Chiral Phase Transfer Research Articles

ChemInform Abstract: Highly Practical Amino Acid and Alkaloid Synthesis Using Designer Chiral Phase Transfer Catalysts as High‐Performance Organocatalysts

AbstractReview: 28 refs.

Highly enantioselective asymmetric Darzens reactions with a phase transfer catalyst

A class of easily accessible and readily tunable chiral phase transfer catalysts based on 6'-OH cinchonium salts was found to efficiently catalyze an unprecedented highly enantioselective Darzens reaction of α-chloro ketones and aldehydes, which directly produces optically active chiral epoxides from readily available carbonyl compounds.

Studies in Asymmetric Epoxidation of Chalcone Using Quaternary Salts and Nonionic Surfactants Based on 6‐Amino‐6‐deoxy‐glucose as Chiral Phase Transfer Catalysts

Quaternary salts and nonionic surfactants based on 6‐amino‐6‐deoxy‐glucose were explored as chiral phase transfer catalysts for the asymmetric epoxidation of chalcone. Quaternary salts used in the present study, were void of any branched chain or long hydrocarbon chain, whereas the sugar based nonionic surfactants have a long hexadecyl moiety as tail. It was observed that quaternary salts showed no activity as phase transfer catalysts but sugar based nonionic surfactants acted as chiral phase transfer catalysts. It was also revealed that hydrophilicity of the surfactant favors more yield whereas stereochemistry governs enantioselectivity. (6,6′‐Hexadecylimino) bis(6‐deoxy‐1,2‐O‐isopropylidene‐α-D‐glucofuranose) was found to be the most suitable chiral phase transfer catalyst, resulting asymmetric epoxidation of chalcone with 90% yield and 16.5% enantiomeric excess (ee).

Highly practical amino acid and alkaloid synthesis using designer chiral phase transfer catalysts as high‐performance organocatalysts

A series of chiral quaternary ammonium salts derived from commercially available (R)- or (S)-binaphthol have been designed as new C(2)-symmetric chiral phase transfer catalysts. In order to realize the flexible design of these phase transfer catalysts, the combinatorial design approach has been developed. These chiral high-performance organocatalysts have been successfully applied to the highly practical asymmetric synthesis of various amino acid derivatives including α-alkyl and α,α-dialkyl-α-amino acids in addition to alkaloids.

ChemInform Abstract: Synthesis of Novel Chiral Crown Ethers Derived from D-Glucose and Their Application to an Enantioselective Michael Reaction.

New chiral monoaza-15-crown-5 derivatives anellated to methyl 4,6-di-O-butyl-α-D-glucopyranoside have been synthesized from 1 using the 4,6-O-benzylidene protecting group (removed by acetic acid) and 2,3-di-O-benzyl groups (removed by catalytic hydrogenolysis). The alkylation of the hydroxy groups in 1 and 5 with benzyl chloride and bis(2-chloroethyl) ether, respectively, were carried out in two-phase reactions using phase-transfer (PT) catalysts. These sugar-based crown ethers showed significant asymmetric induction as chiral PT catalysts in the Michael addition of 2-nitropropane to chalcone (90% ee). The substituent at the nitrogen atom of the crown ethers has a major influence on both the chemical yield and the enantioselectivity.

Chiral bifunctional phase transfer catalysts for asymmetric fluorination of β-keto esters

Chiral bifunctional phase transfer catalysts introducing bis(diarylhydroxymethyl) substituents at 3,3'-positions of the chiral binaphthyl core were successfully applied to asymmetric fluorination of cyclic beta-keto esters with high enantioselectivities.

ChemInform Abstract: Binaphthyl‐Modified Quaternary Phosphonium Salts as Chiral Phase Transfer Catalysts: Application to Asymmetric Amination of β‐Keto Esters.

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.

Design of Sophisticated Bidentate Lewis Acids and Organocatalysts for Fine Organic Synthesis

Abstract Apart from enzymes as biocatalysts, a broad repertoire of chiral reagents, auxiliaries, and catalysts have been developed in recent years. In this respect, the design of new catalysts and new reactions in an efficient manner is increasingly important in this century for the construction of new and useful molecules. Accordingly, by designing and synthesizing sophisticated metal and non-metal catalysts, hitherto unattainable, unusual reactivity and selectivity is pursued in synthetic organic reactions. For example, the rational design of designer Lewis acids, particularly bidentate Lewis acid catalysts and their application to selective organic synthesis is carried out. In addition, the design of chiral phase transfer catalysts, chiral bifunctional organocatalysts, and chiral Brønsted acid catalysts as promising organocatalysts is realized for their application to practical asymmetric synthesis.

Binaphthyl-Modified Quaternary Phosphonium Salts as Chiral Phase Transfer Catalysts: Application to Asymmetric Amination of β-Keto Esters

A chiral quaternary tetraalkylphosphonium salt has been successfully utilized for the first time as a phase-transfer catalyst for asymmetric amination of β - keto esters in high yield with high ee. Asymmetric amination of a cyclic five-membered β-veto ester is a valuable method for preparing a key intermediate for asymmetric synthesis of aldose reductase inhibitor AS-3201 (Ranirestat).

