Highly branched aromatic polymers prepared by single step syntheses

Highly branched polyphenylenes, polyphenylene ethers, aromatic polyesters and polyamides synthesized from AB₂ type monomers are reviewed. Polyphenylenes were obtained by aryl-aryl coupling reactions of 3,5-dihalo-phenyl organometallic reagents. ¹³C NMR indicates about 70% branching efficiency. A T_gat 236°C was observed, but the polymer did not form films. Polyethers were prepared by oxidative coupling of 2,4,6-tribromophenol and 2,4-dibromophenol. The former monomer gave high molecular weight polymers but the latter monomer did not polymerize well. Condensation of 3,5-diaminobenzoic acid (I) and 3-aminoisophthalic acid derivatives in an amide solvent gave lyotropic hyperbranched aromatic polyamides. The GPC indicated a large degree of polymer aggregation in the amide solvent in the absence of a complexing salt.     

Efficient solid-phase synthesis of quinazoline-2,4-diones with various substituents on aromatic rings

We have developed a method for the solid-phase synthesis of quinazoline-2,4-diones with various substituents on the aromatic ring. Although there have been numerous reports of the solid-phase synthesis of quinazoline-2,4-diones, they were not applicable to the synthesis of the quinazoline-2,4-diones with electron-withdrawing substituents on the aromatic ring. Considering the poor nucleophilicity of the amino group of anthranilic acids, coupling of anthranilic acids to solid-supported amines was investigated without protecting the amino group. Various anthranilamides were prepared using anthranilic acids with electron-withdrawing substituents because a wide range of anthranilic acids are commercially available. These anthranilamides were successfully cyclized with carbonyldiimidazole to give quinazoline-2,4-diones with high purity.     

Liquid chromatographic resolution of enantiomers containing single aromatic rings with β-cyclodextrin-bonded phases

Racemic compounds containing two or more ring moieties are thought to be of optimal size for complexation and resolution on β-cyclodextrin (β-CD) bonded-phase liquid chromatographic columns. There are few reports on the separation of racemates containing one or no rings. Here, seventeen single-ring-containing racemates are resolved via β-CD complexation: (±)-1-phenyl- ethyl propionate; (±)-α-methylbenzyl acetate, (±)-2-chloro-2-phenylacetic acid, (±)-ethyl- 3-phenylglycidate, d,l-3,4-dihydroxyphenyl-α-propylacetamide; (±)-2-methoxy-α-methylbenzyl alcohol, d,l-2-phenylpropionaldehyde, d,l-α-amino-3-thiopheneacetic acid, (±)-mandelic acid, (±)-mandelic acid methyl ester, (±)-O-acetylmandelic acid, (±)-ephedrine; d,l-phenyl- alanineamide, d,l-tyrosine, d,l-tyrosine methyl ester, 3-hydroxy-d,l-kynurenine and N-(3,5- dinitrobenzoyl)-d,l-leucine. These compounds can be separated on β-CD media, and have certain common structural properties that enhance chiral recognition. The factors that permit the resolution of single-ring-containing racemates on β-CD columns are discussed.     

Separation of the mineral oil aromatic hydrocarbons of three and more aromatic rings from those of one or two aromatic rings

An analytical method was developed for the quantitation of the mineral oil aromatic hydrocarbons in cosmetic raw materials separating those of one or two aromatic rings from those of three and more aromatic rings. Normal phase high performance liquid chromatography was used with donor‐acceptor complex chromatography. The composition of both fractions and the quantities of respective compounds were determined by comprehensive two dimensional gas chromatography with time of flight mass spectrometry and by liquid chromatography coupled to gas chromatography with flame ionization detection.     

Interactions with aromatic rings in chemical and biological recognition

Intermolecular interactions involving aromatic rings are key processes in both chemical and biological recognition. Their understanding is essential for rational drug design and lead optimization in medicinal chemistry. Different approaches-biological studies, molecular recognition studies with artificial receptors, crystallographic database mining, gas-phase studies, and theoretical calculations-are pursued to generate a profound understanding of the structural and energetic parameters of individual recognition modes involving aromatic rings. This review attempts to combine and summarize the knowledge gained from these investigations. The review focuses mainly on examples with biological relevance since one of its aims it to enhance the knowledge of molecular recognition forces that is essential for drug development.     

Effcient synthesis of functionalized hydroindoles via catalyst-free multicomponent reactions of ninhydrin in water简

An efficient synthesis of hydroindeno[1,2-b]indoles is described via three-component reaction of ninhydrin and cycloalkan-1,3-dione in the presence of primary amines in water as the green solvent in excellent yield.     

Three rings in one step: a quick approach to IKD-8344

A highly efficient enantioselective total synthesis of the natural antibiotic IKD-8344 is achieved through a convergent route. This route features an otherwise impossible concurrent formation of the THF rings from a linear polyketide precursor through intramolecular O alkylations of mesylates in competition with normally rather facile β elimination and/or α racemization reactions (see scheme, Ms=methanesulfonyl).     

