Recoverable Organocatalyst Research Articles

L-Asparagine-EDTA-amide silica-coated MNPs: a highly efficient and nano-ordered multifunctional core-shell organocatalyst for green synthesis of 3,4-dihydropyrimidin-2(1H)-one compounds.

In this study, new l-asparagine grafted on 3-aminopropyl-modified Fe3O4@SiO2 core–shell magnetic nanoparticles using the EDTA linker (Fe3O4@SiO2–APTS–EDTA–asparagine) was prepared and its structures properly confirmed using different spectroscopic, microscopic and magnetic methods or techniques including FT-IR, EDX, XRD, FESEM, TEM, TGA and VSM. The Fe3O4@SiO2–APTS–EDTA–asparagine core–shell nanomaterial was found, as a highly efficient multifunctional and recoverable organocatalyst, to promote the efficient synthesis of a wide range of biologically-active 3,4-dihydropyrimidin-2(1H)-one derivatives under solvent-free conditions. It was proved that Fe3O4@SiO2–APTS–EDTA–asparagine MNPs, as a catalyst having excellent thermal and magnetic stability, specific morphology and acidic sites with appropriate geometry, can activate the Biginelli reaction components. Moreover, the environmental-friendliness and nontoxic nature of the catalyst, cost effectiveness, low catalyst loading, easy separation of the catalyst from the reaction mixture and short reaction time are some of the remarkable advantages of this green protocol.

O-Tms-Α , Α -Diaryl-(S)-Prolinol Tagged with Imidazolium Ionic Liquids as Recyclable and Recoverable Organocatalysts for the Enantioselective Friedel-Crafts Reaction between Indoles and Α , Β -Unsaturated Aldehydes

O-Tms-Α , Α -Diaryl-(S)-Prolinol Tagged with Imidazolium Ionic Liquids as Recyclable and Recoverable Organocatalysts for the Enantioselective Friedel-Crafts Reaction between Indoles and Α , Β -Unsaturated Aldehydes

Recoverable Phospha-Michael Additions Catalyzed by a 4-N,N-Dimethylaminopyridinium Saccharinate Salt or a Fluorous Long-Chained Pyridine: Two Types of Reusable Base Catalysts.

Phospha-Michael addition, which is the addition reaction of a phosphorus-based nucleophile to an acceptor-substituted unsaturated bond, certainly represents one of the most versatile and powerful tools for the formation of P-C bonds, since many different electrophiles and P nucleophiles can be combined with each other. This offers the possibility to access many diversely functionalized products. In this work, two kinds of basic pyridine-based organo-catalysts were used to efficiently catalyze phospha-Michael addition reactions, the 4-N,N-dimethylaminopyridinium saccharinate (DMAP·Hsac) salt and a fluorous long-chained pyridine (4-Rf-CH2OCH2-py, where Rf = C11F23). These catalysts have been synthesized and characterized by Lu’s group. The phospha-Michael addition of diisopropyl, dimethyl or triethyl phosphites to α, β-unsaturated malonates in the presence of those catalysts showed very good reactivity with high yield at 80–100 °C in 1–4.5 h with high catalytic recovery and reusability. With regard to significant catalytic recovery, sometimes more than eight cycles were observed for DMAP·Hsac adduct by using non-polar solvents (e.g., ether) to precipitate out the catalyst. In the case of the fluorous long-chained pyridine, the thermomorphic method was used to efficiently recover the catalyst for eight cycles in all the reactions. Thus, the easy separation of the catalysts from the products revealed the outstanding efficacy of our systems. To our knowledge, these are good examples of the application of recoverable organo-catalysts to the DMAP·Hsac adduct by using non-polar solvent and a fluorous long-chained pyridine under the thermomorphic mode in phospha-Michael addition reactions.

Chiral Imidazolidin-4-one with catalytic amount of Dicationic ionic liquid act as a recoverable and reusable Organocatalyst for asymmetric Diels-Alder reaction.

