Living anionic polymerization of (E)‐1,3‐pentadiene and (Z)‐1,3‐pentadiene isomers

The anionic polymerization of (E)‐1,3‐pentadiene (EP) and (Z)‐1,3‐pentadiene (ZP) together with mixture of the E/Z isomers are investigated, respectively. The kinetic analysis shows that the activation energy for EP (86.17 kJ/mol) is much higher than that for ZP (59.03 kJ/mol). GPC shows that it is the EP rather than the ZP isomer that undergoes anionic living polymerization affording quantitative products of the polymers with well‐controlled molecular weights and narrow molecular weight distributions (1.05 ≤? ≤ 1.09). In addition, THF as polar additive has proved its validity to reduce the molecular weight distribution of poly(ZP) from 1.38 to as low as 1.19. The microstructure and sequence distributions of polypentadiene are characterized by ¹H NMR and quantitative ¹³C NMR. Finally, the distinctive reaction activity of two isomers can be elucidated by two different mechanisms which involve the presence of four forms of zwitterions for EP and the typical [1,5]‐sigmatropic hydrogen‐shift phenomenon for ZP. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2291–2301     

The E and Z isomers of 3‐(benzoxazol‐2‐yl)­prop‐2‐enoic acid

The carboxyl­ic acid group and the double bond are coplanar in (E)‐3‐(benzoxazol‐2‐yl)­prop‐2‐enoic acid, C₁₀H₇NO₃, whereas in isomeric (Z)‐3‐(benzoxazol‐2‐yl)­prop‐2‐enoic acid, also C₁₀H₇NO₃, they are almost orthogonal. In both isomers, a strong O—H⋯N hydrogen bond, with the carboxyl­ic acid group as a donor and the pyridine‐like N atom as an acceptor, and weak C—H⋯O interactions contribute to the observed supramolecular structures, which are completed by π–π stacking interactions between oxazole and benzenoid rings.     

Halogen,hydrogen and electrostatic interactions in 2‐amino‐5‐chloro‐1,3‐benzoxazol‐3‐ium nitrate and 2‐amino‐5‐chloro‐1,3‐benzoxazol‐3‐ium perchlorate

In the title compounds, C₇H₆ClN₂O⁺·NO₃⁻ and C₇H₆ClN₂O⁺·ClO₄⁻, the ions are connected by N—H...O hydrogen bonds and halogen interactions. Additionally, in the first compound, co‐operative π–π stacking and halogen...π interactions are observed. The energies of the observed interactions range from a value typical for very weak interactions (1.80 kJ mol⁻¹) to one typical for mildly strong interactions (53.01 kJ mol⁻¹). The iminium cations exist in an equilibrium form intermediate between exo‐ and endocyclic. This study provides structural insights relevant to the biochemical activity of 2‐amino‐5‐chloro‐1,3‐benzoxazole compounds.     

Charge‐assisted hydrogen bonding in salts of 2‐amino‐1H‐benzimidazole with 3‐phenylpropynoic acid and oct‐2‐ynoic acid

The 100 K structures of two salts, namely 2‐amino‐1H‐benzimidazolium 3‐phenylpropynoate, C₇H₈N₃⁺·C₉H₅O₂⁻, (I), and 2‐amino‐1H‐benzimidazolium oct‐2‐ynoate, C₇H₈N₃⁺·C₈H₁₁O₂⁻, (II), both have monoclinic symmetry (space group P2₁/c) and display N—H...O hydrogen bonding. Both structures show packing with corrugated sheets of hydrogen‐bonded molecules lying parallel to the [001] direction. Two hydrogen‐bonded ring motifs can be identified and described with graph sets R²₂(8) and R⁴₄(16), respectively, in both (I) and (II). Computational chemistry calculations performed on both compounds show that the hydrogen‐bonded ion pairs are more energetically favourable in the crystal structure than their hydrogen–bonded neutral molecule counterparts.     

MNPs@SiO2‐Pr‐AP: A new catalyst for the synthesis of 2‐amino‐4‐aryl thiazole derivatives

A simple and efficient synthesis of 2‐amino‐4‐aryl thiazole derivatives was carried out through the reaction of substituted acetophenones and thiourea using three different types of catalytic systems including N,N,N′,N′‐tetrabromobenzene‐1,3‐disulfonamide [TBBDA], poly(N,N′‐dibromo‐N‐ethylbenzene‐1,3‐disulfonamide) [PBBS] and a combination of TBBDA and nano‐magnetic catalyst supported with functionalized 4‐amino‐pyridine silica (MNPs@SiO₂‐Pr‐AP). The results showed that the use of TBBDA along with the MNPs@SiO₂‐Pr‐AP gains the highest yields of the products in the shortest reaction time.     

