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

Two tribenzotriquinacene-based crown ethers, TBTQdibenio-24-crown-8 5 and-TBTQbenzo-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 multigrarri scale. The host-guest complexation properties of the TBTQbased crown ethers 5 and 6 With a pataquat derivative, 16, and two secondary ammonium salts, 17 and 18, were studied by H-1 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 K-a = (9.2 +/- 1.8) X 10(2) M-1, whereas no complexation was found for 17 and 18. In contrast, the TBTQcrown ether 6 assembles selectively with dibutylammonium hexafluorophosphate 18 as a 1:1 complex in CDCl3/CD3COCD3 [K-a = (5.0 +/- 1.4) X 10(2) M-1]; for which a threaded [2]pseudorotaxane structure is assumed.