Tribenzotriquinacene-Based Crown Ethers: Synthesis and Selective Complexation with Ammonium Salts

Two tribenzotriquinacene-based
crown ethers, TBTQ-dibenzo-24-crown-8 5 and TBTQ-benzo-21-crown-7 6, were prepared
from the key TBTQ intermediate, 2,3-dihydroxy-4b,8b,12b,12d-tetramethyltribenzotriquinacene
(13), which in turn was synthesized in six steps using
two variants of our cyclodehydration method on a multigram scale.
The host–guest complexation properties of the TBTQ-based crown
ethers 5 and 6 with a paraquat derivative, 16, and two secondary ammonium salts, 17 and 18, were studied by 1H NMR spectroscopy and mass
spectrometry. It was found that host 5 binds to the paraquat
derivative 16 as a 1:1 complex in CDCl3/CD3CN solution with an association constant of Ka = (9.2 ± 1.8) × 102 M–1, whereas no complexation was found for 17 and 18. In contrast, the TBTQ-crown ether 6 assembles
selectively with dibutylammonium hexafluorophosphate 18 as a 1:1 complex in CDCl3/CD3COCD3 [Ka = (5.0 ± 1.4) × 102 M–1], for which a threaded [2]­pseudorotaxane
structure is assumed.

本研究以关键TBTQ中间体2,3-二羟基-4b,8b,12b,12d-四甲基三苯并三喹吖烯（13）为起始原料，合成了两种基于三苯并三喹吖烯（tribenzotriquinacene）的冠醚：TBTQ-二苯并-24-冠-8（5）与TBTQ-苯并-21-冠-7（6）；该中间体则通过我们团队开发的环脱水方法的两种变体，以多克级规模经六步反应制备得到。
采用核磁共振氢谱与质谱技术，研究了TBTQ基冠醚5、6分别与一种百草枯衍生物（16）以及两种仲铵盐（17、18）之间的主客体络合性能。
实验结果显示，主体5与百草枯衍生物16在CDCl3/CD3CN混合溶剂中以1:1的化学计量比形成络合物，其结合常数Ka = (9.2 ± 1.8) × 10² M⁻¹；而主体5与17、18均未发生络合作用。
与之相反，TBTQ冠醚6可在CDCl3/CD3COCD3混合溶剂中与六氟磷酸二丁基铵18选择性地以1:1化学计量比组装形成络合物，其结合常数Ka = (5.0 ± 1.4) × 10² M⁻¹，该络合物被认为具有穿线型[2]准轮烷结构。