The reaction of 2-benzoylbenzoic acid with phenylacetic acid in the presence of phosphorus pentachloride gives spiro [3-chloroindene-1, 1′-phthalane-3′-one](II) and 9H, 14H-tribenz [aeh] azulene-9, 14-dione (III). The latter compound can be easily converted into pentaphene.
