The role of the solvent in the asymmetric hydrogenation of β-keto esters with Ru-BINAP

The influence of the solvent on the asymmetric hydrogenation of methyl acetoacetate, as a representative beta-keto esters, with Ru-BINAP was studied. The highest activities were measured when the reaction proceeded in methanol, ethanol or isopropanol. These solvents, which also act as proton donors, accelerate product release from the reaction intermediate. The presence of water in the reaction mixture has been found to be detrimental for both activity and enantioselectivity. All results could be explained by the existence of two different solvent dependent reaction pathways for product release. (C) 2002 Elsevier Science B.V. All fights reserved.