Catalyst For Aldol Reaction Research Articles

A simple route to magnetically separable mesoporous silica with high surface area and large pore: A recyclable catalyst for aldol reaction

Magnetic mesoporous silica composites were prepared by embedding magnetic oxide nanoparticles into abundance of host silica matrix. The resultant composites possess ordered hexagonal mesopores, very high surface area of up to 1124m2/g, large pore volume (1.324cm3/g), and large mesopore (>10nm), as well as good magnetic response. After aminoalkylsilylation, the magnetic SBA-15 composites were demonstrated to be recyclable heterogeneous catalysts for efficient catalytic aldol reaction inside the nanochannels.

Optically active, magnetic microspheres: Constructed by helical substituted polyacetylene with pendent prolineamide groups and applied as catalyst for Aldol reaction

This article reports on the preparation of a novel category of optically active magnetic microspheres (OAMMPs) consisting of Fe3O4 nanoparticles and helical substituted polyacetylene bearing pendent prolineamide groups and the use of them for asymmetric direct Aldol reactions. The microspheres (200–300μm in diameter) were prepared by using chiral acetylenic monomer and alkynyl-Fe3O4 nanoparticles via suspension polymerization approach. They were obtained in high yield (>99%) with regular spheric morphology and exhibited noticeable optical activity, according to circular dichroism spectra and specific optical rotation measurements. The microspheres further served as chiral catalyst for performing direct Aldol reactions between acetone and p-nitrobenzaldehyde, providing the product in moderate yield (68%) and ee (75%). The magnetic microspheres can be easily recycled and reused. Mechanism for the asymmetric catalysis of Aldol reaction was further proposed.

ChemInform Abstract: Synthesis and Characterization of N‐Substituted (S)‐1,2,3,4‐Tetrahydroisoquinoline‐3‐carboxamides and Thioamides as Organocatalysts for Asymmetric Aldol Reaction.

AbstractTitle compounds (I) are synthesized and tested as catalysts for aldol reaction of nitrobenzaldehyde (II) with acetone.

An Enantioselective Recyclable Polystyrene‐Supported Threonine‐Derived Organocatalyst for Aldol Reactions

AbstractA series of primary amino acids covalently supported onto polystyrene through alkyne–azide cycloaddition reactions has been synthesized and evaluated as catalysts in asymmetric aldol reactions. A polymer‐supported threonine behaves as an easily recyclable, highly reactive and stereoselective (up to 99% ee) catalyst in the aldol reaction of both cyclic and acyclic ketone donors with aromatic aldehydes in aqueous environments. While cyclic ketones react with anti diastereoselectivity, syn adducts are predominantly obtained with acyclic substrates. The heterogenized threonine catalyst has been used for the sequential synthesis of a small library of enantiopure aldol products.magnified image

A novel poly(N-isopropyl-acrylamine-co-l-proline) catalyst for aldol reaction: synthesis, catalytic performance and recyclability

A novel homogeneous copolymer catalyst, poly(N-isopropyl-acrylamine-co-l-proline), possesses excellent activity and stereoselectivities. Even after ten cycles, the catalytic activity and stereoselectivities remained almost unchanged. The circular dichroism spectra of the copolymer catalyst are apparently different from the corresponding monomer.

Role of Additives in Chiral Amine-Catalyzed Direct Aldol Reaction

A systematic study of chiral adducts derived from amines as catalysts for aldol reaction revealed that enantioselective outcome depends on the chiral enamine intermediate and not the face-selective activation of aldehyde. A simple addition compound of proline and 8-hydroxy quinoline was found to be a good catalyst. [Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.]