Imidazolidin-4-one is used as a recoverable organocatalyst for the asymmetric Diels-Alder reaction in the presence of catalytic amount of dicationic ionic liquid and trifluoroacetic acid as a co-catalyst. The Diels-Alder reaction between model substrate cyclopentadiene and crotonaldehyde gave the product in 95% conversion and 87% ee of the endo-product. The catalyst was shown better reusability when the 20mol% of dicationic ionic liquid was used and catalyst was reused upto 5 cycles, conversion remains upto 3 recycles but ee of endo-9 was slightly droped.

Chiral Bifunctional Thioureas and Squaramides Grafted into Old Polymers of Intrinsic Microporosity for Novel Applications.

We have prepared different polymeric chiral bifunctional thioureas and squaramides by modification of the very well-known polymers of intrinsic microporosity (PIM), specifically PIM-1 and PIM-CO-1, to be used as recoverable organocatalysts. The installation of the chiral structures into the polymers has been done in two or three steps in high yields. The catalytic activity of the resulting materials has been proved in the stereoselective nitro-Michael addition and in a cascade process, which allows the synthesis of enantioenriched 4H-chromene derivatives. Squaramide II and thiourea III have been used in six cycles maintaining their activity.

Fe3O4 magnetic nanoparticles in the layers of montmorillonite as a valuable heterogeneous nanocatalyst for the one-pot synthesis of indeno[1,2-b]indolone derivatives in aqueous media

In the present work, iron oxide nanoparticles (Fe3O4-NPs) were prepared using a chemical coprecipitation method. At room temperature, Fe3O4-NPs are put in interlamellar space and external surfaces of montmorillonite (MMT) as a supported solid. The MMT@Fe3O4 was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), vibrating sample magnetometer (VSM), thermogravimetric analysis (TGA) and Fourier transform infrared spectrophotometry (FT-IR). Then, indeno[1,2-b]indolone derivatives were catalyzed by magnetic MMT@Fe3O4-NPs. MMT@Fe3O4-NPs were found to be a recoverable organocatalyst for the effective synthesis of the indeno[1,2-b]indolone derivatives via one-pot multicomponent cyclocondensation of ninhydrin, 1,3-diketo compound and amine derivatives in water. The significant advantages of this method are excellent yield, mild conditions, eco-friendly catalyst, low expense, and not using an environmentally harmful catalyst or solvent.

Chiral Bifunctional Thioureas and Squaramides and Their Copolymers as Recoverable Organocatalysts. Stereoselective Synthesis of 2-Substituted 4-Amino-3-nitrobenzopyrans and 3-Functionalized 3,4-Diamino-4 H-Chromenes.

Novel styryl-substituted thioureas and squaramides were obtained in three steps from commercially available 4-hydroxy-3,5-dichloroaniline. These organocatalysts promote cascade reactions in high yields and excellent stereoselection. By using only a 5 mol % loading of catalyst, it is possible to obtain 2,3,4-trisubstituted benzopyrans by reaction of α-amido sulfones derived from salicyladehydes and nitrostyrenes or 2,3,4-trisubstituted 4 H-chromenes by reaction of the same α-amido sulfones with (phenylsulfonyl)acetonitrile in excellent diastereo- and enantioselectivities. Two polymeric thioureas and squaramides were prepared by copolymerization of the best monomeric catalysts with styrene and divinylbenzene and used for the same transformations. These polymers behave also as excellent stereoselective catalysts that can be recovered and reused for five cycles.

Supported and Unsupported Chiral Squaramides as Organocatalysts for Stereoselective Michael Additions: Synthesis of Enantiopure Chromenes and Spirochromanes.

Novel supported chiral bifunctional squaramides have been easily prepared starting from diamines derived from natural amino acids and commercially available aminoalkyl polystyrene resins. These squaramides behave as excellent stereoselective recoverable organocatalysts in different Michael additions, in neat conditions at room temperature. The reaction on 2-(2-nitrovinyl) phenol as electrophile lead, in excellent yields and enantioselectivities, to intermediates that can be easily transformed into 4H-chromenes, and spirochromanones.

