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Relevant academic research and scientific papers

Asymmetric direct aldol reactions catalyzed by a simple chiral primary diamine-Bronsted acid catalyst in/on water

The direct asymmetric aldol reaction catalyzed by the simple and commercially available chiral primary diamines, (1S,2S)-1,2-diphenylethane-1,2- diamine and (1R,2R)-1,2-diphenylethane-1,2-diamine, is presented. The catalyst system is a primary amine with Bronsted acid-catalyzed direct aldol reaction of p-nitrobenzaldehyde and cyclohexanone with high chemo- and stereoselectivity on water, which furnishes the corresponding β-hydroxyketone with up to 94% ee. Copyright Taylor & Francis Group, LLC.

Switching diastereoselectivity in proline-catalyzed aldol reactions

The choice of the anion of an achiral TBD-derived guanidinium salt, used as cocatalyst for proline, allows reacting cycloketones with aromatic aldehydes and preparing either anti- or syn-aldol adducts with very high enantioselectivity. As a proof of princ

(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. (l)-Prolinamide imidazolium hexafluorophosphate ionic liquid (2 mol%) found to be an excellent organocatalyst for direct asymmetric aldol reaction between 4-nitrobenzaldehyde and cyclohexanone using acetic acid (2 mol%) as an additive at -15 °C in solvent-free condition, the aldol product was afforded in excellent yield with diastereomeric ratio (anti/syn; 97:3) and 94% ee of anti-aldol product. Ionic liquids can catalyze the direct aldol reaction between benzaldehyde derivatives and cycloalkanones and the best dr (anti/syn; 99.9/0.01) and 99% ee was obtained for aldol product of 2-trifluoromethyl benzaldehyde and cyclohexanone. (l)-Prolinamide imidazolium hexafluorophosphate ionic liquid was reused up to 6 continuous cycles without decrease in the conversion of the product with 92% ee and found to be superior than its counterpart trans-4-hydroxy-(l)-prolinamide. Continuous cycle experiments do not require isolation of the catalyst after each cycle. The results of reusability of the ionic liquid catalyst were found to be better than most of other reported reusable catalysts.

Polymerization of L-proline functionalized styrene and its catalytic performance as a supported organocatalyst for direct enantioselective aldol reaction

As an alternative approach to the graft modification of polymers to fabricate polymer-supported chiral organocatalysts in a bottom-up fashion, L-prolinamide functionalized polymers were prepared by general solution homopolymerization or copolymerization of L-proline functionalized styrene monomer in the presence of 1,4-divinylbenzene as the crosslinking agent. The catalytic performance of the as-prepared heterogeneous catalysts towards the direct enantioselective aldol reaction of ketones with a series of aromatic aldehydes was explored. Our findings indicate that the as-prepared heterogeneous catalysts can afford relevant aldol addition products with good yields (up to 96%), high diastereoselectivities (up to 8:92 dr) and excellent enantiomeric excess (up to 96%); they also exhibit good recyclability, retaining high yield and rate as well as good selectivity after several cycles.

Pepsin-catalyzed direct asymmetric aldol reactions for the synthesis of vicinal diol compounds

The catalytic promiscuity of pepsin from porcine gastric mucous was observed in catalysis of the direct asymmetric aldol reactions of aromatic aldehydes with acetones, which were substituted by hydroxy-, dihydroxy-, methoxy- and benzyloxy- for the synthes

Synthesis of Hybrid Ferrocene-Proline Amides as Active Catalysts for Asymmetric Aldol Reactions in Water

Ferrocenyl substituents were employed as lipophilic moieties and introduced into a prolinamide scaffold to afford new catalysts that were suitable for use in "on water" conditions. Five proline amides that contain a ferrocene unit were synthesized from ea

Preparation of immobilized L-prolinamide via enzymatic polymerization of phenolic L-prolinamide and evaluation of its catalytic performance for direct asymmetric aldol reaction

Phenolic L-prolinamide was allowed to participate in enzymatic polymerization with horseradish peroxidase as the catalyst, generating immobilized L-prolinamide. The catalytic performance of the resultant polymer-supported L-prolinamide for direct asymmetr

Synergistic effects within a C2-symmetric organocatalyst: The potential formation of a chiral catalytic pocket

This study describes the synthesis of five novel C2-symmetric organocatalysts that facilitate the on-water asymmetric aldol reaction at low catalyst loading (1 mol%) without the use of additives. Each catalyst is composed of two diprolinamide units joined by a symmetric alkyl bridging group allowing for systematic modulation of catalytic site proximity. Typically, catalysts in this manuscript which bear the catalytic units in close proximity gave the best reaction outcomes in terms of conversion (up to >99%), diastereomeric ratio (4/96, syn/anti) and enantiomeric excess (up to 97%). This effect has been attributed to the assembly of a chiral pocket, facilitated by hydrogen bonding at the oil-in-water interface. The Royal Society of Chemistry 2013.

Multifunctional "click" prolinamides: A new platform for asymmetric aldol reactions in the presence of water with catalyst recycling

"Click" chemistry is combined with organocatalysis to fabricate a multifunctional C3-symmetrical dendritic prolinamide with a hydrophobic aromatic core and hydrophilic triazolinium arms that exhibit high efficiency in catalyzing the asymmetric aldol reaction with cyclic ketones. The catalyst is water-compatible and remains active for five consecutive catalytic runs with a low catalyst loading (2 mol%), yielding the aldol products in high yields, diastereo- and enantioselectivities.

An effective heterogeneous l-proline catalyst for the direct asymmetric aldol reaction using graphene oxide as support

Pristine l-proline was non-covalently loaded on the graphene oxide (GO) sheet in a simple route by mixing them in aqueous solution. Technologies of characterization well suggested that l-proline was efficiently loaded on the two sides and edge of the GO sheet through hydrogen-bonding or/and ionic interaction, giving the excellent l-proline/GO hybrid catalyst for the direct asymmetric aldol reaction. The unique multilayered structure of the GO carrier with sufficient interlayer space favored reagents' diffusion toward l-proline chiral moiety and therefore resulted in the high catalytic efficiency of the heterogeneous l-proline. Excellent yield (96%) with high enantiomeric excess (79% ee) was obtained in the direct aldol reaction of 2-nitrobenzaldehyde with acetone catalyzed by l-proline/GO hybrid, which was comparable to that observed in the reactions promoted by l-proline itself. Furthermore, the l-proline/GO hybrid used as a heterogeneous catalyst could be easily recovered and recycled for seven times without significant loss of the reactivity.