- Alkaloid-Catalyzed Enantioselective [3 + 2] Cycloaddition of Ketenes and Azomethine Imines
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A new asymmetric synthesis of bicyclic pyrazolidinones through an alkaloid-catalyzed formal [3 + 2] cycloaddition of in situ generated ketenes and azomethine imines is described. The products were formed in good to excellent yields (52-99% for 17 examples), with good to excellent diastereoselectivity (dr 5:1 to 27:1 for 11 examples), and with excellent enantioselectivity in all cases (≥96% ee). This method represents the first unambiguous example of an enantioselective reaction between ketenes and a 1,3-dipole.
- Mondal, Mukulesh,Wheeler, Kraig A.,Kerrigan, Nessan J.
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- CeO2 Facet-Dependent Surface Reactive Intermediates and Activity during Ketonization of Propionic Acid
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CeO2 rods, octahedrons, and cubes exposing well-defined (110), (111), and (100) surfaces, respectively, were synthesized and investigated for the catalytic ketonization of propionic acid. The intrinsic ketonization rates at 350 °C on the rods, octahedrons, and cubes are 54.3, 40.4, and 25.1 mmol·m-2·h-1, respectively, indicating that the (110) facet is the most active surface for ketonization. The reaction was tracked by both in situ infrared and mass spectroscopies under transient conditions, and the results showed that monodentate propionate, a minority surface species, is responsible for the formation of 3-pentanone. In contrast, bidentate propionate, a dominant species on all three surfaces, appears to a spectator for ketonization. Moreover, the ketonization activity can be correlated with relative concentration of monodentate propionate. A density functional theory study showed that the relative concentration of monodentate propionate (or the adsorption energy difference between monodentate and bidentate configurations) at high coverages is strongly dependent on the surface geometry. The stability of monodentate propionate on the (110) surface exposing both the O and Ce sites in the outermost layer with the well-separated Ce sites exhibits little dependence on the propionate coverage. In contrast, strong steric hindrance due to the top layer O atom and the closely packed Ce atoms in (111) destabilizes monodentate propionate significantly at high coverages. This study demonstrates that the surface geometrical structure of CeO2 can determine the abundance of the active monodentate propionate, which, in turn, will determine the catalytic activity of CeO2 for ketonization.
- Guo, Yonghua,Qin, Yuyao,Liu, Huixian,Wang, Hua,Han, Jinyu,Zhu, Xinli,Ge, Qingfeng
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p. 2998 - 3012
(2022/03/03)
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- Generation of Reactive Ketenes under Flow Conditions through Zinc-Mediated Dehalogenation
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Herein, we describe the generation of highly reactive monoalkyl and phenyl ketenes by using a dehalogenation procedure under flow conditions. All ketenes were generated in good yields (determined by quenching with an appropriate aniline derivative) and showed high reactivity in the [2+2] cycloaddition with imines, resulting in the formation of a range of β-lactams at room temperature in less than 10 minutes. Furthermore, initial experiments were performed by using these reactive ketenes for the synthesis of β-lactams under flow conditions.
- Hafner, Andreas,Ley, Steven V.
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supporting information
p. 1470 - 1474
(2015/06/30)
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- Decomposition of malonic anhydrides
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Malonic anhydrides decompose at or below room temperature, to form a ketene and carbon dioxide. Rate constants for the thermal decomposition of malonic, methylmalonic, and dimethylmalonic anhydrides were measured by NMR spectroscopy at various temperatures, and activation parameters were evaluated from the temperature dependence of the rate constants. Methylmalonic anhydride is the fastest, with the lowest δH?, and dimethylmalonic anhydride is the slowest. The nonlinear dependence on the number of methyl groups is discussed in terms of a concerted [2s + (2s + 2s)] or [2s + 2a] cycloreversion that proceeds via a twisted transition-state structure, supported by computations.
- Perrin, Charles L.,Flach, Agnes,Manalo, Marlon N.
