Chiral Resorcinarenes Research Articles

Inherently chiral resorcinarene cavitands through ionic catalyst-controlled cross-coupling

Inherently chiral resorcinarene cavitands through ionic catalyst-controlled cross-coupling

Synthesis of Distally‐Bridged Chiral Resorcinarene Crowns

Our interest in the potential of chiral tetramethoxy‐resorcinarene as agents for chiral recognition has led us to synthesise twelve distally‐bridged chiral resorcinarene crowns. The fascinating architecture of these partially‐enclosed chiral basket molecules is evident in the solid‐state structures which have been determined by single‐crystal X‐ray crystallography. Moreover, the enantiomers of these chiral resorcinarene crowns have been resolved via diastereomeric resolution, with the absolute configuration of the diastereomers being determined by X‐ray crystallography. This work enables further exploration of these enantio‐pure chiral baskets as possible chiral resolving agents.

Preparation of Methacrylate-based Polymers Modified with Chiral Resorcinarenes and Their Evaluation as Sorbents in Norepinephrine Microextraction.

Aminomethylation reactions between chiral amino compounds (S)-(-)-1-phenylethylamine and l-proline with tetranonylresorcinarene and tetra-(4-hydroxyphenyl)resorcinarene in presence of formaldehyde were studied. The reaction between l-proline and resorcinarenes generated regioselectively chiral tetra-Mannich bases, due to the molecular incorporation of the fragment of the chiral amino acid. On the other hand, tetranonylresorcinarene and (S)-(-)-1-phenylethylamine formed regio- and diasteroselectively chiral tetrabenzoxazines, both by chiral auxiliary functionalization and by the transformation of the molecular structure that confers inherent chirality. The products obtained were characterized using IR, 1H-NMR, 13C-NMR, COSY, HMQC, and HMBC techniques. The reaction of (S)-(-)-1-phenylethylamine with tetra-(4-hydroxyphenyl)resorcinarene did not proceed under the experimental conditions. Once the chiral aminomethylated tetra-(4-hydroxyphenyl)resorcinarene was obtained, the chemical modification of poly(GMA–co–EDMA) was studied, and the results showed an efficient incorporation of the aminomethylated compound. For the physical modification, chiral aminomethylated tetranonylresorcinarenes were employed, finding that the incorporation of modified resorcinarenes occurs, but with less efficiency than that observed using chemical modification. The modified polymers were characterized via FT-IR, scanning electron microscopy imaging, and elemental analysis. Finally, polymers modified with chiral resorcinarenes were used as sorbents in norepinephrine microextraction; for practical purposes, artificial urine was prepared and used. To perform the microextraction, the decision was made to use the modern rotating-disk sorptive extraction technique (RDSE), because of its analytical attributes as a green, or eco-friendly, technique. According to the results, the method preliminarily validated for the determination of norepinephrine in artificial urine shows that the modified polymer with chiral derivative of tetra-(4-hydroxyphenyl)resorcinarene worked effectively as a new sorbent phase for the quantitative microextraction of norepinephrine, exhibiting high stability and homogeneity of composition and structure within the working range.

Metal coordination with an amide-functionalized axially chiral resorcinarene

The synthesis and characterization of an amide-functionalized axially chiral resorcinarene, 14,36,56,76-tetra-2-oxo-2-(2-hydroxyethylamino)ethoxy-16,34,54,74-tetramethoxy-2,4,6,8- tetrapropylresorcin[4]arene, is reported. Metal complexation with picrate salts gave crystalline products that could be structurally characterised for calcium, lanthanum, praseodymium, and ytterbium. While the details of these structures vary, the metal–ligand interactions are remarkably consistent, with coordination polymers formed through interaction between three of the amide O atoms, each binding to a different metal atom. No other potential donor atom of the macrocycle is bound to the metal atoms, with the coordination spheres completed by solvent or picrate donor O atoms.

Solvent driven formation of silver embedded resorcinarene nanorods

Silver complexes of resorcinarene bis-crown-5 were observed to arrange into nanorods of 2.4 nm in diameter. The left- and right-handed isomers of the inherently chiral resorcinarene host are separated into their own entity in the self-assembly process with the periphery of the nanorods consisting of silver cations included in the cavity.

Introduction to the Chirality of Resorcinarenes

Resorcinarenes constitute a very attractive class of macrocycles possessing a cavity capable of complexing small molecules. They can be simply transformed into chiral derivatives by functionalisation of their hydroxy groups as well as the “ortho” position at the resorcinol ring. The appropriate modifications lead to various chiral resorcinarene derivatives. The chirality of these compounds results from their structure (the axial chirality) or from the presence of chiral auxiliaries. Moreover, the synthesis of chiral resorcinarene derivatives from chiral substrates is also possible. In this short review, we wish to present the strategies and methodology of the synthesis of chiral resorcinarenes, treating this article as an introduction to the chirality of resorcinarenes. Keywords: Calixarene, Resorcinarene, Chirality, Symmetry

A Chiral “Frozen” Hydrogen Bonding in C4‐Symmetric Inherently Chiral Resorcin[4]arenes: NMR, X‐ray, Circular Dichroism, and Theoretical Study (Eur. J. Org. Chem. 18/2008)

AbstractThe cover picture shows the X‐ray structure of CC4‐symmetric, chiral resorcinarene substituted with L‐leucine at the upper rim. The molecule is held in the inherently chiral conformation (resembling a chiral CC4‐symmetric propeller) by means of twelve intramolecular hydrogen bonds. The seams of hydrogen bonds can be directed in one particular direction because of diastereomeric preferences. The determination of the direction of the hydrogen‐bonding seam and the correlation with CD spectra is discussed in the article by A. Szumna et al. on p. 3069 ff.

The Synthesis of Axially Chiral Resorcinarenes from Resorcinol Monoalkyl Ethers and Aldehyde Dimethylacetals.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Retro‐Mannich Reactions of 3‐Alkyl‐3,4‐dihydro‐2H‐1,3‐benz[e]oxazines and the Synthesis of Axially Chiral Resorcinarenes.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Retro-Mannich reactions of 3-alkyl-3,4-dihydro-2 H-1,3-benz[ e]oxazines and the synthesis of axially chiral resorcinarenes

Intermediates involved in the conversion of 3-alkyl-3,4-dihydro-2 H-1,3-benz[ e]oxazines into 2- N, N-dialkylaminomethylphenol derivatives, using morpholine and other high boiling secondary amines, have been identified and characterised. Additional experiments have established the involvement of o-quinone methide intermediates in the retro-Mannich reactions. Axially chiral resorcinarenes have been prepared by utilising the exchange reactions.