(2S,4R)-Hyp-(S)-Phe-OMe dipeptide supported on imidazolium tagged molecules as recoverable organocatalysts for asymmetric aldol reactions using water as reaction medium

Four novel chiral imidazolium tagged molecules derived from dipeptide (2S,4R)-Hyp-(S)-Phe-OMe were prepared and evaluated as organocatalysts in the asymmetric aldol reaction using water as solvent. It was found that catalysts incorporating the hexanoyl linker are active down to 5 mol% and afford aldol products with up to 94% yield, up to 98:2 dr and up to 97:3 er. This chiral imidazolium catalyst was reused up to 6 times without any loss in the stereoselectivity of asymmetric aldol reactions. By contrast, organocatalysts containing an acetyl linker proved to be highly unstable in protic solvents, and for that reason they could not be recovered and reused.

Magnetic nanoparticles supported cinchona alkaloids for asymmetric Michael addition reaction of 1,3-dicarbonyls and maleimides

Magnetic nanoparticles Fe3O4@SiO2 supported cinchona alkaloids (quinine and quinidine) were successfully synthesized as magnetically recoverable organocatalysts and characterized by FT-IR, XPS, SEM measurements, and elemental analysis. Their catalytic activity and stereoselectivity were preliminarily evaluated in the asymmetric Michael addition reaction of 1,3-dicarbonyls and maleimides. The supported quinine catalyst exhibited good catalytic efficiency and modest to high enantioselectivity. The magnetic recoverability and recyclability of the catalyst were also examined.

Guanidine Acetic Acid Functionalized Magnetic Nanoparticles: Recoverable Green Catalyst for Transamidation

AbstractIn the presence of a catalytic amount of Fe3O4‐Guanidine acetic acid (GAA) nanoparticles, efficient transamidation of several amides with various amines is described under solvent‐free conditions. Fe3O4‐Guanidine acetic acid nanoparticles provide the first example of a magnetically recoverable organocatalyst for transamidation in the highest catalytic activity. The catalyst could be simply recycled with the assistance of an external magnet and reused for six runs without significant loss of its catalytic activity.

Design and Preparation of Polymer Resin‐Supported Proline Catalyst with Industrial Application Potential

AbstractA polymer resin‐supported proline catalyst was developed. The material might serve as an eco‐friendly recoverable organocatalyst with industrial application potential. Its catalytic activity in acetone condensation was tested. Catalyst prepared under optimized conditions showed good performances, giving mesityl oxide (MO), diacetone alcohol (DAA) and isophorone (IP) in up to 87.7 % total selectivity, while the catalyst could be recovered with less than 5 % mass lost and could be reused for at least seven times without deactivation. Being able to convert market‐excess acetone into useful bulk fine chemicals, the catalyst is of significant industrial value.

ChemInform Abstract: Rapid Conventional and Microwave‐Assisted Decarboxylation of L‐Histidine and Other Amino Acids via Organocatalysis with R‐Carvone under Superheated Conditions.

AbstractThis article reports a new methodology taking advantage of superheated chemistry via either microwave or conventional heating for the facile decarboxylation of alpha amino acids using the recoverable organocatalyst, R-carvone. The decarboxylation of amino acids is an important synthetic route to biologically active amines, and traditional methods of amino acid decarboxylation are time consuming (taking up to several days in the case of L-histidine), are narrow in scope, and make use of toxic catalysts. Decarboxylations of amino acids including L-histidine occur in just minutes while replacing toxic catalysts with green catalyst, spearmint oil. Yields are comparable to or exceed previous methods and purification of product ammonium chloride salts is aided by an isomerization reaction of residual catalyst to phenolic carvacrol. The method has been shown to be effective for the decarboxylations of a range of natural, synthetic, and protected amino acids.

Rapid Conventional and Microwave-Assisted Decarboxylation of L-Histidine and Other Amino Acids via Organocatalysis with R-Carvone Under Superheated Conditions

This article reports a new methodology taking advantage of superheated chemistry via either microwave or conventional heating for the facile decarboxylation of alpha amino acids using the recoverable organocatalyst, R-carvone. The decarboxylation of amino acids is an important synthetic route to biologically active amines, and traditional methods of amino acid decarboxylation are time consuming (taking up to several days in the case of L-histidine), are narrow in scope, and make use of toxic catalysts. Decarboxylations of amino acids including L-histidine occur in just minutes while replacing toxic catalysts with green catalyst, spearmint oil. Yields are comparable to or exceed previous methods and purification of product ammonium chloride salts is aided by an isomerization reaction of residual catalyst to phenolic carvacrol. The method has been shown to be effective for the decarboxylations of a range of natural, synthetic, and protected amino acids.

