Solid-state optical properties of a chiral supramolecular fluorophore consisting of chiral (1R,2R)-1,2-diphenylethylenediamine and fluorescent carboxylic acid derivatives

By using (1R,2R)-1,2-diphenylethylenediamine as a chiral molecule and 2-anthracenecarboxylic acid as a fluorescent molecule, we created a chiral supramolecular organic fluorophore having circularly polarized luminescence properties in the solid-state.     

Stereoselective adduct formation of α-acylcamphorato-copper(II) chelates with some chiral Lewis bases

The formation constants of the mono-adducts of α-acylcamphorato-copper(II) chelates such as (+)-Cu(facam)₂, (?)-Cu(facam)₂, (+)-Cu(hfbc)₂ and (?)-Cu(hfbc)₂ with some chiral Lewis bases were determined spectrophotometrically in benzene. In order to compare the adduct formation constants obtained with the (+)- and (?)-forms, some pairs of chiral Lewis bases such as 1-amino-2-propanol [(R)(?), (S)(+)], 1-(α-naphthyl)ethylamine [(R)(+), (S)(?)], α-phenyl ethylamine [(R)(+), (S)(?)] and also quinine and quinidine were examined as neutral ligands. Although not very pronounced, the effects of combinations obtained for (+)- or (?)-Cu(II) chelates and (+)- or (?)-ligands indicate that formation constants obtained by the formation of adducts with the ligands having different directions of the optical rotation seems to be superior to those with the same direction.     

Tuning mechanism in helical columnar thiophene host system with 2-thienylacetic acid by using (1R,2S)-2-amino-1,2-diphenylethanol

A tunable supramolecular thiophene host system with a chiral channel-like cavity is developed using (1R,2S)-2-amino-1,2-diphenylethanol. This thiophene host system possesses a chiral helical columnar structure. The chiral cavities are formed by the self-assembly of the helical column, and guest molecules are included by varying the helical structure and packing arrangement of this column.     

Base controlled (1,1)- and (1,2)-hydrophosphination of functionalized alkynes

The (1,1)- and (1,2)-addition of diphenylphosphine to 3-butyn-2-one and ethyl propiolate can be controlled chemoselectively by regulating the amount of triethylamine as the external base and in the presence of the chiral organopalladium(II) template derived from (R)-N,N-dimethyl-1-(1-naphthyl)ethylamine.     

The preparation of new chiral diphenyl-substituted macrocyclic polyether-diester compounds and their enantiomeric recognition of chiral organic ammonium salts

A series of chiral diphenyl-substituted macrocyclic polyether-diester ligands have been prepared from the chiral diphenyl-substituted tetraethylene glycol. Enantiomeric recogntion by the chiral diphenyl-substituted pyridino-diester-18-crown-6 compound ( 7 ) was studied by temperature dependent ¹H NMR spectroscopy in deuteriodichloromethane. This ligand exhibited chiral recognition when complexed with the hydrogen per-chlorate salts of (R)- and (S)-α-(1-naphthyl)ethylamine and (R)- and (S)-methyl phenylalaninate.     

Simultaneous separation of five fluoroquinolone antibiotics by capillary zone electrophoresis

A chiral separation method for glycidol enantiomers determination by normal-phase high-performance liquid chromatography coupled to atmospheric pressure chemical ionization mass spectrometry was developed. Two chiral stationary phases, amylose tris-(3,5-dimethylphenylcarbamate) (Chiralpak AD-H) and (S)-indoline-2-carboxylic acid and (R)-1-(α-naphthyl) ethylamine (SUMICHIRAL OA-4900) have been investigated. The effects of the mobile phase composition, elution program and column temperature were also studied. Under the best conditions: Chiralpak AD-H column, mobile phase composition n-hexane:ethanol (70:30, v/v), flow rate of 0.8 mL/min and 40 °C column temperature, a good resolution (Rs = 1.6) for both enantiomers has been achieved with an analysis time of 16 min. The method was found to be linear in the range from 100 to 500 ppm for both glycidol enantiomers with a good determination coefficient (r² higher than 0.99) and good precision. Limits of detection of 31 and 50 ppm for (R)-(+)-glycidol and (S)-(−)-glycidol, respectively, were obtained. The method was applied to the determination of the enantiomeric excess and yield obtained in a asymmetric epoxidation process of allyl alcohol with a chiral titanium-tartrate complex as catalyst.     

