Low-loading asymmetric organocatalysis

Asymmetric organocatalysis is now recognized as the third pillar of asymmetric synthesis. Recent years have witnessed increasing interest towards the use of highly active and stereoselective organocatalysts. This critical review documents the advances in the development of chiral organocatalysts which are systematically used in ≤3 mol% loading in all the sub-areas of the field, namely aminocatalysis, Brønsted acids and bases, Lewis acids and bases, hydrogen bond-mediated catalysis, phase transfer and N-heterocyclic carbene catalyses (194 references).

Novel Hydroxyproline-derivatives as powerful aldolase-I mimics

Multilayered supported ionic liquids as catalysts for chemical fixation of carbon dioxide

Multilayered, covalently supported ionic liquid phase (mlc-SILP) materials were synthesized by using a new approach based on the grafting of bis-vinylimidazolium salts on different types of silica or polymeric supports. The obtained materials were characterized and tested as catalysts in the reaction of supercritical carbon dioxide with various epoxides to produce cyclic carbonates. The material prepared by supporting a bromide bis-imidazolium salt on the ordered mesoporous silica SBA-15 was identified as the most active catalyst for the synthesis of cyclic carbonates and displayed improved productivity compared with known supported ionic liquid catalysts. The catalyst retained its high act…

Proline- and prolinamide-supported polystyrene: powerful and highly recyclable organocatalysts for the asymmetric aldol reaction

Simple and low loading catalysts for asymmetric aldol reaction under aqueous condition

“Nonsolvent” Applications of Ionic Liquids in Organocatalysis

This chapter is organized in three sections (see Figure 10.1 ): 2. Immobilization of ionic liquids and organocatalysts 2.1 Covalently attached “ ionic liquid ” moieties as supports 2.2 Covalently attached “ ionic liquid ” moieties as linkers 2.3 Covalently attached “ ionic liquid ” moieties as organocatalysts

Organocatalisi: catalizzatori e nuovi materiali riciclabili per la sintesi organica.

Polystyrene-supported organocatalysts for alfa-selenenylation and Michael reactions. A common post-modification approach for catalytic differentiation

Three different resin-supported catalysts have been prepared by using the well established post-modification approach by means of thiol-ene coupling reaction. Two catalysts were tested for the first time in the asymmetric α-selenenylation of propanal, while the third catalyst was used in the Michael addition reaction. While the preliminary results are not encouraging in the case of supported Jørgensen’ catalyst, interesting data have been collected with both for the supported MacMillan and prolyl-prolinol catalysts. In fact, these catalysts displayed good activity and selectivity. A reversed enantioselectivity in the α-selenenylation was observed by changing the polarity of the solvent. Fin…

Sali di imidazolio multistrato supportati covalentemente: attività catalitica per la produzione di carbonati ciclici in scCO2 e nuovi supporti per catalizzatori di palladio

I liquidi ionici supportati (SILP) hanno trovato interessanti applicazioni sia nel campo delle reazioni catalizzate da metalli che in organocatalisi [1]. Inoltre, i SILP sono stati efficacemente impiegati in reazioni di apertura di epossidi in CO2 supercritica per fornire carbonati ciclici [2]. I liquidi ionici vengono generalmente supportati covalentemente attraverso la modificazione dei gruppi funzionali presenti sulla superficie del supporto, conducendo in tal modo alla formazione di un monostrato di liquido ionico supportato. Gli esempi di SILP legati covalentemente, in maniera tale da ottenere dei multistrato, sono rari. In questa comunicazione viene riportato un metodo per preparare d…

Synthesis and high-throughput testing of multilayered supported ionic liquid catalysts for the conversion of CO2 and epoxides into cyclic carbonates

Multilayered covalently supported ionic liquid phase (mlc-SILP) materials were synthesised by grafting different bis-vinylimidazolium salts on thiol-functionalised silica. These materials, which contain a cross-linked oligomeric network of imidazolium units, were characterised and tested as catalysts for the reaction of carbon dioxide with various epoxides to produce cyclic carbonates. The materials prepared by supporting a bis-imidazolium iodide salt with xylene or octane as a linker between the imidazolium units were identified as the most active catalysts and displayed high turnover numbers and improved productivity compared to known supported ionic liquid catalysts. The most promising m…

