The behaviour of 3-methyl-5-(o-r-styryl)-4-nitroisoxazoles under electron impact. I

The mass spectra of several 3-methyl-5-(o-R-styryl)-4-nitroisoxazoles have been studied. The fragmentation patterns and mechanisms postulated have been confirmed by the determination of the metastable peaks.     

Friedlander synthesis of highly functionalized isoxazolyl quinoline libraries via addition of C(sp3)–H bond to aldehydes

A novel protocol for ionic liquid (IL)-mediated C(sp³)–H bond functionalization of 3,5-dimethyl-4-nitroisoxazoles 4 to substituted o-amino benzaldehydes 5 was developed in excellent yields. Isoxazolyl aryl ethanones 7 have been synthesized from isoxazolyl aryl ethanol synthon 6. Furthermore, utilizing the later as synthons for IL promoted Friedlander synthesis of highly functionalized isoxazole substituted quinoline libraries 9. The merit of this synthesis is easily available and economical starting materials, effective utilization of all the reactants, and simple workup procedure. It is noteworthy that ionic liquid used in C(sp³)–H bond functionalization and Friedlander synthesis reactions can be recycled and reused five times without significant decrease in activity.     

Synthesis and properties of azoles and their derivatives. 10. Synthesis of 3,5-diaryl-4-nitroisoxazoles

A method was proposed for the synthesis of 3,5-diaryl-4-nitroisoxazoles entailing the brominatian of potassium salts of the corresponding 3,5-diaryl-²-isoxazolinyl-4-nitronic acids. The method may be used for the conversions of both the trans and cis isomers of 3,5-disubstituted 4-nitro-²-isoxazolines.Communication 9, See [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 189–192, February, 1985.     

Synthetic exploitation of the ring-opening of 3,4-dinitrothiophene. Part 4. Synthesis of 1,4-disubstituted 3-hydroximino-2-nitro-1-butenes and their cyclization to 4-nitroisoxazoles

The reduction of a single nitrovinyl moiety in 1,4-dialkyl- and 1,4-diaryl-2,3-dinitro-1,3-butadienes 1 with stannous chloride dihydrate in ethyl acetate furnishes the corresponding 3-hydroximino-2-nitro-l-butenes 4 in satisfactory yields. The oxidative cyclization of the latter compounds gives variable yields of 3,5-disubsti-tuted 4-nitroisoxazoles 5 , most likely arising from aromatization of the corresponding 4,5-dihydroisoxazoles, formed through an intramolecular Michael addition of the hydroximino group in 4 to the nitroalkene functionality. In the case of the l-naphthyl derivative 4d such oxidative cyclization mainly leads to the competitive formation of 3-[(l-naphthyl)methyl]-2-nitrobenzo[f]quinoline N-oxide 7.     

Synthesis of 3-acyl-5-nitroisoxazoles on the base of geminal trinitro- and chlorodinitro-substituted pentan-2-one or 2-oximino-1-phenylbutan-1-one

3-Acyl-5-nitroisoxazoles were synthesized by heating 5,5,5-trinitropentan-2-one with LiCl in DMF at 100 °C as well as by heating oximino derivatives of 5,5,5-trinitro-, 5-chloro-5,5-dinitropentan-2-one or 4,4,4-trinitro- and 4-chloro-4,4-dinitro-1-phenylbutan-1-one in organic solvents.     

All‐electron relativistic computations on the low‐lying electronic states,bond length,and vibrational frequency of CeF diatomic molecule with spin–orbit coupling effects

Ab initio all‐electron computations have been carried out for Ce⁺ and CeF, including the electron correlation, scalar relativistic, and spin–orbit coupling effects in a quantitative manner. First, the n‐electron valence state second‐order multireference perturbation theory (NEVPT2) and spin–orbit configuration interaction (SOCI) based on the state‐averaged restricted active space multiconfigurational self‐consistent field (SA‐RASSCF) and state‐averaged complete active space multiconfigurational self‐consistent field (SA‐CASSCF) wavefunctions have been applied to evaluations of the low‐lying energy levels of Ce⁺ with [Xe]4f¹5d¹6s¹ and [Xe]4f¹5d² configurations, to test the accuracy of several all‐electron relativistic basis sets. It is shown that the mixing of quartet and doublet states is essential to reproduce the excitation energies. Then, SA‐RASSCF(CASSCF)/NEVPT2 + SOCI computations with the Sapporo(‐DKH3)‐2012‐QZP basis set were carried out to determine the energy levels of the low‐lying electronic states of CeF. The calculated excitation energies, bond length, and vibrational frequency are shown to be in good agreement with the available experimental data. © 2018 Wiley Periodicals, Inc.     

ChemInform Abstract: Starlike Aluminum—Carbon Aromatic Species.

Born‐Oppenheimer molecular dynamics simulations and high‐level quantum chemical computations (B3LYP, MP2, CCSD(T)) reveal the starlike D_5h C₅Al₅^‐ global minimum with five planar tetracoordinate carbon atoms to be a promising candidate for detection by photoelectron detachment spectroscopy.     

