- Chlorocarbonylbis(triphenylphosphine)iridium has been shown to be an efficient catalyst at 250°C for isoaromatization of 2,6-diarylidenecyclohexanones. A stepwise migration of the exocyclic double bonds takes place followed by thermal tautomerization of the cyclohexa-2,5-dienone system. 2-Arylidene-1-tetralones undergo similar transformations to the corresponding naphthols. 2,7-Dibenzylidenecycloheptanone, which cannot form an aromatic system without loss of H2, exhibits only E-Z isomerization. 3,7-Dibenzylidenecycloheptane-1,2-dione is partly converted into 3,7-dibenzyltropolone, and partly disproportionates to dibenzylcycloheptanedione and to polymer precursor. Unsaturated cyclopentanones react to give disproportionation products along with double bond migration into the five-membered ring.