Chiral Crown Ethers Research Articles

Asymmetric C–C bond formation via Darzens condensation and Michael addition using monosaccharide-based chiral crown ethers

Liquid–liquid phase asymmetric Darzens condensations were promoted by d-glucose- and d-mannose-based crown ethers. The corresponding aromatic and heteroaromatic α,β-epoxyketones were obtained with moderate to high enantioselectivities (up to 96%) as well as diastereoselectivities (up to 98:2) under mild reaction conditions. The absolute configurations of several of the epoxyketones were determined by single crystal X-ray analysis. The Michael additions of diethyl acetylaminomalonate to trans-β-nitroalkenes were carried out in a solid–liquid two-phase system in the presence of a d-glucose-based crown catalyst with up to 99% ee.

A colorimetric chiral sensor based on chiral crown ether for the recognition of the two enantiomers of primary amino alcohols and amines

A new colorimetric chiral sensor material consisting of three different functional sites such as chromophore (2,4-dinitrophenylazophenol dye), binding site (crown ether), and chiral barrier (3,3'-diphenyl-1,1'-binaphthyl group) was prepared and applied to the recognition of the two enantiomers of primary amino alcohols and amines. Among five primary amino alcohols and two primary amines tested, the two enantiomers of phenylalaninol show the highest difference in the absorption maximum wavelength (Δλ(max)=43.5 nm) and in the association constants (K(S)/K(R)=2.51) upon complexation with the colorimetric chiral sensor material and, consequently, the two enantiomers of phenylalaninol were clearly distinguished from each other by the color difference.

Asymmetric Phase Transfer Reactions Catalyzed by Chiral Crown Ethers Derived from Monosaccharides

One of the practical applications of sugar-based crown ethers involves their use as chiral catalysts in enantioselective phase transfer reactions. Chiral crown ethers incorporating various monosaccharide units in the macrocyclic structure are reviewed which may be efficient enantioselective catalysts in certain asymmetric reactions, such as Michael addition, epoxidation of α,β-enones and Darzens condensation.

Enantioselective Michael Addition of 2-Nitropropane to Substituted Chalcones and Chalcone Analogues Catalyzed by Chiral Crown Ethers Incorporating an α-D-Glucose or an α-D-Mannose Unit

Enantioselective Michael Addition of 2-Nitropropane to Substituted Chalcones and Chalcone Analogues Catalyzed by Chiral Crown Ethers Incorporating an α-D-Glucose or an α-D-Mannose Unit

ChemInform Abstract: Novel Bicyclic Chiral Crown Ethers Having a p-Xylenedioxy Unit with Improved Complex Stability and Rate-Enhancement in the Intra-Complex Thiolysis of α-Amino Acid Ester Salts.

ChemInform Abstract: Novel Bicyclic Chiral Crown Ethers Having a p-Xylenedioxy Unit with Improved Complex Stability and Rate-Enhancement in the Intra-Complex Thiolysis of α-Amino Acid Ester Salts.

ChemInform Abstract: Regioselective Transformations of 2′,3′-Seconucleosides into Anhydro Structures and Chiral Crown Ethers.

ChemInform Abstract: Regioselective Transformations of 2′,3′-Seconucleosides into Anhydro Structures and Chiral Crown Ethers.

ChemInform Abstract: Organofluorine Compounds and Fluorinating Agents. Part 9. From Glycosyl Fluorides to Chiral Crown Ethers.

ChemInform Abstract: Organofluorine Compounds and Fluorinating Agents. Part 9. From Glycosyl Fluorides to Chiral Crown Ethers.

Enantiomeric Resolution of α-Amino Acid Derivatives on Two Diastereomeric Chiral Stationary Phases Based on Chiral Crown Ethers Incorporating Two Different Chiral Units

Two diastereomeric chiral stationary phases (CSPs) were applied to the liquid chromatographic resolution of various racemic α-amino methyl esters, α-amino N,N-diethylamides and α-amino N-propylamides. The CSP incorporating (R)-3,3'-diphenyl-1,1'-binaphtyl and (R,R)-tartaric acid unit as chiral barriers did not show any chiral recognition. In contrast, the CSP incorporating (R)-3,3'-diphenyl-1,1'-binaphtyl and (S,S)-tartaric acid unit as chiral barriers was found to show excellent chiral recognition especially for the two enantiomers of α-amino N-propylamides. Some of α-amino methyl esters and α-amino N,N-diethylamides were also resolved on the CSP incorporating (R)-3,3'-diphenyl-1,1'-binaphtyl and (S,S)-tartaric acid unit. From these results it was concluded that the two chiral units composing the diastereomeric CSPs can show matched or mismatched effect on the chiral recognition according to their absolute stereochemistry.

