- Copper-catalyzed homodimerization of nitronates and enolates under an oxygen atmosphere
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A method for copper-catalyzed oxidative dimerization of nitronates and enolates using oxygen as the terminal oxidant has been developed. Cyclization through oxidative intramolecular coupling is also feasible for both nitronates and enolates. The mild reaction conditions lead to good functional group tolerance.
- Do, Hien-Quang,Tran-Vu, Hung,Daugulis, Olafs
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p. 7816 - 7818
(2013/01/16)
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- Access to original vinylic chlorides in the quinazoline series via a monoelectronic transfer reaction approach
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A series of new quinazoline derivatives bearing a vinylic chloride group on the 2-position was prepared by using a consecutive SRN1 / ERC1 radical strategy. Copyright
- Maillard-Boyer, Martine,Castera-Ducros, Caroline,Verhaeghe, Pierre,Sifredi, France,Rathelot, Pascal,Vanelle, Patrice
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experimental part
p. 2719 - 2729
(2010/07/03)
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- Fast cleavage reactions following electron transfer. Reduction of 1,1-dinitrocyclohexane
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One-electron reduction of 1,1-dinitrocyclohexane is followed by rapid cleavage of a C-N bond, giving nitrite and 1-nitrocyclohexyl radical. The rate constant has been determined in dimethylformamide by homogeneous redox catalysis (1.6 × 106 s-1) and in aqueous solution by pulse radiolysis (1.1 × 106 s-1). These values are of the order of 106 larger than the rate constant for cleavage of mononitroalkane radical anions. In the case of electrochemical reduction, the electron transfer and bond cleavage are followed by further reduction of the nitroalkyl radical to give the nitronate anion of nitrocyclohexane. For scan rates exceeding about 0.1 V/s in cyclic voltammetry, the 1-nitrocyclohexyl radical is reduced by the anion radical of 1,1-dinitrocyclohexane rather than at the electrode. Controlled potential electrolysis and product analysis showed that about 1.2 electrons were required per molecule of 1,1-dinitrocyclohexane; essentially no nitronate was found, but instead some nitrocyclohexane and substantial amounts of 1,1′-dinitrobicyclohexyl (5) were produced. This latter product arises from the radical chain reaction of nitronate with starting material. A key chain-carrying step in this reaction scheme is the reaction of 1-nitrocyclohexyl radical with the nitronate to give the anion radical of 5. The rate constant for this step was found to be 2.6 × 106 L mol-1 in water by pulse radiolysis. Fitting of fast-scan cyclic voltammograms by digital simulation showed that this rate constant must be about 5 × 108 L mol-11 s-1 in dimethylformamide with a termination reaction (kt = 2 × 104 s-1) of hydrogen atom abstraction by 1-nitrocyclohexyl to produce the nitrocyclohexane found in the electrolyzed solutions.
- Rühl, Janet C.,Evans, Dennis H.,Hapiot, Philippe,Neta, Pedatsur
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p. 5188 - 5194
(2007/10/02)
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- Steric Effects on Acidities of 9-Alkyl-, 9-(Alkylthio)-, and 9-Alkoxyfluorenes and on the Electron-Transfer Abilities of Their Conjugate Bases
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Perturbations caused by steric effects in 9-alkylfluorenes (9-R-FIH) account, in part, for the effects of changing alkyl size on acidities and, in turn, for the failure of the acidity-oxidation potential (AOP) method to provide reasonable estimates for the radical-stabilizing effects of large alkyl substituents, such as t-Bu, t-BuCH2, and PhC(Me)2CH2.Increases in alkyl size along the series Me, Et, i-Pr, and t-Bu for 9-RS-FIH fluorenes cause progressive increases in acidities due to increases in polarizability effects, but the radical-stabilizing effects of these substituents on the 9-fluorenyl radical, as estimated by the AOP method, remain essentially contant at 5.4 +/- 0.3 kcal/mol for RS and 6.5 +/- 0.5 kcal/mol for RO.Rate constants (log kobsd) for single-electron transfer to an electron acceptor from 9-R-Fl-, 9-RO-Fl-, 9-RS-Fl-, and 9-R2N-Fl- ions, where R is varied in size, plot linearly with their oxidation potentials, indicating that rates electron transfer from these carbanions are much less subject to steric hindrance than are rates of SN2 reactions of these anions with alkyl halides.
- Bordwell, Frederick G.,Bausch, Mark J.,Wilson, Craig A.
