- Environment Effects on the ESR Spectrum of the Cation Radical of Dimethylketene in Low Temperature Matrices
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The cation radical of dimethylketene produced in γ-irradiated solid solutions of various halocarbons has been investigated by ESR over a temperature range from 77 K to the melting point of each matrix.The cation radical in CCl4 was stable up to about 180 K and the spectrum was well resolved to allow the determination of the anisotropic ESR parameters.In CCl2FCClF2 and CCl2FCCl2F, a series of irreversible spectral changes was observed with an increase in temperature.This process was interpreted in terms of the formation of the dimer cation.In the matrix of CCl3F, the ESR spectrum exhibited extra structure, which varied reversibly with temperature.The analyses of the spectra suggested that the cation radical in CCl3F weakly interacts with surrounding matrix molecules to form adducts.
- Fujisawa, Jun,Shimokoshi, Kazuo,Shida, Tadamasa
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Read Online
- 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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Read Online
- Lessons in Strain and Stability: Enantioselective Synthesis of (+)-[5]-Ladderanoic Acid
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The synthesis of structurally complex and highly strained natural products provides unique challenges and unexpected opportunities for the development of new reactions and strategies. Herein, the synthesis of (+)-[5]-ladderanoic acid is reported. En route to the target, unusual and unexpected strain release driven transformations were uncovered. This occurrence required a drastic revision of the synthetic design that ultimately led to the development of a novel stepwise cyclobutane assembly by an allylboration/Zweifel olefination sequence.
- Hancock, Erin N.,Kuker, Erin L.,Tantillo, Dean J.,Brown, M. Kevin
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supporting information
p. 436 - 441
(2019/11/25)
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- Thioallenoates in catalytic enantioselective [2+2]-cycloadditions with unactivated alkenes
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The application of thioallenoates to catalytic enantioselective [2+2]-cycloadditions with unactivated alkenes is reported. In many cases, the thioallenoates examined exhibit superior reactivity and selectivity compared to the allenic esters generally used in these cycloadditions.
- Conner, Michael L.,Wiest, Johannes M.,Brown, M. Kevin
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supporting information
p. 3265 - 3271
(2019/05/04)
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- PROCESS FOR PREPARING 2,2,4,4-TETRAMETHYL-1,3-CYCLOBUTANEDIOL
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The present invention refers to 2, 2, 4, 4 - tetramethyl - 1, 3 - cyclohexanedimethanol bhutan d this year a number bath method disclosure as follows. the method (A) meta acrylic acid (methacrylic acid, MAA) removed from the raw material (B) use as an intermediate in the mote [lik [lik] it buys [...] (isobutyric acid, IBA), 2, 2, 4, 4 - tetramethyl - 1, 3 - cyclohexanedimethanol [...] (C) dimethyl ketene (dimethyl Ketene, DMK) and (D) (2, 2, 4, 4 a-tetramethyl-a 1, 3 non-cyclobutanedione, CBDK) via a final material sequentially (E) 2, 2, 4, 4 - tetramethyl bhutan d this year cycle - 1, 3 - (2, 2, 4, 4 a-tetramethyl-a 1, 3 non-cyclobutanediol, CBDO) bath a number comprise substrate. According to the present invention number bath step optimization and a green protective environmental 2, 2, 4, 4 - tetramethyl - 1, 3 - cyclohexanedimethanol bhutan d this year through mirror number is encoded number bath method is highly lipophilic ball number. (by machine translation)
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Paragraph 0075-0093
(2019/10/22)
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- Fe-Catalyzed Cycloisomerization of Aryl Allenyl Ketones: Access to 3-Arylidene-indan-1-ones
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A cycloisomerization of aryl allenyl ketones to 3-arylidene-indan-1-ones using a cationic Fe-complex as a catalyst is reported. The catalyst opens a synthetically interesting reaction pathway to this surprisingly underrepresented class of indanones that are not accessible using alternative catalytic systems.
- Teske, Johannes,Plietker, Bernd
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supporting information
p. 2257 - 2260
(2018/04/27)
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- Tfoh-catalyzed formal [3 + 2] cycloaddition of cyclopropane 1,1-diesters with nitriles
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A triflic acid-catalyzed formal [3 + 2] cycloaddition of cyclopropane 1,1-diesters with nitriles was developed. This reaction was expeditious, and the scope of the substituents in both cyclopropanes and nitriles was broad. This supplies an efficient and practical method for the synthesis of 1-pyrrolines.
