Chiral Quaternary Ammonium Research Articles

Chiral Ammonium Betaines: A Bifunctional Organic Base Catalyst for Asymmetric Mannich-Type Reaction of α-Nitrocarboxylates

A chiral ammonium betaine, an intramolecular ion-pairing quaternary ammonium aryloxide 3, has been designed and its vast potential as an enantioselective organic base catalyst has been successfully demonstrated in the highly enantioselective direct Mannich-type reaction of alpha-substituted alpha-nitrocarboxylates 2 with various N-Boc imines 1. The present study provides a conceptually new approach toward the design of bifunctional, chiral quaternary ammonium salts and their utilizations as a homogeneous organic molecular catalyst.

Enantioselective nucleophilic difluoromethylation of aromatic aldehydes with Me3SiCF2SO2Ph and PhSO2CF2H reagents catalyzed by chiral quaternary ammonium salts.

BackgroundAlthough the nucleophilic difluoromethylation of aldehydes, ketones, and imines has been realized with PhSO2CF2H and related reagents, there are still no reports on the enantioselective nucleophilic reactions.ResultsWith a chiral quaternary ammonium salt as the catalyst and KOH as the base, we describe the first enantioselective difluoromethylation of aromatic aldehydes with PhSO2CF2H or Me3SiCF2SO2Ph. The enantioselectivity is substrate-dependent and for 2-chlorinated benzaldehyde an ee up to 64% was obtained.ConclusionThese results provide some insights into the enantioselective nucleophilic difluoromethylation chemistry, which will stimulate further progress in this field.

ChemInform Abstract: Enantioselective Trifluoromethylation of Ketones with (Trifluoromethyl)trimethylsilane Catalyzed by 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 of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Organocatalytic Asymmetric Conjugate Addition to Allenic Esters and Ketones

The first example of an organocatalytic enantioselective conjugate addition of cyclic beta-ketoesters and glycine imine derivatives to electron-deficient allenes is described. We disclose that the corresponding chiral beta,gamma-unsaturated carbonyl compounds are formed exclusively under phase-transfer conditions using either cinchona-alkaloid-derived or biphenyl-based chiral quaternary ammonium salts as catalysts. The scope of the reaction for beta-ketoesters is outlined for allenes having a ketone or ester motif as electron-withdrawing group as well as different substituents in the 3-position, giving the optically active products in high yields and excellent diastereo- and enantioselectivities (90-96% ee). The conjugate addition also proceeds for a number of cyclic beta-ketoesters having different ring sizes, ring systems, and substituents in high yields and enantioselectivities. Glycine imine derivatives also undergo the asymmetric conjugate addition to electron-deficient allenes in high yields and with enantioselectivities in the range of 60-88% ee, thus providing a rapid entry to optically active alpha-vinyl-substituted alpha-amino acid derivatives. It is shown that the enantioselectivity is strongly dependent on the size of the ester moiety of the nucleophile in combination with the catalytic system used. The high synthetic value of the chiral products arising from these new catalytic processes is demonstrated by two straightforward transformations leading in one case to optically active hexahydrobenzopyranones and in the other to substituted pyroglutamates (gamma-lactames).

ChemInform Abstract: Enantioselective Cyanoformylation of Aldehydes Catalyzed by a Chiral Quaternary Ammonium Salt and Triethylamine.

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.

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.

Asymmetric Trifluoromethylation of Ketones with (Trifluoromethyl)trimethylsilane Catalyzed by 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.

Practical Stereoselective Synthesis of β-Branched α-Amino Acids through Efficient Kinetic Resolution in the Phase-Transfer-Catalyzed Asymmetric Alkylations

Phase-transfer-catalyzed alkylation of glycinate Schiff base with racemic secondary alkyl halides proceeded with excellent levels of syn- and enantioselectivities under the influence of chiral quaternary ammonium bromide 1d and 18-crown-6. The alkylation product can be selectively converted to the corresponding anti isomer, allowing the preparation of all the stereoisomers of beta-alkyl-alpha-amino acid derivatives, an extremely valuable chiral building block.

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.

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.

Enantioselective Cyanoformylation of Aldehydes Catalyzed by a Chiral Quaternary Ammonium Salt and Triethylamine

An efficient enantioselective cyanoformylation of aldehydes with ethyl cyanoformate, catalyzed by a chiral quaternary ammonium salt and triethylamine, has been developed. The reaction can be carried out in excellent yields (up to 97%) with moderate enantioselectivity (up to 72% ee).

Design of C2-Symmetric Chiral Phase-transfer Catalysts for Practical Asymmetric Synthesis

A series of structurally rigid, chiral quaternary ammonium salts derived from commercially available (S)- or (R)-1,1?-bi-2-naphthol have been designed as new C2-symmetric chiral phase-transfer catalysts. These chiral organocatalysts have been successfully applied to the highly practical asymmetric synthesis of useful organic molecules including amino acid derivatives.

Polymeric chiral phase-transfer catalysts derived from cinchona alkaloids for enantioselective synthesis of α-amino acids

A series of dimeric/trimeric chiral quaternary ammonium salts derived from cinchona alkaloids were designed as efficient and practical chiral phase-transfer catalysts (PTCs). Presented are the details on the development of the dimeric PTCs for the synthesis of optically active α-amino acid derivatives and the optimization of the reaction variables suitable for the dimeric PTCs. The 1,3-phenyl- and the 2,7-naphthyl-linked dimeric PTCs showed excellent catalytic capability on the reactivity and enantioselectivity in the catalytic phase-transfer alkylation of N-(diphenylmethylene)glycine tert-butyl ester ( 1). A variety of α-amino acid derivatives were obtained with high enantiopurities using the dimeric PTCs, especially the 2,7-naphthyl-dimer 41, in a very practical manner.

Enantioselective trifluoromethylation of aromatic aldehydes catalyzed by combinatorial catalysts

A new combinatorial catalyst system containing the disodium ( R)-binaphtholate prepared in situ and a chiral quaternary ammonium salt was developed for enantioselective trifluoromethylation of aromatic aldehydes in up to 71% ee. A possible intermediate for the binaphtholate activation of the TMSCF 3 and a catalytic cycle were proposed based on the experiments.

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

Abstract Asymmetric trifluoromethylation of ketones with (trifluoromethyl)trimethylsilane catalyzed by cinchonidine-derived quaternary ammonium phenoxides proceeded smoothly to afford the trifluoromethylated compounds in high yields with moderate to high enantioselectivities.

Enantioselective Radical Addition Reactions to the C=N Bond Utilizing Chiral Quaternary Ammonium Salts of Hypophosphorous Acid in Aqueous Media.

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.

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.

Diastereo‐ and Enantioselective Synthesis of 3‐Amino‐3,4‐dihydropyran‐2‐ones by Tandem Michael Addition and Lactonization Using a Chiral Quaternary Ammonium Phenoxide.

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.

Enantioselective desymmetrization of meso- N-sulfonylaziridines with thiols

Desymmetrization of meso- N-sulfonylaziridines with thiols was realized using cinchonine-derived chiral quaternary ammonium salts as the catalyst. The corresponding chiral thio amines were provided in high yields (80–99%) and in good enantioselectivities (40–73% ee).

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.