Cerium(III) chloride mediated addition of mono- and dilithium ferrocene to (+)-camphor and (-)-fenchone: Synthesis and structure of new chiral ferrocenyl alcohols and diols

Cerium(III) chloride activated (+)camphor (1) and (-)-fenchone (2) react with lithiated ferrocene (reagent 3, (Li-Cp)(2)Fe/LiCp-FeCp = 50:1) to give the corresponding optically active ferrocenyl diols 4 and 6 and monosubstituted ferrocenyl alcohols 5 and 7. The preparation of the diols 4 and 6, as well as of the alcohols 5 and 7 respectively, in high yields is optimized depending on the composition of the lithiated ferrocenes (reagent 3 contains mainly 1,1'-dilithium ferrocene; reagent 8 contains mainly monolithium ferrocene) and on the amounts (stoichiometric, diminished or catalytic) of the CeCl3 used for activation of the ketones 1 and 2. The catalytic CeCl3 promotion (5 mol%) of the addition reactions of reagents 3 and 8 to 1 and 2 respectively is observed only in the case of fenchone (2). The new optically active ferrocenyl alcohols 4, 5, 6 and 7 have been studied in detail by NMR, MS and IR spectroscopy, The crystal structure of diol 4 has been determined, and shows an unusual eclipsed conformation of the ferrocenyl moiety, possibly a result of the observed strong intramolecular hydrogen bond formation.