- On the Reactions of Thiols, Sulfenic Acids, and Sulfinic Acids with Hydrogen Peroxide
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The reaction of thiols with H2O2 is central to many processes essential to life, from protein folding to redox signaling. The initial products are assumed to be sulfenic acids, but their observation, and the kinetic and mechanistic characterization of their subsequent reactions, has proven challenging. The introduction of a 9-fluorotriptycene substituent enabled the use of 19F NMR to directly monitor the reaction of a thiol with H2O2 to yield a sulfenic acid, and its subsequent oxidation to sulfinic and sulfonic acids. The oxidations are specific base catalyzed, as revealed by the lack of isotope effects and the dependence of the kinetics on pH but not buffer concentration.
- Chauvin, Jean-Philippe R.,Pratt, Derek A.
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- Carbonyl-Directed Aliphatic Fluorination: A Special Type of Hydrogen Atom Transfer Beats out Norrish II
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Recently, our group reported that enone and ketone functional groups, upon photoexcitation, can direct site-selective sp3 C-H fluorination in terpenoid derivatives. How this transformation actually occurred remained mysterious, as a significant number of mechanistic possibilities came to mind. Herein, we report a comprehensive study describing the reaction mechanism through kinetic studies, isotope-labeling experiments, 19F NMR, electrochemical studies, synthetic probes, and computational experiments. To our surprise, the mechanism suggests intermolecular hydrogen atom transfer (HAT) chemistry is at play, rather than classical Norrish hydrogen atom abstraction as initially conceived. What is more, we discovered a unique role for photopromoters such as benzil and related compounds that necessitates their chemical transformation through fluorination in order to be effective. Our findings provide documentation of an unusual form of directed HAT and are of crucial importance for defining the necessary parameters for the development of future methods.
- Ghorbani, Fereshte,Harry, Stefan Andrew,Capilato, Joseph N.,Pitts, Cody Ross,Joram, Jacob,Peters, Garvin N.,Tovar, John D.,Smajlagic, Ivor,Siegler, Maxime A.,Dudding, Travis,Lectka, Thomas
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p. 14710 - 14724
(2020/10/13)
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- Fluorination of Bi- and polycyclic aromatic hydrocarbons with N-fluorobis(phenylsulfonyl)amine in the absence of solvent
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Reactions of N-fluorobis(phenylsulfonyl)amine with naphthalene, 1-methylnaphthalene, phenanthrene, anthracene, and pyrene without solvent were investigated. Sometimes the fluorination of aromatic compounds with N-fluorobis(phenylsulfonyl)amine without solvent proceeded more selectively than at the use of fluorinating reagents in solution.
- Borodkin,Elanov,Shubin
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experimental part
p. 1317 - 1322
(2011/01/04)
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- N-fluorosulfonimides, process for their production, as well as their use as fluorinating agents
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N-fluorosulfonimides of general formula I in which R1 means a methyl group each or together a group --(CH2)n --with n=1, 2 or 3, especially N-flouromethanesulfonimide, (CH3 SO2)2 NF, their production as well as their use for electrophilic fluorination of activated C--H bonds of organic molecules, are described.
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- Facile one-pot fluorination of polycyclic aromatic hydrocarbons (PAHs) with N-fluoro-2,4-dinitroimidazole; scope and limitation
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The synthetic utility of N-fluoro-2,4-dinitro-imidazole NF-2,4-DNT, a recently introduced NF fluorinating agent, has been tested for direct one-pot fluorination of several classes of polycyclic aromatic hydrocarbons, PAHs, namely pyrene, crowded alkyl(cycloalkyl)-pyrenes; hexahydro-and tetrahydro-pyrene; benzo[a]anthracene; benzo[a]-and benzo[e] pyrene; perylene; 2,7-di-tert-butylphenanthrene;chrysene; 9-imethylanthracene and anthracene, as well as trans-15:16-dimethyl-dihydropyrene: azulene[2-a]lacenaphthylene and azulene. Although the isolated yields are modest, the ease of handling of the reagent, simple operation (reflux in dichloroethane for 3 days) and the use of 1.1 equivalent of the reagent makes the procedure quite attractive for polynuclear aromatics, avoiding multi-step operations (NO2-PAH → NH2-PAH → N2+-PAH → F-PAH) or the use of toxic or costly reagents (CF3OF, XeF2, etc.); it provides direct one-pot access to a variety of F-PAHs that are not readily made using: other fluorinating agents.
- Laali, Kenneth K.,Tanaka, Mutsuo,Forohar, Farhad,Cheng, Michael,Fetzer, John C.
