Mustafa Durmaz

Synthesis and dichromate anion sorption of silica gel-immobilized calix[4]arenes

Three new silica gel-immobilized calix[4]arene polymers 9-11 have been prepared via modification of calix[4]arene mono amido derivatives 3-5 with 3-aminopropyl triethoxysilane (APTES) and activated silica gel, respectively. The polymers were characterized by Fourier transform infrared spectroscopy, elemental analysis and thermal gravimetric analysis. The solid-liquid extraction properties of ligands 3-5 along with their immobilized derivatives 9-11 towards dichromate (HCr(2)O(7)(-)/Cr(2)O(7)(2-)) anions were reported. It was found that these calix[4]arene-based polymers have high extraction abilities towards dichromate anions as compared to their monomeric precursors.

Application of L‐proline derivatives as chiral shift reagents for enantiomeric recognition of carboxylic acids

Four proline-derived chiral receptors 5-8 were readily synthesized starting from L-proline. The enantiomeric recognition ability of chiral receptors was examined with a series of carboxylic acids by (1) H NMR spectroscopy. The molar ratio and the association constants of the chiral compounds with each of the enantiomers of guest molecules were determined by using Job plots and a nonlinear least-squares fitting method, respectively. The Job plots indicate that the hosts form 1:1 instantaneous complexes with all guests. The receptors exhibited different chiral recognition abilities toward the enantiomers of racemic guests. Among the chiral receptors used in this study, prolinamide 6 was found to be the best chiral shift reagent and is effective for the determination of the enantiomeric excess of chiral carboxylic acids.

Calixarene-based highly efficient primary amine–thiourea organocatalysts for asymmetric Michael addition of aldehydes to nitrostyrenes

The synthesis of calix[4]arene-based chiral bifunctional primary amine–thiourea catalysts has been described from p-tert-butylcalix[4]arene for the first time. The calix[4]arene-based catalysts were successfully applied to promote Michael addition of aldehydes with nitroalkenes affording preferentially the (R)- or (S)-adducts in high yields (up to 95%) and excellent enantioselectivities (up to 99% ees).

Synthesis of 1,3-(distal) Diamide Substituted Calix[4]arene Based Receptors for Extraction of Chromium (VI)

The synthesis of novel diamide derivatives of calix[4]arene by aminolysis of calix[4]arene diesters was reported. The 1H and 13C NMR, data showed that the synthesized compounds exist in the cone conformation. The complexation properties of these calix[4]arenes have been studied towards anions and it has been found that the protonated alkyl ammonium forms of calix[4]arene diamide derivatives (5,11,17,23-tetra-tert-butyl-25,27-(diethylpiperidineacetamido)26,28-dihydroxy-calix[4]arene 3 and 25,27-(diethyl-piperidineacetamido)26,28-dihydroxycalix[4]arene 4) are effective extractants for transferring anions.

Synthesis of calix[4]arene mono and diamide derivatives and selective complexation of alkali and alkaline earth cations

The synthesis of mono and diamide derivatives of the p‐tert‐butylcalix[4]arenes/calix[4]arenes from the reaction of 5,11,17,23‐tetra‐tert‐butyl‐25,27‐diethoxycarbonyl‐methoxy‐26,28‐dihydroxycalix[4]arene 1 and 25,27‐diethoxycarbonyl‐methoxy‐26,28‐dihydroxycalix[4]arene 2 with various primary amines were reported. The effect of reaction time and steric hindrance of the primary amines used on the reactions have been investigated. All the amide derivatives of calix[4]arene are in a cone conformation according to the 1H‐NMR doublet–doublet pattern of the protons of the methylene groups between the aromatic rings. The complexing properties of these compounds toward selected alkali and alkaline earth metal cations are also studied. It has been observed that receptor 8 is a selective extractant for Cs+ and Sr2+ cations.

A novel calix[4]arene-based bifunctional squaramide organocatalyst for enantioselective Michael addition of acetylacetone to nitroolefins

A new chiral calix[4]arene-based organocatalyst 3 bearing bis-squaramide moieties was designed and synthesized from p-tert-butylcalix[4]arene. This bifunctional squaramide organocatalyst was used in the enantioselective conjugate addition of acetylacetone to β-nitrostyrenes. The corresponding adducts were obtained in good to excellent yields with high enantioselectivities (up to 94% ee).

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.