Yin Xianglin, Zheng Ke, Jin Zexin, Horst Maggie, Xia Yan
Department of Chemistry, Stanford University, Stanford, California 94305, United States.
J Am Chem Soc. 2022 Jul 20;144(28):12715-12724. doi: 10.1021/jacs.2c02457. Epub 2022 Jul 6.
Contorted carbon structures have drawn much attention in the past decade for their rich three-dimensional geometries, enhanced solubility, and tunable electronic properties. We report a modular method to synthesize contorted polycyclic conjugated hydrocarbons containing helical moieties in controlled topologies. This strategy leverages our previously reported streamlined synthesis of π-systems containing four-membered cyclobutadienoids (CBDs), whose catalyzed cycloaddition with alkynes affords helical structures. Interestingly, we observed exclusive nonbay region regioselectivity in the C-C bond activation of CBDs in our system, which is opposite to the scarce previous examples of []phenylene activation that led to the formation of linear phenacene structures. The quantitative and regioselective nonbay region alkyne cycloaddition yielded a variety of helical carbon structures with their topologies predetermined by the CBD-containing precursor hydrocarbons. The cycloaddition can be inhibited by methyl substituents exocyclic to the four-membered ring, thus allowing selective activation of only certain desired CBD units while leaving the others intact. Calculation elucidated the basis for the observed regioselectivity. The described method provides a new route to multihelical aromatic hydrocarbons with complex yet defined geometries, facilitating the further exploration of such fascinating carbon structures.
在过去十年中，扭曲的碳结构因其丰富的三维几何形状、增强的溶解性和可调节的电子特性而备受关注。我们报道了一种模块化方法，用于合成具有可控拓扑结构且包含螺旋部分的扭曲多环共轭烃。该策略利用了我们先前报道的含四元环丁二烯类（CBDs）的π体系的简化合成方法，其与炔烃的催化环加成反应可得到螺旋结构。有趣的是，我们在该体系中观察到CBDs的C-C键活化具有独特的非湾区区域选择性，这与之前少数导致线性并苯结构形成的[]亚苯基活化的例子相反。定量且区域选择性的非湾区炔烃环加成反应产生了多种螺旋碳结构，其拓扑结构由含CBD的前体烃预先确定。环加成反应可被四元环外的甲基取代基抑制，从而允许仅选择性活化某些所需的CBD单元，而使其他单元保持完整。计算阐明了观察到的区域选择性的基础。所描述的方法为具有复杂但明确几何形状的多螺旋芳烃提供了一条新途径，有助于进一步探索此类迷人的碳结构。