Effect of the eluent composition in HPLC on the retention of bi- and trifunctional aromatic solutes

Summary Adsorption equilibria of aromatic compounds containing two or three polar groups (NH₂, OH, NO₂, CN, aromatic nitrogen) are investigated by high-performance liquid chromatography in chromatographic systems consisting of silica and a binary mobile phase consisting of heptane and a polar modifier (isopropanol or 1,4-dioxane). The relationships between the log k values and the concentration of the modifier (expressed as the logarithm of its mole fraction) are interpreted from the basis of the assumed molecular mechanism of adsorption, including solvation effects, i.e., solute-modifier interactions. Correlation of the log k values obtained for the two modifiers indicates that proton donor solutes can be retained by the adsorbed monolayer of dioxane molecules due to an interaction with the exposed ether oxygen atoms.     

Formation of aromatic rings through enamine annulation

Condensation of pyrrolidine enamine of ketones with 1, 4-diacetoxy-2-butanone provides a new, concise synthetic route to substituted benzenes, dihydroindenes, tetrahydronaphthalenes, and di- and octahydrophenanthrenes. The reaction produced modest yields with regiocontrol of the secondary amine substituent.     

A study of aromatic three membered rings

The resonance energies (REs) of neutral three membered ring analogs of the cyclopropenyl cation, computed using block localized wave function (BLW) methods, reveal considerable variations. The RE's of cyclopropenes substituted with exocyclic double bonded groups C?X, (X = O, NH, CH₂, S, PH, SiH₂) increase with the electronegativity of X in the same row (SiH₂ < PH < S and CH₂ < NH < O). The extra cyclic resonance energies (ECREs) (an energetic measure of aromaticity based on comparisons with the RE's of acyclic models) of these derivatives range from +10.5 kcal/mol for cyclopropenone (X = O) (somewhat aromatic; the benzene ECRE is 29.3 kcal/mol) to ?2.4 kcal/mol (slightly antiaromatic) for X = SiH₂. Additional disubstitution of the C?C double bond by X′ groups (X′ = CH₃, NH₂, OH, SiH₃, PH₂, SH) increases the REs considerably, but has only small effects on the ECREs. Even the ECRE of deltic acid (X = O, X′ = OH) is only increased to +13.3 kcal/mol. The conclusion based on ECRE's, that all 12 of the three membered rings are only marginally aromatic/antiaromatic, is supported by the satisfactorily plot (R² = 0.92) of ECRE against values of NICS(0)_πzz (a superior nucleus chemical independent shift magnetic index of aromaticity), which range only from ?6.1 ppm (diatropic) for deltic acid (cf., ?35.5 ppm for benzene and ?14.2 ppm for the parent cyclopropenium ion) to +8.9 ppm (paratropic) for the silicon derivative, X = SiH₂, X′ = SiH₃. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Synthesis of ferrocenoporphyrinophanes stacked with metals and aromatic rings

Double and triple layered porphyrinophanes bridged with 1,1′- or 1,3-disubstituted ferrocene moieties and their iron complexes have been synthesized.     

Thermal conductance measurements of superconducting bi-2212 rods and a bi-2212-based current leadmodule

We measured from 5 to 300 K the thermal conductance of different superconducting Bi-2212 thin rods and one superconducting module integrating a hybrid current lead based on such rods. The conductance values of the rods are lower than the measurable limits of the set-up and a detailed evaluation of the heat losses is required. The analysis of the heat exchanges permits to introduce a correction function to the measured values and allows to study low thermal conductivity materials. The dependence of the thermal conductivity of Bi-2212 rods on the sample microstructure is analyzed after this correction. We calculate analytically the time required to reach the steady-state for long bars for which extended relaxation times are expected. From the measured conductance data we estimate the heat load introduced by the current lead into a cryogenic bath in static conditions.     

Efficient catalyst-free Domino approach for the synthesis of novel 2-benzazepine derivatives in water

A novel one-pot eco-friendly protocol for the synthesis of 2-benzazepine derivatives in water has been developed. 4-Chloro-3-formyl coumarin reacts with benzyl amines under catalyst-free conditions in aqueous medium to afford substituted 5-(2′-hydroxyaryl)-4-amido-2-benzazepines in excellent yields.     

Convenient magnesiation of aromatic and heterocyclic rings bearing a hydroxy group in presence of LiCl

The reaction of various iodophenols with MeMgCl in presence of LiCl followed by the addition of i-PrMgCl provides the corresponding magnesiated magnesium phenolates as THF soluble reagents; this approach can be extended to heterocyclic compounds bearing a hydroxy group like pyridines and quinolines.     

A cascade palladium-mediated cross-coupling/electrocyclization approach to the construction of fused bi- and tricyclic rings

A versatile palladium-catalyzed cyclization/cross-coupling/electrocyclization strategy for the synthesis of fused bi- and tricyclic ring systems is described. Excellent yields of the polycyclic products are obtained with a range of tethering ring sizes and functionality, including an unprecedented 5,6,4,5-fused tetracycle. The reaction mechanism features two unusual palladium-mediated isomerizations prior to electrocyclization.