Synthesis of 9-substituted tetrahydrodiazepinopurines: studies toward the total synthesis of asmarines

A methodology for the preparation of asmarine analogues has been developed. The asmarines are cytotoxic marine alkaloids with a unique tetrahydro[1,4]diazepino[1,2,3-g,h]purine (THDAP) structure. Three cyclization methods were applied for the preparation of the 9,9-disubstituted 10-hydroxy-THDAP system, namely, aminomercurization, iodocyclization, and acid-catalyzed cyclization. The DMPM group of the NOH functionality and cyanoethyl group of the N-9 atom were found to be the most suitable protecting groups. The structures of all compounds were mainly determined from NMR measurements including (15)N chemical shifts obtained from (15)NH HMBC spectra. The end products are at least about 1 order of magnitude less active than the natural product asmarine B.     

Mechanism of reaction between cobalt(II) oxide and ammonium chloride

A reaction between cobalt oxide and ammonium chloride was studied. A possible mechanism of this reaction was determined by TGA and DSC. The reaction products were identified by IR spectroscopy, chemical and XRD analyses. A multistage mechanism was established for reaction between cobalt oxide and ammonium chloride. Cobalt chloride was determined to be the final product; the reaction occurs via the formation and decomposition of (NH₄)₃CoCl₅, (NH₄)₂CoCl₄, and NH₄CoCl₃.     

Theoretical Studies on the Reactions of 1,1,2,2,3,3,4‐Heptafluorocyclopentane with Hydroxyl and Hydrogen Free Radicals

1,1,2,2,3,3,4‐Heptafluorocyclopentane (F7A) has considerable potential to be a new halon replacement due to its environmental friendliness and low‐toxicity. However, the reaction processes of F7A with hydroxyl and hydrogen free radicals, which are of great importance for investigating its fire suppression mechanisms, are still unclear. In this paper, ab inito and density functional theory are used to deduce the possible reaction pathways for the reactions of F7A with hydroxyl and hydrogen free radicals at the CCSD/cc‐pVDZ//B3LYP/6‐311++G (d,p) level of theory. Two distinct reaction pathways including ten elementary reaction channels for F7A with hydroxyl free radical, and five distinct reaction pathways including twenty elementary reaction channels for F7A with hydrogen free radical are investigated. The geometries, vibrational frequencies and reaction energy barriers are also determined. Based on the calculated results, the possible reaction mechanisms are proposed and discussed. The most feasible reaction channel for F7A with hydroxyl free radical is that leads to CH(OH)CH₂(CF₂)₃+·F, and the most feasible reaction channel for F7A with hydrogen free radical is that leads to (CF₂)₃CH₂CH·+HF. The study is helpful to further study its fire suppression mechanisms and promote it to be a new generation of halon replacement.     

Synthesis of 4-halophosphaisocoumarins via halocyclization of 2-(1-alkynyl)phenylphosphonates

A series of 4-halophosphaisocoumarins were prepared with high regioselectivity in good to excellent yields under mild conditions by the reaction of 2-(1-alkynyl)phenylphosphonic acid diesters with I₂ in CHCl₃ or ICl in CH₂Cl₂, or by the reaction of 2-(1-alkynyl)phenylphosphonic acid monoesters with NBS or NCS in DMF. Whether the alkynylphosphonates could cyclize or not was affected by the substituents, reaction solvents and electrophiles. A rationale for this reaction is discussed.     

A Re2O7 catalyzed cycloetherification of monoallylic diols

A Re₂O₇ catalyzed cycloetherification of monoallylic diols is described. The reaction features short reaction time, mild reaction conditions and exclusive E selectivity. A wide range of monoallylic alcohols with alkyl or aryl substituents on olefin smoothly undergo ring closure to deliver corresponding oxa-heterocycles. The reaction is also operationally simple and not sensitive to air and moisture.     

K2S2O8-Mediated Difunctionalization of C≡C Bonds in Water: A Simple and Efficient Approach to α,α-Dihaloacetophenones from Phenylacetylenes and NaX

A novel K₂S₂O₈-mediated oxy-1,1-dihalogenation of alkynes with NaX in the presence of water has been developed, affording α,α-dihaloacetophenones in moderate to good yields. The advantages of this reaction are mild reaction conditions, operational simplicity, and use of pure water as reaction medium. A plausible reaction mechanism is proposed on the basis of mechanistic studies.     

A conversion route towards tubular SiO2 using rod-like BaSiF6 as a novel template

A simple hydrothermal reaction between Ba(NO₃)₂ and K₂SiF₆ results in the formation of 1D rod-like BaSiF₆. The BaSiF₆ rods can act as efficient precursors for production of tubular SiO₂ by hydrothermal reaction in alkaline solutions. Powder X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), transmission electron microscopy (TEM), high resolution electron microscopy (HRTEM), and field emission scanning electron microscopy (FESEM) were used to characterize the phase and morphology of the final product. The experiments indicated the amount of NaOH, reaction temperature, and reaction time played important roles in the transformation process. A possible growth mechanism of tubular silica was proposed.     

