Department of Chemistry, Johns Hopkins University , 3400 North Charles Street, Baltimore, Maryland 21218, United States.
Department of Chemistry - Ångström Laboratory, Uppsala University , 751 20 Uppsala, Sweden.
J Org Chem. 2017 Dec 15;82(24):13440-13448. doi: 10.1021/acs.joc.7b02512. Epub 2017 Nov 28.
This report documents the synthesis, characterization, and computational evaluation of two isomeric borepin-containing polycyclic aromatics. The syntheses of these two isomers involved symmetrical disubstituted alkynes that were reduced to Z-olefins followed by borepin formation either through an isolable stannocycle intermediate or directly from the alkene via the trapping of a transient dilithio intermediate. Comparisons of their magnetic, crystallographic, and computational characterization to literature compounds gave valuable insights about the aromaticity of these symmetrically fused [b,f]borepins. The fusion of benzo[b]thiophene units to the central borepin cores forced a high degree of local aromaticity within the borepin moieties relative to other known borepin-based polycyclic aromatics. Each isomer had unique electronic responses in the presence of fluoride anions. The experimental data demonstrate that the local borepin rings in these two compounds have a relatively high amount of aromatic character. Results from quantum chemical calculations provide a more comprehensive understanding of local and global aromatic characters of various rings in fused ring systems built upon boron heterocycles.
本报告记录了两种含有同异位素的多环芳烃的合成、表征和计算评估。这两种异构体的合成涉及对称二取代炔烃，这些炔烃被还原为 Z-烯烃，然后通过可分离的锡环中间体或直接从烯烃通过捕获瞬态双锂中间体形成同异位素。对其磁性、晶体学和计算特性与文献化合物的比较为这些对称融合的 [b,f]同异位素的芳香性提供了有价值的见解。苯并[b]噻吩单元与中心同异位素核心的融合使得同异位素部分具有相对于其他已知基于同异位素的多环芳烃更高的局部芳香性。每个异构体在存在氟阴离子时都具有独特的电子响应。实验数据表明，这两种化合物中的局部同异位素环具有相对较高的芳香性。量子化学计算的结果提供了对基于硼杂环构建的稠环体系中各种环的局部和全局芳香性的更全面理解。
