Highly Enantioselective Synthesis of syn-β-Hydroxy α-Dibenzylamino Esters via DKR Asymmetric Transfer Hydrogenation and Gram-Scale Preparation of Droxidopa

A highly efficient preparation of enantiomerically pure syn aryl beta-hydroxy alpha-dibenzylamino esters is reported. The outcome was achieved via dynamic kinetic resolution and asymmetric transfer hydrogentation of aryl alpha-dibenzylamino beta-keto esters. The desired product were obtained in high yield (up to 98%) With excellent diastereoselectivity (>20:1 dr) and enantioselectivity (up to >99% ee). Futhermore, this method was applied for the gram-scale preparation of droxidopa.