Enantioselectivity Of Aldol Reaction Research Articles

A Fluorous Proline Organocatalyst with Acetone‐Dependent Aldolase Behavior

AbstractA polyfluoroalkyl derivative of 4‐hydroxyproline, assembled through a 1,2,3‐triazole linker (i.e., 7), displays high catalytic activity and enantioselectivity in aldol reactions of acetone with aromatic aldehydes featuring electron‐withdrawing groups. The scope of the reaction with respect to the aldehyde acceptor can be expanded with the use of a bifunctional urea cocatalyst. The presence of the fluorous tag allows the aldol reactions to be performed in a perfluorohexane/acetone biphasic system. In this way, both the catalyst and the perfluorinated solvent can be easily recycled and reused (>6 times). In addition, the combination of the fluorous tag, triazole linker, and catalytic proline unit confers unprecedented substrate specificity for acetone upon 7.

ChemInform Abstract: Lithium Ephedrinate Mediated Aldol Reaction of Arylacetonitriles: Thermodynamic Control of Enantioselectivity.

Deracemization, the conversion of a racemic mixture into an enantiomerically enriched material, is achieved with the retro-aldol reaction of rac-1 in the presence of lithium (-)-ephedrinate [Eq. (1)]. Remarkably, two stereogenic centers are simultaneously deracemized. This reaction shows that efficient thermodynamic control of the enantioselectivity of aldol reactions is possible.

Asymmetric Aldol Addition by Oligopeptide Immobilized on Magnetic Particles through an Ionic Liquids Spacer

In this work, oligopeptide was covalently bonded on the surface of magnetic particles through an ionic liquids spacer. When ionic liquids containing bulky cations with strong H-bonding ability or having hydrophobic anions were used, the yield and enantioselectivity of aldol reaction were enhanced greatly. Introducing an ionic liquids spacer between the oligopeptide and magnetic resin decreased the minimum number of amino acids for optimizing the efficiency of aldol addition. Varying the amino acid sequence of the oligopeptide showed limited effect on the yield and enantioselectivity; however, introducing a series of lysine groups on the terminal of the oligopeptide, close to the imidazolium ring, would significantly increase the output. The magnetite-loaded oligopeptide had a broader substrate range for ketone donor but restricted the enantioselectivity of aldehyde acceptor than the free oligopeptide. The combinative unit served as a recyclable catalyst for aldol addition of ketone and aldehyde, and its catalytic efficiency and selectivity can be finely designed by the characteristics of each part of the catalyst.