Hydroxyproline-catalyzed aldol reactions

S)-Proline (1), its derivatives, and related molecules catalyze aldol reactions of ketone donors [6], For example, (S)-proline, (2S,4R)-4-hydroxyproline (2), and... 

Aldol reactions using catalyst 12 were also performed with water without any organic solvent (Table 2.9) [15]. In these examples, it is assumed that the reaction occurred in the organic phase composed of reactants and the catalyst separated from the water phase. A large excess of ketone was used in these reactions. Catalysts possessing a tert-butyldimethylsilyl (TBS) or a triisopropylsilyl (TIPS) group instead of the tert-butyldiphenylsilyl (TBDPS) group on 12 also effectively catalyzed the reaction with water, but hydroxyproline 2 did not catalyze the reaction under the same conditions this indicated that the hydrophobic substituents of... 

The aldol reaction in water is also efficiently catalyzed by polymers 127 and 128, in which the proline moieties are anchored using a different strategy [331]. In this case the N-BOC protected hydroxyproline is reacted with chloromethylstyrene and... 

Ion tagged hydroxyproline derivative 97h (15 mol%) efficiently catalyzed cross-aldol reaction between aldehyde 77a (3 equiv.) and p-nitrobenzaldehyde (2b) giving prodnct 78a in 40% yield and 99% enantiomeric excess [181]. 

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