Enantioselective hydrogenation of activated

1 Enantioselective hydrogenation of activated ketones over supported platinum 

These molecules contain an aromatic quinoline ring system and a saturated quinuclidine ring system separated by the carbon numbered Cg. Chiral centres are present at C3, C4, Cs and Cg, of which Cg and Cg have the S- and R- configuration respectively in cinchonidine 

Hydrogenation of alkyl pyruvates (Fig. 5.10) to their corresponding lactates has received considerable attention both from a 

Enantioselectivity may arise by the operation of either thermodynamic or kinetic factors. If competitive adsorption of ester as configurations A and B occurs at enantioselective sites cognate to adsorbed alkaloid with free energy changes and AG°ads.B 

F re 5.11 Reaction scheme showing the adsorption of pyruvate ester adsorbed by its two enantiofaces and the consequences of hydrogenation. 

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Since the initial work of Onto et al. (1) a considerable amount of work has been performed to improve our understanding of the enantioselective hydrogenation of activated ketones over cinchona-modified Pt/Al203 (2, 3). Moderate to low dispersed Pt on alumina catalysts have been described as the catalysts of choice and pre-reducing them in hydrogen at 300-400°C typically improves their performance (3, 4). Recent studies have questioned the need for moderate to low dispersed Pt, since colloidal catalysts with Pt crystal sizes of <2 nm have also been found to be effective (3). A key role is ascribed to the effects of the catalyst support structure and the presence of reducible residues on the catalytic surface. Support structures that avoid mass transfer limitations and the removal of reducible residues obviously improve the catalyst performance. This work shows that creating a catalyst on an open porous support without a large concentration of reducible residues on the Pt surface not only leads to enhanced activity and ee, but also reduces the need for the pretreatment step. One factor... 

Enantioselective Hydrogenation of Activated Ketones Using Heterogeneous Pt Catalysts Modified with Cinchona Alkaloids... 

Studer, M. and Blaser, H.U. (2005) Enantioselective hydrogenation of activated ketones using heterogeneous Pt catalysts modified with cinchona alkaloids, in Handbook of Chiral Chemicals, 2nd edn, CRC Press LLC, Boca Raton, pp. 345-57. 

The initial transient period (ITP) of the enantioselective hydrogenation of activated ketones (ethyl pyruvate, p5Tiivaldehyde dimethyl... 

Kuenzle, N., Hess, R., Mallat, T., Baiker, A. (1999) Continuous enantioselective hydrogenation of activated ketones, J. Catal. 186, 239-241. 

Balazsik, K., Bartok, M. (2004) New data on enantiomeric excess versus eonversion during enantioselective hydrogenation of activated ketones on a platinum eatalyst, J. Catal. 224,463-472. 

Cserenyi S., Szollosi G., Szori K., Fulop R, BartokM. Reversal of the ee in enantioselective hydrogenation of activated ketones in continuous-flow fixed-bed reactor system, Catal. Commun. 2010 12(1) 14-19. 

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