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.

ChemInform Abstract: Synthesis of Novel C2‐Symmetric Chiral Crown Ethers and Investigation of Their Enantiomeric Recognition Properties.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 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.

Host-guest complexation-triggered chiroptical change of poly(phenylacetylene)s bearing binaphthocrown ether moieties on the main chain

Diacetylene monomers with respective lengths of the oxyethylene chains were cyclopolymerized with a rhodium catalyst to produce novel poly(phenylacetylene)s bearing a different cavity size of the chiral crown ether in the repeating units (2a–c). In the circular dichroism spectra of the resulting polymers, characteristic Cotton effects were observed in the range from 350 to 500 nm corresponding to the absorption of the conjugated polymer backbone, indicating that the polymers possessed a helical structure with an excess single screw sense induced by the covalently bonded binaphthyl units. The host–guest complexation of 2a–c with achiral guests produced a chiroptical change based on the fluctuation in the main chain conformation. The behavior of the complexation-induced chiroptical change was essentially dictated by the cavity size of the binaphthocrown ether units. Additionally, a chirality-responsive helicity change was observed in the case of the complexation of 2a–c with chiral guests, which also depended on the crown ether size. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1197–1206, 2010

Enantiomeric discrimination of chiral crown ether ionophores containing phenazine subcyclic unit by ion-selective potentiometry

In this paper the enatiomeric selectivity of two chiral phenazino-18-crown-6 ether hosts ((R,R)-\textbf1 and (R,R)-\textbf2) is quantified. These hosts were incorporated into plasticized PVC membranes and used as recognition elements of ion-selective electrodes. The potentiometric response towards the two enantiomers of 1-phenylethylammonium ions (PEA+) was measured. Potentiometric selectivity coefficients were calculated which reflect the ratio of the stability constants of the diastereomeric complexes. Ligand (R,R)-\textbf1 does not show enantiomeric recognition, while ligand (R,R)-\textbf2 has a slight preference for the (S)-(-) enantiomer over the (R)-(+) enantiomer manifested by a selectivity coefficient of 0.77. The results were compared to enantioselectivity patterns of the ligands towards α -(1-naphthyl)ethyl ammonium perchlorate (NEA+ClO4-) enantiomers measured by circular dichroism and by 1H NMR titrations.

ChemInform Abstract: Synthesis of Novel C2‐Symmetric Chiral Crown Ethers and Their Application to Enantioselective Trifluoromethylation of Aldehydes and Ketones.

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.

ChemInform Abstract: Asymmetric Synthesis of Substituted α‐Amino Phosphonates with Chiral Crown Ethers as 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.

Synthesis of novel C2-symmetric chiral crown ethers and investigation of their enantiomeric recognition properties

A series of new C 2-symmetric chiral aza crown ether macrocycles 1– 4 have been synthesized from ( S)-3-aryloxy-1,2-propanediol and ( S)-1,2-propanediol for the enantiomeric recognition of amino acid ester derivatives. These new macrocycles have been shown to be strong complexing agents for primary organic ammonium salts (with K up to 176.93 M −1 and Δ G° up to 12.81 kJ mol −1) by 1H NMR titration. These macrocyclic host exhibited enantioselective bonding toward the d-enantiomer of phenylalanine methyl ester hydrochloride with K D/ K L up to 6.87 in CDCl 3 with 0.25% CD 3OD.

