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

The homogeneously-catalyzed hydrogenation reaction of methyl a-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 (H-2) pressure on the conversion and enantioselectivity of MAC hydrogenation were studied. It was shown that with increasing H-2 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.