Enantioselective catalytic hydrogenation of methyl α-acetamido cinnamate in [bmim][BF4]/CO2 media

Abstract

The homogeneously-catalyzed hydrogenation reaction of methyl α-acetamido cinnamate (MAC) was chosen to evaluate the feasibility of combining the advantages of ionic liquids (ILs) as solvents for reactions and the chiral complexes as catalysts for enantioselective reactions. 1-Butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF₄]) and (−)-1,2-bis((2R,5R)-2,5-dimethylphospholano)benzene (cyclooctadiene)rhodium(I) tetrafluoroborate (Rh-MeDuPHOS) were selected as the solvent and the catalyst, respectively. All experiments were carried out in an autoclave. The Rh-MeDuPHOS catalyst dissolved in [bmim][BF₄] was able to hydrogenate MAC with high conversions and enantioselectivities. The effects of hydrogen (H₂) pressure on the conversion and enantioselectivity of MAC hydrogenation were studied. It was shown that with increasing H₂ pressure, the conversion increases while the selectivity decreases. Adding carbon dioxide (CO₂) as a potential enhancer of this reaction was also studied. It was shown that by increasing the partial pressure of CO₂, the conversion decreases, while the selectivity increases. Catalyst recycling by extraction of the product with methyl tert-butyl ether (MTBE) was also possible.