It has been shown that the reaction of the title ketone with phosphorous pentachloride leads to regiospecific chlorine transfer to the diene moiety of the molecule, leaving the carbonyl function intact. Attempted acetalization with ethylene glycol did not give the dioxolane but rather 1,2,3,4,5-pentamethylcyclopenta-1, 3-diene in quantitative yield. An independent synthesis of this hydrocarbon, previously available only by lengthy multistep synthesis, has also been described. The only normal carbonyl reaction of the permethyl-acetyl-cyclopentadiene observed was the reduction by metal hydrides.