Various Polar Tripeptides as Asymmetric Organocatalyst in Direct Aldol Reactions in Aqueous Media

A series of tripeptide organocatalysts containing a secondary amine group and two amino acids with polar side chain units were developed and evaluated in the direct asymmetric intermolecular aldol reaction of 4-nitrobenzaldehyde and cyclohexanone. The effectiveness of short polar peptides as asymmetric catalysts in aldol reactions to attain high yields of enantio- and diastereoselective isomers were investigated. In a comparison, glutamic acid and histidine produced higher % ee and yields when they were applied as the second amino acid in short trimeric peptides. These short polar peptides were found to be efficient organocatalysts for the asymmetric aldol addition reaction in aqueous media.

ChemInform Abstract: Mukaiyama Aldol Reaction of Trimethylsilyl Enolate with Aldehyde Catalyzed by CuI.

Mukaiyama aldol reaction is an efficient methodology for carbon-carbon bond formation reaction 1 . This reaction between enolsilane derivatives and aldehydes provides a route for the stereoselective construction of β-hydroxy carbonyl units which are important building blocks for the construction of many natural products and pharmaceuticals. Since the discovery of the reaction by Mukaiyama, promoted by TiCl4 (ref. 2), a variety of catalysts have been used to activate this process 3 . Many of the catalysts have limitations such as use of stoichiometric amount of catalyst, moisture sensitivity of the catalyst, expensive reagents, etc. Although many recent reports claimed improvement of the process eliminating those drawbacks, new methods are still desirable. Li and coworkers reported the use of MgI2.Et2O as catalyst for aldol reactions 3k . But this method again has the drawback of the requirement of dry reaction medium. Apart from the Lewis acids, Lewis bases were also employed for Mukaiyama aldol reaction 4 . Recently, N-methylimidazole was found to be a good catalyst for aldol reaction between trimethylsilyl ketene acetal and aldehyde 4h . However, this method requires extra addition of LiCl as a promoter. Use of Cu(OTf)2 in presence of various ligands has also been reported by various researchers for such transformations 5 . But Cu(OTf)2 is expensive and moisture sensitive. Due to the selectivity associated with this versatile process, there is a thrust in this area to develop new catalysts to make the process more simple, economic and effective. The use of copper catalyst in organic transformations is more advantageous because it is cheap and relatively benign. CuI has emerged as a very effective catalyst for various organic transformations. In continuation of the work on CuI catalysed reactions 6 , herein is reported the Mukaiyama aldol reaction of silyl keten acetal with various aldehydes (Scheme I).

ChemInform Abstract: Metal‐catalyzed Asymmetric Aldol Reactions

AbstractReview: 104 refs.

ChemInform Abstract: Readily Available (S)‐Proline‐Derived Organocatalysts for the Lewis Acid‐Mediated Lewis Base‐Catalyzed Stereoselective Aldol Reactions of Activated Thioesters.

AbstractThe bisphosphine oxide catalyst PPO is optimal as catalyst in aldol reactions of thioesters (I) with aromatic aldehydes.

ChemInform Abstract: A Tripeptide‐Like Prolinamide‐thiourea as an Aldol Reaction Catalyst.

A tripeptide-like prolinamide-thiourea catalyst with (S)-proline, (1S,2S)-diphenylethylenediamine and (S)-di-tert-butyl aspartate as building blocks provides the products of the reaction between ketones and aromatic aldehydes in high to quantitative yields and high stereoselectivities (up to 99 : 1 dr and 99% ee). Both the chiral centers of the diamine unit are essential, while the thiourea hydrogen originating from the amine and the amide hydrogen play a predominant role for the catalyst efficiency.

Systematic evaluation of a few proline derivatives as catalysts for a direct aldol reaction

A series of pyrrolidine derivatives were prepared and examined as catalysts for an aldol reaction. Structural variations in these molecules involved altering the sterics at the α-position, the position of the carbonyl group, and the acidities of the hydrogen bonding sites. The effect of these factors on catalytic activity and enantioselectivity was studied. The experimental results revealed that additional sterics at the α-position were detrimental. However, no correlation was found between the catalytic activity and N–H acidity.

