Recherches dans la serie des metallocenes—XXVII: Stereochimies comparees de ferrocenylcyclohexenones chirales portant un carbone asymetrique quaternaire en position α ou β. Puretes optiques par dilution isotopique

The two diastereoisomeric pairs of α-phenyl α-methyl and β-phenyl β-methyl ferrocenyl cyclohexenones were prepared in optically active series from a single chiral precursor, (+) phenyl-2 methyl-2 succinic acid, the S configuration of which was established by chemical correlation. The chiral precursor and the four ketones were shown to be optically pure by isotopic dilution with tritium labelled racemates. We infer that diastereogenic cyclisation of the γ-ferrocenyl butyric acids into ketones is under pure kinetic control and leads mainly to the isomer bearing the bulkiest group in an endo position.