Comparison of the hydrogen‐bond patterns in 2‐amino‐1,3,4‐thiadiazolium hydrogen oxalate, 2‐amino‐1,3,4‐thiadiazole–succinic acid (1/2), 2‐amino‐1,3,4‐thiadiazole–glutaric acid (1/1) and 2‐amino‐1,3,4‐thiadiazole–adipic acid (1/1)

The X‐ray single‐crystal structure determinations of the chemically related compounds 2‐amino‐1,3,4‐thiadiazolium hydrogen oxalate, C₂H₄N₃S⁺·C₂HO₄⁻, (I), 2‐amino‐1,3,4‐thiadiazole–succinic acid (1/2), C₂H₃N₃S·2C₄H₆O₄, (II), 2‐amino‐1,3,4‐thiadiazole–glutaric acid (1/1), C₂H₃N₃S·C₅H₈O₄, (III), and 2‐amino‐1,3,4‐thiadiazole–adipic acid (1/1), C₂H₃N₃S·C₆H₁₀O₄, (IV), are reported and their hydrogen‐bonding patterns are compared. The hydrogen bonds are of the types N—H...O or O—H...N and are of moderate strength. In some cases, weak C—H...O interactions are also present. Compound (II) differs from the others not only in the molar ratio of base and acid (1:2), but also in its hydrogen‐bonding pattern, which is based on chain motifs. In (I), (III) and (IV), the most prominent feature is the presence of an R₂²(8) graph‐set motif formed by N—H...O and O—H...N hydrogen bonds, which are present in all structures except for (I), where only a pair of N—H...O hydrogen bonds is present, in agreement with the greater acidity of oxalic acid. There are nonbonding S...O interactions present in all four structures. The difference electron‐density maps show a lack of electron density about the S atom along the S...O vector. In all four structures, the carboxylic acid H atoms are present in a rare configuration with a C—C—O—H torsion angle of ∼0°. In the structures of (II)–(IV), the C—C—O—H torsion angle of the second carboxylic acid group has the more common value of ∼|180|°. The dicarboxylic acid molecules are situated on crystallographic inversion centres in (II). The Raman and IR spectra of the title compounds are presented and analysed.     

2,3‐Dihydro‐3‐methyl‐2‐nitrimino‐1,3‐thiazole

The title compound {alternatively, 3‐methyl‐2‐[oxido(oxo)hydrazono]‐2,3‐dihydro‐1,3‐thiazole}, C₄H₅N₃O₂S, was obtained by methyl­ation of N‐(2‐thia­zolyl)­nitr­amine. The molecule lies on a mirror plane and the thia­zole ring is planar, regular in shape and aromatic. The S atom participates in the aromatic sextet via an electron pair on the 3p_z orbital. In the crystal, the mol­ecules are arranged in parallel layers, bound to each other by weak C—H?O and C—H?N hydrogen bonds and by S?O dipolar interactions, with an interlayer separation of 3.23 Å.     

An amino–imino resonance study of 2‐amino‐4‐methylpyridinium nitrate and 2‐amino‐5‐methylpyridinium nitrate

The contributions of the amino and imino resonance forms to the ground‐state structures of 2‐amino‐4‐methylpyridinium nitrate, C₆H₉N₂⁺·NO₃⁻, and the previously reported 2‐amino‐5‐methylpyridinium nitrate [Yan, Fan, Bi, Zuo & Zhang (2012). Acta Cryst. E 68 , o2084], were studied using a combination of IR spectroscopy, X‐ray crystallography and density functional theory (DFT). The results show that the structures of 2‐amino‐4‐methylpyridine and 2‐amino‐5‐methylpyridine obtained upon protonation are best described as existing largely in the imino resonance forms.     

Heterocyclic tautomerism: reassignment of two crystal structures of 2‐amino‐1,3‐thiazolidin‐4‐one derivatives

