Diastereoselective synthesis of fused [1,3]oxazines from ethyl pyruvate,activated acetylenes and N-heterocycles

The 1:1 zwitterionic intermediates obtained from the reaction between isoquinoline, quinoline, pyridine, or N-methylimidazole with activated acetylenes are trapped by ethyl pyruvate to produce highly functionalized fused [1,3]oxazines in good yields.     

Theoretical and experimental photophysical studies of the tris(4,4,4-trifluoro-1-(1-naphthyl)-1,3-butanedionate) (2,2′-bipiridyl)-europium(III)

The complexes tris(4,4,4-Trifluoro-1-(1-naphthyl)-1,3-butanedionate) (2,2′-bipiridyl) Ln(III), Ln(tan)₃bipy, where Ln(III)=Eu³⁺ and Gd³⁺ have been synthesized, characterized and their photophysical properties (absorption, excitation and luminescence spectra and emission quantum yield) investigated down to 4.2 K. The Eu(tan)₃bipy complex has its molecular structure experimentally determined using X-ray crystallography and theoretically using the SMLC/AM1 method as well as their electronic singlet and triplet states were calculated, using the INDO/S-CI method with a point charge model to represent the Eu³⁺ ion, where two values were adopted, +3.0e and +3.5e, to investigate the imperfect shielding of the 4f shells. The so calculated +3.5e model electronic absorption spectrum and low lying triplet state energies agreed very well with the experimental ones. The emission quantum yield of the Eu³⁺ complex is quite low at room temperature, namely 7%, probably due to the too low lying triplet state, 19,050 cm^-1, and increases by a factor of three when the temperature is lowered to 4.2 K. This strong thermal effect indicates the presence of a channel deactivating the main emitting state, what can be due to a LMCT state possibly lying in the same spectral region, as usually found in Eu³⁺ compounds.     

Photoluminescent properties of heteroleptic cyclometalated platinum(II) complexes bearing 1,3-bis(3,4-dibutoxyphenyl)propane-1,3-dionate as an ancillary ligand

A new series of heteroleptic cyclometalated platinum(II) complexes Pt-1a-f was synthesized, employing 2-arylpyridine (or 1-arylisoquinoline) (HC^∧N-1) and 1,3-bis(3,4-dibutoxyphenyl)propane-1,3-dione (HO^∧O-1) for cyclometalation and as ancillary ligands, respectively, and photoluminescent properties were investigated. Focusing on red-shifted phosphorescence, C^∧N ligands containing π-extended aromatics and electron-rich heterocycles were examined. All obtained complexes exhibited photoluminescence at ambient temperature, and the emission maxima ranged from green (λ_PL=518 nm) to far red (λ_PL=708 nm). The large Stokes shifts of more than 100 nm and sub-microsecond or microsecond emission lifetimes revealed that these complexes are phosphorescent emissive. The quantum yield of Pt-1 ranged from 0.02 to 0.59 at ambient temperature and decreased as the emission maximum was red-shifted. In comparison with the reference platinum(II) complexes, Pt-2 bearing an aliphatic ancillary ligand, such as 2,2,6,6-tetramethylheptane-3,5-dionate (O^∧O-2), the ligand O^∧O-1 did not significantly affect the photoluminescence emission maxima, indicating that the energy gap between the singlet ground state and the triplet level was predominantly dependent on the C^∧N ligand.     

Diastereoselective synthesis of fused [1,3]thiazolo[1,3]oxazins and [1,3]oxazino[2,3-b][1,3]benzothiazoles

An efficient diastereoselective synthesis of 7-ethyl 5,6-dialkyl 7H-[1,3]thiazolo[2,3-b][1,3]oxazin-5,6, 7-tricarboxylates and 2-ethyl 3,4-dialkyl 2H-[1,3]oxazino [2,3-b][1,3]benzothiazole-2,3,4-tricarboxylates via reaction of thiazole and benzothiazole with dialkyl acetylenedicarboxylates in the presence of ethyl pyruvate is described.     

