v-Triazolines. XXXIX . 1,2,4-Triaryl-3-aminopyrroles. Unusual Reaction Products in the Pyrolysis of 5-Amino-v-triazolines and the Crystal Structure of 2-(3-Morpholin-4-yl-2,4-pyrrol-1-yl)benzonitrile

Pyrolysis of 4-aryl-5-amino-v-triazolines affords, generally, amidines and/or benzanilides. Pyrolysis of 4-aryl-5-morpholino-v-triazolines 6 , together with the expected amidines 7 and/or aryanilides 8 , produced the morpholinopyrroles 9 . The reaction mechanism of this unusual transformation is discussed. Influence of solvent dipole moment in pyrrole formation is suggested. Pyrrole 9a [i.e. 2-(3-morpholin-4-yl-2,4-pyrrol-1-yl)-benzonitrile] has been fully characterized and its molecular structure has been determined by X-ray diffraction analysis.     

Determination of manganese in brain samples by slurry sampling graphite furnace atomic absorption spectrometry

A simple procedure for the determination of manganese in different sections of human brain samples by graphite furnace atomic absorption spectrometry has been developed. Brain sections included cerebellum, hypothalamus, frontal cortex, vermix and encephalic trunk. Two sample preparation procedures were evaluated, namely, slurry sampling and microwave-assisted acid digestion. Brain slurries (2% w/v) could be prepared in distilled, de-ionized water, with good stability for up to 30 min. Brain samples were also digested in a domestic microwave oven using 5 ml of concentrated HNO₃. A mixed palladium+magnesium nitrate chemical modifier was used for thermal stabilization of the analyte in the electrothermal atomizer up to pyrolysis temperatures of 1300 °C, irrespective of the matrix. Quantitation of manganese was conducted in both cases by means of aqueous standards calibration. The detection limits were 0.3 and 0.4 ng ml⁻¹ for the slurry and the digested samples, respectively. The accuracy of the procedure was checked by comparing the results obtained in the analysis of slurries and digested brain samples, and by analysis of the NIST Bovine Liver standard reference material (SRM 1577a). The ease of slurry preparation, together with the conventional set of analytical and instrumental conditions selected for the determination of manganese make such methodology suitable for routine clinical applications.     

Asymmetric synthesis of 4,4-disubstituted-2-imidazoli-dinones: potent NK1 antagonists

[structure: see text] A highly efficient and practical synthesis of 4,4-Disubstituted-2-Imidazolidinones utilizing a "self-reproduction of the center of chirality" strategy is described.     

Glycidol syntheses and valorizations: Boosting the glycerol biorefinery

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New Class of Chiral Diphosphine Ligands for Highly Efficient Transition Metal-Catalyzed Stereoselective Reactions: The Bis(diphenylphosphino) Five-membered Biheteroaryls

The synthesis and application of three examples of a new class of chiral (C(2)) atropisomeric diphosphines characterized by two interconnected five-membered heteroaromatic rings, with hindered rotation around the interanular bond, are described. Optically pure (+)- and (-)-2,2'-bis(diphenylphosphino)-4,4',6,6'-tetramethyl-3,3'-bibenzo[b]thiophene (tetraMe-bitianp) (1a) and the parent unsubstituted system (+)- and (-)-bitianp (1b) were synthesized. They were found to be optically stable at 100 degrees C and were successfully employed as ligands in the Ru(II)-catalyzed hydrogenation of alpha- and beta-oxo esters to the corresponding alpha- and beta-hydroxy esters and in the hydrogenation of olefinic substrates. The optical and chemical yields were comparable with those reported for the same Ru(II)-binap-catalyzed reactions carried out under the same experimental conditions. The 2,2'-bis(diphenylphosphino)-3,3'-bibenzo[b]furan (1c), the oxygenated analogue of bitianp, was found to be configurationally unstable at room temperature. Complete structural X-ray elucidation of the Pd complexes of 1a-c is reported. The advantages of these biheteroaromatic ligands over the classical biaryl systems are discussed.     

