Purely organic catalysts asymmetric catalysis

Two patterns are possible in the activation mechanism by simple chiral Lewis base catalysts. One is through the activation of nucleophiles such as aUyltrichlorosilanes or ketene trichlorosilyl acetals via hypervalent silicate formation using organic Lewis bases such as chiral phosphoramides or A-oxides. " In this case, catalysts are pure organic compounds (see Chapter 11). The other is through the activation of nucleophiles by anionic Lewis base conjugated to metals. In this case, transmetal-lation is the key for the nucleophile activation. This type of asymmetric catalysis is the main focus of this section. 

Polymerised preformed [(N,N -dimethyl-l,2-diphenylethane diamine)2Rh] complex allows us to obtain enantioselective material. We have then shown that it is possible to imprint an optically pure template into the rhodium-organic matrix and to use the heterogeneous catalyst in asymmetric catalysis with an obvious template effect. The study of yield versus conversion graphs has shown that the mechanism occurs via two parallel reactions on the same site without any inter-conversion of the final products. Adjusting the cross-linker ratio at 50/50 allows us to find a compromise between activity and selectivity. Phenyl ethyl ketone (propiophenone) was reduced quantitatively in 2 days to (R)-l-phenyl propanol with 7tf% enantiomeric excess We have then shown that the imprinting effect is obvious for molecules related in structure to the template (propiophenone, 4 -trifluoromethyl acetophenone). It is not efficient if the structure of the substrate is too different to that of the template. 

Nakamura, Y. (1940) Formation of optically active amines by the reduction of oximes in the presence of optically active organic acids. Asymmetric synthesis. III., J. Chem. Soc. Jpn. (Pure Chem. Sect.) 61, 1051-1054. Tjandra, S., Smith, G.V., Ostgard, D., Musoiu, M., Wiltowski, T., Notheisz, F., Bartok, M., Stoch, J. (1992) Silicon modification of Pd and Pt catalysts. Chemical Industries Series (Catalysis of Organic Reactions), (Dekker), 47, 137-141. 

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