The structures of 5‐(2‐hydroxyethyl)‐2‐[(pyridin‐2‐yl)amino]‐1,3‐thiazolidin‐4‐one, C₁₀H₁₁N₃O₂S, (I), and ethyl 4‐[(4‐oxo‐1,3‐thiazolidin‐2‐yl)amino]benzoate, C₁₂H₁₂N₂O₃S, (II), which are identical to the entries with refcodes GACXOZ [Váňa et al. (2009). J. Heterocycl. Chem. 46 , 635–639] and HEGLUC [Behbehani & Ibrahim (2012). Molecules, 17 , 6362–6385], respectively, in the Cambridge Structural Database [Allen (2002). Acta Cryst. B 58 , 380–388], have been redetermined at 130 K. This structural study shows that both investigated compounds exist in their crystal structures as the tautomer with the carbonyl–imine group in the five‐membered heterocyclic ring and an exocyclic amine N atom, rather than the previously reported tautomer with a secondary amide group and an exocyclic imine N atom. The physicochemical and spectroscopic data of the two investigated compounds are the same as those of GACXOZ and HEGLUC, respectively. In the thiazolidin‐4‐one system of (I), the S and chiral C atoms, along with the hydroxyethyl group, are disordered. The thiazolidin‐4‐one fragment takes up two alternative locations in the crystal structure, which allows the molecule to adopt R and S configurations. The occupancy factors of the disordered atoms are 0.883 (2) (for the R configuration) and 0.117 (2) (for the S configuration). In (I), the main factor that determines the crystal packing is a system of hydrogen bonds, involving both strong N—H...N and O—H...O and weak C—H...O hydrogen bonds, linking the molecules into a three‐dimensional hydrogen‐bond network. On the other hand, in (II), the molecules are linked via N—H...O hydrogen bonds into chains.     

Synthesis of novel 2‐amino‐1,3‐thiazole‐5‐carboxylates utilising ultrasonic and thermally mediated aminolysis

Novel 2‐amino‐1,3‐thiazole‐5‐carboxylates have been synthesised in high yield by unprecedented ultrasonic and thermally mediated nucleophilic displacement of bromide from ethyl 2‐bromo‐1,3‐thiazole‐5‐car‐boxylate by primary, secondary and aryl amines.     

Ethyl 2‐amino‐4‐phenyl‐1,3‐thia­zole‐5‐carboxyl­ate

The structure of the title compound, C₁₂H₁₂N₂O₂S, (I), comprises mol­ecules that form dimers via N—H?N hydrogen‐bonding interactions and then construct the overall network through N—H?O associations. The dihedral angle between the phenyl and thia­zole rings is 42.41 (6)°.     

The reaction of 2‐amino‐3‐cyano‐4,5,6,7‐tetrahydrobenzo[b]‐thiophene with diethyl malonate: synthesis of coumarin,pyridine, and thiazole derivatives

The reaction of 2‐amino‐3‐cyano‐4,5,6,7‐tetrahydrobenzo[b]thiophene ( 1 ) with diethyl malonate ( 2 ) gave two products: 3 and 4 . The reactivity of 3 toward a variety of chemical reagents was studied to give azoles, azines, and their fused derivatives. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:168–175, 2001     

Complexes of diethyl‐2‐amino‐2‐oxoethylphosphonate with lanthanide nitrates

Lanthanide complexes LnL₂(NO₃)₃ 3a–f are obtained where Ln is La, Ce, Sm, Eu, Er, and Yb and L is the diethyl 2‐amino‐2‐oxoethylphosphonate. They were characterized by elemental analysis, IR, and NMR spectroscopy. Monodentate coordination by the phosphoryl group is suggested for the ligand on the basis of the spectral data. The stabilization is achieved by including a molecule of the solvent in the complexes 3a–d . © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:128–131, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10112     

Polymerization of (E)‐1,3‐Pentadiene and (E)‐2‐methyl‐1,3‐pentadiene with neodymium catalysts: Examination of the factors that affect the stereoselectivity

(E)‐1,3‐Pentadiene (EP) and (E)‐2‐methyl‐1,3‐pentadiene (2MP) were polymerized to cis‐1,4 polymers with homogeneous and heterogeneous neodymium catalysts to examine the influence of the physical state of the catalyst on the polymerization stereoselectivity. Data on the polymerization of (E)‐1,3‐hexadiene (EH) are also reported. EP and EH gave cis‐1,4 isotactic polymers both with the homogeneous and with the heterogeneous system, whereas 2MP gave an isotactic cis‐1,4 polymer with the heterogeneous catalyst and a syndiotactic cis‐1,4 polymer, never reported earlier, with the homogeneous one. For comparison, the results obtained with the soluble CpTiCl₃‐based catalyst (Cp = cyclopentadienyl), which gives cis‐1,4 isotactic poly(2MP), are examined. A tentative interpretation is given for the mechanism of the formation of the stereoregular polymers obtained and a complete NMR characterization of the cis‐1,4‐syndiotactic poly(2MP) is reported. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3227–3232     

Stereoconvergent palladium-catalyzed carbonylation of both E and Z isomers of a 2-trifloxy-1,3-butadiene

[reaction: see text] Carbonylation of the illustrated Z-tetrasubstituted enol triflate followed by tandem silyloxy-Cope rearrangement leads to the CP-263, 114 core ring system with the all-carbon quaternary stereocenter intact in 46% yield. Subjection of the corresponding E isomer to the same conditions gives the same product in 56% yield. This observation is explained by a mechanism involving isomerization of a pi-allyl palladium species involving an allenic intermediate.     

