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

Add time:07/16/2019    Source:sciencedirect.com

Acetophenones o-substituted by halogen and methoxyl groups were hydrogenated in the presence of (NH2Et2){Ru2Cl5[(S)-tol-BINAP]2} at 35°C and 85 kg/cm2 hydrogen pressure. The results showed that o-bromoacetophenone was a very active substrate and its asymmetric hydrogenation gave an o-bromo-α-phenylethanol with very high enantioselectivity (97% ee). o-Chloroacetophenone was moderately active and its hydrogenation product o-chloro-α-phenylethanol had a good enantioselectivity (82% ee). o-Fluoroacetophenone exhibited a low reactivity but its hydrogenation product o-fluoro-α-phenylethanol showed the highest enantioselectivity (99% ee) among all products. o-Methoxyacetophenone showed a low reactivity, and its hydrogenation product o-methoxyl-α-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 addition of acid and base, were investigated.

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