Versuche zur Synthese von [2.2]- und [2.3]Cyclopentadienophanen

Synthetic Attempts towards [2.2]- and [2.3]Cyclopentadienophanes . The first [2.2]Cyclopentadienophane (=2,2,3,3,8,8,9,9-octamethyltricyclo[8.2.1.1^4,7]tetradecatetraene; 1b ) has been synthesized (Scheme 5) by reductive coupling of 6,6-dimethylfulvene 3 → 5 (50%) followed by base-induced twofold condensation of 1,2-di(cyclopentadienyl)-1,2-dimethylbutane 5 with acetone to give difulvene 15 (95%). Reductive coupling of 15 gives a complex mixture of tautomers of 16 , 17 , and 1b , which contains ca. 50% of the target molecule 1b . Other synthetic attempts towards [2.2]cyclopentadienophanes 1a and 1b and [2.3]cyclopentadienophane 18 are discussed.