Catalyst For Asymmetric Aldol Reaction Research Articles

In Situ Assembly of a Metal‐Templated Catalyst for Asymmetric Aldol Reactions: From the Metal Complexes Equilibria to a Practical System

AbstractA zinc(II)‐templated catalyst assembling terpyridine and bipyridine organocatalytic ligands has been developed for the asymmetric aldol reaction. The system has been optimized to maximize the formation of the heteromeric bifunctional species through the determination of the equilibrium constants leading to the formation of all the species present. A practical, easy to synthesize catalytic system providing high stereoselectivity has been achieved in this way.

A Simple Screening and Optimization Bioprocess for Long-Chain Peptide Catalysts Applied to Asymmetric Aldol Reaction.

Peptides have demonstrated their efficacy as catalysts in asymmetric aldol reactions. But the constraints inherent in chemical synthesis have imposed limitations on the viability of long-chain peptide catalysts. A noticeable dearth of tools has impeded the swift and effective screening of peptide catalysts using biological methods. To address this, we introduce a straightforward bioprocess for the screening of peptide catalysts for asymmetric aldol reactions. We synthesized several peptides through this method and obtained a 15-amino acid peptide. This peptide exhibited asymmetric aldol catalytic activity, achieving 77% ee in DMSO solvent and 63% ee with over an 80.8% yield in DMSO mixed with a pH 9.0 buffer solution. The successful application of our innovative approach not only represents an advancement but also paves the way for currently unexplored research avenues.

Fractal features of pH-sensitive bimodal mesoporous silica-supported bipyridine-proline organocatalysts with core-shell structure and their application in asymmetric aldol reaction

Using poly(acrylic acid) (abbreviated as PAA) as a shell, bimodal mesoporous silicas (abbreviated as BMMs) as a core, and bipyridine-proline (abbreviated as Z) as an active species, a facile approach for preparation of the P-Z@BMMs nanocomposites with core–shell structure was proposed, which was used as a suitable pH-sensitive catalyst for asymmetric aldol reaction between p-nitrobenzaldehyde and cyclohexanone. Their microstructural features and physicochemical properties were extensively characterized by various methods, such as powder X-ray diffraction patterns, N2 adsorption–desorption isotherms, the scanning (and transmission) electron microscopy images, the dynamic light scattering measurements, the thermogravimetric analysis, the elemental analysis, and the Fourier transform infrared spectroscopy spectra. Particularly, their fractal evolution, the pair distance distribution function, and the Porod plots were demonstrated via the small-angle X-ray scattering patterns. The results elucidated that the PAA was successfully incorporated onto the external amino-modified surfaces of the mesoporous BMMs, and the particles having PAA grafted thereon had a pH-responsive shell in thickness of around 0.97 nm for controlled release of Z species by adjusting pH value of the reaction medium. Besides, the synthesized P-Z@BMMs presented the satisfactory catalytic yields (around 80%) in comparison with the homo- and heterogeneous catalytic system using Z or Z@BMMs as the catalysts.

Prolinamide and Prolinamide Tagged with Ionic Liquid Intercalated in Bentonite Clay, a Recyclable Catalyst for Asymmetric Aldol Reactions

AbstractThe imidazolium‐based chiral ionic liquids containing prolinamide moiety and prolinamide were intercalated in bentonite clay and evaluated in asymmetric aldol reactions of aromatic aldehydes or isatins with acetone or cyclohexanone. The 10 mol% of chiral ionic liquid having S‐phenylethylamine moiety 2 a catalyzed the direct enantioselective aldol reaction of isatins and acetone in i‐PrOH at −20 °C and afforded the corresponding 3‐alkyl‐3‐hydroxy indolin‐2‐ones in 72–98 % yields and 37–80 % ee's. The prolinamide intercalated in bentonite clay (0.125 g, 10 mol%) gave corresponding aldol products in 32–82 % yields and 38–91 % ee's. However, prolinamide intercalated bentonite clay was found to be less active as compared to chiral ionic liquids containing prolinamide. The prolinamide intercalated bentonite clay 8 was reused in four catalytic cycles, with a slight loss of activity and selectivity of the catalyst after the third recycling.