Conformational studies by dynamic NMR. 94.1 cogwheel pathway for the stereomutations of durene derivatives containing the mesityl ring

The low-temperature NMR spectra of 1,4-bis(mesitoyl)durene, 1, and of 1,4-bis(mesitylethenyl)durene, 2, reveal the presence of syn and anti rotamers at the equilibrium, their relative proportions depending on the dielectric constant of the solvent. In solution the more stable rotamer of 1 is the anti whereas, in the case of 2, the more stable is the syn. Depending on the crystallization solvent employed the more (anti) and the less stable (syn) rotamers were both observed (X-ray diffraction) in the solid state of 1. On the other hand, only the less stable rotamer (anti) was found to be present in the solid state of 2. As shown by MM calculations, the syn-to-anti interconversion occurs via a correlated process (cogwheel pathway) involving the mesityl-C and durene-C bond rotations: the dynamic NMR technique yields an experimental barrier of 8.2 kcal mol(-)(1) for 1 and 13.1 kcal mol(-)(1) for 2. In the case of derivative 2 a second barrier, due to a second type of correlated rotation process (torsion), was also determined (8.6 kcal mol(-)(1)). As a consequence of the restriction of this second torsional motion the anti rotamer of 2 displays two distinguishable NMR spectra at -133 degrees C, corresponding to a pair of conformers with different symmetry (anti C(i)() and anti C(2)).     

Quantum mechanical calculations of conformationally relevant 1H and 13C NMR chemical shifts of calixarene systems

[graphs: see text] QM GIAO calculations of 13C and 1H chemical shift values of the ArCH2Ar group have been performed, using the hybrid DFT functional MPW1PW91 and the 6-31G(d,p) basis set, on some representative calixarenes and on a series of simplified calixarene models allowing derivation of chemical shift surfaces versus phi and chi dihedral angles. A good reproduction of experimental data was obtained. The applicability of chemical shift surfaces in the study of calixarene conformational features is illustrated.     

Dynamic-mechanical properties and melting points of some aliphatic and partially aromatic polyamides

Some aliphatic and partially aromatic polyamides have been prepared from hexamethylene diamine and the following dicarboxylic acids: deca-, octa-, hexa-methylenedicarboxylic, p-carboxymethylphenoxyacetic, p-carboxyethylphenoxyacetic, p-phenylenedipropionic, p-phenylenediacetic, p-carboxymethoxyphenoxyacetic, β(p-carboxymethyl)phenylpropionic.The dynamic-mechanical properties at 110 Hz have been measured between ?140° and about 200. Three relaxation processes α β and γ have been found: only the main transition α appreciably depends on chemical structure.The influences of the length of repeating unit and of in-chain substitution on melting points, crystallinity and the dynamic-mechanical α transition have been investigated. The results have been discussed in terms of chain flexibility, chain packing and intermolecular forces.     

Mass fragmentation pattern of N- and O-substituted 2-morpholinols

The mass spectra of a series of N- and O-substituted 2-morpholinols were considered and the complex fragmentation pattern explained on the basis of evidences reported in the literature and of experimental data (high resolution, metastable ions). The primary fragmentations are given by inductive cleavage due to the heteroatoms, while ring contractions, through retro Diels-Alder reactions, form most of the secondary pattern with different ions related to N- and O-substituents. Moreover, hemiacetals in the tautomeric hydroxyaldehyde form undergo an α-cleavage.     

On the electronic states of macrocycles of the extended porphyrin family and their coordination compounds

The electronic absorption spectra of Ni, Zn and Mg hemiporphyrazine derivatives are presented and discussed together with theoretical results obtained by INDO/S computations. The absorption spectra of all the metal derivatives show marked red shifts of the lowest energy absorption bands with respect to those of the metal free hemiporphyrazine. The possible explanation that in metal derivatives low lying excited states with a fully conjugated π electron system are present is supported by theoretical computations.