Ru-Catalyzed Asymmetric Hydrogenation of α-Ketoesters with CeCl<sub>3</sub>·7H<sub>2</sub>O as Additive

An efficient asymmetric hydrogenation of α-ketoesters is reported with use of a catalyst prepared from [Ru((<i>S</i>)-3)(benzene)Cl]Cl and CeCl<sub>3</sub>·7H<sub>2</sub>O. α-Hydroxy esters are obtained in up to 96% ee. The addition of CeCl<sub>3</sub>·7H<sub>2</sub>O 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 <b>2</b> provides the final compound with 83% yield at 99% ee after a single recrystallization from 1,2-dichloroethylene.