Acetylation of 2-(1-naphthyl)thiophene

Acetylation of 2-(1-naphthyl) thiophene with acetyl chloride in the presence of SnCl₄, or with acetic anhydride in the presence of H₃PO₄ gives 5-aceto-2-(1-naphthyl) thiophene. 5-Ethyl-2-[1-(3, 4-dihydronaphthyl)] thiophene, 5-ethyl-2-(1-naphthyl) thiophene and 3, 4-diacetoxymercuri-5-ethyl-2-(1-naphthyl) thiophene are now synthesized and characterized.     

Enantioseparation of protonated primary arylalkylamines and amino acids containing an aromatic moiety on a pyridino-crown ether based new chiral stationary phase

This paper reports the preparation and testing of a new pyridino-18-crown-6 ether based chiral stationary phase (CSP). The chiral crown ether was covalently bound to silica gel. Circular dichroism (CD) spectroscopy was used for probing the complex formation of the chiral crown ether with the enantiomers of protonated primary arylalkylamines. The (S,S)-dimethylpyridino-18-crown-6 ether selector having a terminal double bond was first transformed to a triethoxysilyl derivative by regioselective hydrosilylation, and then heated with spherical HPLC quality silica gel to obtain the CSP. The discriminating power of the HPLC column filled with the above CSP was tested by using the hydrogenperchlorate salts of racemic α-(1-naphthyl)ethylamine (1-NEA), α-(2-naphthyl)ethylamine (2-NEA) and the hydrochloride salts of aromatic α-amino acids and α-amino acids containing different aromatic side-chain protecting groups.     

Asymmetric synthesis of dimethyl-1,2-bis-(diphenylphosphino)-1,2-ethanedicarboxylate by means of a chiral palladium template promoted hydrophosphination reaction

An optically pure C₂-symmetrical diphosphine ligand containing two ester functional groups at the two chiral carbon stereogenic centres was prepared efficiently from the asymmetric hydrophosphination reaction between diphenylphosphine and dimethyl acetylenedicarboxylate in the presence of an organopalladium(II) complex derived from (S)-N,N-dimethyl-1-(1-naphthyl)ethylamine.     

1-Arylethylamino-substituted s-triazine derivatives as chiral solvating agents for the determination of the enantiomeric composition of chiral compounds

The development of 2-[(R)-1-(9-anthryl)ethylamino]-4-chloro-6-methoxy-1,3,5-triazine, 2-[(R)-1-(9-anthryl)ethylamino]-4-chloro-6-[(R)-1-(1-naphthyl)ethylamino]-1,3,5-triazine and 2-[(R)-1-(9-anthryl)ethylamino]-4,6-bis-[(R)-1-(1-naphthyl)ethylamino]-1,3,5-triazine as chiral solvating agents (CSAs) for the determination of the enantiomeric composition of derivatized and underivatized chiral compounds is presented. The comparison between the efficiency of these chiral auxiliaries with the corresponding 1-(1-naphthyl)ethylamino substituted s-triazine derivatives is also discussed.     

