Ru-Catalyzed Asymmetric Hydrogenation of α-Ketoesters with CeCl₃·7H₂O as Additive

An efficient asymmetric hydrogenation of α-ketoesters is reported with use of a catalyst prepared from [Ru((S)-3)(benzene)Cl]Cl and CeCl₃·7H₂O. α-Hydroxy esters are obtained in up to 96% ee. The addition of CeCl₃·7H₂O not only improves the enantioselectivity, but also enhances the stability of the catalyst. As a result, the hydrogenation of methyl benzoylformate affords the product with 92% ee with a substrate/catalyst ratio of 10 000. Hydrolysis of 2 provides the final compound with 83% yield at 99% ee after a single recrystallization from 1,2-dichloroethylene.