NMR spectroscopic and theoretical study on the isomerism of dimethyl benzodiazepine(diylidene)diacetates

The isomerism of dimethyl 2,2′-(7,8-dichloro-1H-benzo[b][1,4]diazepine-2,4-(3H,5H)diylidene)diacetate ( 1a ) and dimethyl 2,2′-(7,8-dichloro-3-methyl-1H-benzo[b][1,4]diazepine-2,4-(3H,5H)diylidene)diacetate ( 1b ) was investigated by ¹H, ¹³C and ¹⁵N nuclear magnetic resonance (NMR) spectroscopy. In CDCl₃ solution, inversion of the diazepine ring was observed, whereas in (D₆)DMSO and (D₇)DMF solution, besides the ring inversion, a partial cleavage of one chelate ring appeared connected with (E/Z) isomerization about one of the exocyclic C=C bonds. Gibbs free energies (ΔG) and free activation energies (ΔG^≠) were calculated based on B3PW91-SCRF/ZVP DFT computations. Agreement between NMR data and density functional theory (DFT) computations was found.     

Copper(II) complexes derived from substituted 2,2′-bis-(4-isopropyl-4-methyl-4,5-dihydro-1H-imidazol-5-one) ligands: Synthesis,structure and catalytic activity

New chiral N,N-bidentate 2,2′-bis-(4-isopropyl-4-methyl-4,5-dihydro-1H-imidazol-5-one) ligands have been prepared and characterised by their ¹H and ¹³C NMR spectra and/or optical rotation. The ligands prepared were then tested for their ability to form complexes with copper(II) salts. It was found that the most stable complex is formed from the 2,2′-bis-(4-isopropyl-1,4-dimethyl-4,5-dihydro-1H-imidazol-5-one) ligand and copper(II) chloride. The structure of this complex was determined by means of quantum-chemical computations at the B3LYP or UB3LYP/6-31G(d,p) level. According to the computations, the geometry of the copper atom most resembles a tetrahedral arrangement, which was also confirmed by means of X-ray structural analysis. It was found that the structure of this copper(II) complex does not allow the copper atom to coordinate to additional ligands; therefore, it is catalytically inactive in the asymmetric Henry reaction.     

Electron impact mass spectrometry of 3-methyl-4-benzylideneamine-5-styrylisoxazoles. II

The mass spectra of a series of substituted 3-methyl-4-benzylideneamine-5-styrylisoxazoles are reported and discussed. The spectra of these isoxazoles show a characteristic fragmentation pattern different from the 5-styryl-4-nitroisoxazoles. Perhaps this is due to the presence of the Schiff base at position 4.     

Derivatives of 3-Deoxy-3-(N-Hydroxyamino)-D-Ribose

Abstract

A series of 3-(N-arylmethyl-N-hydroxyamino)-l,2-O-cyclopentylidene-3-deoxy-5-O-toluoyl-α-D-riboses has been prepared. The blocking groups used were chosen to allow an easy nucleosidation of these compounds to spin labelled analogs of natural nucleosides. The conformational behavior of the N-arylmethyl-N-hydroxyamino group has been studied using ³/_CH NMR coupling data and molecular mechanics computations. Upon spontaneous oxidation, these hydroxylamines led to the corresponding aminoxyl free radicals which were submitted to EPR spectroscopy and quantum mechanical computations at a semiempirical level (PM3).     

Simulation of isotopic selectivities and isotope ratio enhancement factors for gadolinium and lanthanum using narrow band laser excitation

Isotopic selectivities and isotope ratio enhancement factors have been calculated for 4f⁵5d6s^{2 9}D ₅ ⁰ -4f⁷5d6s6p ⁹D₆ (585.622 nm) transition of gadolinium and for 5d6s^{2 2}D_3/2-5d6s6p ⁴F _3/2 ⁰ (753.9 nm) transition of lanthanum by simulating the spectra assuming natural isotopic abundance of the samples. The atomic line shapes are assumed to be Lorentzian. Isotopic selectivities and isotope ratio enhancement factors for single step excitations have been computed. The isotope ratio enhancement factors estimated by us are half the value obtained by Young. et al. This is because the isotope ratio enhancement obtained by them is for a two colour RIMS where as our computations for selectivities are for a single step excitation. Considering the statistical error in the experimental values, our estimated isotopic selectivities are in good agreement with the available experimental data.     

On the affinity of cytosine towards electrophiles

Ab initio SCF computations on the intrinsic preferences of the H⁺, CH ₃ ⁺ and C₂H ₅ ⁺ cations towards the two principal sites of protonation or alkylation on cytosine, N₃ or O₂, show that this preference undergoes a continuous modification with the increase in size and complexity of the cation. N₃ is the preferred site of fixation of H⁺, O₂ the preferred site of C₂H ₅ ⁺ , while CH ₃ ⁺ has no marked preference. The exchange repulsion term of the binding energy appears responsible for the preference of C₂H ₅ ⁺ for O₂.This work was supported by the Ligue Francaise contre le Cancer and the National Foundation for Cancer Research (USA)     

Ab initio study of the comparative stability of ruthenium(VI) and osmium(VI) oxo hydroxo complexes with different coordination numbers

The comparative stability of oxohydroxoruthenium(VI) and oxohydroxoosmium(VI) anions with different coordination numbers has been calculated by the relativistic density functional theory method with inclusion of spin-orbit coupling. In line with experimental data, the computations point to the stability of the ruthenium complex RuO₃(OH) ₂ ^2? ? with CN = 5, whereas osmium is stabilized in a six-coordinate environment (OsO₂(OH) ₄ ^2? ). The spin state of the stable Ru complex is close to triplet and that of the Os complex, to singlet.     