Calix[n]arenes in Action: Recent Applications in Organocatalysis

AbstractThe use of calix[n]arenes as organocatalysts has increasingly been considered a prime focus due to their adjustable three‐dimensional molecular structure, easy synthesis, and versatile structural modification at the upper and lower edges. For instance, these macromolecules have been described as efficient catalysts for asymmetric aldol reactions, asymmetric Michael addition, esterification and transesterification, dehydration, nucleophilic aromatic substitution, and multicomponent reactions. Furthermore, calix[n]arenes also tolerate aqueous or solvent‐free reaction systems and can be supported on solid and/or magnetic particles, showing cost, time and energy savings, easier experimental procedures, and chemical waste reduction.

A recyclable and highly stereoselective multi-fluorous proline catalyst for asymmetric aldol reactions

A recyclable fluorous proline catalyst with high stereoselectivity that functions as a catalyst for asymmetric aldol reactions is described. Its high stereoselectivity and facile recovery are achieved by employing a multi-fluorous tag attachment strategy. Although a gradual decrease was observed with respect to the catalytic activity, the catalyst can be separated from the reaction mixture by adsorption onto FluoroFlash® and can be reused in that form for a maximum of five times while maintaining a high stereoselectivity.2019 Elsevier Ltd. All rights reserved.

Recyclable helical poly(phenylacetylene)‐supported catalyst for asymmetric aldol reaction in aqueous media

ABSTRACTA novel one‐handed helical poly(phenylacetylene) bearing L‐hydroxyproline pendants (poly(PA‐P)) was synthesized as an eco‐friendly polymer‐supported catalyst for asymmetric reactions. The helical poly(PA‐P) catalyzed the asymmetric aldol reactions of cyclohexanone with p‐nitrobenzaldehyde, and showed good recyclability and higher enantiomeric excess (ee) in aqueous medias than that in organic medias. The one‐handed helicity of poly(PA‐P) was clearly affected by the water content in the aqueous media. The helical poly(PA‐P) showed the higher enantioselectivity (ee = 99%) than its monomer PA‐P (ee = 54%) in THF/H2O (H2O vol % = 25.0 vol %). After the one‐handed helical structure of poly(PA‐P) was destroyed by grinding treatment, the ee of the reaction clearly decreased from 99 to 49%. These indicate that the one‐handed helical structure of poly(PA‐P) played an important role in the high enantioselectivity of the asymmetric aldol reactions in the aqueous media. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1024–1031

Stability of Immobilization of Bipyridine‐proline on Zn‐Modified Bimodal Mesoporous Silicas and Recyclable Catalytic Performance in Asymmetric Aldol Reaction

AbstractThe organic‐inorganic mesoporous materials (ZZnBMMs) were successfully synthesized by Zn‐grafting into the surface of bimodal mesoporous silicas (BMMs) via covalent bond, and then immobilization of (2 S,2’S)‐N,N’‐([2,2’‐bipyridine]‐3,3’‐diyl)bis(pyrrolidine‐2‐carboxamide) (Z) onto the Zn‐modified BMMs through coordination method. The influences of washed parameters such as various solvents (petroleum ether, CH2Cl2, CH3OH, or DMSO) and pretreated temperature on the structural stability of obtained ZZnBMMs were investigated thoroughly, which were extensively characterized by means of XRD patterns, UV‐vis and FT‐IR spectra, N2 sorption isotherms, SEM images, and SAXS patterns. The results showed that petroleum ether could be acted as optimum solvent for washing ZZnBMMs when pre‐treated temperature was around 20 °C. The SAXS patterns evidently demonstrated that ZZnBMMs before and after washing presented the fractal features, suggesting their surface roughness and structural irregularities, in which, the mass fractal (Dm) values were gradually decreased along with not only the increased polarity of used solvents (petroleum ether, CH2Cl2, CH3OH, and DMSO), but also enhanced washing temperature of from 20–60 °C and prolonged time of from 4–168 hrs. Furthermore, the ZZnBMMs as a heterogeneous catalyst for asymmetric aldol reaction exhibited the recycled (at least 6 times) catalytic performances with high efficiency (around 92.1% yield) and good selectivity (up to 68% ee).

