Selective asymmetric hydrogenations over chiral

The asymmetric hydrogenation of C=X ti-bonds (X = O, NR) is estimated to account for over half the chiral drugs manufactured industrially, withstanding physical and enzymatic resolution. For selected reviews on C-C bond forming hydrogenation and transfer hydrogenation, see [11-17]. 

The cationic rhodium catalysts are useful for asymmetric hydrogenation.152 In this variant, the presence of a chiral phosphine leads to differences in the rates of H2 addition to the two faces of a prochiral alkene. Where the alkene has groups such as C02Me suitably placed to bind to the metal, the selectivity can become very great enantiomeric excesses of the product over its enantiomer can reach 95-98% (equation 67). The mechanism has recently been elucidated by Halpern.153... 

Sutyinszki, M., Szori, K., Felfoldi, K., Bartok, M. (2002) 98% Enantio-selectivity in the asymmetric synthesis of a useful chiral building block by heterogeneous method enantioselective hydrogenation of ethyl benzoyl-formate over cinchona modified Pt/Al203 catalysts, Catal. Commun. 3,... 

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