Class Of Organocatalysts Research Articles

Highly Selective O-Phenylene Bisurea Catalysts for ROP: Stabilization of Oxyanion Transition State by a Semiflexible Hydrogen Bond Pocket.

Organocatalyzed ring-opening polymerization (ROP) is a versatile technique for synthesizing biodegradable polymers, including polyesters and polycarbonates. We introduce o-phenylene bisurea (OPBU) (di)anions as a novel class of organocatalysts that are fast, easily tunable, mildly basic, and exceptionally selective. These catalysts surpass previous generations, such as thiourea, urea, and TBD, in selectivity (kp/ktr) by 8 to 120 times. OPBU catalysts facilitate the ROP of various monomers, achieving high conversions (>95%) in seconds to minutes, producing polymers with precise molecular weights and very low dispersities (Đ ≈ 1.01). This performance nearly matches the ideal distribution expected from living polymerization (Poisson distribution). Density functional theory (DFT) calculations reveal that the catalysts stabilize the oxyanion transition state via a hydrogen bond pocket similar to the "oxyanion hole" in enzymatic catalysis. Both experimental and theoretical analyses highlight the critical role of the semirigid o-phenylene linker in creating a hydrogen bond pocket that is tight yet flexible enough to accommodate the oxyanion transition state effectively. These new insights have provided a new class of organic catalysts whose accessibility, moderate basicity, excellent solubility, and unparalleled selectivity and tunability open up new opportunities for controlled polymer synthesis.

Organocatalytic Conversion of Nucleosides to Furanoid Glycals.

A class of organocatalysts that are highly active for the conversion of 2'-deoxynucleosides to furanoid glycals have been discovered. These phosphorimides, (Ph2PS)2NH and (Ph2PSe)2NH, were shown to effectively mediate persilylation of 2'-deoxynucleosides allowing the elimination of the nucleobase giving the corresponding glycal. These mild conditions were demonstrated in the syntheses of glycals with various substitution patterns while minimizing the formation of undesired byproducts and expanding the scope of this methodology.

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.

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.

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

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: 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.

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.

ChemInform Abstract: Chiral Quaternary Phosphonium Salts: A New Class of Organocatalysts

AbstractReview: 50 refs.

Chiral microspheres constructed by helical substituted polyacetylene: A new class of organocatalyst toward asymmetric catalysis

This article reports the first microspheres consisting of helical substituted polyacetylene and showing interesting asymmetric catalysis ability. For preparing such chiral microspheres, two acetylene-based monomers, M1L with l-proline pendant group and MA, underwent precipitation copolymerization in the presence of rhodium catalyst in a solvent mixture of butanone/n-heptane. Regular microspheres (approx. 1μm in diameter) were successfully prepared under suitable conditions. According to CD and UV spectroscopy measurements, the microspheres exhibit considerable optical activity, resulting from the substituted polyacetylene chains adopting helical structures of preferred one-handed screw sense. The microspheres were used as a chiral organocatalyst to heterogeneously catalyze the asymmetric Aldol reaction of p-nitrobenzaldehyde and cyclohexanone in aqueous media. Remarkable catalytic efficiency was obtained (yield 76% and ee 80%). After catalysis, the microspheres can be easily recovered. The methodology created in this study provides opportunities for developing a new class of chiral polymer organocatalyst.

Chiral quaternary phosphonium salts: a new class of organocatalysts

Phase-transfer catalysis has widely been used as a prime synthetic tool for both laboratory and industrial processes. During the last twenty years, asymmetric phase-transfer catalysis using chiral organocatalysts has attracted widespread interest. However, the scope of chiral phase-transfer catalysis has been limited mostly to the quaternary ammonium salts. As an emerging area, the recent developments in the application of quaternary phosphonium salts as chiral phase-transfer catalysts are discussed in this article.

Development of an N-sulfinyl prolinamide for the asymmetric aldol reaction

A new class of organocatalysts is reported that incorporates an N-sulfinyl amide in place of the carboxylic acid of proline to serve as a hydrogen bond donor, chiral directing group, and solubilizing element. The successful application of this type of catalyst to the asymmetric aldol reaction of acetone and aryl aldehydes, for which proline performs poorly, is also described.

One-step, efficient synthesis of combined threonine–surfactant organocatalysts for the highly enantioselective direct aldol reactions of cyclic ketones with aromatic aldehydes in the presence of water

In this work, a new class of organocatalysts have been designed and synthesized in one step by a rational combination of threonine with acyl chlorides at room temperature in trifluoroacetic acid to make a series of novel combined threonine-surfactant organocatalysts readily available on a large-scale. No protecting groups or chromatographic techniques are involved in the procedures, while certain combined threonine-surfactant organocatalysts mediate the direct aldol reactions of cyclic ketones with aromatic aldehydes to provide the aldol products in good yields with enantioselectivities of up to 99%.

ChemInform Abstract: Pyrrolidinyl-Camphor Derivatives as a New Class of Organocatalyst for Direct Asymmetric Michael Addition of Aldehydes and Ketones to β-Nitroalkenes.

ChemInform Abstract: Pyrrolidinyl-Camphor Derivatives as a New Class of Organocatalyst for Direct Asymmetric Michael Addition of Aldehydes and Ketones to β-Nitroalkenes.