Synthesis and properties of a new methano-bridged tetradehydro[22]annulenedione

The title annulenedione 8 was synthesized starting from 1-acetyl-6-(3-oxobut-1-enyl)cyclohepta-1,3,5-triene 25 by aldol condensation with (Z)-3-methylpent-2-en-4-ynal 26 to afford the dione 27 and then by another aldol condensation of the dione 27 with the aldehyde 26, followed by intramolecular oxidative coupling of the resulting acyclic diacetylene 28. Examination of the 1H NMR spectra indicated that compound 8 is paratropic in acidic media.