- Cui, Bo,Ren, Jun,Wang, Zhongwen
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p. 790 - 796
(2014/04/03)
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- Catalytic asymmetric heterodimerization of ketenes
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In this Communication we describe an unprecedented catalytic asymmetric heterodimerization of ketenes of wide substrate scope. The alkaloid-catalyzed method provides access to ketene heterodimer β-lactones and allows even two different monosubstituted ketenes to be cross-dimerized, with excellent enantioselectivity (17 examples with ≥90% ee) and excellent heterodimer regioselectivity observed in all cases.
- Ibrahim, Ahmad A.,Nalla, Divya,Van Raaphorst, Maxwell,Kerrigan, Nessan J.
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supporting information; experimental part
p. 2942 - 2945
(2012/04/10)
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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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- Mild decarboxylative activation of malonic acid derivatives by 1,1′-carbonyldiimidazole
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Chemical equations presented. Malonic acid derivatives undergo unusually mild decarboxylation when treated with N,N′-carbonyldiimidazole (CDI) at room temperature to generate the carbonyl imidazole moiety in high yield, which can be reacted further with a variety of nucleophiles in an efficient one-pot process.
- Lafrance, Danny,Bowles, Paul,Leeman, Kyle,Rafka, Robert
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supporting information; scheme or table
p. 2322 - 2325
(2011/06/26)
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- Histone deacetylase inhibitors
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This invention relates to novel Histone deacetylases inhibitors. Also disclosed is a method for treating mucositis or cancer with these inhibitors.
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Page/Page column 7
(2011/12/03)
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- HISTONE DEACETYLASE INHIBITORS
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This invention relates to novel Histone deacetylases inhibitors. Also disclosed is a method for treating mucositis or cancer with these inhibitors.
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Page/Page column 4-5
(2011/12/12)
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- Polyester from dimethylketene and acetaldehyde: Direct copolymerization and β-lactone ring-opening polymerization
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Two ways to obtain aliphatic polyesters (PEs) from dimethylketene and acetaldehyde were investigated. On the one hand, a direct anionic copolymerization was carried out in toluene at -60 °C. The resulting polymer was mainly composed of PE units. On the other hand, a two-step process involving the synthesis of 3,3,4-trimethyl-2-oxetanone by [2+2] cycloaddition, followed by its ring-opening polymerization, with various initiators and solvents, led to the expected PE. Molecular weights up to 9000 g mol -1 (measured by nuclear magnetic resonance (NMR)), with narrow polydispersity around 1.2, were obtained. These polymers were found stable up to 274 °C under nitrogen and a broad and complex endothermic peak attributed to crystallinity was observed near 139 °C by differential scanning calorimetry (DSC). The crystallinity, measured by X-ray diffraction, was close to 0.45.
- Brestaz, Marc,Desilles, Nicolas,Le, Guillaume,Bunel, Claude
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experimental part
p. 4129 - 4138
(2012/07/13)
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- Total synthesis of epothilones B and D: Stannane equivalents for β-keto ester dianions
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(Chemical Equation Presented) Studies leading to a total synthesis of epothilones B and D are described. The overall synthetic plan was based on late-stage fragment assembly of two segments representing C1-C 9 and C10-C21 of the structure. The C 1-C9 fragment was prepared by elaboration of commercially available (2R)-3-hydroxy-2-methylpropanoate at both ends of the three-carbon unit. Introduction of carbons 1-4 containing the gem-dimethyl unit was achieved in a convergent manner using a diastereoselective addition of a stannane equivalent of a β-keto ester dianion. An enantioselective addition of such a stannane equivalent for a β-keto ester dianion was also used to fashion one version of the C10-C21 subunit; however, the fragment assembly (using bimolecular esterification followed by ring-closing metathesis) with this subunit failed. Therefore, fragment assembly was achieved using a Wittig reaction; this was followed by macrolactonization to close the macrocycle. The C10-C21 subunit needed for this approach was prepared in an efficient manner using the Corey-Kim reaction as a key element. Other key reactions in the synthesis include a stereoselective SmI 2 reduction of a β-hydroxy ketone and a critical opening of a valerolactone with aniline which required extensive investigation.
