Cinchona Alkaloids in Synthesis and Catalysis by …

Cinchona alkaloids in synthesis and catalysis : ligands, immobilization and organocatalysis

Cinchona alkaloids in synthesis & catalysis - ICIQ

N2 - The enantioselective hydrogenation over a Cinchona alkaloid-modified supported platinum catalyst and parallel spontaneous racemization under the reaction conditions of the unreacted enantiomer of ethyl 2-fluoroacetoacetate are described. Using the appropriate reaction conditions an 82% enantiomeric excess in favor of the (2S,3R)-ethyl 2-fluoro-3-hydroxybutanoate and a 99/1 threolerythro ratio were obtained. This novel method for producing optically enriched α-fluoro-β-hydroxy esters is the first example of dynamic kinetic resolution of a chirally labile racemic fluorinated compound over a modified heterogeneous metal catalyst carried out without using supplementary additives except the chiral modifier. The hydrogenation described here shows that the activation of the keto group of acetoacetates by one fluorine atom in the α position is also sufficient for obtaining high enantiomeric excess in the Orito reaction.

Cinchona Alkaloids in Synthesis and Catalysis Edited by Choong Eui Song Further Reading Crabtree, R

1 An Overview of Cinchona Alkaloids in Chemistry (Choong Eui Song)

In the continuing search for improved drugs and agrochemicals, fluorine compounds are known to exert a unique and profound influence on biological activity and selectivity. Most of these compounds are achiral, fluoro aromatics. Occasionally, such fluoro compounds are chiral but the fluorine is rarely attached at a stereogenic center. The importance of chirality in pharmacologically and biologically active molecules associated with the astonishing properties of fluorine has lead to huge efforts in the asymmetric synthesis of chiral non racemic fluoroorganic molecules with fluorine at a stereogenic center.1 The auxiliary controlled asymmetric synthesis of -fluoro carbonyl compounds has so far been superior to the reagent controlled processes. Therefore, it is a very challenging problem to develop efficient processes for enantioselective fluorination. Our contribution to the enantioselective electrophilic fluorination utilises the naturally-occuring alkaloids as the source of chirality. alkaloids have a venerable history in the field of asymmetric synthesis owing to their firmly established ability to induce asymmetry and they are widely used in asymmetric processes both in homogeneous and heterogeneous reactions. Asymmetric- Michael additions, Sharpless dihydroxylation, and hydrogenation with modified Pt-catalysts, as well as the catalytic enantioselective alkylation under phase transfer catalysis are amongst typical examples.2 alkaloids are also used as chiral resolving agents and for chromatographic separation of enantiomers.

Vch Cinchona Alkaloids in Synthesis and Catalysis zł w porównywarce cen Ofertino

The enantioselective hydrogenation over a Cinchona alkaloid-modified supported platinum catalyst and parallel spontaneous racemization under the reaction conditions of the unreacted enantiomer of ethyl 2-fluoroacetoacetate are described. Using the appropriate reaction conditions an 82% enantiomeric excess in favor of the (2S,3R)-ethyl 2-fluoro-3-hydroxybutanoate and a 99/1 threolerythro ratio were obtained. This novel method for producing optically enriched α-fluoro-β-hydroxy esters is the first example of dynamic kinetic resolution of a chirally labile racemic fluorinated compound over a modified heterogeneous metal catalyst carried out without using supplementary additives except the chiral modifier. The hydrogenation described here shows that the activation of the keto group of acetoacetates by one fluorine atom in the α position is also sufficient for obtaining high enantiomeric excess in the Orito reaction.

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Asymmetric synthesis; Catalysis;

PTC has already proven to be a broadly applicable and general method to perform strong base chemistry in a catalytic, asymmetric manner. A number of modified cinchona alkaloids as well as synthetic, quaternary ammonium salts have been introduced for, inter alia: (1) single and double alkylation of glycine imines, (2) ketone alkylations, (3) Michael additions, (4) aldol, Mannich and Darzens reactions, (5) epoxidations, and (6) aziridinations.