Highly enantioselective Ru-catalyzed asymmetric hydrogenation of β-keto ester in ionic liquid/methanol mixtures

The enantioselective hydrogenation of methyl acetoacetate (MAA) was studied in detail using a ruthenium-monodentate binaphthophosphepine complex in a homogeneous solution formed by different ionic liquids and methanol. Remarkably, ionic liquid additives did not only open an attractive way for catalyst recycling in repetitive batch-mode but also led to significantly increased catalytic activity compared to pure methanol. Enantioselectivities up to 95% have been achieved in mixed ionic liquid/methanol systems which are comparable to the values obtained in pure methanol. (C) 2009 Published by Elsevier B.V.