- Keck, Gary E.,Giles, Robert L.,Cee, Victor J.,Wager, Carrie A.,Yu, Tao,Kraft, Matthew B.
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supporting information; experimental part
p. 9675 - 9691
(2009/04/07)
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- Process for the preparation of dimethylketene and then of polydimethylketene fro isobutyric anhydride
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The present invention relates to a process for the preparation of dimethylketene (DMK) and then of polydimethylketene (PDMK) by polymerization of DMK. More specifically, the DMK is obtained by pyrolysis by isobutyric anhydride (IBAN), the latter decomposing under the effect of heat (pyrolysis) to give isobutyric acid (IBA) and DMK. One mole of pyrolyzed IBAN gives one mole of IBA and one mole of DMK.
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Page/Page column 5
(2008/06/13)
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- Asymmetric synthesis of highly substituted β-lactones by nucleophile-catalyzed [2+2] cycloadditions of disubstituted ketenes with aldehydes
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α,α-Disubstituted β-lactones can be obtained by the cycloaddition of the corresponding ketenes with aldehydes (see scheme). For the first time, a chiral PPY derivative, 1, serves as an efficient catalyst for the asymmetric synthesis of β-lactones (PPY = 4-pyrrolidin-1-ylpyridine). To date, this is the only catalyst that is effective for enantioselective cycloadditions of disubstituted ketenes with aldehydes. (Chemical equation presented).
- Wilson, Jonathan E.,Fu, Gregory C.
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p. 6358 - 6360
(2007/10/03)
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- Photochemical generation and matrix-isolation detection of dimethylvinylidene
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We report the spectroscopic characterization of dimethylvinylidene, (CH3)2C=C:, generated within an argon matrix at 14 K from a bisperoxyester precursor. The carbene was identified by comparison of the experimental IR spectrum with vibrational frequencies computed at the B3LYP/6-31G(d) level. Chemical trapping of the carbene within a 9% CO/Ar matrix to form dimethylpropadienone supports this analysis. Additional products produced during photolysis were identified by comparison to the appropriate computed vibrational frequencies. The potential energy surface of dimethylvinylidene and its intramolecular rearrangement products, 2-butyne and methylcyclopropene, were also investigated computationally at the B3LYP/6-31G(d) level. A spin-state analysis of this carbene using a variety of computational methods (CCSD(T), B3LYP, MP2) indicates the singlet state is more stable than the triplet by ~45 kcal mol-1. We anticipate the bisperoxyester precursor used here will be a convenient and general way for initiating future studies of alkylvinylidenes under matrix-isolation conditions.
- Reed,Capitosti,Zhu,Modarelli
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p. 287 - 299
(2007/10/03)
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- Flash vacuum pyrolysis and photolysis of 3,3,5,5-tetramethylpyrazolin-4- one - A matrix isolation study
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The flash vacuum pyrolysis of 3,3,5,5-tetramethylpyrazolin-4-one (4) with subsequent trapping of the products in argon at 10 K results in the formation of a complex product mixture with tetramethylcyclopropanone (5) as one of the minor constituents. The 193 nm photochemistry of matrix-isolated 4 is much cleaner, yielding cyclopropanone 5 and allene oxide 9 as the major products. The reaction of tetramethylallene 13 with oxygen atoms yields the same product mixture of 5 and 9 and thus provides an independent route to these species. The experimental IR spectra of 5 and 9 are in good agreement with the results from DFT calculations.
- Sander, Wolfram,Wrobel, Roman,Komnick, Peter,Rademacher, Paul,Muchall, Heidi M.,Quast, Helmut
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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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- Flash Vacuum Thermolysis of Four Membered Ring Containing Nitrogen Atom. Part III. Thermal Decomposition of β-Lactams
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The thermal decomposition of β-lactams under FVT conditions was studied. It has been found that the regiochemistry of the ring cleavage depends on the nature of substituents. 1,4-Diradical stepwise mechanism of these reactions has been postulated. Key words: β-lactams, flash vacuum thermolysis
- Bartnik, R.,Lesniak, S.
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p. 2605 - 2612
(2007/10/02)
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- Photochemical ring expansion of tetramethylcyclobutanone revisited: Angular dependence of electronic absorption of singlet carbenes
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Tetramethyltetrahydrofuranylidine, produced by the photochemical ring expansion of the corresponding cyclobutanone, has been characterized by IR and UV/Vis spectroscopy in a low-temperature N2 matrix. The angular dependence of the UV/Vis spectra of this and related carbenes is explored by ab initio calculations.
