- The fragmentation of polyfluorinated benzylic alcohols: the first observation of pentafluorophenyl anion as a good leaving group
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Treatment of a series of pentafluorobenzylic alcohols with sodium methoxide in DMSO results in a rapid carbon-carbon cleavage reaction, yielding a ketone or aldehyde as well as pentafluorobenzene, which undergoes subsequent nucleophilic aromatic substitution (NAS). In methanol solvent, the fragmentation is very slow, and NAS without fragmentation occurs almost exclusively. In methanol/DMSO mixtures, both processes are observed simultaneously. This appears to be the first report of the fragmentation of pentafluorobenzylic alcohols.
- Garner, Charles M.,Fisher, Henry C.
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- Diazaphospholene-Catalyzed Hydrodefluorination of Polyfluoroarenes with Phenylsilane via Concerted Nucleophilic Aromatic Substitution
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The metal-free catalytic C-F bond activation of polyfluoroarenes was achieved with diazaphospholene as the catalyst and phenylsilane as the terminal reductant. Density functional theory calculations suggested a concerted nucleophilic aromatic substitution mechanism.
- Zhang, Jingjing,Zhao, Xiao,Yang, Jin-Dong,Cheng, Jin-Pei
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supporting information
p. 294 - 300
(2022/01/03)
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- Transition-Metal-Free Catalytic Hydrodefluorination of Polyfluoroarenes by Concerted Nucleophilic Aromatic Substitution with a Hydrosilicate
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A transition-metal-free catalytic hydrodefluorination (HDF) reaction of polyfluoroarenes is described. The reaction involves direct hydride transfer from a hydrosilicate as the key intermediate, which is generated from a hydrosilane and a fluoride salt. The eliminated fluoride regenerates the hydrosilicate to complete the catalytic cycle. Dispersion-corrected DFT calculations indicated that the HDF reaction proceeds through a concerted nucleophilic aromatic substitution (CSNAr) process.
- Kikushima, Kotaro,Grellier, Mary,Ohashi, Masato,Ogoshi, Sensuke
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supporting information
p. 16191 - 16196
(2017/11/27)
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- Base-Catalyzed Aryl-B(OH)2 Protodeboronation Revisited: From Concerted Proton Transfer to Liberation of a Transient Aryl Anion
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Pioneering studies by Kuivila, published more than 50 years ago, suggested ipso protonation of the boronate as the mechanism for base-catalyzed protodeboronation of arylboronic acids. However, the study was limited to UV spectrophotometric analysis under acidic conditions, and the aqueous association constants (Ka) were estimated. By means of NMR, stopped-flow IR, and quenched-flow techniques, the kinetics of base-catalyzed protodeboronation of 30 different arylboronic acids has now been determined at pH > 13 in aqueous dioxane at 70 °C. Included in the study are all 20 isomers of C6HnF(5-n)B(OH)2 with half-lives spanning 9 orders of magnitude: a and Sδ values, kinetic isotope effects (2H, 10B, 13C), linear free-energy relationships, and density functional theory calculations, we have identified a mechanistic regime involving unimolecular heterolysis of the boronate competing with concerted ipso protonation/C-B cleavage. The relative Lewis acidities of arylboronic acids do not correlate with their protodeboronation rates, especially when ortho substituents are present. Notably, 3,5-dinitrophenylboronic acid is orders of magnitude more stable than tetra-and pentafluorophenylboronic acids but has a similar pKa.
- Cox, Paul A.,Reid, Marc,Leach, Andrew G.,Campbell, Andrew D.,King, Edward J.,Lloyd-Jones, Guy C.
