- Mild aromatic palladium-catalyzed protodecarboxylation: Kinetic assessment of the decarboxylative palladation and the protodepalladation steps
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Mechanism studies of a mild palladium-catalyzed decarboxylation of aromatic carboxylic acids are described. In particular, reaction orders and activation parameters for the two stages of the transformation were determined. These studies guided development of a catalytic system capable of turnover. Further evidence reinforces that the second stage, protonation of the arylpalladium intermediate, is the rate-determining step of the reaction. The first step, decarboxylative palladation, is proposed to occur through an intramolecular electrophilic palladation pathway, which is supported by computational and mechanism studies. In contrast to the reverse reaction (C-H insertion), the data support an electrophilic aromatic substitution mechanism involving a stepwise intramolecular protonation sequence for the protodepalladation portion of the reaction.
- Dickstein, Joshua S.,Curto, John M.,Gutierrez, Osvaldo,Mulrooney, Carol A.,Kozlowski, Marisa C.
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p. 4744 - 4761
(2013/07/11)
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- Meta halogenation of 1,3-disubstituted arenes via iridium-catalyzed arene borylation
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We report the meta halogenation of 1,3-disubstituted arenes to form 3,5-disubstituted aryl bromides and chlorides by using iridium-catalyzed arene borylation chemistry. Iridium-catalyzed borylation of arenes with B2pin2, followed by reaction of the boronic ester with copper(II) bromide or chloride converts arylboronic esters to the corresponding aryl halides. A variety of arenes containing alkoxy, alkyl, halogen, nitrile, ester, amide, and pivaloyl and TIPS-protected alcohols were converted to the corresponding 3,5-disubstituted aryl bromides and chlorides in yields ranging from 46% to 85%. In addition, 2,6-disubstituted and 3-substituted pyridines were converted to the 4-halo and 5-halopyridines, respectively. The utility of this methodology was demonstrated by the formal conversion of nicotine to Altinicline in three steps with an overall yield of 61% using meta bromination of nicotine as the first step. Copyright
- Murphy, Jaclyn M.,Liao, Xuebin,Hartwig, John F.
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p. 15434 - 15435
(2008/09/19)
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- Grindstone chemistry: (Diacetoxyiodo)benzene-mediated oxidative nuclear halogenation of arenes using NaCl, NaBr or I2
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A technique of "Grindstone chemistry" is applied to the solvent-free halogenation of arenes with NaCl, NaBr or I2 using (diacetoxyiodo)benzene as the oxidant. Improved yields and higher purities of the products are observed compared with those from established methods.
- Karade,Tiwari,Huple,Siddiqui
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p. 366 - 368
(2007/10/03)
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- Correlation of Reaction Rates with a Substituent Constant Scale Derived from Calculated Electron Densities for a Computer Control Algorithm
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A new ? substituent scale based on electron density calculations by the AM1 quantum mechanical model has been established and used to correlate rates of O-methylation of substituted phenols, as part of a chemical artificial intelligence to control a fully automated apparatus for methyl iodide labeling.
- Cork, David G.,Hayashi, Nobuyoshi
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p. 1583 - 1585
(2007/10/02)
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- THE REACTIONS OF UNACTIVATED ARYL HALIDES WITH SODIUM METHOXIDE IN HMPA; SYNTHESIS OF PHENOLS, ANISOLES, AND METHOXYPHENOLS
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Sodium methoxide reacts with dichlorobenzenes in HMPA to give the chloroanisoles as a result of a SNAr process.Excess MeONa then effects the demethylation of the ethers to give the chlorophenols via an SN2 reaction.With tri- and tetrachlorobenzenes the initially formed chloroanisoles can be dealkylated to chlorophenols or can suffer further substitution to give the chlorodimethoxybenzenes; these react with excess MeONa to give the chloromethoxyphenols.The results obtained with the various isomers of the di-, tri-, and tetrachlorobenzenes are presented and discussed on the basis of the electronic effects of the substituents.
- Testaferri, L.,Tiecco, M.,Tingoli, M.,Chianelli, D.,Montanucci, M.
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p. 193 - 198
(2007/10/02)
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- Reaction of Some 1,4-Benzoquinone Mono-oximes with Methanolic Hydrogen Chloride
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When 2-methyl-1,4-benzoquinone 4-oxime (1) reacted with methanolic hydrogen chloride at 25-30 deg C the product was 2-chloro-4,6-dimethoxy-3-methylaniline (2).Similarly 1,4-benzoquinone 4-oxime (7) gave 2-chloro-4,6-dimethoxyaniline (8), 3-methyl-1,4-benzoquinone 4-oxime (11) gave 2-chloro-4-methoxy-6-methoxymethylaniline (12) and 2-chloro-4-methoxy-6-methylaniline (13), and 2-methoxy-1,4-benzoquinone 4-oxime (19) gave 2-chloro-4,5-dimethoxyaniline (20).
- Sargent, Melvyn V.
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p. 1095 - 1098
(2007/10/02)
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