Asymmetric Reduction of Acetophenone O‐Methyloxime with Reagents Prepared from L‐Proline and Borane

Abstract Asymmetric reduction of acetophenone O‐methyloxime with reagents in situ prepared from L‐proline and borane has been investigated. A series of conditions optimization were made, including an examination of the effect of the temperature of catalyst pretreatment, the temperature of reduction, the amount of borane, the additive, the solvent, the reducing agent and various chiral auxiliaries on the enantioselectivity. Under the optimal condition, (S)‐α‐phenylethylamine was obtained in 53% yield with 83.1% ee in the presence of 25 mol% L‐proline.