Chiral ketones and aldehydes

Similarly to the asymmetric synthesis by imines and oxazoline, there is also a chiral hydrazone, (S)-l-amino-2-(methoxymethyl)pyrrolidine 51a, which gives chiral hydra-zones on reaction with aldehydes and ketones and is able to form an intermolecular chelate with the methoxy group. Enders and coworkers used this system for enantioselec-tive aldol reactionand for synthesis of chiral ketone and aldehyde (equation 30). 

C3-symmetrical tripodal ligands have been used to obtain amido complexes of family (86). If chiral substituents are present in the ligand periphery, some stereo discrimination is observed in the reaction with several chiral ketones and aldehydes. On the other hand, such systems can generate early-late heterobimetallics with metal-metal bonds (equation 41). Reaction of (91) with MeNC as well as the heteroallenes CO2, CS2, RNCO and RNCS led to insertion into the polar metal-metal bond. Tris (pyrazolyl) borate see Tris(pyrazolyI)borates) Zr and Hf complexes are other interesting examples of the type (86). In combination with MAO, they give promising results in ethylene and ethylene/hexene polymerizations. Substitution of these sterically crowded ligands allows adjustements of the environment of the active site to the... 

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