Stereoisomerism in the series of isoindole-based quaternary salts

Steric structure of quaternary ammonium salts of the 3-[alkyl(aryl)amino]-1-[alkyl(aryl)iminio]-1H-isoindole series was studied by ¹H NMR spectroscopy and X-ray analysis. The examined salts are characterized by E,E configuration of substituents with respect to the exocyclic C-N bonds, and the presence of ortho- and meta-substituents in the benzene rings on the nitrogen atoms gives rise to atropisomers. Sterically hindered N-(2,4,6-trimethylphenyl) derivative was found to exist as Z,Z isomer which undergoes irreversible thermal isomerization into the more stable E,E isomer through intermediate Z,E structure. The reactions of 1,1,3-trichloro-1H-isoindole with secondary aromatic amines having an electron-withdrawing substituent in the ortho position in the presence of organic bases (triethylamine, N,N-dimethylbenzylamine) are accompanied by decomposition of the latter and formation of unsymmetrically substituted salts of the 3-[alkyl(aryl)amino]-1-(dialkyliminio)-1H-isoindole series, which contain both arylamine residue and dialkylamino group and are also characterized by atropisomerism.     

A novel four-component tandem protocol for the stereoselective synthesis of highly functionalised thiazoles

The reaction of bis(aroylmethyl) sulfides with aromatic aldehydes and ammonium acetate in 1:2:1 molar ratio under solvent-free microwave irradiation afforded predominantly a series of thiazoles, viz., 1-aryl-2-[5(Z)-5-arylmethylidene-2,4-diaryl-2,5-dihydrothiazol-2-yl]ethanones stereoselectively. This reaction presumably occurs via a Knoevenagel condensation-Michael addition-cyclocondensation-ring opening-ring closing Michael addition sequence. The intermediacy of (Z,Z)-2,2′-thiobis(1,3-diarylprop-2-en-1-ones) in the above transformation is demonstrated by their conversion to the thiazoles upon reaction with ammonium acetate under solvent-free microwave irradiation.     

Conformational analysis—XIII: Syn and anti [3.2]-, [3.3]-, [4.2]-, and [4.3]-metacyclophanes

While in [3.3]metacyclophane (19) the aromatic rings preferentially adopt the syn arrangement, its lower and higher homologues, i.e. [2,2]-, [3.2]-, [4.2], and [4.3]-metacyclophane (1, 6, 26 and 30), adopt the anti conformation. Substituted [m,n]metacyclophanes do not necessarily behave similarly to the parent hydrocarbons. Substituted compounds exhibiting a different conformation are [3.2]metacyclophane-1,11-dione (7) (syn), [3.3]metacyclophane-2,11-dione (24) and the corresponding bis[propylene thioacetal] (25) (anti), [4.2]metacyclophane-2,12-dione (27) (syn), and [4.3]metacyclophane-2,13-dione (31) (syn). Thus, the solution conformation of an [m.n]metacyclophane is sensitive both to chain length [m.n.] of the bridges and substitution. The ring inversion barriers determined by variable temperature ¹H NMR decrease with increasing length of the bridges and qualitatively correlate with the transanular strain present in the pertinent system.     

Synthesis and characterization of new thermally stable poly(amide-imide)s based on bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetracarboxylic diimide and aromatic diamines

N,N′-bis-(4-carboxyphenyl)bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetracarboxylic diimide was prepared by reaction of bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetra carboxylic dianhydride with p-aminobenzoic acid in a mixture of acetic acid and pyridine (3: 2). Polycondensation of N,N′-bis-(4-carboxyphenyl)bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetracarboxylic diimide with six different aromatic diamines produced a series of new poly(amide-imide)s (PAIs) in high yields with inherent viscosities between 0.49–0.95 dl/g. All PAIs were characterized by means of elemental analysis, viscosity measurement, solubility test, FTIR spectroscopy and ¹H-NMR spectroscopy. Dynamic TGA of PAIs shows 10% weight loss temperatures from 410 to 435°C under nitrogen.     

