CeCl<sub>3</sub>·7H<sub>2</sub>O: An Effective Additive in Ru-Catalyzed Enantioselective Hydrogenation of Aromatic α-Ketoesters
作者:Qinghua Meng、Yanhui Sun、Virginie Ratovelomanana-Vidal、Jean Pierre Genêt、Zhaoguo Zhang
DOI:10.1021/jo800228e
日期:2008.5.1
In the presence of catalytic amounts of CeCl3 center dot 7H(2)O, [RuCl(benzene)(S)-SunPhos]Cl is a highly effective catalyst for the asymmetric hydrogenation of aromatic alpha-ketoesters. A variety of ethyl alpha-hydroxy-alpha-arylacetates have been prepared in up to 98.3% ee with a TON up to 10 000. Challenging aromatic alpha-ketoesters with ortho substituents are also hydrogenated with high enantioselectivities. The addition of CeCl3 center dot 7H(2)O not only improves the enantioselectivity but also enhances the stability of the catalyst. The ratio of CeCl3 center dot 7H(2)O to [RuCl(benzene)(S)-SunPhos]Cl plays an important role in the hydrogenation reaction with a large substrate/catalyst ratio.
A rapid and green approach to chiral α-hydroxy esters: asymmetric transfer hydrogenation (ATH) of α-keto esters in water by use of surfactants
作者:Lu Yin、Xian Jia、Xingshu Li、Albert S.C. Chan
DOI:10.1016/j.tetasy.2009.08.019
日期:2009.9
A series of α-hydroxyesters were rapidly prepared (1.5 h) from α-keto esters via asymmetrictransferhydrogenation (ATH) in water by the use of surfactants for the first time. This green method, catalyzed by a water-soluble and recyclable Ru(II) complex, gave moderate to high enantioselectivities (up to 99.7% ee) with DTAB as an additive and HCOONa as the hydrogen source.