Organometallic compounds: XXXVII. Bridge rearrangements of multibridged ferrocenophanes in the presence of aluminum chloride

Two bridge-rearrangement reactions with AlCl₃ have been found in the cyclization of [4](1,1′)[3](2,2′)[4](4,4′)ferrocenophanebutanoic acids (XIb and XIIb) and in the Friedel-Crafts acylation of [4](1,1′)-α-oxo[3](2,2′)[4](4,4′)ferrocenophane(I). The cyclization of XIb and XIIb with ClCO₂Et/NEt₃/AlCl₃ gives no tetrabridged ferrocenophane but three dibridged ferrocenophanes (XVII, XVIII and XIX) each containing two six-membered condensed-rings which are formed via homoannular cyclization of the side chains followed by rearrangement of the existing tetramethylene bridges. Various multibridged ferrocenophanes were treated with AlCl₃ to account for the reaction mode in the rearrangement of I, and evidence for selective acyl migration of the oxotrimethylene bridge to the other cyclopentadienyl ring has been obtained.