- Matsumura,Ammann,Sheridan
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p. 1843 - 1846
(2007/10/02)
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- Direct Observation of α-Oxo Ketenes from the Photolysis of α-Diazo β-Diketones
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Monitoring by IR spectroscopy of the broad-band irradiation of the symmetrically substituted 2-diazocyclohexane-1,3-dione (11), 3-diazopentane-2,4-dione (19), and 4-diazo-2,2,6,6-tetramethylheptane-3,5-dione (24) in Ar matrices at 12 K showed the formation of 2-carbonylcyclopentanone (s-Z-12), acetyl(methyl)ketene (s-E-20), and tert-butyl(pivaloyl)ketene (s-E-25), respectively, in less than 10 min.On increasing the photolysis time to >3 h, the α-oxo ketenes 12, 20, and 25 decarbonylated to the corresponding oxocarbenes which underwent Wolff rearrangement to carbonylcyclobutane (15), dimethylketene (23), and di-tert-butylketene (28), respectively.The reaction of 2-carbonylcyclopentanone (12) with CH3OH was monitored by IR spectroscopy.Thus, it was found that the reaction started at ca. 100 K and was essentially complete at 140 K, involving the initial formation of the enol form (9) of methyl 2-oxocyclopentanecarboxylate.
- Leung-Toung, Regis,Wentrup, Curt
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p. 4850 - 4858
(2007/10/02)
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- Chemical trapping of electronically excited biradicals upon visible light-induced oxygen-atom transfer from NO2 to allene and dimethylacetylene in a cryogenic matrix
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Oxygen-atom transfer from NO2 to allene and dimethylacetylene was observed upon excitation of reactant pairs in solid Ar at wavelengths as long as 585 (NO2 + allene) and 610 nm (NO2 + dimethylacetylene). Continuous wave dye laser radiation was used to initiate reaction, and product growth was monitored by FT-infrared spectroscopy. In the case of the allene + NO2 reaction 2-allyl nitrite radical was obtained as product, while excitation of dimethylacetylene-NO2 pairs gave acetyl methyl iminoxy radical and dimethylketene + NO. Structures of products were determined by 15N and 18O isotopic substitution and, in the case of allyl nitrite radical, by observation of photodissociation products allene oxide and cyclopropanone. The observed radicals constitute transient biradicals formed upon O-atom transfer that are chemically trapped by NO cage coproduct. Interpretation by aid of literature ab initio results indicates that in the case of allene + NO2 the observed nitrite radical is 2-allenylidoxy biradical trapped in a B1 excited state. The iminoxy radical product of the dimethylacetylene photooxidation is a trapped singlet excited acetylmethyl methylene biradical. This is the first insight into O-atom transfer paths involving cumulene and CC triple bonds gained by chemical trapping of excited-state biradicals.
- Nakata, Munetaka,Frei, Heinz
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p. 1363 - 1372
(2007/10/02)
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- SIND PYRAZOLIN-3,5-DIONE ALS VORSTUFEN FUER CARBENE GEEIGNET ?
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Thermolysis of the 1-pyrazoline-3,5-diones 3a,b yields the ketenes 4a,b.Upon matrix irradiation of 3a,b a second molecule of CO is eliminated under formation of the carbenes 5a,b, which finally lead to propene (6) or allene (7).
- Maier, Guenther,Heider, Marc,Sierakowski, Claudia
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p. 1961 - 1962
(2007/10/02)
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- The Kinetics and Mechanism of Addition of Bulky Alcohols to Dimethyl Ketene and to p-Nitrophenyl Isocyanate in Iso-octane and Carbon Tetrachloride Solutions
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We report on the kinetics of addition of pentan-3-ol to p-nitrophenyl isocyanate and to dimethyl ketene in iso-octane, of t-butyl alcohol to the isocyanate in iso-octane, and of pentan-3-ol to the isocyanate in carbon tetrachloride.The extent of self-association of the alcohols in iso-octane has also been examined.For all the additions, our results are compatible with a mechanism that involves slow attack by both alcohol monomers and trimers, the latter being the more reactive.Conclusions from previous work with pentan-3-ol are not supported.
- Donohoe, Geraldine,Satchell, Derek P. N.,Satchell, Rosemary S.
