Matsuda Chikako, Suzuki Yuto, Katagiri Hiroshi, Murase Takashi
Faculty of Science, Yamagata University, 1-4-12 Kojirakawa-machi, Yamagata, Yamagata, 990-8560, Japan.
Graduate School of Science and Engineering, Yamagata University, 4-3-16 Jonan, Yonezawa, Yamagata, 992-8510, Japan.
Chem Asian J. 2021 Mar 1;16(5):538-547. doi: 10.1002/asia.202001295. Epub 2021 Feb 4.
The intramolecular Diels-Alder reactions of helicenes deform their π-conjugated screw-shaped skeletons. In particular, terminally tetrafluorinated [7]helicene (F -[7]helicene) undergoes a photoinduced Diels-Alder reaction followed by a photoinduced double fluorine atom transfer. Herein, we thoroughly investigated this photochemical domino process by decreasing the level of fluorine substitution. F -[7]Helicenes bearing two fluorine atoms at the dienophile terminal underwent photoinduced Diels-Alder reactions, but the whole domino process became slow. F -[7]Helicene, which is difluorinated only at the dienophile terminal, was also photolabile. As a result, two fluorine atoms were sufficient for the photochemical domino reaction to occur. X-ray crystallographic analysis revealed that F -[7]helicene was less compressed than F -[7]helicene, indicating that terminal polyfluorination enhanced the intramolecular arene-fluoroarene stacking interactions and thus promoted the transformations.
轮烯的分子内狄尔斯-阿尔德反应会使其π共轭螺旋形骨架发生变形。特别是，末端四氟化的[7]轮烯（F -[7]轮烯）会发生光诱导狄尔斯-阿尔德反应，随后是光诱导双氟原子转移。在此，我们通过降低氟取代水平对这一光化学多米诺过程进行了深入研究。在亲双烯体末端带有两个氟原子的F -[7]轮烯发生了光诱导狄尔斯-阿尔德反应，但整个多米诺过程变得缓慢。仅在亲双烯体末端二氟化的F -[7]轮烯也对光不稳定。结果表明，两个氟原子足以引发光化学多米诺反应。X射线晶体学分析表明，F -[7]轮烯的压缩程度低于F -[7]轮烯，这表明末端多氟化增强了分子内芳烃-氟芳烃堆积相互作用，从而促进了转化。
