New Class Of Organocatalysts Research Articles

Zwitterionic imidazolium salt: an effective green organocatalyst in synthetic chemistry

Abstract An environmentally benign, stable yet efficient organocatalyst is highly desirable from the viewpoint of green chemistry and catalysis. Imidazole-based zwitterionic-type molten salts are a new type of organocatalysts with high catalytic application in various organic transformations with added advantage of room temperature ionic liquid (RTIL) property. Most importantly, these ionic-liquid catalysts are easily recyclable and subsequently reusable for multiple times without loss of significant catalytic efficiency. It has also been evident that C2–H of the imidazole has a vital role in catalyzing the reaction via electrophilic activation. Moreover, by changing the cations and/or anions, the properties of ILs can be tuned in many ways. In this article, the role of imidazolium zwitterionic molten salts as an organocatalyst for selective organic transformations including syn-selective aza-Henry reaction, Erlenmeyer reaction, synthesis of different heterocycles and their functionalization and regioselective ring-opening reactions has been elaborated chronically which will definitely be helping to the readers to explore this new class of organocatalyst for further applications.

Theoretical designing and understanding of the performances of BH bridged organocatalysts by π‐conjugated molecules in CO2 hydroboration

AbstractDesigning and introducing a new class of organocatalysts in CO2 hydroboration are the main purposes of this study. Reduction is an essential reaction in the conversion of CO2 into value‐added materials. The first part of this research is focused on organocatalyst designing, which is performed by a reaction between some of the π‐conjugated molecules and borane. This step produces a bridged structure for the developed organocatalysts (BH bridged organocatalysts). π contributions of electron localized function (ELFπ) and nucleus‐independent chemical shift (NICSπZZ) analyses are valuable for understanding and justifying the calculated ∆G≠ and ∆E≠ values of the organocatalysts formation step. In the second part of this research, CO2 reduction was investigated using designed BH bridged organocatalysts. The reduction reaction can proceed through two different barrier energies. The results revealed that, among 9‐borabicyclo[3.3.1]nonane (9‐BBN) and BH2 segments of the BH bridged organocatalysts, hydride transfer of 9‐BBN moiety is more favorable kinetically. Finally, kinetic studies of CO2 hydroboration using the energetic span model (ESM) showed that the barrier energy of CO2 reduction is the rate‐determining step of the reduction reaction.

Evaluation and understanding the performances of various derivatives of carbonyl-stabilized phosphonium ylides in CO2 transformation to cyclic carbonates.

The kinetic and mechanism evaluations of the formation of cyclic carbonates by carbonyl-stabilized phosphonium ylides as an efficient and new class of organocatalysts are the main purposes of this research. Recently, it has been reported that tetraarylphosphonium salts play the role of organocatalysts in carbon dioxide conversion to cyclic carbonates. However, in this research, the oxygen atom of the carbonyl-stabilized phosphonium ylides was treated as the nucleophilic atom for the carbon dioxide activation. Two probable mechanisms were considered and analyzed by the energetic span model. The kinetic behavior of the carbonyl-stabilized phosphonium ylides in the carbon dioxide or ethylene oxide activation was justified by the molecular electrostatic potential (ESP) analysis at the nuclear position. However, it was confirmed that the activation strain model (ASM) was a more efficient tool in explaining the kinetic behaviors in the carbon dioxide or ethylene oxide activation. A change in the ESP value of the donor-acceptor interacting system (ΔΔVn) and distortion energy at the transition states (ΔEstrain(ζ)) were the outcomes of the ESP and ASM models, respectively, which showed a linear correlation. The electron localization function (ELF) concept was used to justify the kinetic behavior of the second step of the preferred mechanism, revealing that the electron-donating/withdrawing groups substituted on the organocatalysts have a remarkable effect on the electron density of the involved basin at the transition states. On the basis of different analyses, it was proposed that carbonyl-stabilized phosphonium ylides having electron-donating substituents are the best candidates for carbon dioxide conversion to cyclic carbonates.

Synthesis of [6]helicene-based sulfonic acid, sulfonamide, and disulfonimides

The synthesis of helically chiral [6]helicene-based sulfonic acid and sulfonamide from enantiomerically pure 1-acetylthio-5,6,9,10-tetrahydro[6]helicene is reported. The first helically chiral disulfonimides were developed as a synthetic application of [6]helicene-based sulfonamide. This new class of organocatalysts was tested in an asymmetric Mukaiyama aldol reaction to obtain up to quantitative yields and enantioselectivities up to 24%.

