Microwave-assisted asymmetric ring opening of meso-epoxides with aromatic amines catalyzed by a Ti-S-(−)-BINOL complex

Catalytic asymmetric ring opening of cyclohexene oxide and meso-stilbene oxide with anilines was catalyzed by a Ti-(S)-(−)-BINOL complex to afford β-amino alcohols in high yield (up to 95%) and good enantioselectivities (ee up to 55%) under microwave irradiation. The reaction using a microwave was found to be 10 times faster than traditional oil-bath heating with retention of enantioselectivity.     

Ion population fraction calculations using improved screened hydrogenic model with l-splitting

Ion population fraction(IPF) calculations are very important to understand the radiative spectrum emitted from the hot dense matter. IPF calculations require detailed knowledge of all the ions and correlation interactions between the electrons of an ion which are present in a plasma environment. The average atom models, e.g., screened hydrogenic model with l-splitting(SHML), now have the capabilities for such calculations and are becoming more popular for in line plasma calculations. In our previous work [Ali A, Shabbir Naz G, Shahzad M S, Kouser R, Rehman A and Nasim M H 2018 High Energy Density Phys. 26 48], we have improved the continuum lowering model and included the exchange and correlation effects in SHML. This study presents the calculation of IPF using classical theory of fluctuation for our improved screened hydrogenic model with l-splitting(I-SHML) under local thermodynamic equilibrium conditions for iron and aluminum plasma over a wide range of densities and temperatures. We have compared our results with other models and have found a very good agreement among them.     

Cross-coupling reactions towards the synthesis of natural products

Molecular Diversity - Cross-coupling reactions are powerful synthetic tools for the formation of remarkable building blocks of many naturally occurring molecules, polymers and biologically active...     

Asymmetric addition of trimethylsilylcyanide to N-benzylimines catalyzed by recyclable chiral dimeric V(V) salen complex

Chiral dimeric vanadium (V) salen complex (10 mol%) derived from 5,5-Methylene di-[(S,S)-{N-(3-tert-butyl salicylidine)-N′-(3′,5′-di-tert-butyl salicylidene)]-1,2-cyclohexanediamine] with vanadyl suphate followed by auto oxidation was used as efficient catalyst for enantioselective Strecker reaction of N-benzylimines with TMSCN at −30 °C. Excellent yield (92%) of α-aminonitrile and high chiral induction was achieved (ee up to 94%) in case of 2-methoxy substituted N-benzylimines in 10 h. The catalytic system worked well up to four cycles with retention of enantioselectivity.     

Cyclization of lithiated pyridine and quinoline carboxamides: synthesis of partially saturated pyrrolopyridines and spirocyclic beta-lactams

Lithiation of N-benzyl pyridine and quinoline carboxamides alpha to nitrogen gives anions that undergo intramolecular attack on the pyridine or quinoline ring, either directly or on activation of the ring by N-acylation. The resulting four-, five-, or six-membered-ring-containing compound may be oxidized, protonated, alkylated, or acylated to give a range of polycyclic heterocycles, including pyrrolopyridines, pyrroloquinolines, benzonaphthyridines, and azaspirocyclic beta-lactams. [reaction: see text]     

Synthesis of new dinuclear dicopper(II) and dinickel(II) complexes. The kinetics of catechol oxidase and electrochemistry of a dicopper(II) complex

A new dinuclear ligand L, ethylene[OO-bis-salicylidene--diketone] bearing two symmetrical coordination sites was synthesized by the condensation of salicylaldehyde and acetylacetone, L, with 1,2-dibromoethane under reflux. The ligand L in a 1:1 ratio was treated with CuCl₂ and NiCl₂ to yield the complexes, tetrachloro bis[OO-bis- salicylidene--diketone copper(II)] and bis[OO-bis-salicylidene--diketone nickel(II)] chloride. The complexes were subsequently characterized by spectroscopic techniques, elemental analysis, i.r., ¹H-n.m.r., ¹³C-n.m.r., u.v.–vis., e.p.r. spectroscopy, and conductance measurements. The conductance measurements in DMF reveal that the Cu^II complex is covalent while the Ni^II complex is ionic and the spectral data support the Cu^II complex to be distorted octahedral whereas the Ni^II complex has square-planar geometry. The dioxygen binding was studied spectrophotometrically by the oxidation of tetrachloro bis[OO-bis-salicylidene--diketone copper(II)] with pyrocatechol in the presence of oxygen. The kinetic experiments were performed with the copper complex in DMF by monitoring the increase in absorbance over time at pH 8.0 in the presence of pyrocatechol at 25 °C. The kinetic parameters V_max and K_M were determined on the Michaelis–Menten Approach. Redox behavior of the dinuclear copper(II) complex was investigated by cyclic voltammetry in the presence of O₂ with the pyrocatechol (substrate) and also without the substrate. The large difference in potentials E⁰ is indicative of reversible oxygen binding of the complex and distinct catalytic activity.     