Preparation and evaluation of 1,3-alternate 25,27-bis-(pentafluorobenzyloxy)-26,28-bis-(3-propyloxy)-calix[4]arene-bonded silica gel high performance liquid chromatography stationary phase

A 1,3-alternate 25,27-bis-(pentafluorobenzyloxy)-26,28-bis-(3-propyloxy)-calix[4]arene-bonded silica gel stationary phase (CalixBzF₁₀) was synthesized, structurally characterized, and used as a selector in liquid chromatography. The selectivity study of this phase was done by using fluorine-containing compounds (fluorobenzenes, fluoro-pyrimidine bases), as well as non-fluorinated analytes (non-steroidal anti-inflammatory drugs, sulfonamides, xanthines and polynuclear aromatic hydrocarbons). The effects of organic modifiers on the retention of various compounds possessing basic, acidic and neutral characteristics were studied. It was shown that only basic analytes exhibit a “U-shaped” retention profile and that retention depends on the mobile phase pH. Selectivity comparisons of the novel phase vs. the 1,3-alternate 25,27-bis-(benzyloxy)-26,28-bis-(3-propyloxy)-calix[4]arene phase (CalixBz) were performed. The retention mechanism is also discussed. The results indicate that the fluorinated calixarene stationary phase behaves like reversed-phase packing material; however, fluorine–fluorine interactions seem to be involved in the separation process of fluorine-containing analytes.     

Highly efficient one-pot synthesis of tetrahydropyridines

The combination of aromatic aldehydes, and 1,3-dicarbonyl compounds in the presence of a catalytic amount of poly(N,N′-dibromo-N-ethyl-benzene-1,3-disulfonamide) [PBBS] and N,N,N′,N′-tetrabromobenzene-1,3-disulfonamide [TBBDA] leads to the formation of highly substituted tetrahydropyridines. In this way, a series of pharmacologically interesting substituted piperidine derivatives were obtained in moderate to high yields at room temperature.     

Studies on electroreduction mechanisms of selected aromatic hydrocarbons in tetrahydrofuran

Detailed mechanisms of electrochemical reductions of seven polynuclear aromatic hydrocarbons (PAHs) including benzo[a]pyrene (BaP), benzo[e]pyrene (BeP), dibenz[a,h]anthracene, dibenz[a,c]anthracene, 3-methylcholanthrene, 7,12-dimethylbenz[a]anthracene, and benz[a]anthracene were studied using cyclic voltammetry, single potential step chronoamperometry, voltammetry at rotating disk electrodes, and controlled potential coulometry in tetrahydrofuran solution using 0.1 M tetra-n-butylammonium perchlorate as a supporting electrolyte. Results indicate that these compounds undergo ECE reactions to a final product reduced at L-regions of each PAH with the exception of BaP and BeP. For these two PAHs, unreduced hydrocarbons were identified after exhaustive electrolysis. Heterogeneous electron-transfer rate constants, as well as homogeneous reaction rate constants, for the addition of the proton to electrogenerated anion radicals are also reported.     

Novel aromatic polyimides derived from benzofuro[2,3-b]benzofuran-2,3,8,9-tetracarboxylic dianhydride (BBTDA)

Benzofuro[2,3-b]benzofuran-2,3,8,9-tetracarboxylic dianhydride (BBTDA) is introduced as a monomer for the synthesis of a series of novel polyimides with enhanced high thermal stability. Polyimides derived from BBTDA and aromatic diamines showed high glass transition (T_g>296 °C) and degradation (T₅>455 °C) temperatures, and were soluble in organic solvents (i.e. N-methyl pyrrolidone (NMP), N,N^′-dimethylformamide (DMF), N,N^′-dimethylacetamide (DMAc)). The polymerization yielded high-molecular-weight polyimides with inherent viscosities ranging from 1.75 to 2.14 dl/g. The polymers were characterized by IR and elemental analysis.     

