Synthesis of 1′-substituted derivatives of 1,2,3,4,5-pentaphenylferrocene

Pentaphenylferrocene was synthesized in 57% overall yield from 1-bromopentaphenyleyclopentadiene. Functionalization of the unsubstituted cyclopentadienyl ring using the Friedel-Crafts reaction gave 1'-formyl-and 1'-(2-chlorobenzoyl)-substituted derivatives. Hydrolysis of the latter provided the corresponding 1'-carboxylic acid. This was readily transformed via a modified Curtius rearrangement into 1'-amino-1,2,3,4,5-pentaphenylferrocene. This methodology also provided (eta(5)-aminocyclopentadienyl)(eta(4)-tetraphenylcyclobutadiene)cobalt and gave an improved synthesis of aminoferrocene.