Enantiomeric separation of chiral dipeptides by CE‐ESI‐MS employing a partial filling technique with chiral crown ether

Enantiomer of chiral dipeptides were separated by CE-ESI-MS in a bare fused-silica capillary using (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid (18C6H4) as the chiral selector. As 18C6H4 is a kind of nonvolatile chiral selector, in order to prevent from 18C6H4 into the ion-source of CE-ESI-MS, a partial filling technique was employed in this study. Some dipeptides with one chiral center or two chiral centers, such as DL-Leu-DL-Leu, D-Ala-D-Ala and L-Ala-L-Ala, Gly-D-Phe and Gly-L-Phe were used to evaluate this CE-ESI-MS system. Optimized conditions were achivevd with 2.0 mol/L acetic acid (pH 2.15) as the running electrolyte, 5 mM 18C6H4 in 3.0 mol/L acetic acid (pH 2.00) was injected hydrodynamically (50 mbar for 960 s) before sample injection. In total 7.5 mM acetic acid in 80% v/v methanol-water was used as the sheath liquid, and 20 kV applied voltage was used. Under the optimum conditions, these dipeptides were separated and detected. LODs (defined as S/N=3) of this method were 0.20, 0.10, 0.05 and 0.10 micromol/L for D-Ala-D-Ala, L-Ala-L-Ala, DL-Leu-DL-Leu, Gly-L-Phe and Gly-D-Phe, respectively. The RSDs (n=7) of the method were 0.68-2.08% for migration times and 2.32-5.24% for peak areas. The proposed method was also successfully applied to the enantioselective analysis of these dipeptides in the spiked serum samples with satisfactory results.

The role of central ion in chiral recognition by taking phenylalanine as an example

Chiral recognition of phenylalanine (Phe) was achieved in the gas phase by electrospray ionization Q-TOF tandem mass spectrometry. In this method, two central ions, i.e. proton and divalent copper, were used and chiral crown ether, (+)-2,3,11,12-tetracarboxylic acid-18-crown-6 (18-C-6-TCA), was used as a chiral host. Dimeric complexes were readily formed by electrospray ionization of a methanol/water (50/50, V/V) solution containing central ions, Phe and 18-C-6-TCA. The dimeric complex included proton-bound (18-C-6-TCA)(Phe)H+ and copper-bound deprotonated [Cu2+(18-C-6-TCA)(Phe)-H]+ ions were mass selected and then collided with Ar in the CID experiments. The chiral recognition capability of these complexes was evaluated using the relative abundance of daughter ion to parent ion. A higher degree of chiral recognition ability was observed with Cu2+ compared to that of H+. Different central ions exhibited distinctive dissociation pathways and unique chiral recognition characteristics. The chiral recognition mechanism was also discussed in detail with the help of the structure of copper-bound complex predicted by theoretical calculation.

Synthesis of novel C2-symmetric chiral crown ethers and their application to enantioselective trifluoromethylation of aldehydes and ketones

Synthesis of novel C2-symmetric chiral crown ethers and their application to enantioselective trifluoromethylation of aldehydes and ketones are discussed. The use of a series of C2-symmetric chiral crown ethers 2 or 3 derived from commercially available ( R)-1,1′-bi-2-naphthol for the enantioselective trifluoromethylation of 2-naphthyl aldehyde 1a with (trifluoromethyl)trimethylsilane in the presence of a base was attempted. Iodo-substituted crown ether 2b was found to be the most effective in the model reaction. Moderate enantioselectivities were observed for the trifluoromethylation of both aryl or alkyl aldehydes and alkyl aryl ketones in 21–44% ees. Although the ees are still improvable, this is the first example of a chiral crown ether-catalyzed enantioselective trifluoromethylation reaction.

Asymmetric Synthesis of Substituted α-Amino Phosphonates with Chiral Crown Ethers as Catalysts

A simple, phase-transfer catalytic synthesis of enantioenriched phosphonoglutaminic acid derivatives (ee up to 86%) has been developed by using 'sugar-based' crown ether catalysts.

Unprecedented synthesis of chiral calix[4](aza)crowns and its potent encapsulating methanol

Unprecedented synthesis of chiral (aza)crown ethers of calix[4]arene derivatives bearing a carboxyl amide bridge was described. The synthesis proceeds through condensation of the corresponding dinitriles with optically active 1,2-aminoalcohols, and is catalyzed by the ZnCl2 Lewis acid at elevated temperature in a very efficient one-pot process. The cavity of calix[4](aza)crowns can encapsulate methanol molecules by O-H⋯п interaction, which has been confirmed by X-ray crystal structures and ESI-MS.