Two‐Dimensional Acetylenic Scaffolding: Extended Donor‐Substituted Perethynylated Dehydroannulenes

Starting from (Z)‐bis(N,N‐diisopropylanilino)‐substituted tetraethynylethene (TEE), perethynylated octadehydro[12]‐ and dodecadehydro[18]annulenes were prepared by oxidative Hay coupling. The dodecadehydro[18]annulene with six peripheral N,N‐diisopropylanilino substituents was characterized by X‐ray crystallography. Elongation of the Z‐bisdeprotected TEE by Cadiot–Chodkiewicz coupling with 1‐bromo‐2‐(triisopropylsilyl)ethyne provided a Z‐configured bis(butadiyne), which after alkyne deprotection afforded under Hay coupling conditions N,N‐diisopropylanilino‐substituted perethynylated hexadecadehydro[20]‐ and tetracosadehydro[30]an‐nulenes. The diisopropylanilino substituents enhance the properties of these unprecedented all‐carbon perimeters in several distinct ways. They ensure their solubility, increase their stability, and importantly, engage in strong intramolecular charge‐transfer interactions with the electron‐accepting all‐carbon cores, resulting in intense, bathochromically shifted charge‐transfer bands in the UV/Vis spectra. The charge‐transfer character of these bands was confirmed by protonation‐neutralization experiments. The redox properties of the new carbon‐rich chromophores were investigated by cyclic voltammetry and rotating disk voltammetry, which indicated different redox behavior for aromatic (4n+2 π electrons) and antiaromatic (4n π electrons) dehydroannulenes.     

Ring expansion of 11H-benzo[b]fluorene-11-methanols and related compounds leading to 17,18-diphenyldibenzo[a,o]pentaphene and related polycyclic aromatic hydrocarbons with extended conjugation and novel architectures

Condensation between 7-(1,1-dimethylethyl)-13-phenyl-8H-indeno[2,1-b]phenanthrene and paraformaldehyde produced the corresponding 9-fluorenylmethanol derivative, which on treatment with P₂O₅ to promote a Wagner-Meerwein rearrangement for ring expansion furnished 14-phenyldibenzo[a,j]anthracene in 88% yield. Similarly, 17,18-diphenyldibenzo[a,o]pentaphene possessing a helical twist and bearing two phenyl substituents at the most sterically congested C17 and C18 positions and other related compounds were likewise synthesized. Subsequent intramolecular arylation reactions involving the phenyl substituents produced polycyclic aromatic hydrocarbons with novel architectures.     

Infrared spectroscopic study of the configuration of some alkylaryl ureas

The conformation of a series of 1-aryl-3-(n-butyl)ureas and 1-aryl-1-methyl-3-(n-butyl)-ureas having an orthohydroxyl group in the aromatic ring is studied by infrared spectroscopy. The spectral data show that in organic solvents (CHCl₃, CH₂Cl₂, CCl₄) the compounds are in a Z,Z-conformation. Conclusive evidence is obtained for the existence of an intramolecular hydrogen bond between the OH and CO groups in all N-methylated ureas.     

Reactions of polycyclic aromatic hydrocarbon radical cations with model biological nucleophiles

The determination of gas-phase reactivity of a series of polycyclic aromatic hydrocarbons (PAHs) with nucleophiles is directed at achieving isomer differentiation through ion-molecule reactions and collisionally activated decomposition spectra. A series of PAH isomers form gas-phase [adduci — H]⁺ ions with the reagent nucleophiles pyridine and N-methylimidazole. Collisionally activated decomposition spectra of the [adduct — H]⁺ ions of the pyridine/PAH systems are dominated by products formed by losses of C₅H₄N, C₅H₅N (presumably neutral pyridine), and C₅H₆N. Collisional activation of PAH/N-methylimidazole [adduct — H]⁺ ions causes analogous losses of C₄H₅N₂, C₄H₆N₂ (presumably neutral N-methylimidazole), and C₄H₇N₂. The relative abundances of the ions that result from these losses are highly isomer specific for N-methylimidazole but less so for pyridine. Furthermore, PAH/N-methylimidazole [adduct — H]⁺ ions undergo a series of metastableion decompositions that also provide highly isomer-specific information. The C₄H₇N₂ (from PAH/N-methylimidazole product ions) and C₅H₆N (from PAH/pyridine product ions) losses tend to increase with the ΔH _f of the PAH radical cation. In addition, it is shown that the fragmentation patterns of these gas-phase PAH/nucleophile adducts are similar to fragmentation patterns of PAH/nucleoside adducts generated in solution, which suggests that the structures of products formed in gas-phase reactions are similar to those produced in solution.     