Synthesis of Novel Chiral Phase-Transfer Catalysts and Their Application to Asymmetric Synthesis of α-Amino Acid Derivatives

To investigate the electronic and steric influences on enantioselectivities of asymmetric phase-transfer reactions, a series ofchiral quaternary ammonium salts were synthesized from cinchona alkaloids and 2-chloromethylbenzimidazole or 1-chloromethyl benzotriazole. Using one of the cinchonine-derived alkaloid catalysts, enantioselective alkylations of N-(diphenylmethylene) glycine tert-butyl ester were efficiently carried out with various alkyl halides to give products in high enantiomeric excess (94-99% ee).

Rate Enhancement of Phase Transfer Catalyzed Conjugate Additions by CsCl

A rate enhancement of phase transfer catalyzed conjugate additions was accomplished using a catalytic amount of CsCl. The utility of this method was demonstrated in the asymmetric synthesis of glutamic acid derivatives by using a chiral phase transfer catalyst.

ChemInform Abstract: Highly Practical Amino Acid Synthesis with Designer Chiral Phase Transfer Catalysts

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.

Chiral Anion-Mediated Asymmetric Ring Opening of meso-Aziridinium and Episulfonium Ions

Reactions proceeding through cationic intermediates that lack a Lewis or Brønsted basic site present a challenge for traditional asymmetric catalysis based on chiral metals or organocatalysts. We present an enantioselective ring opening of tetrasubstituted meso-aziridinium ions with alcohol nucleophiles proceeding through a chiral ion pair with a binaphthol-phosphate anion. The reaction is initiated by silver-induced ring closure of beta-chloroamines using the Ag salt of the chiral anion as in situ generated catalyst. Use of insoluble Ag2CO3 as silver source is essential to obtain high enantioselectivity; we believe the chiral phosphate acts as a "chiral anion phase transfer catalyst" to bring silver ion into the organic phase. The chiral anion concept can also be extended to the related asymmetric opening of meso-episulfonium ions generated by protonation of trichloroacetimidates vicinal to sulfides.

Asymmetric Transformation of Monolayer-Protected Gold Nanoclusters via Chiral Phase Transfer

Phase transfer of aqueous racemic penicillamine-protected gold nanoclusters into chloroform is achieved by hydrophobizing the anionic nanocluster surface with a chiral ephedrinium cation (that is, chiral phase transfer), yielding asymmetric transformation or symmetry breaking of the optically inactive gold nanoclusters: The phase-transferred nanoclusters display appreciable optical activity in the metal-based electronic transition region. The ephedrinium cation contains chiral substituents with R,S absolute configuration, so that “nanocluster diastereomers” also can be produced via the phase transfer of enantiopure (S)- or (R)-penicillamine-protected gold nanoclusters with the chiral cations. Upon phase transfer, absorption spectra of the gold nanoclusters are almost invariant, whereas their circular dichroism (CD) signals exhibit a significant change in the metal-based electronic transition region. On the basis of the optical/chiroptical responses of the asymmetrically transformed gold nanoclusters as well as model quantum chemical calculations, the induced optical activity is most likely due to the ligand dissymmetric field brought about by the surface stereostructures.

Synthesis of methyl-α-d-glucopyranoside-based azacrown ethers and their application in enantioselective reactions

New chiral monoaza-15-crown-5 compounds anellated to methyl-4,6-O-(1-naphthyl)methylene-α-d-glucopyranoside (2a–2b), to methyl-4,6-O-isopropylidene-α-d-glucopyranoside (3a–3b) and to methyl-α-d-glucopyranoside (4a–4b) have been synthesized. Several representatives of these crown ethers showed significant asymmetric induction as chiral phase transfer catalysts, among them 2a proved to be the most efficient one inducing 90% ee in the Michael addition of 2-nitropropane to chalcone, 48% ee in the Darzens condensation of phenacyl-chloride with benzaldehyde and 89% ee in the epoxidation of chalcone with tert-butyl hydroperoxide. The catalytic results were compared with those obtained earlier with macrocycles 1a–1b incorporating a 4,6-O- benzylidene protecting moiety. It occurred that the enantioselectivity is influenced to a great extent by the substituents on the C(4) and C(6) atoms of the monosaccharide. Lower enantioselectivities were obtained in the reactions of the chalcone analogues in the presence of catalyst 2a than in the case of the proper chalcone.

Asymmetric Conjugate Additions of α‐Substituted‐α‐cyanoacetates to Acetylenic Ketones by Chiral Phase Transfer Catalysis.

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.

Design of Chiral Phase Transfer Catalyst with Conformationally Fixed Biphenyl Core: Application to Asymmetric Alkylation of Glycine Derivatives.

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.

Synthesis of New Dimeric‐PEG‐Supported Cinchona Ammonium Salts as Chiral Phase Transfer Catalysts for the Alkylation of Schiff Bases with Water as the Solvent.

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.

A novel N-acetophenone cinchona ammonium salts as chiral phase transfer catalysts for the alkylation of Schiff base in water

Novel N-acetophenone cinchona ammonium salts have been successfully synthesized and used as chiral phase transfer catalysts for the asymmetric alkylation of tert-butyl benzophenone Schiff base derivatives in aqueous media at room temperature with the highest ee and yield up to 96 and 98%, respectively. We have also studied the influence of substituted acetophenone groups in quaternary ammonium salts derived from the cinchona alkaloids.

New, Chiral Phase Transfer Catalysts for Effecting Asymmetric Conjugate Additions of α‐Alkyl‐α‐cyanoacetates to Acetylenic Esters.

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.