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experimental part
p. 9698 - 9707
(2012/07/14)
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- Promotion of asymmetric aza-claisen rearrangement of N-allylic carboxamides using excess base
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The aza-Claisen rearrangement of the enolate of N-(Z)-crotyl-N-(S)- phenethylpropanamide did not proceed in the presence of 1.5 equivalents of LHMDS as a base. However, the use of a large excess of base (10 equiv) promoted the reaction to give N-(S)-phenethyl-anti-2,3-dimethylpent-4-enamide with good stereoselectivities (anti/syn = ca. 95:5). An excess of base stabilized the amide enolates and prevented the decomposition to the ketene to prompt the rearrangement of various carboxamides with good stereoselectivity. This reaction provided a new method for the construction of asymmetric quaternary carbon centers. Georg Thieme Verlag Stuttgart · New York.
- Yoshizuka, Makoto,Nishii, Takeshi,Sasaki, Hiromi,Kitakado, Junko,Ishigaki, Noriko,Okugawa, Shinobu,Kaku, Hiroto,Horikawa, Mitsuyo,Inai, Makoto,Tsunoda, Tetsuto
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scheme or table
p. 2967 - 2970
(2012/01/05)
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- Concerted wolff rearrangement in two simple acyclic diazocarbonyl compounds
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The photochemistry of two simple acyclic diazo carbonyl compounds, azibenzil and diazoacetone, were studied using the tools of ultrafast time-resolved spectroscopy. In the former case, UV-vis detection allows observation of an absorption band of singlet benzoylphenylcarbene, decaying with a 740 ± 150 ps time-constant in acetonitrile. IR detection shows that the ketene product of Wolff rearrangement (~2100 cm-1) is formed by two parallel pathways: a stepwise mechanism with carbene intermediacy with a slow rise time-constant of 660 ± 100 ps, and directly in the diazo excited state as confirmed by the immediate formation of an IR band of a nascent hot ketene species. Photolysis (270 nm) of diazoacetone in chloroform leads mainly to the ketene species through a concerted process, consistent with the predominance of the syn conformation in the diazoacetone electronic ground state and a zero quantum yield of the internal conversion process.
- Burdzinski, Gotard,Zhang, Yunlong,Wang, Jin,Platz, Matthew S.
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experimental part
p. 13065 - 13068
(2011/02/28)
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- Catalytic, Asymmetric Preparation of Ketene Dimers from Acid Chlorides
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(Matrix presented) The cinchona alkaloid-catalyzed dimerization of monosubstituted ketenes generated in situ from the reaction of acid chlorides and diisopropylethylamine yields ketene dimers in high yields and enantioselectivities. This reaction tolerates sterically demanding and functionally diverse substituents. Kinetic studies suggest that the rate-determining step for the reaction is the deprotonation of the acid chloride by the tertiary amine to form ketene and that the stereochemistry- forming step is addition of an ammonium enolate with ketene.
- Calter, Michael A.,Orr, Robert K.,Song, Wei
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p. 4745 - 4748
(2007/10/03)
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- Tandem [4+2] cycloaddition versus electrocyclisation reactions of 1-aryl-2-phenyl-5-alkyl/aryl-1,3-diazapenta-1,3,4-trienes in aza-Wittig reactions of N′-aryl-N-(triphenylphosphoranlidene) benzenecarboximidamides with ketenes
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1-Aryl-2-phenyl-5-alkyl/aryl-1,3-diazapenta-1,3,4-triene 3 generated in situ aza-Wittig reactions of N′-aryl-N-(triphenylphosphoranylidene)carboximidamides 1 which are shown to undergo selective [4+2] cycloaddition and electrocyclisation reactions leading to the formation of novel pyrimidinone derivatives 5 and quinazoline derivatives 7 with monosubstituted ketenes and diphenylketene, respectively.
- Jayakumar,Kumar, Vipan,Mahajan, Mohinder P.
