The Hajos–Parrish–Eder–Sauer–Wiechert reaction, reported in 1971 by several research teams, is an early example of an enantioselective catalytic reaction in organic chemistry. Its scope has been modified and expanded through the development of related reactions including the Michael addition, asymmetric aldol reaction, and the Mannich reaction. This reaction has likewise been used to perform asymmetric Robinson annulations. The general scheme of this reaction follows:
This example illustrates a 6-enolendo aldolization. In the , proline catalyses an asymmetric aldol reaction.  The zwitterionic character and the H-bonding of proline in the transition state determine the reaction outcome. An enamine  is formed during the reaction and only one proline molecule is involved in forming the transition state.
Asymmetric synthesis of the Wieland-Miescher ketone is also based on proline.  Additional reactions include aldol reactions, Mannich reaction, Michael reaction, amination, α-oxyamination, and α-halogenation.
Modifications on the basic proline structure improved the enantioselectivity and regioselectivity of the catalysis. These proline-derived auxiliaries and catalysts, including the Enders hydrazone reaction and Corey–Itsuno reduction, have been reviewed, as have MacMillan’s iminium catalysts, Miller catalysts, and CBS-oxazaborolidines.
Illustrating an enolexo intramolecular aldolization, dicarbonyl (dials,diketones) can be converted to anti-aldol products with a 10% L-proline catalyst loading.
A prominent example of proline catalysis is the addition of acetone or hydroxyacetone to a diverse set of aldehydes catalyzed by 20-30% proline catalyst loading with high (>99%) enantioselectivity yielding diol products. As refined by List and Notz, the aforementioned reaction produces diol products as follows: