I. Electrophilic aromatic substitution of metallocenes. II. Stereochemistry of halogen addition to 4-t-butylcyclohexene. III. Lithium aluminum hydride reduction of cis-2,6-dimethylcyclohexanone.

Abstract

Part I. The mechanism of electrophilic substitution of metallocenes was investigated by the competitive acetylation of ferrocene and ruthenocene and of ferrocene and l,l'-diethylferrocene. Solvolyses of ω -ferrocenylalkyl p-bromobenzenesulfonates did not show any significant aryl participation. These results lead to the hypothesis that direct interaction between the metal and the electrophile is of great importance in electrophilic substitution reactions f metallocenes. Part II. The bromination and chlorination of 4-t-butylcyclohexene have been shown to produce diequatorial dihalides as well as diaxial dihalides. The amount of diequatorial dichloride produced increases with solvent polarity. The results are explained in terms of two competing mechanisms, the classical, planar trans-addition and a carbonium ion process which increases in importance in the more polar solvents. Part III. Lithium aluminum hydride reduction of cis-2,6-dimethylcyclohexanone gave only 14% of the 2(e), 6(e) -dimethyl- l(e)-cyclohexanol. This is in striking contrast to other results for lithium aluminum hydride reductions. Two equatorial groups adjacent to a reaction center on a cyclohexane ring thus cause an especially severe steric hindrance at that center.