On the low-temperature chemistry of 1,3-butadiene

In this paper, species versus temperature profiles were measured during the oxidation of 1,3-butadiene in a jet-stirred reactor (JSR) at 1 atm, at different equivalence ratios (φ = 0.5, 1.0 and 2.0), in the temperature range 600 – 1020 K. Both synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) and gas chromatography (GC) methods were used to analyze the species. The experimental results show that a large proportion of the products are aldehydes (formaldehyde, acetaldehyde, acrolein, etc.) and ketenes (ketene, methyl-ketene), with acrolein being one of the major products. Moreover, furan, 1,3-cyclopentadiene and benzene are also present as intermediates in significant amounts. The reaction pathways leading to the formation of these species are discussed in detail. A new detailed mechanism, NUIGMech1.3, was developed to simulate these new data as well as other experimental data available in the literature. The validation results indicate that quantum calculations are also needed to explore the formation of some important species formed in the oxidation of 1,3-butadiene. Overall, the new 1,3-butadiene mechanism agrees well with various experimental data in the low- to high-temperature regimes and at different pressures. Flux and sensitivity analyses show that 1,3-butadiene shares some common reaction chemistry pathways with 1- and 2-butene via Ḣ atom and HȮ₂ radical addition to the C = C double bond in 1,3-butadiene, reactions which are important for both systems. The low temperature chemistry of 1,3-butadiene is mainly controlled by the reaction pathways of ȮH radical addition to the C = C double bond of the fuel molecule. The 1-buten-4-ol-3-yl radicals so formed subsequently add to O₂ and react via the Waddington mechanism, which is important in accurately simulating the oxidation and auto-ignition of 1,3-butadiene at engine relevant conditions.     

Kinetic analysis of the pathways to naphthalene formation from phenyl + 1,3-Butadiyne reaction

Having a better understanding of polycyclic aromatic hydrocarbon (PAH) formation under flame conditions contributes to optimizing the fuel reforming process, where soot poisons the downstream catalyst. In this work, the phenyl + 1,3-Butadiyne reaction is systematically investigated to examine its contribution to naphthalene formation. The reaction potential energy surfaces were calculated using DFT/M06–2X/cc-pvtz and G4 methods. The temperature- and pressure-dependent reaction rate constants were calculated using RRKM theory with solving master equation. The results revealed that 2-naphthyl could be directly formed by phenyl + 1,3-Butadiyne reaction. With H assistance, naphthalene could be formed by the pathway of phenyl + 1,3-Butadiyne → C₆H₅CHCCCH (+H) → C₆H₅CHCHCCH (+H) →naphthalene +H. The proposed pathway is kinetically favorable, and featured by relatively low energy barrier. The importance of the proposed pathway reaction was confirmed in a premixed and a diffusion C₂H₄/O₂/Ar flame simulations, where the enhancement of naphthalene by the investigated reactions is notable. The mole fraction of A₂ is promoted by a factor of 10% in premix C₂H₄/O₂/Ar flame and 30% in C₂H₄/O₂/Ar counterflow flame, bringing the prediction results closer to the experimental results. The relative contribution of different reaction route to A₂ formation is evaluated for HACA, cyclopentadienyl radical-cyclopentadienyl radical, phenyl-vinylacetylene[1], benzyl radical-propargyl radical, indene-CH₂ and phenyl-1,3-Butadiyne routes in premixed and diffusion C₂H₄/O₂/Ar flames. This work suggests that the PAH growth by 1,3-Butadiyne addition reaction is an effective pathway for A₂ formation, which should be considered in future PAH mechanism.     