Synthesis and mutagenic potency of structural isomers of 2‐amino‐1‐methyl‐6‐phenylimidazo[4,5‐b]pyridine

Synthesis of 2‐amino‐1‐methyl‐6‐phenylimidazo[4,5‐b]pyridine (PhIP), three structural isomers, and two desphenyl PhIP congeners has been carried out. Mutagenic potency was evaluated using S. typhimurium strain TA98 in the Ames test. Mutagenic potency increased in relation to structural features in these heterocyclic amines that allow extended resonance between the phenyl and imidazo[4,5‐b]pyridine N²‐amino substituents. By contrast, PhIP isomers, whose substitution disallows involvement of the phenyl group in their aminoimidazo resonance hybrids, and desphenyl congeners were from 86‐ to 234‐fold less mutagenic than PhIP.     

A facile synthesis of 2‐amino‐1,3‐selenazole by reaction of N,N‐unsubstituted selenourea with ketone

2‐Dialkylamino‐1,3‐selenazoles were yielded by the reaction of N,N‐unsubstituted selenoureas with ketones in the presence of ferric chloride. © 2006 Wiley Periodicals, Inc. Heteroatom Chem 17:88–92, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20180     

Synthesis of 1‐amino‐2‐methylindoline by Raschig process: Kinetics of the oxidation of 1‐amino‐2‐methylindoline by chloramine

The synthesis of 1‐amino‐2‐methylindoline by the Raschig process was undertaken in aqueous solution. The principal side reaction that occurs in the medium is the oxidation of 1‐amino‐2‐methylindoline formed by chloramine. To increase the yield of 1‐amino‐2‐methylindoline, its oxidation by chloramine was studied by GC and HPLC at various concentrations of reactants and for a pH interval ranging between 9.9 and 13.5. The reaction is bimolecular and exhibits a specific acid catalysis. In alkaline medium, 1‐amino‐2‐methylindole is the principal product. The enthalpy and entropy of activation were determined at pH 12.89. In unbuffered solution, the interaction was autocatalyzed by the ammonium ions formed, which indicates a competitive oxidation of neutral and ionic forms of 1‐amino‐2‐methylindoline by chloramine. A mathematical treatment based on one implicit equation allows a quantitative interpretation of all the phenomena observed over the above pH interval. It takes both acid–base dissociation equilibrium and alkaline hydrolysis of chloramine into account. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 515–523, 2002     

Intramolecular hydrogen bonding in derivatives of 3‐amino‐propenethial

Intramolecular H‐bonds existing for derivatives of 3‐amino‐propenethial have been studied using the B3LYP/6‐311++G** level of theory. The nature of these interactions, known as resonance assisted hydrogen bonds, has been discussed. The topological properties of the electron density distributions for N—H—S intramolecular bridges have been analyzed in terms of the Bader theory of atoms in molecules. Correlations between the H‐bond strength and topological parameters have been also studied. Furthermore, we obtained the exact value of the intramolecular hydrogen bond energies by the related rotamers method. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Five pseudopolymorphs of 6‐amino‐2‐thiouracil: absence of N—H...S hydrogen bonds

In order to study the preferred hydrogen‐bonding pattern of 6‐amino‐2‐thiouracil, C₄H₅N₃OS, (I), crystallization experiments yielded five different pseudopolymorphs of (I), namely the dimethylformamide disolvate, C₄H₅N₃OS·2C₃H₇NO, (Ia), the dimethylacetamide monosolvate, C₄H₅N₃OS·C₄H₉NO, (Ib), the dimethylacetamide sesquisolvate, C₄H₅N₃OS·1.5C₄H₉NO, (Ic), and two different 1‐methylpyrrolidin‐2‐one sesquisolvates, C₄H₅N₃OS·1.5C₅H₉NO, (Id) and (Ie). All structures contain R₂¹(6) N—H...O hydrogen‐bond motifs. In the latter four structures, additional R₂²(8) N—H...O hydrogen‐bond motifs are present stabilizing homodimers of (I). No type of hydrogen bond other than N—H...O is observed. According to a search of the Cambridge Structural Database, most 2‐thiouracil derivatives form homodimers stabilized by an R₂²(8) hydrogen‐bonding pattern, with (i) only N—H...O, (ii) only N—H...S or (iii) alternating pairs of N—H...O and N—H...S hydrogen bonds.