Preparation and characterization of magnetic graphene nanocomposite containing Cu(proline)2 as catalyst for asymmetric aldol reactions

A new catalyst has been prepared via immobilization of Cu(proline)2 complex onto the surface of magnetic graphene. The fabricated nanocatalyst was characterized by Fourier-transform infrared (FT-IR) spectroscopy, powder X-ray diffraction (PXRD) analysis, vibrating-sample magnetometry (VSM), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, transmission electron microscopy (TEM), inductively coupled plasma (ICP) techniques, and elemental analysis. Its catalytic performance was investigated in the aldol reaction using a mild and ecofriendly procedure. The synthesized nanocomposite, which contains Cu(II) center as Lewis acid, was found to be an efficient catalyst for asymmetric aldol reactions, affording corresponding aldol products in high yield and excellent enantiomeric excess (> 90 %). The examined catalyst was prepared from low-cost, easily available starting materials and can be readily isolated by magnetic decantation for recycling and reuse in consecutive reactions without significant loss of activity.

POSS supported C2-symmetric bisprolinamide as a recyclable chiral catalyst for asymmetric Aldol reaction

POSS supported prolinamide-type catalysts were synthesized and used to catalyze asymmetric Aldol reactions between unmodified ketones and aldehydes. Immobilization of the prolinamide-type catalysts onto POSS resulted in good yields and improved diastereoselectivity as well as enantioselectivity. The POSS-supported catalysts were recycled simply by precipitation and filtration, and could be reused in five consecutive cycles without losing its effectiveness.

ChemInform Abstract: AZT‐Prolinamide: The Nucleoside Derived Pyrrolidine Catalysts for Asymmetric Aldol Reactions Using Water as Solvent.

AbstractNew nucleoside‐based chiral prolinamides are synthesized and applied in enantioselective aldol reaction of aldehydes with ketones to give β‐hydroxyl carbonyl compounds in high yields with good stereoselectivity.

Efficient synthesis of supported proline catalysts for asymmetric aldol reactions

l-Proline is grafted onto silica (MCM-41) in a single step and shows high activity and enantioselectivity in an aldol reaction.

Green and Sustainable Heterogeneous Organo-Catalyst for Asymmetric Aldol Reactions

Linear amino acids covalently supported on graphene sheet were employed as catalysts for asymmetric aldol reactions between cyclohexanone and aldehydes (aliphatic and/or aromatic) in a batch type reactor in the presence of water. The reactions were found to exhibit high yield as well as excellent ee value. Additionally, the catalysts were found to be truly heterogeneous and eco-friendly.

ChemInform Abstract: The Application of a Structurally Simple, Recyclable, and Large‐Scale L‐Prolinamide Catalyst for Asymmetric Aldol Reactions.

AbstractA bifunctional catalyst having a trans‐cyclohexane and a proline amide moiety is developed and successfully applied to the asymmetric aldol condensation of cyclic ketones with aldehydes.

ChemInform Abstract: Synthesis of Hybrid Ferrocene‐Proline Amides as Active Catalysts for Asymmetric Aldol Reactions in Water.

AbstractSome new ferrocene‐proline amides are prepared.

