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 1 H NMR spectroscopy and mass spectrometry. It was found that host 5 binds to the paraquat derivative 16 as a 1:1 complex in CDCl3 /CD3 CN 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 /CD3 COCD3 [Ka = (5.0 ± 1.4) × 102 M-1 ], for which a threaded [2]pseudorotaxane structure is assumed.