摘要:
                                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-dimethylfulvens 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 thr target molecule 1b. Other synthetic attempts towards [2.2]cyclopentadienophanes 1a and 1b and [2.3]cyclopentadienophane 18 are discussed.