Third-order optical nonlinearities of an organometallic complex: Bis(tetra-n-propylammonium)bis(2-thioxo-1,3-dithiole-4,5-dithiolato)cuprate(II) doped in solid PMMA films

An organometallic complex, bis(tetra-n-propylammonium)bis(2-thioxo-1,3-dithiole-4,5-dithiolato)cuprate(II), [(C₃H₇)₄N]₂[Cu(dmit)₂] (dmit^2?=4,5-dithiolate-1,3-dithiole-2-thione), abbreviated as PrCu, was synthesized. The films of PrCu were prepared using spin coating method. The third-order nonlinear optical properties of PrCu in acetone solution and PMMA films were investigated by Z-scan technique at 1064 nm with laser duration of 20 ps. The Z-scan spectra reveal that the composite films exhibit large negative nonlinear refractive indices of the order of 10^?15 m²/W, which are three orders larger than that in acetone solution. The nonlinear absorption coefficients were calculated to be 9.416×10^?10 m/W. For the composite films, the figure of merit, W and T, meet the requirement of all-optical switching devices. The experimental results show that the PrCu-doped PMMA films have potential applications for nonlinear optical devices.     

Pathway exploration in low-temperature oxidation of a new-generation bio-hybrid fuel 1,3-dioxane

The joint and flexible utilization of renewable electricity, ligno-cellulosic biomass, and/or CO₂ point sources to produce so-called bio-hybrid fuels is a promising solution to achieve carbon neutrality while still meeting the energy demand of the transportation sector. One of the new-generation bio-hybrid fuels is 1,3-dioxane. It has a special chemical structure with two oxygen atoms in a six-membered ring. In this work, the low-temperature oxidation of 1,3-dioxane was studied theoretically and experimentally. Potential energy surfaces of the products of the O₂ recombination with the three radicals formed from the H-atom abstraction of 1,3-dioxane were calculated at the DLPNO-CCSD(T)/CBS//B2PLYP-D3/cc-pVTZ level. The reaction rate coefficients were calculated with the RRKM/master equation method (T = 500–2000 K, p = 0.01–100 atm). To validate the proposed pathways, low-temperature oxidation experiments of 1,3-dioxane were performed in a jet stirred reactor (JSR) coupled with a synchrotron photon ionization time of flight molecular beam mass spectrometer (T = 590 K, p = 1 bar). Key intermediates in the investigated pathways were captured and identified by the combination of measured photon ionization efficiency curves and calculated ionization energies. Compared to cyclohexane, which has no oxygen in the six-membered ring, 1,3-dioxane has much weaker C-H bonds for the carbon between the two oxygen atoms, thus enabling faster internal H-atom migration from ROO to QOOH. Furthermore, oxidation of 1,3-dioxane tends to favor cyclic ethers + OH (chain propagation) instead of alkenes + HO₂ (chain termination), explaining its high reactivity in the low-temperature regime.     

Processing of poly(1,3-bis-(p-carboxyphenoxy propane)-co-(sebacic anhydride)) 20:80 (P(CPP:SA)20:80) by matrix-assisted pulsed laser evaporation for drug delivery systems

We have demonstrated successful thin film growth of poly(1,3-bis-(p-carboxyphenoxy, propane)-co-(sebacic anhydride)) (20:80) by matrix-assisted pulsed laser evaporation using a KrF* excimer laser (λ = 248 nm, τ = 25 ns, ν = 10 Hz). The deposited thin films have been investigated by Fourier transform infrared spectroscopy, and atomic force microscopy. We have demonstrated that the main functional groups of poly(1,3-bis-(p-carboxyphenoxy, propane)-co-(sebacic anhydride)) (20:80) are present in the deposited film. The effect of matrix on both thin film structure and surface morphology was also examined. The goal of this work is to explore laser processing of this material to create suitable constructs for drug delivery applications.     

