了当2E−氧化时，循环变得全局芳香，而沿着外环的轮烯路径变得Hück el芳香。从1H 核磁共振谱中可以清楚地看到氧化循环中环电流的变化，因为噻吩环和呋喃环的质子在场下移动了近6 ppm。这项工作突出了在基于呋喃的大环中进行顺序控制以调整电子性质的潜力。
A new class of conjugated macrocycle, the cyclo[4]thiophene[4]furan hexyl ester (C4TE4FE), is reported. This cycle consists of alternating α‐linked thiophene‐3‐ester and furan‐3‐ester repeat units, and was prepared in a single step using Suzuki–Miyaura cross‐coupling of a 2‐(thiophen‐2‐yl)furan monomer. The ester side groups help promote asynconformation of the heterocycles, which enables formation of the macrocycle. Cyclic voltammetry studies revealed that C4TE4FE could undergo multiple oxidations, so treatment with SbCl5resulted in formation of the [C4TE4FE]2+dication. Computational work, paired with1H NMR spectroscopy of the dication, revealed that the cycle becomes globally aromatic upon 2e−oxidation, as the annulene pathway along the outer ring becomes Hückel aromatic. The change in ring current for the cycle upon oxidation was clear from1H NMR spectroscopy, as the protons of the thiophene and furan rings shifted downfield by nearly 6 ppm. This work highlights the potential of sequence control in furan‐based macrocycles to tune electronic properties.