Hydrazones directed lithiation

Hydrazones may also direct lithiation, and are particularly effective after deprotonation to an azaenolate 131 (Scheme 59). ... 

SAMP hydrazones derived from acylferrocenes will direct the diastereoselective lithiation of the ferrocene ring (Scheme 14). For example, treating benzoylfer-rocene 50 with (S)-N-amino-O-methylproUnol 51 generates 52 after siHca-cata-lysed equilibration to the more stable -hydrazone [42]. Lithiation of 52 gives or-ganolithium 53 selectively after electrophihc quench, products 54 were obtained in 80-95% yield and with <2% of a minor diastereoisomer. Removal of the auxiliary is achieved by oxidative or reductive means. 

In late 1975, Enders et al.156) started a research project directed towards the development of a new synthetic method for asymmetric carbon-carbon bond formation. A new chiral auxiliary, namely the (S)-proline derivative SAMP (137), was allowed to react with aldehydes and ketones to give the hydrazones (138), which can be alkylated in the a-position in an diastereoselective manner 157,158). Lithiation 159) of the SAMP hydrazones (138), which are formed in excellent yields, leads to chelate complexes of known configuration 160). Upon treatment of the chelate complexes with alkyl halogenides the new hydrazones (139) are formed. Cleavage of the product hydrazones (139) leads to 2-alkylated carbonyl compounds (140). 

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