Reaction of Z isomers of alkylaromatic 1,2-hydroxylamino oximes with 1,2-diketones

The reactions of Z isomers of alkylaromatic 1,2-hydroxylamino oximes containing the hydroxylamino group at the primary or secondary carbon atom with diacetyl afford 6-acetyl-5,6-dihydro-4H-1,2,5-oxadiazines. The reactions of these compounds with alkylaromatic 1,2-diketones produce N-substituted α-aroylnitrones or 6-aroyl-5,6-dihydro-4H-1,2,5-oxadiazines or, alternatively, their tautomeric mixtures. Dedicated to the memory of Academician V. A. Koptyug on the occasion of the 75th anniversary of his birth. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1008–1013, June, 2006.     

A novel method of synthesis of 1,2-diketones from 1,2-diols using N-bromosuccinimide

A simple and convenient procedure is reported for the synthesis of benzils and aliphatic 1,2-diketones of cyclic and open chain compounds from corresponding hydrobenzoins and 1,2-diols by refluxing with N-bromosuccinimide in carbon tetrachloride in presence or absence of pyridine.     

Chiroptical properties of cyclic α-diketones

The chiroptical properties of dissymmetric cyclopentanedione, 3-methylcyclopentane-1,2-dione, and glyoxal structures are examined on a theoretical model in which the electronic wave functions are obtained from semiempirical all-valence-shell molecular orbital calculations. Excited state wave functions are constructed in the virtual orbital-configuration interaction approximation. The rotatory strengths, dipole strengths, oscillator strengths, and dissymmetry factors of the lower energy singletsinglet transitions in eleven cyclopentanedione and ten glyoxal structures are calculated and reported. The signs and relative magnitudes of the rotatory strengths associated with the two lowest energy singlet transitions are found to be extraordinarily sensitive to ring substituents and ring conformational parameters as well as to inherent chirality within the -dicarbonyl moiety of the cyclopentanedione structures. Vicinal effects play a significant role in determining the signs and magnitudes of the electronic rotatory strengths. For a given configurational isomer of an inherently dissymmetric -dicarbonyl group (i.e., P or M), the signs of the electronic rotatory strength of the lowest energy transition in glyoxal and in cyclopentanedione are opposite. This result suggests that cisoid glyoxal structures may not be useful models for the chiroptical properties of cyclic -diketone systems with cisoid dicarbonyl moieties.This work was supported in part by a grant from the Petroleum Research Fund administered by the American Chemical Society, the Camille and Henry Dreyfus Foundation, and a computing grant from the University of Virginia Computer Science Center.     

Theoretical study of deactivation and isomerization pathways of 1,2-dithiete in excited electronic states

The potential energy surface crossings for 1,2-dithiete have been investigated using the complete active space self-consistent field(CASSCF) method and simple group theory.Using the full Pauli-Breit spin-orbit coupling(SOC) operator(■) SO) which consists of the one-electron(■) SO1) and two-electron(■) SO2) terms,we estimate the strengths of the SOC(198.37 cm-1 when symmetry is imposed,and 211.35 cm-1 with no symmetry constraints),which plays an essential role in the spin transitions between different spin s...     

Samarium diiodide promoted formation of 1,2-diketones and 1-acylamido-2-substituted benzimidazoles from N-acylbenzotriazoles

N-Acylbenzotriazoles, when treated with samarium diiodide in THF, undergo self-coupling reaction to afford 1,2-diketones in good to excellent yields; while when treated with samarium diiodide in CH₃CN, they undergo ring-opening reaction to afford 1-acylamido-2-alkyl (or aryl) benzimidazoles in reasonable to good yields. A plausible mechanism was suggested.     

Theoretical study on the structures and electronic spectra of C120On (n=1,2)

ZINDO series calculations have been carried out to study the double‐cage oxides C₁₂₀O_n (n=1,2). The results show that the formation of a furan ring by the bridge‐bond between the two cages connected the two C₆₀ fullerene units and formed the C₁₂₀O with C_2v symmetry. C₁₂₀O₂ has two isomers with C_2v symmetry depending on either 6–6 or 6–5 connection between the two cages. Two furan rings and a pure four‐member ring form in this molecule. The formation of C₁₂₀O assuages the constraint of epoxide structure in C₆₀O, shortens the distance of the monomers, and produces some finite interaction between the two balls. More bonding in C₁₂₀O₂ shortens the distance of the two cages further and brings about stronger interaction. However, the two cages in C₁₂₀O_n (n=1,2) behave somehow independently that the electronic spectra of C₁₂₀O_n (n=1,2) are similar to those of C₆₀. The 6–6 connection isomer of C₁₂₀O₂ is more stable; its spectra are in good agreement with those of the experiment. The calculated electronic spectra of C₁₂₀O not only are in good agreement with the experiment in the ultraviolet region but also get some weak peaks in the visible region (>400 nm) not observed in experiment. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 79: 291–307, 2000     

Theoretical study of electronic spectra of the DNA bases

Excited π-electronic states of cytosine and uracil are calculated by the CI method. The effects of a transition from the single-excited configuration set to the set involving all double-excited configurations are considered. The set expansion is shown to affect essentially the transition energies and oscillator strengths, in particular, an additional electron transition related to the first absorption band occurs in the singlet uracil spectrum. When doubly excitations are taken into account the triplet transition energies considerably increase and become practically insensitive to repulsion integral parametrization.     