AZT-prolinamide: the nucleoside derived pyrrolidine catalysts for asymmetric aldol reactions using water as solvent

New pyrrolidine catalysts based on a nucleoside and proline, AZT-prolinamides, were synthesized and successfully employed for the enantioselective direct aldol reaction of aldehydes with ketones. These catalysts proved to be effective in promoting the reaction, in additive free water media with 15mol% loading. The products, β-hydroxy carbonyl compounds were obtained in high yields and stereoselectivities.

The application of a structurally simple, recyclable, and large-scale l-prolinamide catalyst for asymmetric aldol reactions

A highly efficient, bifunctional prolinamide catalyst, which consists of chiral proline and trans-cyclohexanediamine moieties, was prepared and evaluated in the direct asymmetric aldol reactions of various ketones and aldehydes. The catalyst displayed impressive catalytic activity toward heterocyclic ketones containing oxygen, sulfur, or nitrogen, which have not been sufficiently explored. The substrate scope also covered cyclic and acyclic ketones. With heterocyclic ketones or cyclohexanone, the aldol reactions gave products in high yields and with respectable enantioselectivities (87–99% ee) and diastereoselectivities (up to >99:1 anti/syn). The catalyst could be recycled and reused up to seven times resulting in good yields and with good selectivities. This catalyst is also efficient in large-scale reactions with the enantioselectivities remaining at the same level as in the experimental scale reactions.

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

AbstractFerrocenyl 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 easily accessible ferrocenylamines and evaluated as catalysts in the asymmetric direct aldol condensation of cyclohexanone with aldehydes in an aqueous medium. Optimal substrate conversion and stereoselectivity were achieved in brine and in the presence of benzoic acid as an additive. All the examined catalysts displayed good activity with a catalyst loading of 5 mol‐%, and the best results in terms of enantioselectivity were obtained by using a ferrocenyl‐prolineamide with an additional (S) chiral center. In the presence of this catalyst, a variety of aromatic aldehydes underwent a reaction in a reasonable amount time with just 2 equiv. of the cyclic ketone to give the expected aldol products in high yields (65–98 %) and with high stereoselectivities (up to 94 % ee, dr up to 93:7).

Polyvinylidene chloride supported L‐prolineamide as recoverable catalyst for asymmetric aldol reaction between ketone and aromatic aldehyde

AbstractA series of prolineamide modified by polyvinylidene chloride (PVDC) was synthesized and used as green recoverable organocatalysts for the asymmetric Aldol reactions between various ketones and aromatic aldehydes. The effects of solvent and catalyst dosage on the catalytic performances of as‐synthesized organocatalysts were investigated. It was found that as‐synthesized PVDC‐supported L‐prolineamides possessed good catalytic performance for the asymmetric Aldol reactions between cyclohexanone and a variety of aromatic aldehydes, affording high yields of up to 99%, excellent diastereoselectivities of up to above 8 : 92 d.r. value, and high enantioselectivities of up to above 92.3% e.e. value. In general, the catalytic performance of as‐synthesized organocatalysts closely depended on the catalyst dosage and solvent type as well. Particularly, as‐synthesized organocatalyst 1c, at a dosage of 5 mol % in 10 μL of water, exhibited high catalytic activity and stereoselectivity for the asymmetric Aldol reaction between cyclohexanone and p‐nitrobenzaldehyde at room temperature. In the meantime, it could be easily recovered and recycled, while the activity and enantioselectivity were nearly completely retained even after five cycles of recovery, showing promising application as an efficient green organocatalyst for the aforementioned asymmetric Aldol reactions. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

In Situ Formed Bifunctional Primary Amine–Imine Catalyst for Asymmetric Aldol Reactions of α‐Keto Esters

In prime condition: The hydrolysis of a chiral diimine precursor can be carried out by a Brønsted acid to form an in situ primary amine–imine intermediate as a bifunctional primary aminocatalyst, which promoted direct asymmetric aldol reactions between α-keto esters and ketones in high yields (up to 88 %) and with excellent enantioselectivities (see scheme; R1, R2, R4=alkyl; R3=aryl). Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.