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p. 2235 - 2237
(2007/10/03)
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- Gas-phase kinetics of elimination reactions of pentane-2,4-dione derivatives. Part II. Thermolysis of derivatives and analogues of 3-phenylhydrazonopentane-2,4-dione
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Six analogues and derivatives (1-6) of 3-phenylhydrazonopentane-2,4-dione (7) were subjected to gas-phase thermolysis. The Arrhenius log A (s-1) and Ea (kJ mol-1) of the analogues (1-5) are, respectively: 10.42 and 140.8 for 1-cyano-1-phenyl-hydrazonopropanone (1), 11.19 and 135.4 for 1-cyano-1-(p-nitrophenylhydrazono)-propanone (2), 10.68 and 144.9 for 1-cyano-1-(p-methoxyphenylhydrazono)propanone (3), 11.76 and 137.8 for 1-cyano-3-phenyl-1-phenylhydrazonopropanone (4), and 11.29 and 145.9 for 1-cyano-1-phenylhydrazonobutanone (5). The corresponding values for ethyl 3-oxo-2-phenylhydrazonobutanoate (6) are 11.90 s-1 and 143.3 kJ mol-1. The rates of reaction at 600 K are compared with those of the title diketone (7) and of pentane-2,4-dione (8) and rationalized in terms of a plausible elimination pathway involving a semiconcerted six-membered transition state.
- Al-Awadi,Elnagdi,Al-Awadhi,El-Dusouqui
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p. 457 - 462
(2007/10/03)
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- Thermokinetic Determination of Gas-Phase Basicities. Application to Ketene, Methylketene, and Formaldimine
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Rate constants have been determined for proton transfer reactions of the type (1+) + B ->/(1+), where M is ketene, methylketene, and formaldimine and B is a reference base.A quantitative relationship between the rate constant and the free energy (or enthalpy) of the reaction allows the determination of the gas-phase basicity, GB, (or proton affinity, PA) of M.This thermokinetic method gives results comparable to that obtained from equilibrium constant measurements.The values derived for ketene, methylketene, and formaldimine follow: GB(ketene) = 788 +/- 3 kJ/mol, PA(ketene) = 817 +/- 3 kJ/mol; GB(methylketene) = 809 +/- 3 kJ/mol, PA(methylketene) = 842 +/- 3 kJ/mol; GB(formaldimine) = 830 +/- 3 kJ/mol and PA(formaldimine) = 860 +/- 5 kJ/mol.Heats of formation of methylketene and of formaldimine that may be deduced from a combination of these results with literature data are as follows: ΔHf0300(CH3CHCO) = -97 +/- 5 kJ/mol and ΔHf0300(CH2=NH) = 75 +/- 5 kJ/mol.
- Bouchoux, Guy,Salpin, Jean-Yves
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p. 16555 - 16560
(2007/10/03)
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- Isomerization and Decomposition of 3,5-Dimethylisoxazole. Studies with a Single Pulse Shock Tube
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The isomerization and decomposition of 3,5-dimethylisoxazole were studied behind reflected shocks in a pressurized driver single pulse shock tube over the temperature range 880-1050 K and overall densities of ca. 2.5 * 10-5 mol/cm3.The main thermal reaction of 3,5-dimethylisoxazole is an isomerization to 2-methyl-3-oxobutyronitrile (CH3COCH(CH3)CN).Acetonitrile, which is the main decomposition product in the system, is obtained from 3,5-dimethylisoxazole by a unimolecular process: 3,5-dimethylisoxazole -> CH3CN + CH3CHCO.The unimolecular decomposition of the thermally excited isomer, (CH3COCH(CH3)CN) -> CH2CH2CN + CH3CO, is assumed to be the source for a large concentration of free radicals and for carbon monoxide.Thus, ethane, methane, and carbon monoxide are the major products among the species without nitrogen.It is believed that hydrogen cyanide, acetaldehyde, and 2-buten-3-one, which are found in the postshock mixtures, are obtained by a four-center unimolecular elimination from 2-methyl-3-oxobutyronitrile from both the thermally excited state (low temperatures) and a state of thermal equilibrium (high temperatures).The isomerization reaction, which involves cleavage of the N-O bond and migration of a methyl group from position 3 to 4 in the ring, is a first-order process with a rate constant given by k1st = 1015.90 exp(-61.5 * 103/RT) s-1 where R is expressed in units of cal/(K mol).The overall decomposition of 3,5-dimethylisoxazole in terms of a first-order rate constant is given by ktotal = 1015.57 exp(-59.5 * 103/RT) s-1.A reaction scheme containing 26 species and 32 elementary reactions was constructed to describe the overall mechanism of 3,5-dimethylisoxazole decomposition and isomerization.