Site-blocking effects of preadsorbed H on Pt(1 1 1) probed by 1,3-butadiene adsorption and reaction

The influence of hydrogen coadsorption on hydrocarbon chemistry on transition metal surfaces is a key aspect to an improved understanding of catalytic selective hydrogenation. We have investigated the effects of H preadsorption on adsorption and reaction of 1,3-butadiene (H₂CCHCHCH₂, C₄H₆) on Pt(1 1 1) surfaces by using temperature-programmed desorption (TPD) and Auger electron spectroscopy (AES). Preadsorbed hydrogen adatoms decrease the amount of 1,3-butadiene chemisorbed on the surface and chemisorption is completely blocked by the hydrogen monolayer (saturation) coverage (θ_H = 0.92 ML). No hydrogenation products of reactions between coadsorbed H adatoms and 1,3-butadiene were observed to desorb in TPD experiments over the range of θ_H investigated (θ_H = 0.6-0.9 ML). This is in strong contrast to the copious evolution of ethane (CH₃CH₃, C₂H₆) from coadsorbed hydrogen and ethylene (CH₂CH₂, C₂H₄) on Pt(1 1 1). Hydrogen adatoms effectively (in a 1:1 stoichiometry) remove sites from interaction with chemisorbed 1,3-butadiene, but do not affect adjacent sites. The adsorption energy of coadsorbed 1,3-butadiene is not affected by the presence of hydrogen on Pt(1 1 1). The chemisorbed 1,3-butadiene on hydrogen preadsorbed Pt(1 1 1) completely dehydrogenates to H₂ and surface carbon upon heating without any molecular desorption detected, which is identical to that observed on clean Pt(1 1 1). In addition to revealing aspects of site blocking that should have broad implications for hydrogen coadsorption with hydrocarbon molecules on transition metal surfaces in general, these results also provide additional basic information on the surface science of selective catalytic hydrogenation of butadiene in butadiene-butene mixtures.     

Synthesis of 5-aryl-1,3-dimethyl-6-(alkyl- or aryl-amino) furo [2,3-d]pyrimidine derivatives by reaction between isocyanides and pyridinecarbaldehydes in the presence of 1,3-dimethylbarbituric acid

5-Aryl-6-(alkyl- or aryl-amino)-1,3-dimethylfuro [2,3-d]pyrimidine derivatives were obtained by in situ reaction alkyl or aryl isocyanides and pyridinecarbaldehyde derivatives in the presence of 1,3-dimethylbarbituric acid in dichloromethane without any prior activation or modifications.     

Optical and electrochemical characteristics of Ir(III) complexes with metalated 4-(4-bromophenyl)-2-methyl-1,3-thiazole and isocyanide,ethylenediamine, and diethyldithiocarbamate ligands

The influence of donor–acceptor properties of tert-butyl-, 2.6-dimethylphenyl-, and 4-bromophenyl-isocyanides (BuNC, XylNC, BpNC), ethylenediamine (En), and diethyldithiocarbamate ions (Dtc–) on the ¹H and ¹³C NMR, IR, optical, and electrochemical characteristics of Ir(III) complexes with metalated 4-(4-bromophenyl)-2-methyl-1,3-thiazole is studied. Enhancement of the donor properties of BpNC, XylNC, BuNC, En, and Dtc^– ligands leads to a bathochromic shift of metal-to-ligand charge transfer (MLCT) bands and to a decrease in the difference between the one-electron oxidation and reduction potentials of complexes. The bathochromic shift of the low-temperature phosphorescence of complexes in frozen (77 K) solutions with increasing donor properties of BpNC, XylNC, BuNC, En, and Dtc–ligands is caused by a decrease in the admixture of MLCT to the intraligand excited state of {Ir(bptz)₂}. Quenching of the phosphorescence of complexes in liquid solutions is attributed to the thermally-induced population of excited d–d* states with subsequent nonradiative deactivation.     