Theoretical study of cyclic conjugation in phenes: Some hitherto unnoticed features

Summary Cyclic conjugation in phenes is examined by means of theBosanac-Gutman-Aihara method. In contrast to the predictions based on the analysis ofKekulé orClar structures, we find that when going along the hexagons of a phene molecule, cyclic conjugation varies in a rather non-uniform manner. In contrast to a number of other homologous series of benzenoid hydrocarbons, the intensity of cyclic conjugation in phenes increases when going towards the center of the molecule.

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Theoretische Untersuchung der cyclischen Konjugation in Phenen: Einige bisher unbekannte Eigenschaften

Zusammenfassung Die cyclische Konjugation in Phenen wird mittels derBosanac-Gutman-Aihara-Methode untersucht. Im Gegensatz zu auf der Analyse vonKekulé- oderClar-Strukturen beruhenden Voraussagen variiert die cyclische Konjugation entlang der Sechsecke eines Phenmoleküls ziemlich unregelmäßig. Anders als bei anderen homologen benzenoiden Kohlenwasserstoffen nimmt bei Phenen die Intensität der cyclischen Konjugation zum Zentrum des Moleküls hin zu.

     

Theoretical study of 1,2‐rearrangement in silylmethanethiol

The 1,2‐rearrangements in silylmethanethiol were studied by ab initio molecular orbital theory. The structures of reactants, transition states, and products were fully optimized at the MP2(full)/6‐31G(d) levels. Based on the MP2(full)/6‐31G(d) geometries, harmonic frequencies were obtained. Energies were computed at the G3 level of theory with MP2(full)/6‐31G(d) zero‐point corrections. The results indicate that the 1,2‐rearrangement in silylmethanethiol may occur via two pathways. Pathway A involves the 1,2‐migration of mercapto group from carbon to silicon via a double three‐membered ring transition state, forming methylsilanethiol. The barrier for reaction A is 275.0 kJ/mol. Pathway B involves the 1,2‐migration of silyl group from carbon to sulfur via a four‐membered ring transition state, forming methylthiosilane. The barrier for reaction B is 262.3 kJ/mol. Thermodynamic and kinetic properties of the reactions were analyzed over a temperature range of 300–1,300K. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Electrochemical oxidation of 1,3-diketones in the presence of hydrohalic acid salts

In the presence of a mediator (sodium iodide) acetylacetone dimerizes with the formation of 3,4-diacetylhexane-2,5-dione, with a yield up to 90%. Salts of 2-halosubstituted 1,3-diketones form more highly enolized cyclic 1,3-diketones — 1,3-cyclohexanedione and dimedone under analogous conditions, with a yield up to 90%.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 154–158, January, 1992.     

Controlled radical polymerization of styrene in the presence of cyclic 1,2‐disulfides

The thermal polymerization of styrene (St) in the presence of cyclic 1,2‐disulfides at 120 °C was investigated. In the polymerization of St in the presence of 1,2‐dithiane (DT), that is, six‐member cyclic 1,2‐disulfide, the polymer yields and molecular weights increased with the reaction time. The linear relation between the polymer yields and molecular weights was observed, and the line passed through an original point. The molecular weight distributions of the polymers remained almost constant but were not narrow. For this polymerization with a living nature, we proposed the following mechanism: the propagating St radical reacted with thiyl radicals derived from DT, leading to the formation of dormant species, and the formed C S bond of the dormant was dissociated again to give the propagating polystyryl radical and thiyl radical. Similar results were obtained in the thermal polymerization of St at 120 °C in the presence of 1,2‐dithiacycloheptane, that is, seven‐member cyclic 1,2‐disulfide. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 145–151, 2001     

Sterically hindered 1,3-diketones in the Michael reaction

The base catalyzed addition of sterically hindered 1,3-diketones to the activated multiple bond of ethyl acrylate and 4-methyl-4-methoxy-1-phenylpent-2-yne-1-one has been studied. The addition of methyl(2-propenyl)ketone is partially accompanied by intramolecular cyclization of the resulting adduct.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 147–149, January, 1996.     

A facile one-pot highly chemo- and regioselective synthesis of the novel heterocyclic system indolo[1,2-c]azolo[1,5-a]quinazoline-8,10-dione

A series of novel indolo[1,2-c]azolo[1,5-a]quinazoline-8,10-diones was obtained by a multi-component reaction between cyclic 1,3-diketones, α-aminoazoles, and glyoxal. The unexpected cyclization process was established by NMR spectroscopy and X-ray diffraction measurements.     

Theoretical study of the polarized electronic absorption spectra of vanadium-doped zircon

The polarized electronic absorption spectra of a blue vanadium-doped zircon single crystal, grown by the flux method, has been studied by quantum chemical (CI) calculations in order to determine the position of the V⁴⁺ dopant in the zircon host structure. Particularly, the excitation energies and polarizations of V⁴⁺ occupying alternate positions, either the zirconium or silicon position or the interstitial site 16g, have been considered. It is concluded that the observed electronic absorption spectra and the color of zirconblue can only be explained if the V⁴⁺ chromophore is placed on the respective interstitial position.     