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p. 1671 - 1674
(2007/10/02)
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- Oxirenes and ketocarbenes from α-diazoketone photolysis: Experiments in rare gas matrices. Relative stabilities and isomerization barriers from MNDOC-BWEN calculations
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Matrix-isolated α-diazoketones (DZ) RCOCN2R (R = CH3 or CD3) were photolyzed and their reactions were monitored by FT-IR spectroscopy. The ketene (KE) products from the Wolff rearrangement were always more abundant than the α,β-unsaturated ketones (ON); this selectivity increased when a broad band source (λ > 230 nm) was used instead of a monochromatic laser source (457.9 nm). Oxirenes (OX) were detected as minor, but well-identified reaction products, stable at temperatures less than 25 K, even under the monochromatic irradiation; they isomerized to KE when irradiated at λ > 230 nm. With matrices doped with carbon monoxide, the reaction diverted toward ketoketene, which certainly resulted from ketocarbene (KC) trapped by CO molecules. The kinetic data showed that the rate constants of DZ → KC, KC → KE, KC → ON, and KC → OX processes have the same order of magnitude. After complete DZ photolysis, the KE concentration still increased under extended irradiation; therefore, KC(T0) is suspected to be another reaction product that slowly photoisomerized to KE. Some 1R absorption bands might correspond to that intermediate, but unambiguous assignments could not be made. On the other hand, our previous oxirene identification has been supported by ab initio calculations at the SCF level, which justified the high-frequency value of oxirene v(C=C). To account for the results of matrix isolation experiments and for those previously recorded during the gas-phase photolysis of several DZ [R = CH3, (CH3)3C; R-R = -(CH2)4-], the relative stabilities of different isomers (KC, OX, and KE) were computed, and the assumed reaction paths from KC to reaction products were studied, in each series, through the MNDOC semiempirical method. Substituent effects and ring strain deeply influence the oxirene stability. Considering that the photolysis and photoisomerization processes occur on the singlet potential energy surface, we finally established a unified energy diagram, approximately scaled, that gathers together the different species in different electronic states and allows the interpretation of the main reaction features.
- Bachmann, Christian,N'Guessan, Thomas Yao,Deb?, Fabrice,Monnier, Maurice,Pourcin, Jean,Aycard, Jean-Pierre,Bodot, Hubert
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p. 7488 - 7497
(2007/10/02)
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- Surface Reactions, 9 / Dehydrohalogenation of Halohydrocarbons at Raney Nickel
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Raney nickel, a highly reactive and air-sensitive solid, if prepared and investigated under oxygen-free conditions, exhibits interesting catalytic properties.Using photoelectron spectroscopy for real-time gas analysis in a flow reactor, the following results are obtained with alkyl and acylhalides: Dehydrohalogenation temperatures are lowered relative to thermal HHal elimination up to 350 K.Monochloro and bromo propanes and butenes yield propene and butadiene, respectively. 1,1-Dichloro ethane or 1,1-dibromo propane only split off one HHal and form chloroethene or 1,1-bromopropene-2.HCl elimination from 2-methyl propionic acid chloride, expectedly, produces dimethyl ketene.Most interesting, however, is the ring opening of monobromo cyclobutane to 1-bromo-butene-3, observed already at room temperature, which strongly suggests the intermediate formation of a chemisorbed surface carbene at Raney nickel.The formation of hexadiene-1,5 as a by-product in the HCl elimination of 1-chloropropane, i.e. a surface carbene dimer, indicates their presence also in other dehydrohalogenations heterogeneously catalyzed by Raney nickel.
