Asymmetric Organocatalysts Research Articles

An Organocatalytic Synthesis of cis‐N‐Alkyl‐ and N‐Arylaziridine Carboxylates

AbstractAn extremely mild protocol that employs readily available starting materials, i.e., aldehyde, amine and alkyl diazoacetate, returns structurally diverse N‐substituted‐C‐2/3‐difunctionalised aziridines in excellent yields and stereoselectivities when pyridinium triflate is incorporated as an organocatalyst. The reaction process is environmentally benign affording water and nitrogen as the only by‐products. This racemic protocol paves the way for the development of novel asymmetric organocatalysts capable of generating optically active aziridines.

ChemInform Abstract: Functionalized Chiral Ionic Liquids: A New Type of Asymmetric Organocatalysts and Nonclassical Chiral Ligands

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Functionalized Chiral Ionic Liquids: A New Type of Asymmetric Organocatalysts and Nonclassical Chiral Ligands

By judiciously anchoring functional groups onto chiral ionic liquids, functionalized chiral ionic liquids (FCILs) are emerging as a new type of asymmetric organocatalysts and nonclassical chiral ligands. This Focus Review highlights the applications of FCILs from the viewpoint of asymmetric catalysis. We focus mainly on the de novo designed and synthesized FCILs which likely still maintain the typical ionic liquids properties, and in a few cases relevant ionic liquid immobilized chiral catalysts are briefly discussed.

Synthesis of functional poly(phenyl isocyanide)s with macromolecular helicity memory and their use as asymmetric organocatalysts

To develop a novel polymer-based asymmetric organocatalyst, a series of helical poly(phenyl isocyanide)s with functional pendant groups were prepared by modifying the side groups of the optically active helical poly(4-carboxyphenyl isocyanide) with a macromolecular helicity memory. Helical polyisocyanides partially modified with achiral amines, such as piperazine, maintained their chiral memory and enantioselectively catalyzed a direct aldol reaction. Although the enantioselectivity was low, the original helical poly(4-carboxyphenyl isocyanide) showed no catalytic activity. These results indicated that the macromolecular helicity of the modified polyisocyanides together with bifunctional amino and carboxy acid pendant residues arranged in a helical array along the polymer backbones plays an important role in the enantioselectivity.

Molecular-Sieves Controlled Diastereo- and Enantioselectivity: Unexpected Effect in the Organocatalyzed Direct Aldol Reaction

An efficient asymmetric organocatalyst was developed for the direct aldol reaction between ketones and aldehydes to afford β-hydroxy ketones in high stereoselectivity ( ANTI/ SYN up to 92:8, ee up to <99%). The key of the success was the use of activated molecular sieves (4 A MS), which acted as a water scavenger. The influence of additives such as water or different types of molecular sieves on the reactivity and stereoselectivity of the reaction was also studied.

Noncovalently Supported Heterogeneous Chiral Amine Catalysts for Asymmetric Direct Aldol and Michael Addition Reactions

A new strategy for the immobilization of asymmetric organocatalysts by combining polystyrene (PS)/sulfonic acids and chiral amines in situ through acid-base interactions is presented. The PS/sulfonic acids play a dual role as catalyst anchors and modulators for activity and stereoselectivity. Different types of polymeric sulfonic acids were examined and 1% divinylbenzene (DVB) cross-linked PS/sulfonic acid 1 e with a medium loading of sulfonic acid moieties was found to be the optimal support. Furthermore, the noncovalency of this system allows combinatorial screening of optimal catalysts for the targeted reactions. In this regard, highly efficient and enantioselective heterogeneous catalysts were identified for the asymmetric direct aldol and Michael addition reactions. The catalysts could be easily recovered by filtration and reused for six cycles with similar stereoselectivity but slightly decreased activity. Significantly, the deactivated catalysts could be regenerated following an acidic washing/amine recharging procedure.

Three and Counting

Three and Counting

Enantioselective Trifluoromethylation of Ketones with (Trifluoromethyl)trimethylsilane Catalyzed by Chiral Quaternary Ammonium Phenoxides

Abstract Chiral quaternary ammonium phenoxides were prepared readily from commercially available cinchona alkaloids and employed as novel useful asymmetric organocatalysts. Among these chiral quaternary ammonium phenoxides, a cinchonidine-derived phenoxide that possesses a sterically hindered N(1)-3,5-bis[3,5-bis(trifluoromethyl)phenyl]benzyl group was the most effective for asymmetric trifluoromethylation. In the presence of a catalytic amount of Lewis bases, such as cinchonidine-derived quaternary ammonium phenoxides, catalyzed the reaction of various ketones with (trifluoromethyl)trimethylsilane to afford the corresponding trifluoromethylated adducts in high yields and with moderate to high enantioselectivities.