Highly efficient resolutions of 1,4-benzodioxane-2-carboxylic acid with para substituted 1-phenylethylamines

The salts of (S)- and (R)-1,4-benzodioxane-2-carboxylic acid with eight (S)-1-arylethylamines were prepared. The determination of their melting points and of their solubilities in alcohol solvents revealed large differences between the diastereomeric benzodioxanecarboxylates of (S)-1-(p-nitrophenyl)ethylamine and of (S)-1-(p-methylphenyl)ethylamine. Therefore, these latter amines were selected to resolve (±)-1,4-benzodioxane-2-carboxylic acid by diastereoselective crystallization finding that both of them display a very high resolution ability for such a substrate, which contrasts with the null efficiency of unsubstituted 1-phenylethylamine. These results are consistent with DSC evidences, which indicated that the two successfully resolved diastereomeric systems are binary mixtures exhibiting a eutectic with a high content of the more soluble diastereomeric salt. The new procedures can advantageously replace the two resolutions we had previously reported, that of the same acid with dehydroabietylamine and that of glycerol acetonide, a precursor of 1,4-benzodioxane-2-carboxylic acid, with 1-phenylethylamine.     

Preparation of a new chiral acridino-18-crown-6 ether-based stationary phase for enantioseparation of racemic protonated primary aralkyl amines

Starting from commercially available and relatively cheap chemicals first enantiopure dimethyl-substituted monoaza-18-crown-6 ether (R,R)-21 containing a diphenylamine unit was prepared, which was then transformed to dimethyl-substituted acridino-18-crown-6 ligand (R,R)-19 having an N-allyl-carbamoyl linker by several steps. The terminal double bond of the latter made possible to attach (R,R)-19 to γ-mercaptopropyl-functionalized spherical HPLC quality silica gel obtaining a new chiral stationary phase (R,R)-CSP-37. Based on electronic circular dichroism (ECD) studies the N-allyl-carbamoyl group attached to the acridine ring of the chiral host (R,R)-19 does weaken exciton interaction between the host and guest molecules, but does not destroy the discriminating power of the chiral host. An HPLC column filled with (R,R)-CSP-37 was tested for the enantioseparation of racemic 1-(1-naphthyl)- and 1-(2-naphthyl)ethylamine hydrogenperchlorates using isocratic conditions.     

Facile Synthesis of 5-Aryl-N-(pyrazin-2-yl)thiophene-2-carboxamides via Suzuki Cross-Coupling Reactions,Their Electronic and Nonlinear Optical Properties through DFT Calculations

Synthesis of 5-aryl-N-(pyrazin-2-yl)thiophene-2-carboxamides (4a–4n) by a Suzuki cross-coupling reaction of 5-bromo-N-(pyrazin-2-yl)thiophene-2-carboxamide (3) with various aryl/heteroaryl boronic acids/pinacol esters was observed in this article. The intermediate compound 3 was prepared by condensation of pyrazin-2-amine (1) with 5-bromothiophene-2-carboxylic acid (2) mediated by TiCl₄. The target pyrazine analogs (4a–4n) were confirmed by NMR and mass spectrometry. In DFT calculation of target molecules, several reactivity parameters like FMOs (E_HOMO, E_LUMO), HOMO–LUMO energy gap, electron affinity (A), ionization energy (I), electrophilicity index (ω), chemical softness (σ) and chemical hardness (η) were considered and discussed. Effect of various substituents was observed on values of the HOMO–LUMO energy gap and hyperpolarizability. The p-electronic delocalization extended over pyrazine, benzene and thiophene was examined in studying the NLO behavior. The chemical shifts of ¹H NMR of all the synthesized compounds 4a–4n were calculated and compared with the experimental values.     

Practical method for the synthesis of (R)-homopipecolinic acid and (R)-homoproline esters from ω-chloroalkanoic acids and available chiral amines

A practical synthesis of (R)-homopipecolinic acid methyl ester 1 and (R)-homoproline methyl ester 2 was performed utilizing (i) a direct intramolecular cyclization of ω-chloro-β-enamino esters 11 and 12, which were prepared from available (S)-1-phenylethylamine or (S)-1-(1-naphthyl)ethylamine and ω-chloro-β-keto esters 5 and 10, respectively and (ii) a highly diastereoselective NaBH₄ reduction followed by hydrogenolysis. The present method is a short-step process using inexpensive and readily available substrates and reagents with fewer wasted materials.     