Theoretical study of the shifts of electronic spectra from solute-solvent interaction

Previous theories of spectral solvent shifts are briefly discussed. The basic dipole approximation is analyzed both theoretically and in relation to experimental information. On account of the restricted validity of this approximation — especially for molecules consisting of several polar groups — another, electrostatic model, originating from the Born charging, is investigated. This model is applied to semi-empirical PPP-calculations of spectral solvent shifts of some quinones. Among other things, this model predicts that not only n → π⁸ transitions may be blue shifted but also certain π → π* transitions. When the electrostatic effect is small, other terms may be responsible for the solvent shift, e.g. polarizability. The cavity effect is not expected to be important in the present context.     

Nitro derivatives of cyclic sulfoximides of the 1,2-benzoisothiazole series

Nitro derivatives of 1-R-1,2-benzoisothiazol-3-one 1-oxide were synthesized by the reactions of 2-alkyl(phenyl)thio-4-nitro- and 4,6-dinitro-2-(phenylthio)benzamides with chlorine in 60% acetic acid. Analogous reactions of 2-(n-butylthio)-4-nitro- and 2-(tert-butylthio)-4-nitrobenzamides with chlorine afforded 2-butyl- and 2-H-1,2-benzoisothiazol-3-one 1-oxides, respectively. The proposed reaction mechanism includes the formation and subsequent transformations of S-alkyl-S-aryl- and S,S-diarylchlorosulfonium chlorides.     

Theoretical study on the structures and electronic spectra of TCNE2-.

Investigations into the charge-separated states and electron-transfer transitions in tetracyanoethylene (TCNE) complexes have recently generated much interest. In this work we present theoretical calculations showing that the most stable structure of the dianion TCNE2- has D2d symmetry in vacuum as well as in the solvents dichloromethane and acetonitrile. By means of the coupled cluster linear response, we compute the vertical electronic spectrum in both the gas phase and solution. The theoretical results are compared to the experimental data and good agreement is achieved.     

Theoretical study of solvent influence on the electronic absorption and emission spectra of kynurenine

Neutral/zwitterionic form equilibrium, excited state wave functions, absorption and emission spectra of kynurenine (KN) in various solvents (water, methanol, ethanol, and dimethylsulfoxide) have been studied theoretically. The ground electronic state geometries have been optimized by density functional theory methods; the geometries of the first two singlets excited electronic states have been optimized using the CASSCF technique. The influence of the solvent was taken into account by the calculation of the solvation free energies using the Polarizable Continuum Model (PCM). The spectra of electronic absorption and fluorescence emission have been calculated by the CS‐INDO S‐CI and SDT‐CI methods [Momicchioli, Baraldi, and Bruni, Chem Phys, 1983, 82, 229]. The calculated data reproduce the experimental positions of maxima and the solvent‐induced shifts of the absorption and emission bands well. The energy gap between the two lowest excited states of KN increases from aprotic to protic solvents. This fact suggests that the “proximity effect” cannot be responsible for the ultrafast decay of KN fluorescence in protic solvents. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Theoretical study of the electronic spectra ofcis-1,3,5-hexatriene andcis-1,3-butadiene

Summary The electronic spectra forcis-1,3-butadiene andcis-1,3,5-hexatriene have been studied using multiconfiguration second-order perturbation theory (CASPT2) and extended ANO basis sets. The calculations comprise all singlet valence excited states below 8.0 eV, the first 3s, 3p, 3d Rydberg states, and the second 3s state. The four lowest triplet states were also studied. The resulting excitation energies forcis-hexatriene have been used in an assignment of the experimental spectrum, leading to a maximum deviation of 0.13 eV for the vertical transition energies. The calculations place the 1¹ B ₂ state 0.04 eV below the 2¹ A ₁ state. 16 excited states were studied incis-butadiene, using a CASPT2 optimized ground state geometry. The 1¹ B ₂ state was located at 5.58 eV, 0.46 eV below the 2¹ A ₁ state and 0.09 eV above the experimental value. No experimental assignments are available for the 15 other transitions. On leave from: Departmento de Quimica Física, Universidad de Valencia, Dr. Moliner 50, Burjassot, E-46100-Valencia, Spain     

Rh(III)-catalyzed C-H activation of primary benzamides and tandem cyclization with cyclic 2-diazo-1,3-diketones for the synthesis of isocoumarins

A simple and efficient Rh(III)-catalyzed C-H activation and tandem intramolecular cyclization for the synthesis of isocoumarins has been developed. The protocol uses easily available primary benzamides and cyclic 2-diazo-1,3-diketones as starting materials. This reaction proceeds via C-C and C-O bond formation in a single reaction vessel, and the corresponding isocoumarins were obtained in moderate to excellent yields (58%–97%). The well established protocol showed high functional group tolerance, which provided an efficient and alternative route to isocoumarin backbone.