Synthesis of ‘three-petal’ carbocyclic systems based on s-cis-diferrocenyltrienes

Acid-catalyzed intramolecular, homoannular alkylation of one of the ferrocenyl substituents in spirocyclodimers derived from 1,3-bis(ferrocenylmethylidene)-2-methylidene-cyclohexane, -cycloheptane, and 3,5-bis(ferrocenylmethylidene)-4-methylidene-N-methylpiperidine results in a fused system with a ‘three-petal’ moiety in the center. The structure of 1-ferrocenyl-3,11-bis(ferrocenylmethylidene)-2,3,4,5,6,6b,10,10a,11,12,13,14-dodecahydro-1H-benzo[d](ferroceno[a])phenanthrene was established by X-ray diffraction analysis.