- Lifshitz, Assa,Wohlfeiler, Dror,Tamburu, Carmen
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p. 11436 - 11446
(2007/10/02)
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- The Nature of the Transition State in Amides Pyrolysis. The Rates of Pyrolysis of N-benzoyl and N-acetylpropanamide, N-benzoyl and N-acetyl-2-methylpropanamide, and N-thioacetylpropanamide
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The rates of gas-phase elimination reactions of N-benzoyl and N-acetyl-propanamide and N-benzoyl and N-acetyl-2-methylpropanamide are measured and discussed.They undergo unimolecular first-order elimination reactions.The reactivities of N-benzoylamides have been compared with each other and with those of N-acetylamides.The kinetic data together with the product analysis reveals that, the statistical factor of the availability of β-hydrogen atoms for elimination as well as steric factor are obscured by polar factor in gas-phase elimination reactions of N-benzoylamides while the statistical factor rather than electronic effect operates in each of N-acetylamides.
- Al-Awadi, Nouria A.,Al-Omran, Fatima A.,Mathew, Tommy
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- Visible Light-Induced Oxygen Transfer from Nitrogen Dioxide to Ethyne and Propyne in a Cryogenic Matrix. 1. Identification of Products
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Photochemical reaction of ethyne*NO2 and propyne*NO2 pairs isolated in solid Ar has been observed at wavelengths as long as 582 nm (HCCH*NO2) and 615 nm (CH3CCH*NO2).Continuous wave dye laser radiation was used to excite the reactants, and the chemistry was monitored by FT-infrared spectroscopy.In the case of ethyne + NO2, the sole products were CH2=C=O and NO.The reaction of NO2 with propyne gave methylketene plus a trapped intermediate, CH3C(=NO.)C(=O)H (formyl methyl iminoxy radical).Infrared spectra of this radical are reported for the first time.Product identification was based on D, 18O, and 15N isotopic substitution.Selective interconversion with tuned visible laser light revealed the presence of four conformers, most probably originating from isomerism about the C-C and the C=N bonds.Photoelimination of NO from the iminoxy radical was observed at wavelengths as long as 625 nm.Propynol and methylketene could be identified among the secondary photolysis products.
- Harrison, James A.,Frei, Heinz
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p. 12142 - 12151
(2007/10/02)
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- Visible Light-Induced Oxygen Transfer from Nitrogen Dioxide to Ethyne and Propyne in a Cryogenic Matrix. 2. Mechanism and Regioselectivity
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The kinetics of visible ligth-induced oxidation of ethyne and propyne by NO2 in solid Ar has been monitored as a function of photolysis wavelength.CW dye and Ar ion laser emission was used for irradiation, and FT-infrared spectroscopy for the measurement of product growth.Determination of the wavelength dependence of quantum efficiencies from the kinetic measurements revealed that the photolysis threshold of HCCH + NO2 lies approximately 6 kcal mol-1 higher than that of CH3CCH + NO2.This and other parameters derived from the product growth measurements, and the formyl methyl iminoxy radical trapped in the case of the CH3CCH + NO2 reaction are interpreted in terms of a direct O transfer mechanism.The proposed path involves large-amplitude O transfer from photoexcited NO2 to the CC group to yield a transient ketocarbene.Formation of iminoxy radical is attributed to trapping of the ketocarbene by NO cage coproduct, which is in competition with Wolff rearrangement to yield ketene.From the structure of the iminoxy radical, it is inferred that the photoinduced O transfer from NO2 to the unsymmetrical CC bond of propyne is completely regioselective, leading exclusively to the carbene transient with oxygen at the terminal carbon.This regiochemical outcome is interpreted in terms of potential energy profiles for central and terminal carbon attack of the triple bond.
