THE INFLUENCE OF STERIC HINDRANCE ON THE LITHIATION OF FERROCENYLALKYLAMINES

1-{N,N-Dimethylamino[(1R,2S,5R)-2-isopropyl-5-methylcyclohexyl]-(R)-methyl}-ferrocene and 1-{N,N-dimethylamino[(1R,2S,5R)-2-isopropyl-5-methylcyclohexyl]-(S)-methyl}ferrocene have been prepared from (-)-menthone and ferrocene, and their conformation in solution elucidated by NMR spectroscopy. Upon lithiation, neither amine shows the high regio- and diastereo-selectivity observed in the case of the simple (N,N-dimethylamino-1-ethyl)ferrocene. Reasons for this behaviour are discussed. Reaction of the mixture of lithiation products with chlorodiphenylphosphine leads to mixtures of phosphine derivatives, which have been used as chiral chelating ligands in rhodium-catalyzed asymmetric hydrogenation of N-acetyl-2-aminocinnamic acid. © 1990.