Highly Asymmetric Aldol Reaction of Cyclohexanone and Aromatic Aldehydes Catalyzed by Bifunctional Cyclohexane Derived Thiourea Organocatalyst

Novel two L-proline analogues as thiourea organocatalysts were synthesised, first is the assembly of a structurally well-defined cyclohexane scaffold with a thiourea moieties and amine functionalities could constitute a new class of organocatalysts. Second is the triazole-3-thione analogue. The first one found to be efficient catalysts for the direct asymmetric aldol reaction between ketone and aromatic aldehydes. The catalysts exhibited high catalytic activity, diastereoselectivity and excellent enantioselectivity at room temperature with a low loading.

Monofunctional primary amine: A new class of organocatalyst for asymmetric Aldol reaction

A new class of organocatalysts involving a primary amine as the only functional group is developed for catalytic asymmetric aldol reaction of cyclohexanone/cyclopentanone with various aryl aldehydes in the presence of benzoic acid as an additive at −10∘C. In an unexpected observation, the primary amine catalyzed reactions gave excellent yield and good to excellent stereoselectivity, while secondary amines were found to have little or no reactivity under similar reaction conditions. A new class of aminocatalysts with a primary amine as the only catalytically active functional group was developed for catalytic asymmetric aldol reaction of cyclohexanone/cyclopentanone with various aryl aldehydes in the presence of benzoic acid as an additive at -10oC under neat conditions.

Tertiary amines: A new class of highly efficient organocatalysts for CO2 fixations

To realize a true green CO2 utilization process, the development of a catalytic system having no toxic components is essential. Herein, tertiary amines without any metal or halide additives are introduced as simple and green organocatalysts to activate CO2 and insert into epoxides, producing synthetically important cyclic carbonates. Among those amines, diamine such as N,N,N′,N′-tetraethylethylenediamine exhibited a moderate to excellent efficiency. This new class of organocatalyst which does not have any toxic metals and halides is easy to handle and only requires as low as a 0.1mol% loading. Additional favorable features include solvent free conditions and broad substrate scopes.

ChemInform Abstract: Zwitterionic Imidazolium Salt: Recent Advances in Organocatalysis

AbstractReview: [50 refs.

ChemInform Abstract: The Resurgence of the Highly Ylidic N‐Heterocyclic Olefins as a New Class of Organocatalysts

AbstractReview: [22 refs.

Zwitterionic Imidazolium Salt: Recent Advances in Organocatalysis

Imidazole-based zwitterionic-type molten salts have been explored as a new class of organocatalyst in various chemical transformations. It is known that imidazolium motifs provide an unconventional C–H bond for bonding. It is experimentally proven that C2–H of the imidazole moiety plays a crucial role in catalyzing the reaction via electrophilic activation. This review is based on the role of imidazole-based zwitterionic-type molten salts as an organocatalyst for some useful chemical transformations in organic synthesis. One of the most important features of this catalyst is that it can easily be recovered from the reaction media. The recovered catalyst can be reused for subsequent reactions without losing its catalytic activity significantly. 1 Introduction 2 Zwitterionic-type Molten Salt Catalyzed syn-Selective Aza-Henry Reaction 3 Synthesis of 1-(Amidoalkyl)- and 1-(Carbamatoalkyl)-2-naphthols 4 Synthesis of 3-Aminoalkylated Indoles 5 Synthesis of Highly Substituted Imidazoles 6 Synthesis of 5-Substituted 1H-Tetrazoles by the Cycloaddition of Arenecarbonitriles with Sodium Azide 7 Synthesis of 4-Arylidene-2-phenyloxazol-5(4H)-ones 8 Zwitterion-Promoted Ethylene Methoxycarbonylation 9 Synthesis of 5,6-Unsubstituted 1,4-Dihydropyridines 10 Regioselective Ring Opening of Aziridines 11 Conclusions

The Resurgence of the Highly Ylidic N-Heterocyclic Olefins as a New Class of Organocatalysts.

In recent decades, N-heterocyclic carbenes have become established as a prevalent family of organocatalysts. N-Heterocyclic olefins, the alkylidene derivatives of N-heterocyclic carbenes, have recently also emerged as efficient promoters for CO2 fixation and polymerization reactions. Their extraordinarily strong Lewis/Brønsted basicity suggests great potential as a new class of organocatalysts for a broad range of reactions in synthetic chemistry.

