Synthesis and properties of tetramethyloctadehydrodihydro-[26]-, -[28]-, -[30]-, -[32]- and [34]-annulenediones

Abstract

Title annulenediones 5–9 were synthesized by intermolecular oxidative coupling of 6-methylocta 3,5-dien-7-yn-2-one 13 or its vinylogous ketones 14 and 15 to afford the diones 17–21 and then by an aldol condensation of these diones 17–21 with (Z)-3-methylpent-2-en-4-ynal 10, followed by intramolecular oxidative coupling of the resulting acyclic diacetylenes 22–26. The properties of the title compounds 5–9 are discussed on the basis of ¹H NMR and electronic spectra.