Quantum Mechanics Rate Constant for the N+ND Reaction

We present nonadiabatic quantum dynamical calculations on the two coupled potential en-ergy surfaces (1²A′ and 2²A′) [J. Theor. Comput. Chem. 8, 849 (2009)] for the reaction. Initial state-resolved reaction probabilities and cross sections for the N+ND→N₂+D reaction and N′+ND→N′D+N reaction for collision energies of 5 meV to 1.0 eV are determined, re-spectively. It is found that the N+ND→N₂+D reaction is dominated in the N+ND reaction.In addition, we obtained the rate constants for the N+ND→N₂+D reaction which demand further experimental investigations.     

Fractality and activity of acid catalysts in the liquid-phase synthesis of ethyl <Emphasis Type="Italic">tert-</Emphasis>butyl ether

A study was carried out on the synthesis of ethyl tert-butyl ether from ethanol and 2-methylpropene on silica gel samples modified by the addition of ZrO₂ and Al₂O₃. A decrease in the turnover frequency (TOF) of the reaction is observed with increasing acidity of surface of the modified silica gels. A relationship was found between the TOF of the reaction and the fractal dimension of the catalyst. The TOF of the reaction decreases with increasing fractal dimension of the catalyst.     

Synthesis of 3-Phenyl and 5-Phenyl-2-pyrrolidinone via Rhodium Catalysed Carbonylation of Allylamines

The Rh₄(CO)₁₂ catalysed reaction with CO and H₂ of 1-phenyl- and 3-phenyl allylamine gives 5-phenyl- and 3-phenyl-2-pyrrolidinone respectively, in good yield. A reasonable reaction pathway of the carbonylation reaction is presented.     

Internal Transfer Reactions in the Copolymerization of Vinyl Acetate with Chlorinated Monomers

In the copolymerization of vinyl acetate (A) with either vinyl chloride (C) or vinylidene chloride (V), an internal transfer (backbiting) reaction—of the C- or V-ended radi-cals on an antepenultimate A unit—is proposed to be responsible for the deviation of the copolymerization kinetics from the Lewis and Mayo theory. The deviations disappear if A is replaced by isopropenylacetate [I_p], Then one gets, for the I_p -C copolymerization. r_{I p} =0.35 and :r_c=2.4, and for I -V copolymerization, r_{I p}=0.13 and r_v=5.9. The internal transfer reaction causes the formation of branches which may be evidenced by NMR analysis of constant composition suspension A-C copolymers. A kinetic scheme is proposed and the corresponding reactivity ratios derived r_A=0.29, r_c=1.60, r=0.3 (radical resulting from the transfer reaction), and k_T=1500 (rate constant of the transfer reaction at 50°C). The distribution of branches is calculated together with the sequence distribution functions for the .A. or Cunits.     

Oxidation of the 1-naphthyl radical C10H7• with oxygen: Thermochemistry,kinetics, and possible reaction pathways

The reaction of the 1-naphthyl radical C₁₀H₇• (A2•) with molecular (³O₂) and atomic oxygen, as part of the oxidation reactions of naphthalene, is examined using ab-initio and DFT quantum chemistry calculations. The study focuses on pathways that produce the intermediate final products CO, phenyl and C₂H₂, which may constitute a repetitive reaction sequence for the successive diminution of six-membered rings also in larger polycyclic aromatic hydrocarbons. The primary attack of ³O₂ on the 1-naphthyl radical leads to a peroxy radical C₁₀H₇OO• (A2OO•), which undergoes further propagation and/or chain branching reactions. The thermochemistry of intermediates and transition state structures is investigated as well as the identification of all plausible reaction pathways for the A2• + O₂ / A2• + O systems. Structures and enthalpies of formation for the involved species are reported along with transition state barriers and reaction pathways. Standard enthalpies of formation are calculated using ab initio (CBS-QB3) and DFT calculations (B3LYP, M06, APFD). The reaction of A2• with ³O₂ opens six main consecutive reaction channels with new ones not currently considered in oxidation mechanisms. The reaction paths comprise important exothermic chain branching reactions and the formation of unsaturated oxygenated hydrocarbon intermediates. The primary attack of ³O₂ at the A2• radical has a well depth of some 50 kcal mol⁻¹ while the six consecutive channels exhibit energy barriers below the energy of the A2• radical. The kinetic parameters of each path are determined using chemical activation analysis based on the canonical transition state theory calculations. The investigated reactions could serve as part of a comprehensive mechanism for the oxidation of naphthalene. The principal result from this study is that the consecutive reactions of the A2• radical, viz. the channels conducting to a phenyl radical C₆H₅•, CO₂, CO (which oxidized to CO₂) and C₂H₂ are by orders of magnitude faster than the activation of naphthalene by oxygen (A2 + O₂ → A2• + HO₂).     