Metal-catalyzed asymmetric aldol reactions

The aldol reaction is one of the most powerful and versatile methods for the construction of C-C bonds. Traditionally, this reaction was developed in a stoichiometric version; however, great efforts in the development of chiral catalysts for aldol reactions were performed in recent years. Thus, in this review article, the development of metal-mediated chiral catalysts in Mukaiyama-type aldol reaction, reductive aldol reaction and direct aldol reaction are discussed. Moreover, the application of these catalysts in the total synthesis of complex molecules is discussed.

Supported La2O3 and MgO Nanoparticles as Solid Base Catalysts for Aldol Reactions While Suppressing Dehydration at Room Temperature

AbstractLa2O3 and MgO nanoparticles (3–4 nm) supported on carbon nanofibers were evaluated as solid base catalysts for the aldol reaction of benzaldehyde and acetone at room temperature. Both catalysts were found to be highly active and selective with respect to 4‐hydroxy‐4‐phenylbutan‐2‐one, thus suppressing the elimination of H2O, which is a challenge for this reaction. La2O3 nanoparticles were more stable towards water, which makes them more applicable than MgO nanoparticles as a solid base catalyst for this reaction.

Exploration of acid–base geometric influence on cooperative activation for aldol reaction

Bifunctionalized material with organized pairs of carboxylic acid and primary amine structurally similar to β3-amino acid derivatives has been prepared through post-grafted approach. Then the organized acid–base bifunctionalized material and the base monofunctionalized material were used as catalysts in aldol reaction to study the influence of the acid–base geometry on acid–base cooperativity. The catalytic result using acid–base bifunctionalized material towards aldol reaction was almost as same as the result obtained with the monofunctional amino catalyst, indicating that cooperative activation is not able to act efficiently unless the acid and the base active centers are positioned with appropriate geometry for the aldol reaction (e.g. about 2.6Å).

Proline–cyclodextrin conjugates: synthesis and evaluation as catalysts for aldol reaction in water

The synthesis of six conjugates of l-proline and β-cyclodextrin and their evaluation as catalysts of aldol reaction in water are described. The results indicated that the nature of the linker between proline and β-cyclodextrin is important for catalytic activity; the one with the most flexible linker gave the best results. Inhibition experiments showed that the cavity of β-cyclodextrin plays a role in the catalysis. Permethylation of the cyclodextrin hydroxyl groups led to higher conversion rates.

A tripeptide-like prolinamide-thiourea as an aldol reaction catalyst

A tripeptide-like prolinamide-thiourea catalyst with (S)-proline, (1S,2S)-diphenylethylenediamine and (S)-di-tert-butyl aspartate as building blocks provides the products of the reaction between ketones and aromatic aldehydes in high to quantitative yields and high stereoselectivities (up to 99:1 dr and 99% ee). Both the chiral centers of the diamine unit are essential, while the thiourea hydrogen originating from the amine and the amide hydrogen play a predominant role for the catalyst efficiency.

Linear Copolymers of Proline Methacrylate and Styrene as Catalysts for Aldol Reactions in Water: Effect of the Copolymer Aggregation on the Enantioselectivity

The synthesis and catalytic activity of linear copolymers of proline methacrylate and styrene with different molar ratios are reported. The compounds are soluble catalysts for aldol reactions betwe...

ChemInform Abstract: Prolinamides Bearing Thiourea Groups as Catalysts for Asymmetric Aldol Reactions.

AbstractA catalyst based on (S)‐proline and (1S,2S)‐diphenylethylenediamine proved to be an excellent catalyst for aldol reactions between ketones and aromatic aldehydes.

Silica-immobilized piperazine: A sustainable organocatalyst for aldol and Knoevenagel reactions

Silica-supported piperazine was found to be an efficient catalyst for aldol reactions of aromatic aldehydes and ketones with straightforward product isolation and catalyst reuse. Furthermore, the catalyst is active in Knoevenagel-type reactions to afford coumarin derivatives, using 2-methyltetrahydrofuran (2-MeTHF) as a novel bio-based solvent.