Screening of chiral ferrocenyl amino alcohols as ligands for ruthenium-catalysed transfer hydrogenation of ketones

A variety of ferrocenyl amino alcohols possessing central chirality have been screened as ligands for ruthenium(II)-catalysed transfer hydrogenation of acetophenone using 2-propanol in the presence of KOH as the hydrogen source. Enantiomerically enriched 1-phenylethanol was obtained in high yield and 70% e.e. using ligand 9. This ligand was employed in the asymmetric reduction of different arylalkyl ketones and the corresponding alcohols were obtained in up to 80% e.e. A comparison of the catalytic properties of ferrocenyl amino alcohols and their phenyl analogues is discussed briefly.