- Harrison, James A.,Frei, Heinz
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p. 12152 - 12157
(2007/10/02)
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- Tetrahydropyridine oxime compounds
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Pharmaceutically useful compounds in the treatment of depression, psychoses, and inflammatory diseases having the following structure: STR1
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- Photochemistry of the Matrix-isolated α,β-Unsaturated Aldehydes Acrolein, Methacrolein and Crotonaldehyde at 4.2 K
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The UV photolysis of the α,β-unsaturated aldehydes acrolein, methacrolein and crotonaldehyde in argon matrices at λ > 300 nm has shown a major photochemical deactivation pathway to be conformational isomerism to the thermodynamically less stable s-cis form.This type of isomerization may account for the rapid internal conversion observed in the gas phase.Matrix-isolated crotonaldehyde undergoes further isomerization to ethylketene and enol-crotonaldehyde, as observed in the analogous gas-phase photolysis.In addition, another H-abstraction product was detected (νOH = 3674 cm-1) which is probably derived from the photolysis of s-cis-crotonaldehyde.At shorter excitation wavelenths (λ > 230 nm) acrolein and methacrolein isomerize to methylketene and dimethylketene, respectively.
- Johnstone, Duncan E.,Sodeau, John R.
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p. 409 - 415
(2007/10/02)
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- A Semiempirical (AM1, MNDO, and MINDO/3) Study on the Thermolysis of 1-Alkynyl Ethers. Reaction Analysis by Correlation of Localized Molecular Orbitals
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The thermolyses of ethoxyethyne (2a), isopropoxyethyne (2b), tert-butoxyethyne (2c), 1-ethoxy-1-propyne (3a), 1-isopropoxy-1-propyne (3b), 1-tert-butoxy-1-propyne (3c), and 1-ethoxy-1-butyne (4) leading to ketenes and olefins have been studied by means of the semiempirical SCF MO methods AM1, MNDO, and MINDO/3 at the RHF level.The reactions have been found in all cases to be concerted and to exhibit a highly synchronous character.The predicted order of reactivity, -CCO-t-Bu > -CCO-i-Pr > -CCOEt, fully coincides with the experimental one, the AM1 calculated activation entha lpies being the closest to the experimentally determined Arrhenius activation energies.Observed deuterium primary and secondary kinetic isotope effects are well reproduced by the calculation.A reaction analysis by correlation of localized molecular orbitals identifies the direction of flow of electron density along the reaction coordinate and suggests that the lack of adaptation of the ?-component of the initial triple bond to the geometrical changes taking place along the reaction path makes an important contribution to the activation energy of the reaction.
- Moyano, Albert,Pericas, Miquel A.,Serratosa, Felix,Valenti, Eduard
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p. 5532 - 5538
(2007/10/02)
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- PYROLYSE-ECLAIR SOUS VIDE DE 1,2,4-TRIAZOLIDES = UNE ETUDE PAR SPECTROMETRIE DE MASSE EN TANDEM
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A real-time analysis of the flash-vacuum pyrolysis products of some 1,2,4-triazolides has been performed by tandem mass spectrometry.Beside decay products, ketenes and the parent 1,2,4-triazole, 1-acyltriazoles give rise to 5-alkyloxazoles and nitrogen.This ring transformation reaction implies a sigmatropic shift of the acyl group from nitrogen to carbon, loss of nitrogen and cyclisation of the biradical intermediate. 5-aryloxazoles are similarly obtained from 1-aroyltriazoles.
- Maquestiau, A.,Puk, E.,Flammang, R.