NIR-luminescence from ternary lanthanide [Ho, Pr and Tm] complexes with 1-(2-naphthyl)-4,4,4-trifluoro-1,3-butanedionate

The ligand 1-(2-naphthyl)-4,4,4-trifluoro-1,3-butanedionate (Htfnd) has been employed to synthesize six novel ternary-lanthanide complexes in which the synergic ligands were 1,10-phenanthroline-5,6-dione (dione) and 4,5-diazafluoren-9-one (dafone), respectively. Two series of complexes Ln(tfnd)₃dione and Ln(tfnd)₃dafone (Ln=Ho, Pr, Tm) were obtained. These complexes were characterized by elemental analysis, Fourier Transform Infrared spectra and diffused reflectance. After ligand-mediated excitation, Ln(tfnd)₃dione and Ln(tfnd)₃dafone all show the characteristic NIR luminescence of the corresponding Ln³⁺ ions (Ln=Ho, Pr, Tm). This can be attributed to the efficient energy transfer from ligands to central Ln³⁺ ions, via an antenna effect. The indirect energy transfer in the complexes has been investigated and the differences in the luminescence intensity between Ln(tfnd)₃dione and Ln(tfnd)₃dafone were discussed in detail. The excellent luminescent performances enable these NIR-luminescent complexes to have potential applications in optical amplification operating at 1300 or 1500 nm.     

Three-Component Synthesis of Dialkyl 2-(Alkylimino-Methylene)3- (2,2,5-Trimethyl-4,6-Dioxo-1,3-Dioxan-5-Yl)-Succinates

The adduct produced in the reaction between alkyl isocyanides and dialkyl acetylenedicarboxylates was trapped by 2,2,5-trimethyl-1,3-dioxane-4,6-dione (methyl Meldrum's acid), to afford highly functionalized ketenimines in good yields.     

N,N,N^{\prime },N^{\prime }-Tetrabromobenzene-1,3-disulfonamide and poly(N-bromo-N-ethylbenzene-1,3-disulfonamide) as new and efficient catalysts for the synthesis of highly substituted 1,6-dihydropyrazine-2,3-dicarbonitrile derivatives

Various mono and bis-1,6-dihydropyrazine-2,3-dicarbonitrile derivatives were efficiently synthesized by reacting 2,3-diaminomaleonitrile (DAMN), isocyanides and ketones in the presence of a catalytic amount of $N,N{,}N^{\prime }{,}N^{\prime }$ -tetrabromobenzene-1,3-disulfonamide [TBBDA] and poly( $N$ -bromo- $N$ -ethylbenzene-1,3-disulfonamide) [PBBS] in EtOH/H $_{2}$ O at ambient temperature. Graphic abstract $N,N,N^{\prime },N^{\prime }$ -Tetrabromobenzene-1,3-disulfonamide and poly( $N$ -bromo- $N$ -ethylbenzene-1,3-disulfonamide) as new and efficient catalysts for the synthesis of highly substituted 1,6-dihydropyrazine-2,3-dicarbonitrile derivatives.      

On the second rotational isomeric form of butadiene-1,3

Eleven lines of the “hot” band progression of the torsional overtone 2ν₁₃ have been measured in the Raman spectra of cis,cis-1,4-d₂-butadiene-1,3 and d₆-butadiene-1,3. The potential of Carreira (J. Chem. Phys.62, 3851–3854 (1975)) (V₁ = 600, V₂ = 2068, V₃ = 273, and V₄ = ?49 cm^?1) and that of Bock et al. (J. Chem. Soc. Perkin II, 26–34 (1979)) (V₁ = 347.3, V₂ = 1790.0, V₃ = 612.8, and V₄ = 179.8 cm^?1) have been used to interpret the results obtained. For the accepted expansion of the Pitzer function F(φ), it is shown that the potential of Bock et al. reproduces the frequencies of the torsional overtones of these two molecules and h₆-butadiene-1,3 more closely. The improtance of data on isotopic molecules in the calculation of potential curves from spectroscopic information is emphasized.     