Synthesis of N-[chloro(diorganyl)silyl]anilines

A series of N-[chloro(diorganyl)silyl]anilines RR′Si(NR″Ph)Cl (R, R′ = Me, Ph, CH₂=CH, ClCH₂, Cl(CH₂)₃; R″ = H, Me) was prepared via the reaction of diorganyldichlorosilanes with aniline or N-ethylaniline in the presence of triethylamine.     

Mild and regioselective iodination of aromatic compounds with N,N′-diiodo-N,N′-1,2-ethanediylbis(p-toluenesulphonamide)

N,N′-Diiodo-N,N′-1,2-ethanediylbis(p-tolouenesulphonamide) [NIBTS] and catalytic trifluoroacetic acid can be used for the regioselective iodination of aromatic compounds in acetonitrile under mild conditions in excellent yields.     

Preparation and properties of new ortho-linked polyamide-imides bearing ether, sulfur, and trifluoromethyl linkages

A CF₃-containing diamine, 2,2′-thiobis-[4-methyl(2-trifluoromethyl)4-aminophenoxy) phenyl ether] (DA), was successfully synthesized from 2-2′-sulfide-bis-(4-methyl phenol) and 2-chloro-5-nitrobenzotrifluoride. The sulfur containing diimide-diacid (DIDA) was prepared by condensation reaction of diamine DA and trimellitic anhydride. A series of novel organic-soluble polyamide-imides (PAIs) bearing flexible ether and sulfide links, electron-withdrawing trifluoromethyl groups and ortho-phenylene units were synthesized from DIDA, by direct polycondensation with various aromatic diamines in N-methyl-2-pyrrolidone using triphenyl phosphite and pyridine as a condensing agent in the presence of dehydrating agent (LiCl). The polyamide-imides were obtained in high yields and possessed inherent viscosities in the range of 0.42-0.95 dL g⁻¹. All of the polymers were amorphous in nature, showed outstanding solubility and could be easily dissolved in amide-type polar aprotic solvents (e.g., N-methyl-2-pyrrolidone, N,N-dimethylacetamide, and N,N-dimethylformamide) and even dissolved in less polar solvents (e.g., pyridine and tetrahydrofuran). They showed good thermal stability with glass transition temperatures between 195-245 °C, 10% weight loss temperatures in excess of 485 °C, and char yields more than 50% at 700 °C in nitrogen atmosphere. Moreover, these PAIs possessed low refractive indexes (n = 1.57-1.59) and low birefringence (Δ ≈ 0.02) due to the trifluoromethyl pendent groups and thioether bridged ortho-catenated aromatic rings that interrupt chain packing and increase free volume.     

Stereo- and regioselective synthesis of β-amino-β-tetrazolylvinylphosphonates

Addition of 5-substituted tetrazoles to dimethyl [(N,N-diisopropylamino)ethynyl]phosphonate proceeds regio- and stereoselectively to yield (Z)-[2-diisopropylamino-2-(tetrazolyl)vinyl]phosphonic acid dimethyl esters. The Z-configuration of the products was confirmed by ¹Н NMR spectroscopy and single-crystal X-ray diffraction. The reactions occur via nucleophilic attack of tetrazole involving predominantly the N-1 atom of the tetrazole ring.     