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p. 181 - 190
(2007/10/02)
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- A New Synthesis of Reactive Ketenes (Solutions)
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Distilled solutions of reactive ketenes are conveniently prepared by the reaction of α-bromoacyl chlorides pentacarbonylmanganese anion.
- Masters, Andrew P.,Sorensen, Ted S.,Ziegler, Tom
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p. 3558 - 3559
(2007/10/02)
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- Methyl- and Dimethylketene: He I Photoelectron Spectra and Vertical Ionization Potentials Calculated by Using Perturbation Corrections to Koopmans' Theorem
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He I photoelectron spectra are reported for the monomethyl and dimethyl derivatives of ketene, H2CCO.The spectra, which beyond the first structured ionization potential show a complicated series of bands in the 12-18-eV range, have been fully assigned by using calculations employing perturbation corrections to Koopmans' theorem.
- Chong, D. P.,Westwood, N. P. C.,Langhoff, S. R.
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p. 1479 - 1481
(2007/10/02)
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- Photochemical 2 + 2-Cycloadditions of Sulphur Dioxide and Ketenes in Low-temperature Matrices
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U.v. irradiation at 12 K of Ar or N2 matrices containing ketenes and SO2 yielded the corresponding 1,2-oxathietan-4-one 2-oxides as 2 + 2-cycloadducts; this reaction was shown to be distinct from the thermal 1 + 2-cycloaddition of ketene and SO2.The 2 + 2-adducts decomposed on prolonged irradiation to CO2, sulphur atoms, and the corresponding aldehydes or ketones, presumably via sulphines, which, however, could not be detected.Interpretation of the spectra was complicated by strong interactions between carbonyl compounds and SO2, and this phenomenon was also explored.
- Dunkin, Ian R.,MacDonald, J. Gavin
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p. 2079 - 2084
(2007/10/02)
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- Substituted aryloxyamino propanols, and process for their use
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Substituted aryloxyamino propanols and pharmaceutically acceptable acid addition salts thereof according to the following formula STR1 wherein X is selected from oxygen and NH, R1 is selected from hydrogen, amino and acylamino having 1 to 8 carbon atoms, R2 is selected from isopropyl, tertiarybutyl, and 2-(3,4-dimethoxyphenethyl), are disclosed which are useful as anti-hypertensive and β-adrenolytic agents. Also, substituted aryl azoles selected from 3-aryl pyrazoles and 5-aryl oxazoles having the formula STR2 wherein X and R1 are the same, and R3 is selected from hydrogen, the radical STR3 are disclosed which are useful in the preparation of the substituted aryloxyamino propanols of Formula I. Compositions containing the aryloxyamino propanols, and methods of preparation are also disclosed.
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- Trimethylsilyl Cyanide - A Reagent for Umpolung, VIII. Derivatives of 2-(Trimethylsilyloxy)-2-propenenitrile. Syntheses and General Properties
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Rather different derivatives of the new title compuond 7 were synthesized by routes A - H (Table 2 and 3).The effects of substituents and reaction routes on the E/Z ratios (NMR) is discussed.Replacement of SiMe3 in 7 by RCO- and MeSO2- yields other alkenes with donor (O - X) and acceptor groups (CN) at the same C-atom.Their opposite effects on the β-C-atom is estimated from the corresponding 1H- and 13C-NMR signals.
- Hertenstein, Ulrich,Huenig, Siegfried,Reichelt, Helmut,Schaller, Rainer
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p. 261 - 287
(2007/10/02)
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- Gasphasen-Reaktionen, 21. Thermische Erzeugung von Alkyl- und Halogenketenen
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Thermal gas phase reactions for the generation of ketenes can be optimized PE-spectroscopically.To eliminate HX from acetyl derivatives R2CH-COX increasing temperatures are required in the sequence HO2CCH3 ca.HCl HBr H2O ca.ROH CH4.By adding NH3, HCl can be removed from the gaseous mixture and thus the PE spectra of pure alkyl ketenes R2C=C=O (R e.g.H, CH3, C2H5) may be recorded. "Fulvene ketene" (4) is obtained from cyclopentadienecarbonyl chloride (this from the dimer) and ethyleneketene (7) by pyrolysis of cyclopropyl spirosubstituted Meldrum's acid (6).Chloro- and bromoketenes are generated as follows: ClHC=C=O from ClH2C-COCl, Cl2C=C=O from Cl3C-COBr with Zn, BrHC=C=O from 2-bromocyclobutanone and NC-HC=C=O from NC-HC=C=O from NC-H2C-COCl.The PE spectra are assigned by radical cation state comparison based on MNDO calculations.
