Synthesis of Tetraoxygenated Terephthalates via a Dichloroquinone Route: Characterization of Cross-Conjugated Liebermann Betaine Intermediates

Lukas Hintermann, Philipp J. Altmann, Pance Naumov, Keisuke Suzuki

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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.

Original languageEnglish (US)
JournalHelvetica Chimica Acta
Volume100
Issue number4
DOIs
StatePublished - Jan 1 2017

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Keywords

  • Betaines
  • Conjugation
  • Nitrogen heterocycles
  • Quinones
  • Structure elucidation

ASJC Scopus subject areas

  • Catalysis
  • Biochemistry
  • Drug Discovery
  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

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