Hydroxyproline Derivatives as Asymmetric Organocatalysts

Zelinslq Institute of Organic Chemistry, Russian Academy of Sciences, Leninslq prosp. 47, Moscow 119991, Russia Email zlotin ioc.ac.ru 

The extremely high interest in asymmetric organocatalysis today has been driven by the seminal publications of Eder et al. in 1971 and of List et al. in 2000 who recognised that the natural amino acid (S)-proline acted as an efficient catalyst in asymmetric intra- or intermolecular aldol reactions. Subsequently, numerous proline derivatives (amides,  

Sustainable Catalysis Without Metals or Other Endangered Elements, Part 1 

During the past decade, 4-hydro)g roline-derived synthesised from (25,4I )-4-hydro3yproline (1) by 

Remarkably, no reaction occurred when proline, hydroxyproline or proline-tetrazole that did not exhibit surfactant properties were employed as organocatalysts in the presence of water. 

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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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