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- Title
Synthesis of Tetraoxygenated Terephthalates via a Dichloroquinone Route: Characterization of Cross-Conjugated Liebermann Betaine Intermediates.
- Authors
Hintermann, Lukas; Altmann, Philipp J.; Naumov, Panče; Suzuki, Keisuke
- Abstract
Cross-conjugated quinoid betaines 4 (2,5-bis(alkoxycarbonyl)-3,6-dioxo-4-(1-pyridinium-1-yl)cyclohexa-1,4-dien-1-olates; Liebermann betaines) were synthesized from 2,5-dichloro-3,6-dioxocyclohexa-1,4-diene-1,4-dicarboxylates ( 2) and pyridines in acetone containing H2O. Their structure was secured by NMR spectroscopy and by X-ray diffraction analysis of 4f (alkoxy = EtO, pyridine = 4-Me2N-C5H4N). Betaines 4 show comparatively high reactivity towards nucleophiles as a consequence of their cross-conjugated character. Betaine 4a and hydroxy-3,4-methylenedioxybenzene (sesamol) condense to give a pyridinium quinolate salt 14 which has a bifurcate H-bond from a pyridinium N+-H donor to both carbonyl (C=O) and olate (C-O−) acceptors in the solid state. Betaine 4b hydrolyzes in aqueous solution to give diethyl 2,5-dihydroxy-3,6-dioxocyclohexa-1,4-diene-1,4-dicarboxylate ( 11) as a pyridinium salt, or as polymeric zinc(II) complex of the dianion of 11 in the presence of ZnCl2. Dihydroxyquinone 11 was analytically differentiated from its independently prepared hydroquinone form, diethyl 2,3,5,6-tetrahydroxyterephthalate ( 12), by NMR analysis in solution and X-ray crystal structure determination of both compounds.
- Subjects
BETAINES; BIOCONJUGATES; PYRIDINIUM compounds; X-ray diffraction; PYRIDINE; TETRAOXYGEN
- Publication
Helvetica Chimica Acta, 2017, Vol 100, Issue 4, pn/a
- ISSN
0018-019X
- Publication type
Article
- DOI
10.1002/hlca.201600392