An approach to the synthesis of chemically modified bisazocalix[4]arenes and their extraction properties

Bisazocalix[4]arenes [N,N′-bis(5-azo-25,26,27-tribenzoyloxy-28-hydroxycalix[4]arene)benzene (1), N,N′-bis(5-azo-25,26,27-tribenzoyloxy-28-hydroxycalix[4]arene)biphenyl (2) and N,N′-bis(5-azo-25,26,27-tribenzoyloxy-28-hydroxycalix[4]arene)-2,2′-dinitro biphenyl (3)] have been synthesized from 25,26,27-tribenzoyloxy-28-hydroxycalix[4]arene by diazocoupling with the corresponding aromatic diamines (p-phenylenediamine, 4,4′-diamino biphenyl and 4,4′-diamino-2,2′-dinitrobiphenyl). Extraction studies of bisazocalix[4]arenes 1, 2, and 3 show no difference in their extraction behavior and selectivity, whereas azocalix[4]arenes are a poor extractant for heavy metal cations. The absorption spectra of the prepared bisazocalix[4]arenes are discussed, both the effect of varying pH and solvent upon the absorption ability of bisazocalix[4]arenes.     

Solute Retention in Column Liquid Chromatography. V. the Column Dead Volume

Abstract

Methods of determination of the column void volume with two homologous series of solutes (alkyl-substituted aromatic hydrocarbons and phenyl-substituted aliphatic alcohols) are considered in terms of correlation coefficients r of plots of log V'_R against carbon number over the temperature range 10[ddot]-30[ddot]C. The homologous series methods provide self-consistent fits as well as temperature-invariant data for the aromatic hydrocarbons, but not for the alcohols, for which a mixed retention mechanism is said to obtain. A new graphical method of determining the best-fit value of V_A is introduced that makes use of plots of r against assumed V_A. In contrast to work reported elsewhere by others, each of the series of compounds studied in this work clearly exhibits a maximum. Those for the aromatic hydrocarbons are temperature-invariant; however, this is not so for the alcohols, which is taken as evidence of thermal and/or multiple sorption interactions of these solutes with the stationary phase.     

Direct determination of selected polynuclear aromatic hydrocarbons in a coal liquefaction product by synchronous luminescence techniques

Synchronous fluorescence and the room-temperature phosphorescence methods were used to determine selected polynuclar aromatic hydrocarbons in a coal liquid (solvent-refined coal) product without a preseparation step. The procedure identified and quantified ten polynuclear aromatic compounds including anthracene, 2,3-benzofluorene, benzo[a]pyrene, benzo[e]pyrene, carbazole, dibenzothiophene, fluoranthene, fluorene, perylene and pyrene. Standard deviations for repeated determinations ranged from 10–30% for concentrations in the range of 0.1–6 mg g^-1. The data obtained by these methods agree with results by other methods within the estimated experimental uncertainty.     

Differential scanning calorimetry study of charge-transfer complexes of polynuclear aromatic hydrocarbons with the asymmetric acceptors 3- and 4-nitrophthalic anhydride

Charge-transfer, crystalline complexes of 3- and 4-nitrophthalic anhydrides with a number of unsubstituted polynuclear aromatic hydrocabons were studied by differential scanning calorimetry. The 3- and 4-nitrophthalic anhydrides are complexing agents more selective than s.trinitrobenzene and pyromellitic dianhydride, and only form complexes with a few of the twelve hydrocarbons investigated.Under the adopted conditions 3-NPA forms complexes with: pyrene, 3,4-benzopyrene, and 1,2,5,6,-dibenzoanthracene; 4-NPA forms complexes with these hydrocarbons and with anthracene, phenanthrene, 1,2-benzoanthracene benzoperylene, and coronene. Though having an electron affinity close to that of s.trinitrobenzene, 4-NPA forms less stable complexes with the polynuclear aromatic hydrocarbons, due to the asymmetry and non-planarity of its molecule.