Alejandro Cárdenas

Ultrasound-assisted phase-transfer catalysis method in an aqueous medium to promote the Knoevenagel reaction: Advantages over the conventional and microwave-assisted solvent-free/catalyst-free method

Given the broad spectrum of uses of acrylonitrile derivatives as fluorescent probes, AChE inhibitors, and others, it is necessary to find easy, efficient and simple methods to synthesize and diversify these compounds. We report the results of a comparative study of the effects of three techniques on the reactions between heterocyclic aldehydes and 2-(benzo[d]thiazol-2-yl)acetonitrile: stirring; ultrasound coupled to PTC conditions (US-PTC); and MW irradiation (MWI) under solvent and catalyst-free conditions. The effects of conditions on reaction parameters were evaluated and compared in terms of reaction time, yield, purity and outcomes. The US-PTC method is more efficient than the MWI and conventional methods. The reaction times were considerably shorter, with high yields (>90%) and good levels of purity. In addition, X-ray diffraction analysis and quantum mechanical calculations, at the level of density functional theory (DFT), ratify obtaining acrylonitrile isomers with E configurations. The crystal structure of 3c is stabilized by weak C-Ho⋯N intermolecular interactions (Ho⋯NC=2.45 Å, Co⋯NC=3.348(3) Å, Ho⋯NC=162°), forming centrosymmetric ring R2(2) (20) along the crystallographic a axis.

Propane-1,3-diyl bis­(pyridine-4-carboxyl­ate)

The title compound. C15H14N2O4, (I), has a gauche–gauche (O/C/C/C—O/C/C/C or GG) conformation and is a positional isomer of propane-1,3-diyl bis(pyridine-3-carboxylate), (II). The molecule of (I) lies on a twofold rotation axis, which passes through the central C atom of the aliphatic chain, giving one half-molecule per asymmetric unit. There is excellent agreement of the geometric parameters of (I) and (II). The most obvious differences between them are the O/C/C/C—O/C/C/C torsion angles [56.6 (2)° in (I) and 174.0 (3)/70.2 (3)° in (II) for GG and TG conformations, respectively] and the dihedral angle between the planes of the aromatic rings [80.3 (10)° in (I) and 76.5 (3)° in (II)]. The crystal structure is stabilized by weak C—H⋯ N and C—H⋯ O hydrogen bonding.

X-RAY CRYSTALLOGRAPHIC STRUCTURAL STUDY ON A CINNAMOLIDE-CLASS SESQUITERPENE LACTONE FROM DRIMYS WINTERIFORST. VAR. CHILENSIS

In order to ascertain the structure and secure the assignment of the stereochemistry of the title compound an X-ray analysis was performed, the absolute configuration was not determined by this analysis. 1 . Chemical studies has shown the presence of a variety of sesquiterpenes with drimano skeleton 2 and flavonoids. Some of these structures have shown significant antibacterial, antifungi, antitumor and insecticide properties 3, 4 . The extract of Drimys winteri leaves afforded Cinnamolide and Drimenin two lactones with drimano skeleton. Cinnamolide have not been previuosly reported for these specie. Recently it has been reported that the title compound was also isolated of Cinnamosma macrocarpa 5 . In order to ascertain the structure and secure the assignment of the stereochemistry of the title compound an X-ray analysis was performed, the absolute configuration was not determined by this analysis. The X-ray crystallographic analysis confirms the previously proposed molecular structure, including the molecular conformation. The molecular structure is shown in Fig.1 and selected geometric parameters are given in Table I. The structure consists of a drimane skeleton. The methyl group at C9a is seen to be β-oriented. The cyclohexene ring A and cyclohexane ring B exist in a half-chair and a chair conformation, respectively (Q T = 0.538(3) A, ϕ 2 = 227.4(4) °, q 2 = 0.428 (3) A for ring A; Q T = 0.556(4) A , ϕ 2 = 21 (4)o, q 2 = 0.060 (4) A for ring B) , and the lactone ring an envelope on C3a conformation 6 . The A and B rings are trans-fused. Bond lengths are within expected ranges 7

Self-Assembly of Discrete Metallocycles versus Coordination Polymers Based on Cu(I) and Ag(I) Ions and Flexible Ligands: Structural Diversification and Luminescent Properties

Three new Ag(I) and one Cu(I) coordination compounds with two different positional isomers, propane-1,3-diyl bis(pyridine-4-carboxylate) (L1) and propane-1,3-diyl bis(pyridine-3-carboxylate) (L2), of a bis-(pyridyl-carboxylate) ligand have been synthesized. X-ray diffraction analysis revealed that the self-assembly of L1 with AgCF3SO3 and AgClO4 salts leads to the formation of discrete binuclear metallocycles {Ag(L1)CF3SO3}2 (1) and {Ag(L1)ClO4}2 (2), respectively. However, self-assembly of the other ligand, L2, with AgCF3SO3 and CuCl salts, results in a 1-D zig-zag chain {Ag(L2)CF3SO3}∞ (3) and a 1-D double-stranded helical chain {Cu2Cl2(L2)2}∞ (4) coordination polymers, respectively. Solid emission spectra recorded at room temperature show interesting luminescence properties for all four compounds in the range from 438 to 550 nm, especially for compound 4 that was found to change its emission color when the wavelength of the excitation radiation is switched from 332 to 436 nm.

A monoclinic modification of propane-1,3-diyl bis-(pyridine-3-carboxyl-ate).