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p. 185 - 190
(2007/10/03)
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- Substituent-Dependent Nitration of 9-Substituted 9,10-Dihydro-9,10-ethanoanthracenes
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Mononitration of 9-substituted ethanoanthracenes, bearing Me, But, F, Br, I, OMe, NO2, CN, CHO or CO2Me substituents at the bridgehead carbon, was found to occur exclusively at the β-positions of the aromatic ring.The mononitro products were isolated, identified by 1H n.m.r. spectroscopy, and their relative proportions were estimated by quantitative g.l.c. and/or by 1H n.m.r. spectroscopy.For all the above substrates the proportion of nitration at the β-position meta to the bridgehead carbon bearing the substituent was greater than the proportion of nitration at the corresponding β-position para to the bridgehead substituent .Whilst the preferential nitration at the β-positions of the aromatic rings is consistent with the previously reported nitration of 9,10-dihydro-9,10-ethanoanthracene (2a) itself, no observations of this preferential meta attack have been made previously.No correlation could be made of this behaviour with available substituent parameters for the widely sterically and electronically disparate set of substituents used in this study, and the origin of this preferential attack remains unclear.Dinitration in this system was studied only superficially.The influence of the bridgehead substituent together with that of the nitro group already present on one aromatic ring appear to combine with quite unpredictable results in orienting the position of attack of the incoming nitro group onto the other (non-nitrated) aromatic ring.
- Harsanyi, Michael C.,Norris, Robert K.,Sze, Gary,Witting, Paul K.
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p. 1949 - 1968
(2007/10/02)
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- Reactions of Aldehydes with Cesium Fluoroxysulfate
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Various aromatic and aliphatic aldehydes reacted at 35-40 deg C in CH3CN with CsSo4F giving acid fluorides in a good yield.In some cases formation of fluorohydrocarbons was also observed.Hammett correlation analysis of the transformation of various substituted benzaldehydes (p-OCH3, p-CH3, p-F, p-CF3, m-NO2) gave the reaction constant ρ+ = -0.38.Solvent polarity strongly influenced the conversion of aldehydes into acid fluorides, being in acetonitrile almost quantitative and completely halted in CH2Cl2, n-hexane, or tetrahydrofuran.The presence of nitrobenzene, often used as a radical scavenger, considerably reduced the acid fluoride formation.Based on experimental observations was concluded that the main intermediates involved in the conversion of aldehydes into acid fluorides with CsSO4F must be of a radical nature.
- Stavber, Stojan,Planinsek, Zdenka,Zupan, Marko
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p. 5334 - 5337
(2007/10/02)
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- New, Mild Method for Directed Introduction of a Fluorine Atom into Aromatic Molecules
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Hydroxyalkyl groups in various aromatic molecules are replaced with a fluorine atom by CsSO4F at room temperature thus regioselectively forming aryl fluorides in high to excellent yields.
- Stavber, Stojan,Kosir, Iztok,Zupan, Marko
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p. 274 - 275
(2007/10/02)
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- Structural Effects Controlling the Rate of the Retro-Diels-Alder Reaction in Anthracene Cycloadducts
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We have undertaken a fairly broad study of how the structure of an anthracene cycloadduct affects the rate of its cycloreversion reaction.Based on the rate constants for retro-Diels-Alder (rDA) reactions of a variety of anthracene-type adducts conducted in diphenyl ether, we draw the following conclusions.The rDA reaction of anthracene cycloadducts is influenced by diene substituents in the following ways: (1) electron-donating groups increase the reaction rate, and the accelerating effect is subject to geometric modulation for a conjugating substituent like dimethylamino; (2) electron-withdrawing groups may decrease or increase the reaction rate , although the effect is rarely large; and (3) steric acceleration is relatively small and demonstrates an unprecedented bell-shaped structure-reactivity profile.Peripheral substitution of the adduct with siloxy groups results in a significant acceleration, even though the groups are three bonds removed from the reaction site.The same reaction is influenced by dienophile substituents in the following ways: (1) electron-withdrawing groups increase the rate of the reaction; (2) strongly conjugating substituents make the reaction much faster than predicted by classical electron-withdrawing or -donating ability due to a change to polar mechanism; and (3) there is no observable steric effect.
- Chung, Yongseog,Duerr, Brook F.,McKelvey, Timothy A.,Nanjappan, P.,Czarnik, Anthony W.
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p. 1018 - 1032
(2007/10/02)
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- MILD CONVERSION OF PRIMARY ALCOHOLS AND ALDEHYDES TO ACID FLUORIDES WITH CAESIUM FLUOROXYSULPHATE
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Caesium fluoroxysulphate in acetonitrile medium at 35 deg C converts primary alcohols and alkyl, as well as aryl aldehydes, to acid fluorides in high yield.
- Stavber, Stojan,Planinsek, Zdenka,Zupan, Marko
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p. 6095 - 6096
(2007/10/02)
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- Fluorination of Polycyclic Aromatic Hydrocarbons: Charge vs. Frontier Orbital Control in Substitution Reactions of Radical Cations
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The anodic fluorination of perylene and pyrene in acetonitrile occurred at potentials consistent with the intermediacy of dications, but that of triphenylene with its radical cation.Fluorination of anthracene compounds at a meso position occurred by the a
- King, Patrick F.,O'Malley, Robert F.
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p. 2803 - 2807
(2007/10/02)
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