- Bock, Hans,Wolf, Hans Peter
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p. 699 - 714
(2007/10/02)
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- The Thermolysis of 2,2-Dimethyl-1-vinylcyclobutane
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The kinetics of thermolysis of 2,2-dimethyl-1-vinylcyclobutane have been investigated as a function of temperature from 263 to 301 deg C.Primary products produced in the reaction include isobutene and butadiene, 4,4-dimethylcyclohexene, 2-methylhepta-1,6-diene, and cis-2-methylhepta-1,5-diene. trans-2-Methylhepta-1,5-diene and 2,4-dimethylhexa-1,5-diene are produced from cis-2-methylhepta-1,5-diene by way of a 3,3-sigmatropic rearrangement.The reaction obeys first-order kinetics and is unaffected by surface.Activation energies (kcal mol-1) and (logA/s-1) for the overall decomposition and for formation of the primary products are 45.73 +/- 0.3 (14.427 +/- 0.12), 47.71 +/- 0.7 (15.087 +/- 0.3), 44.35 +/- 1.6 (12.53 +/- 0.6), 45.0 +/-1.3 (12.24 +/- 0.5), and 38.38 +/- 1.7 (10.785 +/- 0.7), respectively.The regiochemistry observed in fragmentation and in the 1,3-sigmatropic rearrangement of the starting material is discussed in terms of substituent effects found in other cyclobutane and vinylcyclobutane thermolyses.The fragmentation process and the isomerization to 4,4-dimethylcyclohexene and 2-methylhepta-1,6-diene is believed to proceed through the intervention of 6-methylhept-1-ene-3,6-diyl. cis-2-Methylhepta-1,5-diene is formed from a concerted 1,5-sigmatropic rearrangement of the starting material.The factors which affect the stereochemistry of the 1,5-hydrogen shift are discussed.
- Chickos, James S.,Frey, H. Monty
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p. 365 - 370
(2007/10/02)
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- Fourier Transform Infrared Kinetic Study of the Thermal Decompositon of Tetramethyl-1,3-cyclobutanedione and Dimethylketene
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The vapor phase thermolysis of tetramethyl-1,3-cyclobutanedione (TMCBD) has been studied in the temperature range 383-430 degree by Fourier transform infrared spectroscopy.The first order decay constant is log (k1/s-1)=13.78-(48400 cal mol-1/2.303 RT).The decomposition of TMCBD leads exclusively to dimethylketene (DMK) whose buildup and subsequent decay were also followed kinetically.Studied at higher temperatures (450-520 degree), a first order decay constant of log (k2/s-1)=10.72-(48800 mol-1/2.303 RT) was determined for the thermal decomposition of DMK.Rates of decomposition of TMCBD and the corresponding cyclobutanone are compared and shown to be consistent with a twisted quasizwitterionic transition state.Long time (2 h) pyrolysis of TMCBD leads to tetramethylethylene and isopropenyl isopropyl ketone products but no DMK.These observations are rationalised by the scheme involving formation of tetramethylcyclopropanone (TMCP) from DMK and dimethylmethylene radicals, followed by decay of TMCP to the observed products.
- Vala, Martin,Baiardo, Joseph,Latham, David,Mukherjee, Ranajit,Pascyz, Stefan
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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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- PHOTOCHEMISTRY OF BIS(2-METHYL-1-PROPENYL)ETHER AND 2,2,4,4-TETRAMETHYL-6-OXABICYCLOHEXAN-3-ONE: ON THE SEARCH FOR THE OXYDI-?-METHANE REARRANGEMENT
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?,?*-Excitation of bis(2-methyl-1-propenyl)ether leads to products derived from a vinyl-vinyloxy radical pair; photochemical decarbonylation (n,?*) of the title ketone provides an entry into the diradical manifold of the oxydi-?-methane rearrangement.
- Adam, Waldemar,Berkessel, Albrecht,Krimm, Stefan
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p. 619 - 622
(2007/10/02)
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- Intramolecular Trapping of an Intermediate in the Deoxygenation of a Carbonyl Compound by Atomic Carbon
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Deoxygenation of 2,3-butanedione by atomic carbon generates acetylethylidene, CO, CO2, 2-butyne and 1,2-butadiene.
- Biesiada, Keith A.,Shevlin, Philip B.
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p. 1151 - 1153
(2007/10/02)
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- The intermediate formation of ketocarbenes and the conformational control in the Wolff rearrangement of α-diazoketones
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The conformational control of the Wolff rearrangement (WR) has been studied by means of a comparative study of the low temperature photolysis of argon-matrix isolated α-diazo ketones, 1, and of vinylene thioxocarbonates, 2.Under these conditions the s-E, s-Z conformational equilibrium of 1 will be hindered whereas 2 has a fixed s-Z conformation.The results indicate that the conformational control observed in the WR of α-diazo ketones is not per se a proof for a concerted mechanism and that a mechanism involving a ketocarbene intermediate is the most reasonable.
- Torres, Manuel,Ribo, Juan,Clement, Allan,Strausz, Otto P.
