Department of Chemistry, Stanford University , Stanford, California 94305, United States.
Advanced Light Source, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
J Am Chem Soc. 2017 Nov 8;139(44):15933-15939. doi: 10.1021/jacs.7b09222. Epub 2017 Oct 9.
Polycyclic conjugated hydrocarbons containing four-membered cyclobutadienoids (CBDs) are of great fundamental and technical interest due to the antiaromaticity brought by CBD circuits. However, their synthesis has been challenging, hampering the exploration and understanding of such systems. We report efficient synthesis of a series of unprecedented [3]naphthylene regioisomers in high yields, where three naphthalenoids are fused through two CBDs in linear, angular, and bent regioconnectivity. Their synthesis was enabled by exclusively regioselective catalytic arene-norbornene annulation (CANAL) between dibromonaphthalenes and benzooxanorbornadienes, followed by aromatization. [3]Naphthylene regioisomers exhibited distinct optoelectronic properties. Nucleus-independent chemical shift calculations, NMR spectroscopy, and X-ray crystallography revealed the strong effect of the fusion pattern on the local antiaromaticity and aromaticity in fused CBDs and naphthalenoids, respectively. Thus, our synthetic strategy allows facile access to extended CBD-fused π-systems with tunable local antiaromaticity and aromaticity.
含有四环[4.4.0]癸-1,3,5-三烯（CBD）的多环共轭烃由于 CBD 环带来的反芳香性而具有重要的基础和技术意义。然而，它们的合成具有挑战性，阻碍了对这类体系的探索和理解。我们报告了一系列前所未有的[3]萘并[2,1-b]呋喃区域异构体的高效合成，其中三个萘并[2,1-b]呋喃通过两个 CBD 以线性、角形和弯曲的区域连接性连接。它们的合成是通过二溴代萘与苯并氧杂降冰片二烯之间的专一地区域选择性芳构化催化芳基-降冰片烯环加成（CANAL）实现的。[3]萘并[2,1-b]呋喃区域异构体表现出明显的光电性质。核独立化学位移计算、NMR 光谱和 X 射线晶体学揭示了融合模式对融合 CBD 和萘并[2,1-b]呋喃中局部反芳香性和芳香性的强烈影响。因此，我们的合成策略允许方便地获得具有可调局部反芳香性和芳香性的扩展 CBD 稠合的π-体系。