Thiourea-functionalized magnetic hydroxyapatite as a recyclable inorganic–organic hybrid nanocatalyst for conjugate hydrocyanation of chalcones with TMSCN

The recoverable nanomagnetic catalyst was manufactured based on thiourea modified magnetic hydroxyapatite. Magnetic hydroxyapatite (mHAp) as the inorganic–organic hybrid support was fabricated using co-precipitate condition and then modified via the covalently anchoring of 1-(3,5-bis(trifluoromethyl)phenyl-3-propyl)thiourea. The hybrid nano-catalyst has been identified by TEM, SEM, FTIR, BET, TGA, and XRD. This nanocatalyst appeared efficient and robust in the 1,4-addition reaction of TMSCN to α,β-unsaturated aromatic enones in excellent yields (85–96%) under mild reaction condition and simple work-up process. This recoverable organocatalyst has a great potential as an industrially viable and eco-safe catalyst.

(+)‐Cinchonine‐Decorated Dendrimers as Recoverable Organocatalysts

AbstractFirst‐ and fourth‐generation phosphorus dendrimers decorated on their surface with (+)‐cinchonine moieties for the use as organocatalysts have been prepared. The first‐generation dendrite showed the highest activity and enantioselectivity in the α‐amination of several β‐dicarbonyl compounds. A positive dendritic effect was observed. Its recovery and reuse over 10 cycles was demonstrated without loss of activity. Preliminary studies of the scope of the reaction have been performed.

N-Heterocyclic Carbenes Supported on Vinylic Addition Polynorbornene: A Recyclable and Recoverable Organocatalyst

A bromoalkyl functionalized vinylic addition polynorbornene has been used as an inert new scaffold to support imidazolium salts by straightforward nucleophilic substitution using different imidazoles ImR (R=Me, mesityl, 2,6-iPr2C6H3). These polymers, VA-PNB-(CH2)4ImRBr, are precursors of N-heterocyclic carbenes which are useful as heterogeneous organocatalysts. The polymeric carbenes have been tested in two model reactions: The synthesis of saturated esters from α,β-unsaturated aldehydes and the conjugate umpolung reaction of α,β-unsaturated aldehydes for the synthesis of γ-butyrolactones. The supported catalyst (R=mesityl) is fully recyclable and can be recovered as an imidazolium salt and stored for further use.

Chitosan decorated Fe3O4nanoparticles as a magnetic catalyst in the synthesis of phenytoin derivatives

In the present work, Fe3O4 nanoparticles were synthesized by the chemical coprecipitation process. Subsequently, the synthesized nanoparticles were modified with chitosan by a simple method and characterized by X-ray diffractometry (XRD), Fourier transform infrared spectrophotometry (FT-IR), vibrating sample magnetometry (VSM), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). Then, phenytoin derivatives were catalyzed by magnetic Fe3O4–chitosan nanoparticles. Fe3O4–chitosan nanoparticles were found to be a recoverable organocatalyst for the efficient synthesis of 5,5-diphenylhydantoins and 5,5-diphenyl-2-thiohydantoins from substituted benzils and urea or thiourea derivatives. The nanocatalyst could be recovered easily under a magnetic field for reuse, and considerable loss of its catalytic activity was not observed after reuse in seven consecutive runs.

ChemInform Abstract: Dendrimers or Nanoparticles as Supports for the Design of Efficient and Recoverable Organocatalysts?

AbstractDendrimers grafted with (S)‐α,α‐diphenylproline trimethylsilyl ether moieties are presented as organocatalysts.

ChemInform Abstract: Asymmetric Organocatalysis: From Proline to Highly Efficient Immobilized Organocatalysts

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