Direct Asymmetric Aldol Reactions in Water Catalysed by a Highly Active C 2 ‐Symmetrical Bisprolinamide Organocatalyst

(l)-Prolinamide imidazolium hexafluorophosphate ionic liquid as an efficient reusable organocatalyst for direct asymmetric aldol reaction in solvent-free condition

We have designed a new hydrophobic ionic liquid derived from bromoester of trans-4-hydroxy-(l)-prolinamide and N-methylimidazole.

Triggering activity of catalytic rod-like supramolecular polymers

Supramolecular polymers based on benzene-1,3,5-tricarboxamides (BTAs) functionalized with an L- or D-proline moiety display high catalytic activity towards aldol reactions in water. High turnover frequencies (TOF) of up to 27×10(-4) s(-1) and excellent stereoselectivities (up to 96% de, up to 99% ee) were observed. In addition, the catalyst could be reused and remained active at catalyst loadings and substrate concentrations as low as 0.1 mol % and 50 mM, respectively. A temperature-induced conformational change in the supramolecular polymer triggers the high activity of the catalyst. The supramolecular polymer's helical sense in combination with the configuration of the proline (L- or D-) is responsible for the observed selectivity.

Supramolecular polymers for organocatalysis in water

An l-proline-functionalised benzene-1,3,5-tricarboxamide derivative self-assembles in water into well-defined, one-dimensional, helical, supramolecular polymers that efficiently catalyse aldol reactions.

The smallest organocatalyst in highly enantioselective direct aldol reaction in wet solvent-free conditions

The catalytic efficacy of the smallest organocatalyst, l-proline hydrazide, prepared from a cheaply available natural amino acid, such as l-proline, was studied for the direct asymmetric aldol reaction of various ketones with aromatic aldehydes at room temperature in the presence of several acid additives.

A Snapshot of Ionic-Liquid-Tagged Proline-Based Organocatalysts

This highlight focuses on the developments in ionic-liquid (IL)-tagged proline-based organocatalysts. An overview of catalyst structure and application to asymmetric transformations is provided, and a representative synthesis of an IL-tagged organocatalyst is also discussed.

Investigating ionic effects applied to water based organocatalysed aldol reactions

Saturated aqueous solutions of various common salts were examined for their effect on aqueous aldol reactions catalysted by a highly active C₂-symmetric diprolinamide organocatalyst developed in our laboratory. With respect to the aldol reaction between cyclohexanone and 4-nitrobenzaldehyde, deionised water was always a superior medium to salt solutions though some correlation to increasing anion size and depression in enantiomeric excess could be observed. Additionally, the complete inhibition of catalyst activity observed when employing tap water could be alleviated by the inclusion of ethylenediaminetetraacetate (EDTA) into the aqueous media prior to reaction initiation. Extension of these reaction conditions demonstrated that these ionic effects vary on a case-to-case basis depending on the ketone/aldehyde combination.