Synthesis of new 14- and 16-membered macrocycles and their transition metal complexes

Summary Benzoylacetic acid (1 mol) interacts with ethylenediamine or with propanediamine (2 mol) to yield new N₄ macrocycles 1,5,8,12-tetraazacyclotetradeca-2,4,9,11-tetraphenyl-3, 10-dicarboxylic-4,11-diacetic acid- 1,8-diene (L¹) and 1,5,9,13-tetraazacyclohexadeca-2,4,10,12-tetraphenyl-3, 11-dicarboxylic-4,12-diacetic acid-1,9-diene (L²), respectively. These macrocycles have been successfully complexed with Cr^III, Fe^III, Mn^II, Co^II, Ni^II, Cu^II and Zn^II. The complexes of the divalent metal ions are non-electrolytes, while those of Fe^III and Cr^III are 1:1 electrolytes in DMSO. On the basis of ligand field spectra and magnetic moments an octahedral geometry has been proposed for all the complexes.     

Transformation of Acetaminophen by Dichromate Oxidation Produces the Toxicants 1,4-Benzoquinone and Ammonium Ions

The reaction of the common pain reliever acetaminophen (paracetamol, 4-acetamidophenol) with dichromate was investigated over time under conditions that simulate wastewater disinfection. The occurrence of the acetaminophen in the water bodies, especially in drinking water resources, has received considerable attentions. In situ chemical oxidation is a promising cost-effective treatment method to remove acetaminophen from water body as it degrades the drug to large extent. Experimental results indicate that the reaction is second order overall and first order with respect to both dichromate and acetaminophen, and has activation energy of 14.1 kJ/mol. The second-order rate constant ranges from 1.56 × 10^?3 to 13.4 × 10^?3 min^?1 at temperature from 35 to 65°C. The acetaminophen degradation rates can be accelerated through increasing reaction temperature and oxidant concentration. The reaction under acid conditions was slightly faster than under alkaline or neutral conditions. Two of the products were unequivocally identified as the toxic compounds 1,4-benzoquinone and ammonium ions. These results demonstrate that acetaminophen is likely to be transformed significantly into toxic product if dichromate is used as an oxidizing agent during wastewater treatment.     

Synthesis,Characterization, Solution Stability Studies,Electrochemistry, and DNA‐Binding Behavior of Cu(II) Complexes of D‐Gluconic Acid

The chemistry of saccharides has emerged as a new subarea of pharmaceuticals. Condensation reactions of D‐gluconic acid with [M(en)₂]Cl₂/[M(ea)₂]Cl₂ where M=Cu, Ni, en=ethylenediamine, and ea=ethanolamine were carried out and a new series of chiral complexes have been isolated and characterized. Molar conductance measurements show that the complexes are ionic, and the spectral data are indicative of octahedral geometry of the complexes [Cu(D‐GlcCO₂H en*)₂ (H₂O)₂] · Cl₂ (1b), [Cu(D‐GlcCO₂H ea*) (H₂O)₂] · Cl₂ (3b) and [Ni(D‐GlcCO₂H ea*) (H₂O)₂] · Cl₂ (4), and the square planar geometry of complex [Ni(D‐GlcCO₂H en*)₂] · Cl₂ (2b). Polarimetric data along with CD spectra establish the chiral nature of complexes. Solution stabilities of these complexes were evaluated by cyclic voltammetric techniques as a function of pH. Electrochemical behavior of the complexes was studied in aqueous solution and showed an irreversible Cu^II/Cu^I couple. Kinetic studies of complex 1b and 3b with calf thymus DNA have been investigated spectrophotometrically under pseudo‐first order conditions, and k _obs values have been evaluated. Circular dichroism, cyclic voltammetry determinations, and viscosity measurements have also been carried out to authenticate the binding of DNA with metal complexes. Complexes 1b and 3b bind to DNA by covalent bond formation.