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p. 996 - 998
(2007/10/02)
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- Photolysis of α-Diazo Ketones in the Gas Phase Monitored by Fourier Transform Infrared Spectrometry
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3-Diazo-2-butanone (1),2,2,5,5-tetramethyl-4-diazo-3-hexanone (2), and 2-diazocyclohexanone (3) were photolyzed in the gas phase at low pressure.The course of the reactions was followed by FT IR spectroscopy.The Wolff rearrangement occured to an extent of 70percent for 1 and of about 40percent for 2; the resulting ketenes were respectively somewhat photolabile and photostable.The ketene from 3 was quite unstable to photolysis, although it could be indentified in the early part of the reaction.For irradiations at the laser line λ = 457,9 nm, the ratio of photolysis rates k1/k2 was at least 300, which suggests a concerted mechanism for the rearrangement of 1.Photolysis of 1 in the presence of argon to increase intermolecular collisions raised the production of dimethylketene to over 95percent.In contrast, the Wolff rearrangement of 2 occured in the gas phase but not in solution.The gas-phase reaction path may have its origin in the excited vibrational states of an electronic isomer of 2 or in those of the corresponding carbene.
- Marfisi, Claude,Verlaque, Patrick,Davidovics, Gisele,Pourcin, Jean,Pizzala, Louis,et al.
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p. 533 - 537
(2007/10/02)
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- Keten. Part 19. Reactions of 2,4,6-Trimethylbenzonitrile N-Oxide with Ketens
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Diphenylketen, t-butylcyanoketen, and dimethylketen react with the title nitrile oxide to form 1:1 adducts shown to have the oxazolinone structures (5); keten, t-butylethoxycarbonylketen, and phenyl isocyanate fail to react.The nitrile oxide is deoxygenated by diphenylketen and dimethylketen; in the latter case a new type of deoxygenation process occurs forming the unsaturated ketone (11) and thence the isoxazoline (8).
- Evans, Andrew R.,Taylor, Giles A.
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p. 979 - 983
(2007/10/02)
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- Small Rings, 42. Attempts to Prepare Oxirenes via Photochemical Cycloreversions
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Photochemically induced cycloreversions, which are ideally suited for the matrix isolation of cyclobutadienes, cannot be used for an analogous preparation and identification of oxirenes.In some cases ketenes are formed instead.
- Maier, Guenther,Sayrac, Tugmac,Reisenauer, Hans Peter
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p. 2202 - 2213
(2007/10/02)
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- Small Rings, 41. Oxirene: Intermediate or Transition State? Matrix Irradiation of Diazoketones
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On irradiation of diazoketones - even of those which do not undergo a Wolff rearrangement under standard conditions - in an argon matrix at 10 K oxirenes (or acylcarbenes) cannot be detected directly.
- Maier, Guenther,Reisenauer, Hans Peter,Sayrac, Tugmac
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p. 2192 - 2201
(2007/10/02)
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- The Mechanism of Ozone-Alkene Reactions in the Gas Phase. A Mass Spectrometric Study of the Reactions of Eight Linear and Branched-Chain Alkenes
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The stable products of the low-pressure (4 - 8 torr (1 torr = 133.33 Pa)) gas-phase reactions of ozone with ethene, propene, 2-methylpropene, cis-2-butene, trans-2-butene, trans-2-pentene, 2,3-dimethyl-2-butene, and 2-ethyl-1-butene have been identified by using a photoionization mass spectrometer coupled to a stirred-flow reactor.The products observed are characteristic of (i) a primary Criegee split to an oxoalkane (aldehyde or ketone) and a Criegee intermediate, (ii) reactions of the Criegee intermediates such as unimolecular decomposition, secondary ozonide formation, etc., and (iii) secondary alkene chemistry involving OH and other free-radical products formed by the unimolecular decomposition of the Criegee intermediates.The secondary OH - alkene - O2 reactions account for a significant fraction of the alkene (CnH2n) consumed and lead to characteristic products such as Cn dioxoalkanes nH2n + 30)>, Cn acyloins nH2n + 32)>, and Cn alkanediols nH2n + 34)>.Cn oxoalkanes and Cn epoxyalkanes observed at m/e (CnH2n + 16) are probably formed primarily via epoxidation of the alkene by O3.A general mechanism has been proposed to account for the observations.
- Martinez, Richard I.,Herron, John T.,Huie, Robert E.