Chiral Ionic Liquid Containing L‐Proline Unit as a Highly Efficient and Recyclable Asymmetric Organocatalyst for Aldol Reaction.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Facile evolution of asymmetric organocatalysts in water assisted by surfactant Brønsted acids

Simple mixing of chiral amines and surfactant Brønsted acids such as p-dodecyl benzenesulfonic acid (DBSA) leads to highly effective and selective organocatalysts in water. The in situ generated catalysts catalyze highly stereoselective desymmetrization of prochiral ketones via direct aldol reactions (up to >16:1 dr, >99% ee) in water using micelle as reaction media. The current strategy was also applied in asymmetric Michael addition leading to a catalytic system with good activity and stereoselectivity.

Chiral Ionic Liquid Containing l-Proline Unit as a Highly Efficient and Recyclable Asymmetric Organocatalyst for Aldol Reaction

Abstract A functionalized chiral ionic liquid (CIL) containing l-proline unit exhibits as a highly efficient and recyclable asymmetric organocatalyst for aldol condensation of aldehydes and ketones in [Bmim][BF4] at room temperature, which afford the corresponding products with satisfactory isolated yields and enantiomeric excesses.

Enantioselective Synthesis of 3,4‐Dihydropyran‐2‐ones by Domino Michael Addition and Lactonization with New Asymmetric Organocatalysts. Cinchona‐Alkaloid‐Derived Chiral Quaternary Ammonium Phenoxides.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Evolution of Pyrrolidine‐Type Asymmetric Organocatalysts by “Click” Chemistry.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Surfactant‐Type Asymmetric Organocatalyst: Organocatalytic Asymmetric Michael Addition to Nitrostyrenes in Water.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Efficient Synthesis of Substituted 3-Amino-3,4-dihydropyran-2-ones Diastereo and Enantioselective Tandem Michael Addition and Lactonization between α,β-Unsaturated Ketones and Glycine-Derived Silyl Enolates Using a Chiral Quaternary Ammonium Phenoxide

Chiral quaternary ammonium phenoxides are readily prepared from commercially available cinchona alkaloids and are employed as useful new asymmetric organocatalysts. The cinchonidine-derived catalyst is highly effective on Michael addition and successive lactonization between glycine-derived silyl enolates and α,β-unsaturated ketones. According to this asymmetric reaction, the corresponding 3-amino-3,4-dihydropyran-2-ones are formed in high yields with complete diastereoselectivities and excellent enantioselectivities.

Enantioselective Synthesis of 3,4‐Dihydropyran‐2‐ones by Domino Michael Addition and Lactonization with New Asymmetric Organocatalysts: Cinchona‐Alkaloid‐Derived Chiral Quaternary Ammonium Phenoxides

Chiral quaternary ammonium phenoxides were readily prepared from commercially available cinchona alkaloids and proved to be useful new asymmetric organocatalysts. Among various chiral quaternary ammonium phenoxides, a cinchonidine-derived catalyst that bears both a sterically hindered N1-9-anthracenylmethyl group and a strongly electron withdrawing 9-O-3,5-bis(trifluoromethyl)benzyl group were found to be highly effective for the Michael addition of ketene silyl acetals (derived from phenyl carboxylates) and alpha,beta-unsaturated ketones followed by lactonization. Optically active 3,4-dihydropyran-2-one derivatives were obtained in high yields with excellent control of enantio- and diastereoselectivity. This catalyst can be handled in air and stored at room temperature in a sealed bottle without decomposition for at least one month.

Evolution of Pyrrolidine-Type Asymmetric Organocatalysts by “Click” Chemistry

Click chemistry has been employed to construct a library of the pyrrolidine-type asymmetric organocatalysts. The clicked organocatalysts were evaluated in asymmetric Michael addition of ketones to nitroolefins, showing good catalytic activity and stereoselectivity (up to 100% yield, syn:anti = 99:1, 96% ee).

Functionalized Chiral Ionic Liquids as Highly Efficient Asymmetric Organocatalysts for Michael Addition to Nitroolefins.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Functionalized Chiral Ionic Liquids as Highly Efficient Asymmetric Organocatalysts for Michael Addition to Nitroolefins

Catalytic combination: By combining the advantages of organocatalysts and ionic liquids, a functionalized chiral ionic liquid such as 1 can act as a highly efficient and reusable organocatalyst for the asymmetric Michael addition reaction of ketones and aldehydes with nitroalkenes.

Functionalized Chiral Ionic Liquids as Highly Efficient Asymmetric Organocatalysts for Michael Addition to Nitroolefins

Functionalized Chiral Ionic Liquids as Highly Efficient Asymmetric Organocatalysts for Michael Addition to Nitroolefins