Wang Jinjian, Wang Guangxia, Li Chunli, Dong Yuexia, Ma Zhiying, Wang Hua
Engineering Research Center for Nanomaterials, Henan University, Kaifeng, 475004, People's Republic of China.
J Org Chem. 2021 Mar 19;86(6):4413-4422. doi: 10.1021/acs.joc.0c02629. Epub 2021 Mar 8.
Three unsymmetric thiophene-based [7]helicenes, namely, --, --, and --, with different isomeric locations of sulfur atoms in two terminal thiophene rings were efficiently synthesized using dithieno[2,3-:3',2'-]thiophene (-), dithieno[2,3-:2',3'-]thiophene (-), and dithieno[2,3-:3',4'-]thiophene (-) as building blocks via Suzuki cross-coupling and intramolecular cyclization reactions. Aside from these racemic [7]helicenes, two novel heterocyclic isomers, namely, trithienothiepines and , were simultaneously obtained during the intramolecular cyclization. Two novel deprotonations of bi-s and cyclization for synthesizing target compounds showed high selectivity and efficiently constructed both s and s. X-ray crystallographic analyses revealed that the s have typical helical molecular structures. The isomeric location of sulfur atoms in the two terminal thiophene rings in --, --, --, and allowed multiple intermolecular interactions, such as S···S, S···C, and S···H interactions, resulting in different crystal-packing patterns. Moreover, the absorption behaviors of these [7]helicenes, , and were examined and theoretically calculated. Results indicated that the isomeric location of sulfur atoms plays a key role in tuning intramolecular π-electronic conjugation.
以二噻吩并[2,3 - :3',2'-]噻吩（-）、二噻吩并[2,3 - :2',3'-]噻吩（-）和二噻吩并[2,3 - :3',4'-]噻吩（-）为构建单元，通过铃木交叉偶联和分子内环化反应，高效合成了三种不对称噻吩基[7]螺旋烯，即--、--和--，其两个末端噻吩环中硫原子的异构位置不同。除了这些外消旋[7]螺旋烯外，在分子内环化过程中还同时得到了两种新型杂环异构体，即三噻吩并噻庚因 和 。用于合成目标化合物的双 - s的两种新型去质子化和环化反应显示出高选择性，并有效地构建了s和s。X射线晶体学分析表明，s具有典型的螺旋分子结构。--、--、--和 中两个末端噻吩环中硫原子的异构位置允许多种分子间相互作用，如S···S、S···C和S···H相互作用，从而导致不同的晶体堆积模式。此外，还对这些[7]螺旋烯、 和 的吸收行为进行了研究和理论计算。结果表明，硫原子的异构位置在调节分子内π电子共轭中起关键作用。