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p. 3807 - 3820
(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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- Herbicidal isoxazolidine-3,5-diones
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2-Substituted isoxazolidine-3,5-diones and isoxazolidine-3-one-5-thiones exhibit herbicidal activity, controlling effectively the growth of a wide spectrum of grassy and broad-leaved plant species. The preparation and herbicidal activity of the compounds is exemplified.
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- Linear-reactor-infrared-matrix and Microwave Spectroscopy of the cis-2-Butene Gas-phase Ozonolysis
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Investigation of the formation of complex products in the gas-phase ozonolysis of cis-2-butene by linear-reactor-infrared-matrix and linear-reactor-microwave spectroscopy is reported.The following species have been unequivocally detected: secondary 2-butene ozonide, acetic acid, peracetic acid, glycolaldehyde, dimethyl ketene, the simple mixed anhydrides of formic and acetic acid, 2,3-epoxy-butane and 2-butanone, besides polyatomic products alredy known.In contrast, the primery ozonide has been detectable neither by LR.-MW. nor by LR.-IR.Observation of both stereoisomeric epoxides and kinetic modelling are used to support the intermediate formation of the O'Neal-Blumstein radical CH3CH(O2)CH(O)CH3 and the existence of a reaction channel in which the two carbon atoms of the C,C double bond of the olefin remain connected.As the dominant reaction path a mechanism with a Criegee type split into methyldioxirane (ethylidene peroxide) and acetaldehyde is considered and subsequently proposed to explain formation of many complex products by either unimolecular or bimolecular processes of the peroxide.For the reactions considered, thermochemical estimates of reaction enthalpies and activation data are included.Kinetic modelling for a partial reaction mechanism involving at least two different paths of decay of the O'Neal-Blumstein biradical into Criegee-type intermediates and the 2,3-epoxy-butanes is discussed.
- Kuehne, Heinz,Forster, Martin,Hulliger, Juerg,Ruprecht, Heidi,Bauder, Alfred,Guenthard, Hans-Heinrich
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p. 1971 - 1999
(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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- Keten. Part 17. Addition Reactions of Ketens with N-Phenyl Nitrones
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The N-phenyl nitrones (1a), (4b), and (15) react with ketens in two totally different ways.Triphenylnitrone (4b) forms oxidolones (6) whereas (1a) and (15) form oxazolidinones (2) and (17).The differences appear to be caused by steric interactions in (1a) and (15) which distort the nitrone function and prevent the N-phenyl group adopting the conformation necessary for the oxindole-forming pathway.
- Hafiz, Mushtag,Taylor, Giles A.
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p. 1700 - 1705
(2007/10/02)
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- Acylation of aromatic substrates with ketenes. An example of vinyl oxocation reactivity.
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Acylations of aromatic substrates with ketenes involve the reactivity of species similar to vinyl cations.Resonance stabilization of ketene-aluminum chloride complexes seems to make these complexes less reactive than corresponding vinyl cations.The kinetic isotope effect of the reaction with dimethylketene and benzene is 1.06, compatible with vinylcation cases, but not with acylation with CH3COBF4 types of electrophiles.Substrate specificity was determined from k (toluene)/k (benzene) values.It was 47.2 for dimethylketene and 173.7 for diphenylketene.The diphenylketene-aluminum chloride complex could be isolated.
- Fountain, K.R.,Heinze, Pamela,Sherwood, Mark,Maddex, Dave,Gerhardt, Greg
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p. 1198 - 1205
(2007/10/02)
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- Acylation of aromatic substrates with ketenes. II. Hammett-Brown studies on substituted aromatic compounds
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Competition reactions using dimethylketene (DMK) - aluminium chloride complexes on a variety of substituted benzene derivatives gave partial rate factors.The logs of these Pfx values when plotted versus ?+ values gave two line segments of ρ = -6.59 for less active substrates, and ρ = -0.92 for more active substrates.Similar results were found for diphenylketene (ρ = -9.47 and -1.07).These results were rationalized by analogy to vinyl cation alkylations.A pair of ? complexes (outher then inner) occur between initial approach of the reagent and final, product-determining ?-complex formation.In one of these complexes the C=C bond of the ketene complex may be able to back-bond in a manner similar to that found in inorganic complexes of CO and metals.
- Fountain, K. R.,Heinze, Pamela,Maddex, Dave,Gerhardt, Greg,John, Paul
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p. 1939 - 1946
(2007/10/02)
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