Overcrowded molecules. Part 15. Some reactions of (E,E)-, (E,Z)-, and (Z,Z)-2,5-dibenzylidene-3,4-diphenylcyclopentenones and 2,5-dibenzylidene-1,3,5-triphenylcyclopenten-1-ols

Abstract

Acid-catalysed condensation of 3,4-diphenylcyclopent-2-en-1-one or 3,4-diphenylcyclopent-3-en-1-one with benzaldehyde gives a mixture of (E,E)-, (E,Z)-, and (Z,Z)-2,5-dibenzylidene derivatives, each of which undergoes thermal, acid-catalysed, and photochemical equilibration with its geometrical isomers but not photochemical ring-closure to yield phenanthrene derivatives. These ketones react with phenyl-lithium to give the corresponding 2,5-dibenzylidene-1,3,5-triphenylcyclopenten-1-ols, which undergo acid-catalysed rearrangement to a benzyl diphenyldibenz[eg]azulene.