Formation of chiral 21-helical columnar host system with phenylacetylene unit by using (1R,2S)-2-amino-1,2-diphenylethanol

A tunable supramolecular phenylacetylene host system with a chiral channel-like cavity is developed by using (1R,2S)-2-amino-1,2-diphenylethanol. This host system possesses a chiral 2₁-helical columnar structure; chiral cavities are constructed by the self-assembly of the 2₁-helical column, and guest molecules are included by varying the packing of this column.     

Optically active palladacycles containing imines derived from 1-(1-naphthyl)ethylamine: new resolving agents for P-chiral phosphines

The synthesis of the new palladium metallacycles containing imines derived from 1-(1-naphthyl)ethylamine is reported. These new organometallic complexes have been used to resolve the P-chiral ligand benzylcyclohexylphenylphosphine. The absolute configuration of (R_C,S_P)-[PdCl{2-[HCN-CH(Me)C₁₀H₆]-3-ClC₆H₃}(PBzCyPh)] has been determined by single crystal X-ray analysis.     

Chiral N-heterocyclic carbenes as asymmetric acylation catalysts

Chiral N-heterocyclic carbenes are generated from C₂-symmetric 1,3-bis(1-arylethyl)imidazolium salts and potassium tert-butoxide. These C₂-symmetric imidazolidenyl carbenes catalyze enantioselective acylation of racemic secondary alcohols. The asymmetric acylation of 1-(1-naphthyl)ethanol was achieved in up to 68% ee of the acylated product, using (R,R)-1,3-bis[(1-naphthyl)ethyl]imidazolium tetrafluoroborate as a precursor of the chiral N-heterocyclic carbene and vinyl propionate as the acyl donor.     

The use of (S)-(−)-1-(1-naphthyl)ethylamine as a resolving agent for α-methoxy fatty acids

A general method was developed for the diastereoselective resolution of α-methoxy fatty acids utilizing (S)-(−)-1-(1-naphthyl)ethylamine as resolving agent. The diastereomeric amides can be easily separated by silica gel column chromatography and/or capillary gas chromatography, thus allowing for a preparative and analytical method for determining the enantiomeric purity of naturally occurring and/or synthetic α-methoxy fatty acids. The first synthesis of the naturally occurring (R)-2-methoxyhexadecanoic acid was also accomplished in four steps starting from commercially available (±)-2-hydroxyhexadecanoic acid.     

Synthesis of tricyclic isoindoles and thiazolo[3,2-c][1,3]benzoxazines

The thermolysis of (3R,9bS)-5-oxo-2,3,5,9b-tetrahydrothiazolo[2,3-a]isoindole-3-carboxylic acids in Ac₂O led to novel 3-methylene-2,5-dioxo-3H,9bH-oxazolo[2,3-a]isoindoles and chiral (9bS)-5-oxo-2,3,5,9b-tetrahydrothiazolo[2,3-a]isoindoles were obtained on FVP. Starting from l-cysteine methyl ester (3R,10bR)-5-oxo-2,3-dihydro-10bH-[1.3]thiazolo[3,2-c][1,3]benzoxazines were obtained as single stereoisomers. The thermolysis of (3R,10bR)-5-oxo-2,3-dihydro-10bH-[1.3]thiazolo[3,2-c][1,3]benzoxazine-3-carboxylic acid in Ac₂O gave 5-acetyl-2-phenyl-2,3-dihydrothiazole. The structures of methyl (3R,9bS)-5-oxo-2,3,5,9b-tetrahydrothiazolo[2,3-a]isoindole-3-carboxylate 1a and methyl (2R,4R)-N-chlorocarbonyl-2-(2-hydroxyphenyl)thiazolidine-4-carboxylate 9 were determined by X-ray crystallography.