Asymmetric organocatalysts carboxylic acids

Alcohols, Phenols and Carboxylic Acids as Asymmetric Organocatalysts... 

Isothioureas (148) and (149) have been developed as organocatalysts for asymmetric intramolecular Michael addition-lactonization of carboxylic acids R CH2C02H with... 

A series of (carboxylic acid derivatives has been synthesised and examined as chiral organocatalysts by Zhang et al. in the asymmetrie reduction of both para-trifluoromethylphenyl methyl ketone and iV-phenyl methyl phenyl imine.These catalysts afforded moderate enantios-electivities of 41% ee and 52% ee, respeetively, for the asymmetric reductions of both the ketone and the imine. The best results are shown in Scheme 8.5. 

Extensive molecular dynamic simulations of proline-catalysed asymmetric aldol condensation of propionaldehyde in water have revealed that the stereoselectivity can be attributed to differences in transition-state solvation pattems. " The hydrogen bond concept has been applied to design new proline-based organocatalysts. " 4-Hydroxyproline derivatives bearing hydrophobic groups in well-defined orientations have been explored as catalysts in water an advantage of aromatic substituents syn to the carboxylic acid moiety has been attributed to a stabilizing transition-state hydrophobic interaction and this is supported by quantum mechanics (QM) calculations. " Catalysts and solvents were screened for reaction between cyclohexanone andp-nitrobenzaldehyde. 

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