In the title compound, C15H14N2O4, (I), the molecule lies on a twofold rotation axis which passes through the central C atom of the aliphatic chain, giving one half-molecule per asymmetric unit. The structure is a monoclinic polymorph of the triclinic structure previously reported [Brito, Vallejos, Bolte & López-Rodríguez (2010). Acta Cryst. E66, o792], (II). The most obvious difference between them is the O/C/C/C—O/C/C/C torsion angle [58.2 (7)° in (I) and 173.4 (3)/70.2 (3)° in (II) for GG and TG conformations, respectively]. Another important difference is observed in the dihedral angle between the planes of the aromatic rings [86.49 (7)° for (I) and 76.4 (3)° for (II)]. The crystal structure features a weak π–π interaction [centroid–centroid distance = 4.1397 (10)Å]; this latter kind of interaction is not evident in the triclinic polymorph.

Supramolecular Structure, Thermal and Spectroscopic Properties of a New Coordination Polymer: Catena-Bis(μ2-4,4′-dipyridyldisulfide-κ2N,N′)-Bis(AQUO)-Copper(II)di-trifluoromethanesulfonate

A new supramolecular network of copper (II), [{Cu(bpds)2(H2O)2}] • 2CF3SO3]n, (I), (bpds = 4,4′-bipyridildisulfide) has been synthesized and characterized by elemental analysis and Fourier transform infrared (FT-IR) and its structure determined using X-ray crystallography. The thermal decomposition mechanism of the complex was studied by using thermogravimetry-derivative thermogravimetry (TG-DTG) techniques. X-ray structural analysis revealed that the coordination polymer displays 1D chains. The octahedral O2N4 chromophore surrounding the metal ion forms via two trans located water oxygen and four nitrogen from four bpds ligand. The structure consists of Cu(H2O)2 fragments linked by pairs of bpds ligand to form a double-stranded chain. The thermogravimetric analysis indicates sequential loss of adsorbed and coordinated water and triflate counter ion, prior to more comprehensive ligand fragmentation at elevated temperatures.

Ethane-1,2-diyl bis­(pyridine-3-car­box­ylate)

The title compound, C14H12N2O4, has twofold imposed crystallographic symmetry in the solid state. The asymmetric unit contains one half-molecule. An intramolecular C—H⋯O hydrogen bond is formed between the carboxylate O group and one H atom of the aromatic ring such that a five-membered ring is formed. The angle between the planes of symmetry-related aromatic rings is 44.71 (19)°.

Synthesis, Characterization and Supramolecular Structure of Two New Isotypic Coordination Polymers: Poly-Bis(μ2-ethane-1,2-diyl bis(pyridine-3-carboxylate)κ2N,N′–Bis(aquo)-Copper(II)X2 (X = ClO4 −; NO3 −)

Two novel coordination polymers, {[CuL2(H2O)2]X2}n, with L = ethane-1,2-diyl bis(pyridine-3-carboxylate) and X = ClO4 −; NO3 − have been prepared by self-assembly of Cu(II) salts with L in THF/H2O system. The IR, TGA, and the reflectance spectra in the solid state have been recorded, and both complexes were structurally characterized by X-ray crystallography confirming that the complexes are one-dimensional coordination isotypic polymers, and L acts in a μ2-N,N′-bidentate fashion to link Cu(II) cations to form a double-stranded chain along [001]. The main structural motifs difference between both compounds is related to supramolecular self-assembly.

4′,5-Dihy­droxy-7-meth­oxy­flavanone dihydrate

The title compound, C16H14O5·2H2O [systematic name: 5-hydroxy-2-(4-hydroxyphenyl)-7-methoxychroman-4-one dihydrate], is a natural phytoalexin flavone isolated from the native chilean species Heliotropium taltalense and crystallizes with an organic molecule and two water molecules in the asymmetric unit. The 5-hydroxy group forms a strong intramolecular hydrogen bond with the carbonyl group, resulting in a six-membered ring. In the crystal, the components are linked by O—H⋯O hydrogen bonds, forming a three-dimensional network. The 4-hydroxyphenyl benzene ring is bonded equatorially to the pyrone ring, which adopts a slightly distorted sofa conformation. The title compound is the hydrated form of a previously reported structure [Shoja (1990 ▶). Acta Cryst. C46, 1969–1971]. There are only slight variations in the molecular geometry between the two compounds.

4-[3-(Isonicotino­yloxy)propoxycarbon­yl]pyridinium diiodidoargentate(I)

The structure of the title compound, (C15H15N2O4)[AgI2], consists of an organic 4-[3-(isonicotinoyloxy)propoxycarbonyl]pyridinium cation which has a gauche–gauche (O/C/C/C—O/C/C/C or GG’) conformation and lies on a twofold rotation axis, which passes through the central C atom of the aliphatic chain, and an inorganic [AgI2]− anion. In the complex anion, the Ag+ cation is bound to two I− anions in a linear geometry. The anion was modelled assuming disorder around a crystallographic inversion centre near the location of the Ag+ cation. The crystal packing is stabilized by a strong intermolecular N—H⋯N hydrogen bond, which links the cations into zigzag chains with graph-set notation C(16) running along the face diagonal of the ac plane. The N-bound H atom is disordered over two equally occupied symmetry-equivalent sites, so that the molecule has a pyridinium ring at one end and a pyridine ring at the other.