Synthesis and properties of methano-bridged tetradehydro-[20]-, -[24]-, -[26]-, -[28]-, -[30]- and -[32]-annulenediones

Abstract

The title annulenediones 4–9 have been synthesized by first an aldol condensation of cyclohepta1,3,5-triene-1,6-dicarbaldehyde 10 or its vinylogous dialdehydes 11–14 with acetone to afford the dimethyl diketones 16–20 and then by a second aldol condensation of 1,6-diacetylcyclohepta1,3,5-triene 15 or the dimethyl diketones 16–20 with (Z)-3-methylpent-2-en-4-ynal 21, followed by intramolecular oxidative coupling of the resulting acyclic diacetylenes. The properties of the title compounds are discussed on the basis of ¹H NMR and electronic spectra as well as cyclic voltammetry.