Central chiral ferrocenes

Ferrocene behaves like an aromatic compound activated for electrophilic substitution reactions. Thus, only minor modifications of experimental procedures developed for aromatics are necessary to obtain ferrocene derivatives (a useful review on general methods is given by Schldgl and Falk [42]). For central chiral ferrocenes, resolution of the racemate is a frequently applied technique. Traditionally, resolutions are best achieved by salt formation between a chiral acid or base and the... 

Asymmetric induction in ring closure reactions of central chiral ferrocene derivatives has been reported. Moderate diastereoselectivity was found in the ring closure of the enantiomeric 4-ferrocenyl-2-methyl-2-phenyl-butanoic acids by treatment with trifluoroacetic anhydride (Fig. 4-211) [10]. The diastereoisomeric ketones could be separated by chromatography. A higher induction was observed in an asymmetric Pictet — Spengler type cyclization of a reactive imine formed from enantiomerically pure 2-ferrocenyl-2-propylamine and formaldehyde, as only one isomer of the product was detected (Fig. 4-21 g) [135, 136]. 

Fig. 4-7. Synthesis of racemic central chiral ferrocene derivatives.

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