Direct asymmetric hydrogenation of 2-oxo-4-arylbut-3-enoic acids.

A challenging direct asymmetric hydrogenation of (E)-2-oxo-4-arylbut-3-enoic acids to give 2-hydroxy-4-arylbutanoic acids (85.4-91.8% ee) was achieved with a Ru catalyst based on SunPhos as the chiral ligand. Further investigation of the reaction revealed that partial isomerization of 2-hydroxy-4-arylbutenoic acids was involved in the hydrogenation process. Employing the reaction conditions to the hydrogenation of 2-oxo-4-phenylbutanoic acid resulted in better enantioselectivity (91.8% ee) and efficiency (TON = 2000, TOF = 200 h(-1)), which offers a useful method for the synthesis of a common intermediate for ACE inhibitors.