Static Combinatorial Chemistry: A High-Pressure Approach to the Synthesis of Macrocyclic Benzoamide Libraries

We investigated the yield and distribution of macrocyclic products formed in combinatorial libraries (CLs) obtained via double-amidation reactions of methyl diesters with α,ω-diamines. The application of the static combinatorial chemistry (SCC) approach allowed us to generate a large number of macrocyclic diamides and tetraamides in single experiments. We show that high-pressure conditions accelerate the macrocyclization process but also have a great impact on the distribution of macrocyclic products in the presented libraries, promoting the formation of macrocyclic compounds and eliminating the linear ones. The distribution of macrocyclic products was also found to be strongly dependent on the structural features of the substrates employed. Furthermore, in three- and four-substrate CLs we observed the formation of a new type of hybrid tetraamides consisting of three different components.

A General Method for High-Pressure-Promoted Postfunctionalization of Unclosed Cryptands: Potential Phase-Transfer Catalysts

We report a high-pressure approach to facile late-stage functionalization of unclosed cryptands (UCs) (11 examples, yield up to 99%). Direct comparison of classic and high-pressure conditions of the quaternization reaction in a sterically crowded intraannular position is investigated, and differences in the reactivity of tertiary amine substrates are discussed. Finally, we demonstrated the application of UCs as catalysts for synthetically important alkylation reactions under phase-transfer conditions.

Recent applications of chiral calixarenes in asymmetric catalysis

The use of calixarenes in asymmetric catalysis is receiving increasing attention due to their tunable three-dimensional molecular platforms along with their easy syntheses and versatile modification at the upper and lower rims. This review summarizes the recent progress of synthesis and use of chiral calixarenes in asymmetric syntheses which emerged later than 2010.

Synthesis and conformational studies of chiral macrocyclic [1.1.1]metacyclophanes containing benzofuran rings

A novel hemisphere-shaped inherently chiral calixarene analogoue [1.1.1]metacyclophane containing both benzene and benzofuran rings was synthesized by fragment coupling approach.

Inherently chiral calix[4]arenes via oxazoline directed ortholithiation: synthesis and probe of chiral space

The diastereoselective oxazoline-directed lithiation of calix[4]arenes is reported with diastereoselective ratios of greater than 100:1 in some instances. Notably, it has been found that the opposite diastereomer can be accessed via this approach merely through the choice of an alkyllithium reagent. The inherently chiral oxazoline calix[4]arenes have also been preliminarily examined as ligands in the palladium-catalyzed Tsuji–Trost allylation reaction, returning results comparable to their planar chiral ferrocene counterparts pointing towards future application of these types of compounds.

Qualitative analysis of the helical electronic energy of inherently chiral calix[4]arenes: an approach to effectively assign their absolute configuration

For all microhelices on aromatic rings of inherently chiral calix[4]arene, an expression was derived from one approximation and one hypothesis on the basis of the electron-on-a-helix model of Tinoco and Woody as follows: , where µ = 1 for the right-handed microhelix and µ = −1 for the left-handed microhelix; and H and K are constant and greater than zero. The expression correlates microhelical electronic energy (E) with the atom polarizability difference (Δα) on both microhelix ends, which intuitively and clearly shows the impact of helical substituent polarizability on helical electronic energy. The case analysis almost entirely proves that the qualitative analysis of the helical electronic energy of inherently chiral Calix[4]arenes with the expression is scientific and can be used to effectively assign their absolute configuration.

Recent developments in asymmetric phase-transfer reactions

Phase-transfer catalysis has been recognized as a powerful method for establishing practical protocols for organic synthesis, because it offers several advantages, such as operational simplicity, mild reaction conditions, suitability for large-scale synthesis, and the environmentally benign nature of the reaction system. Since the pioneering studies on highly enantioselective alkylations promoted by chiral phase-transfer catalysts, this research field has served as an attractive area for the pursuit of "green" sustainable chemistry. A wide variety of asymmetric transformations catalyzed by chiral onium salts and crown ethers have been developed for the synthesis of valuable organic compounds in the past several decades, especially in recent years.

Synthesis of inherently chiral calix[4]arenes: stereocontrol through ligand choice

Employing a chiral oxazoline as an ortholithiation directing group allows the synthesis of inherently chiral calix[4]arenes suitable for elaboration into planar chiral molecules. An important finding has been that the diastereoselectivity of the reaction can be tuned by the choice of additive. These results have bearing on the elucidation of the general mechanism of oxazoline-directed ortholithiation.

Inherently chiral calixarenes: synthesis, optical resolution, chiral recognition and asymmetric catalysis

Inherently chiral calixarenes, whose chirality is based on the absence of a planar symmetry or an inversion center in the molecules as a whole through the asymmetric array of several achiral groups upon the three-dimensional calix-skeletons, are challenging and attractive chiral molecules, because of their potential in supramolecular chemistry. The synthesis and optical resolution of all varieties of inherently chiral calixarenes are systematically discussed and classified, and their applications in chiral recognition and asymmetric catalysis are thoroughly illustrated in this review.

Synthesis of chiral calix[4]arenes bearing aminonaphthol moieties and their use in the enantiomeric recognition of carboxylic acids

Two armed chiral calix[4]arenes 8-16 functionalized at the lower rim with chiral aminonaphthol units have been prepared and the structures of these receptors characterized by FTIR, (1)H, and (13)C, DEPT and COSY NMR spectroscopy and elemental analysis. The enantioselective recognition of these receptors with various carboxylic acids has been studied by (1)H NMR and UV/Vis spectroscopy. The receptors exhibited different chiral recognition abilities towards the enantiomers of racemic materials and formed 2 : 1 or 1 : 1 complexes between host and guest. It was also demonstrated that chiral calix[4]arenes 9 and 16 could be used as chiral NMR solvating agents to determine the enantiomeric purity of mandelic acid.