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supporting information
p. 13156 - 13165
(2017/09/26)
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- Synthesis of K[4-ROC6F4BF3] from potassium pentafluorophenyltrifluoroborate and O-nucleophiles
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A new route to potassium polyfluoroaryltrifluoroborates, K[4-ROC 6F4BF3], consisting in the nucleophilic alkoxydefluorination of K[C6F5BF3] with MOR (M = K, Na) in a polar aprotic solvent is suggested. Reaction of K[C 6F5BF3] with KO-t-Bu proceeds smoothly at 25 °C in DME, but the attempted alkoxydefluorination of K[C6F 5BF3] with other NaOR at 30 °C in DME failed. A series of K[4-ROC6F4BF3] (R = Me, Et, Pr, i-Pr, Bu, PhCH2) is prepared using the corresponding sodium alkoxides in DMF at 130 °C in 80-90% isolated yield. Salt K[4-CH2CHCH 2OC6F4BF3] is prepared at 100 °C whereas at 130 °C formation of 2,3,5,6-C6F4HOCH 2CHCH2 occurs. Salt K[4-PhOC6F 4BF3] is obtained in 82% yield using KOPh (2 equivalents) in DMSO at 130 °C.
- Shabalin, Anton Yu.,Adonin, Nicolay Yu.,Bardin, Vadim V.,Prikhod'Ko, Sergey A.,Timofeeva, Maria N.,Bykova, Maria V.,Parmon, Valentin N.
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- Copper-catalyzed hydrodefluorination of fluoroarenes by copper hydride intermediates
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Breaking bad: Efficient copper-catalyzed C-F bond activation has been achieved by replacing fluorine with hydrogen. A copper hydride is proposed as the active intermediate, which proceeds through a nucleophilic attack on the fluorocarbon, as determined by experimental and theoretical results (see structure; C gray, H white, Cu light red, F light blue; distances in ?).
- Lv, Hongbin,Cai, Yuan-Bo,Zhang, Jun-Long
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supporting information
p. 3203 - 3207
(2013/04/23)
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- Reaction of polyfluoroaromatic compounds with electrophilic agents in the presence of tris(dialkylamino)phosphines: 7. * Replacement of a halogen by hydrogen in halogenopolyfluoroaromatic compounds
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A method was developed for the replacement of chlorine, bromine, and iodine in halopolyfluoroaromatic compounds by hydrogen under the action of P(NEt2)3 and a proton donor.
- Bardin,Pressman
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p. 786 - 788
(2007/10/03)
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- REACTION OF AROMATIC COMPOUNDS WITH NUCLEOPHILIC REAGENTS IN LIQUID AMMONIA IV.* THE NUCLEOPHILIC AND PROTOPHILIC ACTIVITY OF METHOXIDE AND HYDROXIDE IONS IN REACTIONS WITH POLYFLUORINATED AROMATIC COMPOUNDS
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In the reaction of polyfluorinated derivatives of benzene with potassium methoxide in liquid ammonia a fluorine atom is substituted by a methoxy group.With potassium hydroxide reactions involving removal of a proton from a ring carbon atom take place preferentially.The possibility of polyfluoroarylation and methylation catalyzed by potassium hydroxide in polyfluorinated aromatic compounds, based on capture of the polyflurinated aryl anion by the electrophile, was demonstrated.
- Shtark, A. A.,Chuikova, T. V.,Shteingarts, V. D.
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p. 960 - 967
(2007/10/02)
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- Mechanisms for Reactions of Halogenated Compounds. Part 3. Variation in Activating Influence of Halogen Substituents in Nucleophilic Aromatic Substitution
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Rate constants are reported for reactions of polyhalogeno-pyridines and -benzenes with sodium methoxide in methanol.Relative activating effects of individual fluorine and chlorine atoms at positions ortho, meta, and para to the reaction site are determined and compared with orders determined from reactions involving ammonia in aqueous dioxan.The results are remarkably similar.Additional support is provided for earlier explanations of the activating effects of ortho-fluorine and -chlorine.Activation parameters, determined for reactions of polyhalogenepyridines with ammonia in aqueous dioxan, clearly demonstrate that differences in reactivity along the series arise mainly from changes in activation energy.
- Chambers, Richard D.,Close, Deborah
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p. 778 - 780
(2007/10/02)
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