Planar chiral mimetics. A new approach to ligand design for asymmetric catalysis

(S)-Serine methyl ester is readily transformed into 4-(hydroxymethyl)oxazoline ligands containing either a 2-(η5-cyclopentadienyl)(η4-tetraphenylcyclobutadiene)cobalt or a 2-(1,2,3,4,5-pentaphenyl)-ferrocene substituent. The influence of the bulky metallocenes result in these ligands mimicking planar chirality, as demonstrated by their catalysis of the addition of diethylzinc to benzaldehyde resulting in (R)-1-phenylpropanol (75% e.e.).