The behavior of 3-ferrocenyl-1-methyl-1,2-pentamethyleneallyl and 1,5-diferrocenyl-3-methyl-2,4-tetramethylene-1,4-dienyl carbocations in the cationic dimerization of 1,3-dienes

3-Ferrocenyl-1-methyl-1,2-pentamethyleneallyl carbocation 9 and 1,5-diferrocenyl-3-methyl-2,4-tetramethylene-1,4-dienyl carbocation 10 are transformed into linear 21 and cyclic 28 dimers, respectively, in low yields under conditions of the cationic dimerization (treatment with N,N-dimethylaniline). The former is preferentially deprotonated into 1-ferrocenylmethylidene-2-methylidenecycloheptane (19) and 3-ferrocenylmethylidene-2-methylcycloheptene (20), while the latter is reduced into 1,3-bisferrocenylmethylidene-2-methylcycloheptane (26). However, a linear dimer was obtained in the reaction of salt 9 with s-cis-diene 19, while the reaction of salt 10 with 1,3-bisferrocenylmethylidene-2-methylidenecycloheptane (27) results in a cyclodimer 28 together with a linear dimer 29. The results obtained corroborate the stepwise mechanism of cationic cycloaddition of 1,3-dienes and manifest the role of the electronic factor in the intramolecular cyclization of an intermediate linear dimeric allylic cation.