ChemInform Abstract: A New Class of Organocatalysts: Sulfenate Anions.

AbstractIt is proposed that sulfenate anions generated from sulfoxides act as catalysts in the base promoted conversion of benzyl halides into trans‐stilbenes.

A New Class of Organocatalysts: Sulfenate Anions

AbstractSulfenate anions are known to act as highly reactive species in the organic arena. Now they premiere as organocatalysts. Proof of concept is offered by the sulfoxide/sulfenate‐catalyzed (1–10 mol %) coupling of benzyl halides in the presence of base to generate trans‐stilbenes in good to excellent yields (up to 99 %). Mechanistic studies support the intermediacy of sulfenate anions, and the deprotonated sulfoxide was determined to be the resting state of the catalyst.

A new class of organocatalysts: sulfenate anions.

Sulfenate anions are known to act as highly reactive species in the organic arena. Now they premiere as organocatalysts. Proof of concept is offered by the sulfoxide/sulfenate-catalyzed (1-10 mol%) coupling of benzyl halides in the presence of base to generate trans-stilbenes in good to excellent yields (up to 99%). Mechanistic studies support the intermediacy of sulfenate anions, and the deprotonated sulfoxide was determined to be the resting state of the catalyst.

ChemInform Abstract: Amino Oxazolines as a New Class of Organocatalyst for the Direct Intermolecular Asymmetric Aldol Reaction Between Acetone and Aromatic Aldehydes.

AbstractThe synthesis of chiral amino oxazolines is described and the utility of the products is demonstrated in the asymmetric aldol reaction of acetone with reactive carbonyl compounds.

ChemInform Abstract: Terpene‐Derived Bifunctional Thioureas in Asymmetric Organocatalysis

AbstractReview: 110 refs.

ChemInform Abstract: New Glycosyl‐α‐aminotetrazole‐based Catalysts for Highly Enantioselective Aldol Reactions.

Direct aldol reactions of acetone with aromatic aldehydes have been achieved in high yielding and enantioselective processes using glycosyl-α-aminotetrazoles as a new class of organocatalysts. Computational studies at DFT level have been performed to account for the experimental observations.

Amino oxazolines as a new class of organocatalyst for the direct intermolecular asymmetric aldol reaction between acetone and aromatic aldehydes

A series of chiral amino oxazolines were synthesized and screened as organocatalysts for asymmetric intermolecular aldol reactions between acetone and aromatic aldehydes. The reaction works well with a range of aromatic aldehydes showing good to high selectivity. The present new system of the organocatalyst was effective for the asymmetric aldol reaction for a wide range of aromatic aldehydes and isatin to carry out an asymmetric carbon–carbon bond forming reaction with a high enantioselectivity of up to 91%.

New glycosyl-α-aminotetrazole-based catalysts for highly enantioselective aldol reactions

Direct aldol reactions of acetone with aromatic aldehydes have been achieved in high yielding and enantioselective processes using glycosyl-α-aminotetrazoles as a new class of organocatalysts. Computational studies at DFT level have been performed to account for the experimental observations.

Terpene‐Derived Bifunctional Thioureas in Asymmetric Organocatalysis

AbstractChiral hydrogen‐bond donors have played a crucial role in the progress of asymmetric catalysis as an essential tool in modern organic synthesis. Among these donors, thioureas have been found to be one of the most powerful systems in organocatalytic approaches. Within the last three years, a new generation of bifunctional thiourea catalysts has emerged as an effective way to promote highly demanding chemical transformations, frequently with success rates that are intriguingly higher than with other traditional thioureas. This new class of organocatalysts incorporates a bulky, rigid, and chiral terpene skeleton as one of the thiourea substituents, thus providing an additional and effective rigidifying (entropic) effect on the electrophile activation profile of thioureas. Structural integrations, either with additional Lewis basic nucleophile‐activating motifs or with amino groups for enamine catalysis, have enabled their implementation in a wide repertoire of stereocontrolled catalytic processes. This Review charts the development of these new catalysts, as well as their applications in a wide variety of reactions and reaction sequences, with the hope of encouraging further progress in the field of thiourea‐catalyst discovery and of bringing attention to the countless possibilities that are opened up by the tremendous success of terpene‐derived thiourea catalysts.