Zhou Zheng, Egger Dominic T, Hu Chaowei, Pennachio Matthew, Wei Zheng, Kawade Rahul K, Üngör Ökten, Gershoni-Poranne Renana, Petrukhina Marina A, Alabugin Igor V
Department of Chemistry, University at Albany, State University of New York, Albany, New York 12222, United States.
School of Materials Science and Engineering, Tongji University, Shanghai 201804, China.
J Am Chem Soc. 2022 Jul 13;144(27):12321-12338. doi: 10.1021/jacs.2c03681. Epub 2022 Jun 2.
We describe reductive dehydrogenative cyclizations that form hepta-, nona-, and decacyclic anionic graphene subunits from mono- and bis-helicenes with an embedded five-membered ring. The reaction of bis-helicenes can either proceed to the full double annulation or be interrupted by addition of molecular oxygen at an intermediate stage. The regioselectivity of the interrupted cyclization cascade for bis-helicenes confirms that relief of antiaromaticity is a dominant force for these facile ring closures. Computational analysis reveals the unique role of the preexisting negatively charged cyclopentadienyl moiety in directing the second negative charge at a specific remote location and, thus, creating a localized antiaromatic region. This region is the hotspot that promotes the initial cyclization. Computational studies, including MO analysis, molecular electrostatic potential maps, and NICS(1.7) calculations, evaluate the interplay of the various effects including charge delocalization, helicene strain release, and antiaromaticity. The role of antiaromaticity relief is further supported by efficient reductive closure of the less strained monohelicenes where the relief of antiaromaticity promotes the cyclization even when the strain is substantially reduced. The latter finding significantly expands the scope of this reductive alternative to the Scholl ring closure.
我们描述了还原脱氢环化反应，该反应从具有嵌入五元环的单螺旋烯和双螺旋烯形成七元、九元和十元环的阴离子石墨烯亚基。双螺旋烯的反应既可以进行完全的双环化，也可以在中间阶段通过添加分子氧而中断。双螺旋烯中断的环化级联反应的区域选择性证实，反芳香性的缓解是这些容易的闭环反应的主导力量。计算分析揭示了预先存在的带负电荷的环戊二烯基部分在将第二个负电荷引导至特定远程位置从而创建局部反芳香区域方面的独特作用。该区域是促进初始环化的热点。包括分子轨道分析、分子静电势图和NICS(1.7)计算在内的计算研究评估了包括电荷离域、螺旋烯应变释放和反芳香性在内的各种效应之间的相互作用。即使应变大幅降低，反芳香性的缓解促进环化的较不紧张的单螺旋烯的有效还原闭环进一步支持了反芳香性缓解的作用。后一发现显著扩展了这种还原替代肖尔闭环反应的范围。