Advances towards highly active and stereoselective simple and cheap proline-based organocatalysts

Ten 4-acyloxy-L-prolines were screened as catalysts at loadings of 2–0.1 mol-% for the direct asymmetric aldol reaction in water by using variable amounts of water. Among them, a new catalyst, the L-proline carrying a trans-4-(2,2-diphenylacetoxy) group, and a catalyst previously synthesized by us, the L-proline carrying a trans-4-(4-phenylbutanoyloxy) group, were found to be excellent catalysts for the aldol reaction between cyclohexanone or cyclopentanone and substituted benzaldehydes when employed in only 1 and 0.5 mol-%,respectively, at room temperature without additives. For such catalysts, high turnover numbers were obtained, which are among the highest values obtained for enamine org…

Polystyrene-supported organocatalysts for α-selenenylation and Michael reactions

Abstract Three different resin-supported catalysts have been prepared by using the well established post-modification approach by means of thiol-ene coupling reaction. Two catalysts were tested for the first time in the asymmetric α-selenenylation of propanal, while the third catalyst was used in the Michael addition reaction. While the preliminary results are not encouraging in the case of supported Jorgensen’ catalyst, interesting data have been collected with both for the supported MacMillan and prolyl-prolinol catalysts. In fact, these catalysts displayed good activity and selectivity. A reversed enantioselectivity in the α-selenenylation was observed by changing the polarity of the sol…

Enhanced Activity and Stereoselectivity of Polystyrene-Supported Proline-Based Organic Catalysts for Direct Asymmetric Aldol Reaction in Water

Several polystyrene-supported proline dipeptides and a prolinamide derivative were prepared by thiol–ene coupling. These materials were used as catalysts for the direct asymmetric aldol reaction in water, and results compared with unsupported catalysts in water. Such an approach gave more active or stereoselective catalysts compared to the unsupported compounds, showing that our immobilization procedure may be useful to develop catalytic materials with enhanced performance. Moreover, these catalysts can be recovered and reused for at least nine times without loss of activity or can be easily regenerated when their activity has decreased. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, …

Highly cross-linked imidazolium salt entrapped magnetic particles – preparation and applications

Magnetic particles entrapped into highly cross-linked imidazolium salts were synthesized using a straightforward approach by radical polymerization of bis-vinylimidazolium salts in the presence of superparamagnetic iron oxide particles. Potential applications for these new materials as (i) catalysts for conversion of propylene oxide to propylene carbonate, (ii) supports for organocatalysts, and (iii) scavenger materials for palladium removal are outlined.

Simple and Cheap Highly Active Proline-Based Organocatalysts

Novel supported dipeptides as recyclable catalysts for asymmetric aldol reaction

New proline derivatives as recyclable catalysts for aldol reaction

ChemInform Abstract: Low-Loading Asymmetric Organocatalysis

Asymmetric organocatalysis is now recognized as the third pillar of asymmetric synthesis. Recent years have witnessed increasing interest towards the use of highly active and stereoselective organocatalysts. This critical review documents the advances in the development of chiral organocatalysts which are systematically used in ≤3 mol% loading in all the sub-areas of the field, namely aminocatalysis, Bronsted acids and bases, Lewis acids and bases, hydrogen bond-mediated catalysis, phase transfer and N-heterocyclic carbene catalyses (194 references).

ChemInform Abstract: Enhanced Activity and Stereoselectivity of Polystyrene-Supported Proline-Based Organic Catalysts for Direct Asymmetric Aldol Reaction in Water.

Several polystyrene-supported proline dipeptides and a prolinamide derivative were prepared by thiol–ene coupling. These materials were used as catalysts for the direct asymmetric aldol reaction in water, and results compared with unsupported catalysts in water. Such an approach gave more active or stereoselective catalysts compared to the unsupported compounds, showing that our immobilization procedure may be useful to develop catalytic materials with enhanced performance. Moreover, these catalysts can be recovered and reused for at least nine times without loss of activity or can be easily regenerated when their activity has decreased. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, …

Novel supported substituted prolinamide as recyclable catalyst for asymmetric aldol reaction