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p. 5465 - 5470
(2007/10/02)
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- UNSYMMETRICAL CONNECTIVE OLEFINATION BY KORNBLUM NITRO-SYNTHESIS : APPLICATIONS IN PHYTUBERIN CHEMISTRY
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Kornblum unsymmetrical olefin synthesis employing radical-anion chain crossed-coupling (light catalysed) of a mono- and a gem-di-nitro-compound, followed by reductive NO2 removal, is examined in the context of a hindered olefin structure required for phytuberin synthesis.Whilst successful for a tetrasubstituted olefin model (for which a Witting approach failed), increasing substitution on the β-position of the mono-nitro component supressed the coupling reaction, presumably for steric reasons.An alternative coupling involving a bromonitrocyclohexane and a mononitroacetal caused symmetrical coupling of the mononitro-component in high yield, rather than a crossed reaction.Reductive elimination (using Na2S/DMF) from either rac.- or meso- 1,2-dinitro-1,2-diphenylethane leads to (E)-stilbene 98percent (E) > probably through a stabilised radical or anion.A convenient preparation of triphenylisoxazoline-N-oxide is reported.
- Crombie, Leslie,Roughley, Brian S.
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p. 3147 - 3156
(2007/10/02)
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- Correlation of Electron-Transfer Rate Constants of Carbinons with Their Oxidation Potentials and Basicities
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Acidity-oxidation-potential (AOP) values for seven 9-substituted fluorenide ions, 9-ArFl(1-), relative to that of fluorene, have revealed the presence of small radical-stabilizing effects for 4-MeO and 4-Me substitutents in the aryl ring and a 3-Me substituent in the fluorene ring and their absence for 3-Cl and 4-MeSO2 substituents in the aryl ring and 2-Br and 2-PhSO2 substituents in the fluorene ring.Measurements of redox potentials have shown that electron-transfer (eT(1-)) reactions of these 9-ArFl(1-) ions with 1,1-dinitrocyclohexane are endergonic by 6.6-13 kcal/mol.A Bronsted-type plot of log kobsd for these reactions vs. pKHA was linear with scatter.A Bronsted-type plot of log kobsd vs.Eox gave an improved plot (β = 1.04; R2 = 0.999) that covered a rate range of >1E5 and an Eox range of 7.3 kcal/mol.Mechanistic schemes are presented to account for the products formed in the eT(1-) reaction and to reconcile the strict linearity of the latter plot with the Marcus equation.
- Bordwell, Frederick G.,Bausch, Mark J.
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p. 1985 - 1988
(2007/10/02)
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- Electron-Transfer Substitution Reactions of Anions Derived from Malonic Esters, β-Keto Esters, and β-Diketones
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Electron-transfer substitution reactions of carbanions derived from malonic esters, β-keto esters, and β-diketones with α,α-dinitro compounds are compared with oxidative coupling of these carbanions to nitroparaffin salts using potassium ferricyanide; the former routinely give better yields.
- Kornblum, Nathan,Kelly, William J.,Kestner, M. M.
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p. 4720 - 4724
(2007/10/02)
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- Broensted Correlations for Electron Transfer from Carbanions to Halomethyl Phenyl Sulfone and 1,1-Dinitroalkane-Type Acceptors
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9-Substituted fluorenyl carbanions, 9-G-Fl(1-), with G = Ar or Me, have been dimerized to (9-G-Fl)2 by reaction in Me2SO solution with PhSO2CH2X and R2C(NO2)X electron acceptors.Rate measurements revealed the following electron-accepting abilities: c-C6H10(NO2)2 > Me2C(NO2)2 > PhSO2CH2Br, PhSO2CH2I > c-C6H10(NO2)CN > c-C6H10(NO2)SO2C7H7 > Me2C(NO2)SO2C7H7 > PhSO2CH2Cl.The rate-limiting step in these reactions is electron transfer from 9-G-Fl(1-) to the electron acceptor.Plots of log k vs. pKa of 9-G-FlH are linear with a slope near unity for all seven electron acceptors studied.We conclude that a Broensted β of unity is characteristic of electron transfer from carbanions to electron acceptors in Me2SO solution.This is interpreted to mean that the changes in ΔG0 brought about by changes in the basicity of the carbanion are matched by changes in ΔG(excit.), which correspond to the difference in the energy gap between the HOMO of the donor and the LUMO of the acceptor.
- Bordwell, Frederick G.,Clemens, Anthony H.
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p. 2510 - 2516
(2007/10/02)
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- Radical-Nucleophilic Substitution (SRN1) Reactions: Preparation and Reactions of α-Nitrosulphides
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α-Nitrosulphides were prepared by SRN1 reaction of 2-bromo-2-nitropropane with thiolate anions, and by SN2 attack of sodium 2-nitropropan-2-ide on symmetrical disulphides.The α-nitrosulphides undergo radical-nucleophilic substitution (SRN1) by nitronate, sulphinate, and malonate anions, but not by thiolate anions.
- Bowman, W. Russell,Richardson, Geoffrey D.
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p. 1407 - 1413
(2007/10/02)
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