Reaction of tetramethylcyclopentenone and cyclopentadienyl anion gave the title pentafulvalene derivative. Its deprotonation with sodium or potassium hydride proceeded selectively at one of the methyl groups. The resulting 3,4-dihydro-1,3,4-trimethyl(2-methylene)pentafulvalenide ion was converted to the corresponding ferrocene which was obtained as two diasteroisomers in the ratio of 1/1.