One-pot three-component synthesis of 3-hydroxy-5,5-dimethyl-2-[phenyl(phenylthio)methyl]cyclohex-2-enone derivatives under ultrasound

3-Hydroxy-5,5-dimethyl-2-[phenyl(phenylthio)methyl]cyclohex-2-enone is synthesized via one-pot three-component reactions of aromatic aldehyde, substituted thiophenol and 5,5-dimethyl-1,3-cyclohexanedione catalyzed by p-dodecylbenzene sulfonic acid (DBSA) under ultrasound. Under ultrasound irradiation the yields are much higher (sometimes substantially, by almost double) and the reaction time decreases substantially, the reaction conditions are milder. This method provides several advantages such as environment friendliness, high yields and simple work-up procedure and the protocol provides a novel alternative for the synthesis of thioether.     

Ultrasound promoted greener synthesis of spiro[indole-3,5′-[1,3]oxathiolanes in water

An aqueous mediated novel synthesis of substituted 2′amino-4′benzoyl-2′-methyl spiro[indole 3,5′-[1,3]oxathiolane]-2(1H)-ones (2a–f) was carried out from the reaction of spiro [indole-3,2′-oxiranes] (1a–f) with thioacetamide in the presence of LiBr as catalyst. The reaction was carried out under both microwaves and sonication and results were also compared with conventional method. In general, improvement in rate and yields observed when reaction was carried out under sonication as compared to microwave irradiation and conventional method.     

Experimental counterflow ignition temperatures and reaction mechanisms of 1,3-butadiene

The ignition temperatures of nitrogen-diluted 1,3-butadiene by heated air in counterflow were experimentally determined for pressures up to 5 atmospheres and pressure-weighted strain rates from 100 to 250 s⁻¹. The experimental data were compared with computational results using the mechanism of Laskin et al. [A. Laskin, H. Wang and C.K. Law, Int. J. Chem. Kinet. 32 (10) (2000) 589-614], showing that while the overall prediction is approximately within the experimental uncertainty, the mechanism over-predicts ignition temperature by about 25-40 K, with the differences becoming larger at high pressure/low temperature region. Sensitivity analyses for the near-ignition states were performed for both reactions and diffusion, which identified the importance of H₂/CO chain reactions, three 1,3-butadiene reaction pathways, and the binary diffusion between 1,3-butadiene and N₂ on ignition. The detailed mechanism, consisting of 94 species and 614 reactions, was then simplified to a skeletal mechanism consisting of 46 species and 297 reactions by using a new reduction algorithm combining directed relation graph and sensitivity analysis. The skeletal mechanism was further simplified to a 30-step reduced mechanism by using computational singular perturbation and quasi-steady-state assumptions. Both the skeletal and reduced mechanisms mimic the performance of the detailed mechanism with good accuracy in both homogeneous and heterogeneous systems.     

Phase transition and proton exchange in 1,3-diazinium hydrogen chloranilate monohydrate

In the hydrate crystal of 1:1 salt with 1,3-diazine and chloranilic acid (H₂ca), (1,3-diazineH)·H₂O·Hca, an unique hydrogen-bonded molecular aggregate is formed. There exists proton disorder in the N–H...O hydrogen bond between 1,3-diazinium ion and water (H₂O) of crystallization. In order to reveal dynamic aspect of this disorder, ³⁵Cl NQR measurements were conducted. Two resonance lines observed at 35.973 and 35.449 MHz at 321 K split into four lines below T _c?=?198 K clearly showing occurrence of a solid–solid phase transition; 36.565, 36.357, 36.011, 35.974 MHz at 77 K. Temperature dependence of spin-lattice relaxation time T ₁ in high-temperature phase was observed to obey an Arrhenius-type relation with the activation energy of 8.5 kJ mol^???1. This result leads to the conclusion that proton exchange in the N–H...O hydrogen bond takes place in the high-temperature phase. Specific heat measurements by DSC resulted in the transition entropy ΔS?=?1.3 J K^???1 per 1 mole [(1,3-diazineH)·H₂O·Hca]₂ which is far less than 2R ln2 = 11.5 J K^???1 mol^???1. It is expected that proton exchange in the two hydrogen bonds within the aggregate does not occur independently but concertedly with strong correlation in the high-temperature phase.