- Bock, Hans,Hirabayashi, Takakuni,Mohmand, Shamsher
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p. 2595 - 2608
(2007/10/02)
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- METHYLKETENE, A MINOR BUT HIGHLY REACTIVE BYPRODUCT IN THE PYROLYSIS GAS OF ACETONE
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Methylketene was identified during the pyrolysis of acetone, and proved to be much more reactive than ketene: METHYL-β-LACTAMS were the dominant cycloaddition products when imines are reacted with the pyrolysis gas of acetone at ROOM TEMPERATURE.
- Tschamber, Theophile,Streith, Jacques
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p. 4503 - 4506
(2007/10/02)
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- Copper(I) Chemical Ionization-Mass Spectroscopic Analysis of Esters and Ketones
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The present work lays the foundation for the understanding and evaluation of atomic metal ions as a new class of chemical ionization reagent ions.In particular, a thorough study of the gas phase ion chemistry of Cu(1+), generated by laser ionization from the pure metal, with a series of oxygenated compounds is reported.Definite patterns of reactivity for different classes of oxygenated compounds are observed which, together with an understanding of the reaction mechanisms, provide the basis for predicting the Cu(1+) chemical ionization mass spectra of new compounds with analogous functional groups.The chemistry of Cu(1+) is found to be dramatically different from that of Ti(1+) and Li(1+) reported earlier providing a significant indication of the flexibility and selectivity afforded by atomic metal reagent ions.
- Burnier, R. C.,Byrd, G. D.,Freiser, B. S.
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p. 1641 - 1650
(2007/10/02)
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- Methylketene. Ion Chemistry and Proton Affinity
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The gas-phase ion chemistry of methylketene has been investigated using a quadrupole ion store (quistor) as an ion/molecule reaction chamber.The reaction sequences have been elucidated by the new technique quistor resonance ejection (QRE), which closely resembles ion cyclotron double resonance (ICDR).The ion chemistry of methylketene is analogous to that of ketene, and the nonreactive species m/z 57 (C3H5O+) is a major product at long storage times.The equilibrium for proton transfer between methyl acetate and methyl ketene ((CH3COOCH3)H+ + CH3CHCO = CH3CH2CO+ = CH3COOCH3) has been studied and the proton affinity (PA) of methylketene was found to be 845 +/- 3 kJ mol-1, based on a value for PA(CH3CO2CH3) of 839 kJ mol-1 relative to the PA(i-C4H8) at 828 kJ mol-1.
- Armitage, Mary Alison,Higgins, Michael Joseph,Lewars, Errol George,March, Raymond Evans
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p. 5064 - 5068
(2007/10/02)
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- Cyanoketenes. Mechanism of tert-Butylcyanoketene Cycloaddition to Aldo- and Ketoketenes
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tert-Butylcyanoketene cycloadds to ketene, methylketene, dimethylketene, and ethylmethyketene.The first two examples give 2-oxetanones and the last two result in cyclobutane-1,3-diones.These cycloadditions are shown to proceed by a nonconcerted dipolar mechanism involving zwitterionic intermediates.Establishment of the intermediacy of the zwitterions was accomplished by their independent generation from the thermolysis of substituted 4-azido-5-tert-butylcyclopentene-1,3-dione precursors.The mechanistic consequences of these cycloadditions and how they may apply to other ketene dimerizations are discussed.
- Moore, Harold W.,Wilbur, D.Scott
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p. 4483 - 4491
(2007/10/02)
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