Synthesis of [60]fullerene-functionalized rotaxanes

Synthesis of [60]fullerene (C₆₀)-functionalized rotaxanes via Diels-Alder reactions with C₆₀ is described. Diels-Alder reaction of C₆₀ and sulfolene moiety as masked diene attached on the wheels of rotaxanes results in high yields of C₆₀ incorporation. Rotaxanes are prepared by tin-catalyzed urethane-forming end-capping reaction with isocyanate of pseudorotaxane having the wheel carrying C₆₀ functionality as introduced by the Diels-Alder reaction. The Diels-Alder reaction was accomplished as end-capping reaction between C₆₀ and pseudorotaxane bearing sultine moiety as masked diene on the axle terminal. A variety of C₆₀-containing [2]rotaxanes was prepared in moderate to good yields by these Diels-Alder protocols.     

Dynamics of SO(A3Π) formation in an argon + SO2 afterglow

The SO(A → X) fluorescence resulting from the Ar(³P_2,0)+SO₂ reaction has been studied in a flowing afterglow system. Various reaction pathways for the formation of the SO(A) fragment have been considered. A linear surprisal analysis of the vibrational distributions indicates that the resonance excitation with subsequent predissociation of the intermediate bound state is responsible for the formation of SO(A). A significant fraction of the available energy has been found to be partitioned into translation. Because the predissociation of SO₂ in the exit channel is dominating the reaction pathway in the Ar^*+SO₂ → Ar+O+SO(A) system, all the dynamical features can then be explained by the simple classical treatments on the dissociation of SO₂.     

A new reforming process based on CH4 decomposition using a hydrogen-permeating membrane reactor

A new reforming process was studied using Ni/SiO₂ with a hydrogen-permeating membrane reactor. Nickel catalyst supported on SiO₂ is highly active for CH₄-H₂O-O₂ reaction in membrane reactor and the reaction close to CH₄ + 0.35O₂ + 1.3H₂O → CO₂ + 3.3H₂ proceeds at 873 K. Since the selectivity to carbon and CO₂ increased and decreased with decreasing contact time respectively, it is considered that the reaction was started by decomposition of CH₄ followed by oxidation of C and water shift reaction. Therefore, the reaction mechanism was different from so-called autothermal reforming (ATR) reaction.     

A Low‐Temperature Synthesis Route for CaAlSiN3 Doped with Eu2+

A new low‐temperature synthesis route of the strongly red‐emitting Eu²⁺ activated nitride phosphor CaAlSiN₃ is presented. The fluorides CaSiF₆ and AlF₃ were used as a source of metal ions and Li₃N as a nitrogen source. A KCN/LiCl flux system was employed to lower the temperature of the reaction from 1100 to 750 °C. The course of the reaction was studied by differential thermal analysis, and the product of the reaction was inspected by X‐ray powder diffraction and luminescence measurements of CaAlSiN₃:Eu.     

Stereoselective glycosidation reactions of activated glycals with a c1-oxygenated allylsilane: Synthesis of a cis-pyrano[2,3-b]pyran

A highly stereoselective synthesis of a cis-pyrano[2, 3-b]pyran has been developed utilizing a BF₃·OEt₂ catalyzed glycosidation reaction of activated glycals with 1-hydroxy-2-propenyltrimethylsilane (1). The reaction resulted in incorporation of a 1-trimethylsilyl-2-propenyloxy-1-yl function. A subsequent fluoride ion promoted internal conjugate addition reaction was used for the construction of the cis-pyranopyran.     

Catalytic Decomposition of H2O2over Supported ZnO

 Transition metal sulfates of Cu(II), Co(II), Ni(II), Cr(III), Mn(II), and Fe(III) supported on ZnO were prepared and characterized by SEM, EDX, and XRD. The kinetics of the heterogeneous decomposition of H₂O₂ over these supported catalysts was investigated. The reaction rate is correlated with both the amount of supported metal ion and its redox potential. The rate of reaction increases with increasing initial concentration of H₂O₂, attains a maximum, and decreases thereafter. It also increases with pH and reaches a maximum at high pH values. A reaction mechanism is proposed that implies the formation of a peroxo intermediate at the early stages of the reaction. A second intermediate is assumed to be formed at high [H₂O₂]_o which inhibits the progress of the reaction.     

A new reaction of fluorodinitromethyl group

A general reaction of the transformation of the fluorodinitromethyl group into the fluoronitromethyl group by denitration upon treatment with Na₂SO₃ or KI in aqueous formaldehyde was found. A preparative method for synthesizing fluoronitroalcohols was developed on the basis of this reaction.     

A convergent and stereoselective synthesis of a seco-precursor of macrolactin A

A seco-precursor of macrolactin A was synthesized by coupling two advanced segments. Wittig reaction and Horner-Emmons reaction were utilized to construct the three characteristic E,Z and E,E dienes. The C₁-C₁₀ segment was synthesized through Horner-Emmons reaction with phosphonate reagent. The α-alkylation of sulfone stabilized anion with allyl bromide followed by desulfonation gave the C₁₁-C₂₄ segment.