Homogeneous asymmetric hydrogenation of o-substituted acetophenones catalyzed by NH2Et2{Ru2Cl5[(S)-tol-BINAP](2)}

Acetophenones o-substituted by halogen and methoxyl groups were hydrogenate d in the presence of (NH2Et2){Ru2Cl5[(S)-tol-BINAP](2)} at 35 degrees C and 85 kg/cm(2) hydrogen pressure. The results showed that o-bromoacetophenone was a very active substrate and its asymmetric hydrogenation gave an o-bro mo-alpha-phenylethanol with very high enantioselectivity (97% ee). o-Chloro acetophenone was moderately active and its hydrogenation product o-chloro-a lpha-phenylethanol had a good enantioselectivity (82% ee). o-Fluoroacetophe none exhibited a low reactivity but its hydrogenation product o-fluoro-alph a-phenylethanol showed the highest enantioselectivity (99% ee) among all pr oducts. o-Methoxyacetophenone showed a low reactivity, and its hydrogenatio n product o-methoxyl-alpha-phenylethanol gave a low enantioselectivity (27% ee). The effects of various reaction conditions, such as hydrogen pressure , reaction temperature, solvents, reaction time, ligand concentration and a ddition of acid and base, were investigated. (C) 2000 Elsevier Science B.V. All rights reserved.