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In this work, we would like to present the development of a highly optimized method for generating the quaternary stereogenic centers in β-keto esters. This enantioselective phase-transfer alkylation catalyzed by hybrid Cinchona catalysts allows for the efficient generation of the optically active products with excellent enantioselectivity, using only 1 mol% of the catalyst. The vast majority of phase-transfer catalysts in asymmetric synthesis work by creating ionic pairs with the nucleophile-attacking anionic substrate. Therefore, it is a sensible approach to search for new methodologies capable of introducing functional groups into the precursor's structure, maintaining high yields and enantiomeric purity. [ABSTRACT FROM AUTHOR]

This short review is devoted to asymmetric phase-transfer reactions that employ hybrid ammonium Cinchona catalysts supported by possessing hydrogen-bond donor groups. We present recent advances utilizing this type of catalyst in the field of biphasic reaction systems. The main emphasis is placed on the advantages of additional functional groups present in the structure of the catalyst, such as hydroxy, amide, (thio)urea or squaramide. 1 Introduction 2 Phase-Transfer Hybrid Cinchona Catalysts with a Free Hydroxy Group 3 (Thio)urea Hybrid Cinchona Catalysts 4 Hybrid Amide-Based Catalysts Bearing a Cinchona Scaffold 5 Conclusions [ABSTRACT FROM AUTHOR]

Herein we present the synthesis and association analysis of a new family of "pincer" receptors containing units of stable 26-membered tetraamidic macrocyclic scaffolds in their structures. These units, linked by aliphatic or aromatic chains, are capable of binding an anionic guest due to the presence of amide functions playing the role of hydrogen bond donating systems. Such neutral receptors show strong binding properties with respect to dicarboxylate anions. Despite the discovery that we observed a complexed, mixed binding model in all the systems tested, we can infer that the receptor region to which the guest chain is associated depends on the latter's length. [ABSTRACT FROM AUTHOR]

The symmetrical molecular receptors 1a and 1b consisting of a photochemically addressable azobenzene tether functionalized with urea hydrogen-bonding groups and D-carbohydrates as chiral selectors were developed to achieve control over the chiral recognition of α-amino acid-derived carboxylates. The photo- and thermally interconvertible planar E-1 and concaved Z-1were found to exhibit different affinities, selectivities, and binding modes toward these biologically important anions in a highly polar medium (DMSO + 0.5% H2O). Binding affinity for the same enantiomerically pure guest was up to 3 times higher for E-1 than for Z-1 (cf. parameter β). In addition, the rate of thermal Z → E isomerization was found to depend on the chiral binding ability of Z-1, i.e., more strongly bound carboxylate enantiomer as well as higher enantiomer concentration caused faster relaxation to E-1. [ABSTRACT FROM AUTHOR]

Recognition of anionic species plays a fundamental role in many essential chemical, biological, and environmental processes. Numerous monographs and review papers on molecular recognition of anions by synthetic receptors reflect the continuing and growing interest in this area of supramolecular chemistry. However, despite the enormous progress made over the last 20 years in the design of these molecules, the design of receptors for chiral anions is much less developed. Chiral recognition is one of the most subtle types of selectivity, and it requires very precise spatial organization of the receptor framework. At the same time, this phenomenon commonly occurs in many processes present in nature, often being their fundamental step. For these reasons, research directed toward understanding the chiral anion recognition phenomenon may lead to the identification of structural patterns that enable increasingly efficient receptor design. In this review, we present the recent progress made in the area of synthetic receptors for biologically relevant chiral carboxylates. [ABSTRACT FROM AUTHOR]

Herein, we present the synthesis and anion binding studies of a family of homologous molecular receptors 4–7 based on a DITIPIRAM (8-propyldithieno-[3,2-b:2′,3′-e]-pyridine-3,5-di-amine) platform decorated with various urea para-phenyl substituents (NO2, F, CF3, and Me). Solution, X-ray, and DFT studies reveal that the presented host–guest system offers a convergent array of four urea NH hydrogen bond donors to anions allowing the formation of remarkably stable complexes with carboxylates (acetate, benzoate) and chloride anions in solution, even in competitive solvent mixtures such as DMSO-d6/H2O 99.5/0.5 (v/v) and DMSO-d3/MeOH-d3 9:1 (v/v). The most effective derivatives among the series turned out to be receptors 5 and 6 containing electron-withdrawing F- and -CF3para-substituents, respectively. [ABSTRACT FROM AUTHOR]

We present the synthesis, using combinatorial chemistry methodology, of a series of 11 selective anion receptors with special affinity for carboxylates. These compounds contain a urea function and their macrocyclic platform has the structure of previously reported "Unclosed Cryptand". The use, at the stage of postfunctionalisation of the lariat arm, of properly selected templates allows for non-statistical synthesis of the expected products, whose concentration in the reaction mixture depends on the geometrical factors of the substrates used and their electronic properties. Postfunctionalization of the said arm, after the yield limiting macrocyclization reaction, makes it possible to influence the selectivity of complexing the guest molecules introduced into the system. Image 1 • Combinatorial synthesis of macrocyclic compounds. • Strong influence on the composition of the reaction mixture by adding a template. • Parallel postfunctionalization of the lariat arm containing urea moieties. • Analogy of anion receptor affinity with the promotion of the formation of the macrocyclic compound using the template. [ABSTRACT FROM AUTHOR]

Some of 19-membered unclosed cryptands were recognized as chiral species in a solid state. While, in terms of 20-membered macrocycle, we tune the lariat arm, developing the synthesis of α- and β-naphthyl terminated moieties to gain the structural control over chirality phenomena of these systems. Indirect synthetic approach delineates the way to reach both target structures. Solely, macrocycle functionalized with the β-naphthyl group is capable of desirable interactions with the frame of entity inducing its stronger bending that leads to the chiral crystals formation. Their structural features were examined by single crystal X-ray diffraction and chiroptical method, represented by ECD/UV spectroscopy. [ABSTRACT FROM AUTHOR]