Design, synthesis and application of chiral tetraoxacalix[2]arene[2]triazine-based organocatalysts in asymmetric Michael addition reactions.

A novel type of oxacalix[2]arene[2]triazine-based organocatalysts for asymmetric Michael reactions are reported for the first time. Chiral subunits were attached to the heteroatom-bridged calixaromatic platform by a reaction of (R)- and (S)-1-aminotetraline with tetraoxacalix[2]arene[2]triazine in both enantiomeric forms. To evaluate the catalytic efficiency of the novel organocatalysts, isobutyraldehyde reacted with various substituted and unsubstituted aromatic trans-ß-nitrostyrenes in tetrahydrofuran (THF), leading to Michael adducts in excellent yields and enantioselectivites (up to 97% yield and 99% ee).

Chiral calix[4]arenes bearing amino alcohol functionality as membrane carriers for transport of chiral amino acid methylesters and mandelic acid.

Novel chiral calix[4]arene derivatives bearing amino alcohol moieties at the lower rim have been synthesized from the reaction of p-tert-butylcalix[4]arene diester with various amino alcohols. The transport of amino acid esters (phenylglycine, phenylalanine, and tryptophan methyl esters hydrochloride) and mandelic acid were studied through chloroform bulk liquid membrane system using chiral calix[4]arenes 15-20. All these receptors have been found to act as carriers for transport of aromatic amino acid methylesters and mandelic acid from the aqueous source phase to the aqueous receiving phase. The influence of calixarene and guest structures upon transport through liquid membrane is discussed.

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.

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.

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.

Chiral mono and diamide derivatives of calix[4]arene for enantiomeric recognition of chiral amines.

Novel chiral mono and diamide derivatives of calix[4]arene have been prepared from the aminolysis 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 chiral (S)-(-)-1-phenylethylamine (PEA) and (1S,2S)-(+)-2-amino-1-(4-nitrophenyl)-1,3-propanediol, respectively. Spectrophotometric titrations have been performed in CHCl(3) at 20-30 degrees C in order to obtain the binding constants (K) and the thermodynamic quantities (DeltaH and DeltaS) for the stoichiometric 1:1 inclusion complexation of various chiral amines with these new host compounds. Preliminary experiments were undertaken to confirm the complexation properties of receptors 9 and 13 with PEA by (1)H NMR in CDCl(3) at room temperature. The molecular recognition abilities and enantioselectivities for guests (R and S)-alpha-PEA and (R and S)-cyclohexylethylamine (CHEA) are discussed from a thermodynamic point of view.