Parallel ab initio and molecular mechanics investigation of polycoordinated Zn(II) complexes with model hard and soft ligands: Variations of binding energy and of its components with number and charges of ligands

In this study we compare the binding energies of polycoordinated complexes of Zn²⁺ within cavities composed of model “hard” (H₂O, OH⁻) or “soft” (CH₃SH, CH₃S⁻) ligands. Ab initio supermolecule computations are performed at the HF and MP2 levels using extended basis sets to determine the binding energies and their components as a function of: the number of ligands, ranging from three to six; the net charge of the cavity; and the “hard” versus “soft” character of the ligands. These ab initio computations are used to test the reliability of the SIBFA molecular mechanics procedure, originally formulated and calibrated on the basis of ab initio computations, for such charged systems. The SIBFA intermolecular interaction energies match the corresponding ab initio values using a coreless effective potential split‐valence basis set with a relative error of ≤3%. Extensions to binuclear Zn²⁺ complexes, such as those that occur in the Zn‐binding sites of Gal4 and β‐lactamase proteins, are performed to test the applicability of the methodology for such systems. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 1011–1039, 2000     

Selective Preparation of Phosphorus Mononitride (P≡N) from Phosphinoazide and Reversible Oxidation to Phosphinonitrene

The interstellar candidate phosphorus mononitride PN, a metastable species, was generated through high-vacuum flash pyrolysis of (o-phenyldioxyl)phosphinoazide in cryogenic matrices. Although the PN stretching band was not directly detected because of its low infrared intensity and possible overlaps with other strong bands, o-benzoquinone, carbon monoxide, and cyclopentadienone as additional fragmentation products were clearly identified. Moreover, an elusive o-benzoquinone-PN complex formed when (o-phenyldioxyl)phosphinoazide was exposed to UV irradiation at λ=254 nm. Its recombination to (o-phenyldioxyl)-λ⁵-phosphinonitrile was observed upon irradiation with the light at λ=523 nm, which demonstrates for the first time the reactivity of PN towards an organic molecule. Energy profile computations at the B3LYP/def2-TZVP density functional theory level reveal a concerted mechanism. To provide further evidence, UV/Vis spectra of the precursor and the irradiation products were recorded and agree well with time-dependent DFT computations.     

Ionic liquid-promoted [3+2]-cycloaddition reactions of nitroformonitrile oxide generated by the cycloreversion of dinitrofuroxan

A new approach to the synthesis of 3-nitroisoxazoles and 3-nitroisoxazolines based on the [3+2]-cycloaddition of nitroformonitrile oxide (NFNO), generated by the cycloreversion of dinitrofuroxan (DNFO), to acetylene and ethylene derivatives, under ionic liquid catalysis is developed. The approach is of a general nature and applicable to cycloaddition reactions with other dipolarophiles.     

Spectral studies of Fe(III) complexes of dipodal tridentate chelating agents

The dipodal ligands (Im) and (BIm) as well as complexes [FeLCl₃] [L = Im (1) and BIm (2)] have been prepared and studied using spectroscopic techniques. The magnetic moment, IR, electronic (ligand field), FAB-mass and NMR spectral data indicate a hexa-coordinate geometry around high-spin state Fe³⁺ where the ligands coordinate as a tridentate [N,N,N] chelating agent. ⁵⁷Fe-Mössbauer spectral data confirmed the presence of a ligand asymmetry around Fe³⁺ in a high-spin state electronic configuration (t_2g³,e_g², S = 5/2) with nuclear transition Fe(±3/2 → ±1/2) exhibiting Kramer's double degeneracy. The molecular computations provided the optimum energy perspective plots for the molecular geometries giving the important structural data.     

NMR investigation and theoretical studies on the tautomerism of β,β′-tricarbonyl compounds

The behaviour on keto–enol tautomeric equilibration of ethyl 2-benzoyl-5-(2-furyl)-3-hydroxy-penta-2,4-dienoate (1) and ethyl 2-acetyl-3-hydroxy-5-phenyl-penta-2,4-dienoate (2) was investigated by ¹H and ¹³C NMR spectroscopy in different solvents and BP86/TZVP density functional theory computations. The spectral assignment to enol and keto tautomers was performed with one- and two-dimensional techniques. The percentage of the keto form in the tautomeric equilibrium depends on solvents and rises by increasing solvent polarity. The enol–enol tautomerism is also discussed on the basis of the coupling constants ²J_C,OH, ³J_C,OH and ⁴J_H,OH, respectively.