Highly enantioselective hydrogenation of 2-oxo-4-arybutanoic acids to 2-hydroxy-4-arylbutanoic acids

The Ru-catalyzed asymmetric hydrogenation of 2-oxo-4-arybutanoic acids to afford 2-hydroxy-4-arybutanoic acids was accomplished by employing SunPhos as chiral ligand and 1 M aq HBr as additive. The high enantioselectivities (88.4%-92.6% ee) and efficiency (TON=10,000, TOF=300 h−1) make this method efficient for the synthesis of an important intermediate, (R)-2-hydroxy-4-phenylbutanoic acid, for ACE inhibitors.