- A versatile approach for the synthesis of para -substituted arenes via palladium-catalyzed C-H functionalization and protodecarboxylation of benzoic acids
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While a great number of ortho C-H functionalization reactions have been developed and several breakthroughs have been achieved in meta C-H activation, para C-H functionalization is still in its infancy stage. In this article, a versatile strategy for the synthesis of para-substituted arenes has been developed via a tandem process consisting of palladium-catalyzed C-H functionalization and subsequent copper-catalyzed protodecarboxylation of benzoic acids. Both electron-withdrawing and electron-donating functionalities can be introduced into the para positions of arenes bearing a variety of substituents.
- Pan, Shulei,Zhou, Bo,Zhang, Yanghui,Shao, Changdong,Shi, Guangfa
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supporting information
p. 277 - 281
(2016/01/20)
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- The reaction of hydroxylamine with aspirin
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Hydroxylamine reacts with aspirin in aqueous solution at 25 °C predominantly through oxygen, to give O-acetylhydroxylamine as the initial product (Scheme 3). The reaction is much faster than the intramolecular general base catalysed hydrolysis of the carboxylate anion, as it is also for the CO2H form of aspirin. Both reactions are faster than expected, consistent with moderate activation and/or proton transfer catalysis of hydroxylaminolysis by both CO2- and CO2H groups. Calculations support oxygen attack as the preferred reaction, but do not permit a clear choice between mechanisms involving NH2OH and +NH3-O- as the effective nucleophile. ARKAT-USA, Inc.
- Medeiros, Michelle,Souza, Bruno S.,Orth, Elisa S.,Brandao, Tiago A. S.,Rocha, Willian,Kirby, Anthony J.,Nome, Faruk
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scheme or table
p. 461 - 476
(2011/10/05)
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- Fluorophenols and (trifluoromethyl)phenols as substrates of site-selective metalation reactions: To protect or not to protect
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O-Methoxymethyl (MOM) protected fluorophenols can be cleanly metalated and subsequently be submitted to site-selective electrophilic substitution. The 2- and 4-isomers exhibit ambivalent reactivity: deprotonation occurs at the position adjacent to the oxygen when butyllithium is employed whereas the position adjacent to the fluorine is attacked by the superbasic mixture of butyllithium and potassium tert-butoxide (LIC-KOR). The MOM-protected (trifluoromethyl)-phenols react exclusively at oxygen-neighboring positions. The meta isomer provides another example of optional site selectivity, undergoing hydrogen/metal exchange at the 2-position with the LIC-KOR reagent and at the 6-position with sec-butyllithium. Unprotected (trifluoromethyl)phenols can also be ortho-metalated after O-deprotonation, although the products are formed in only moderate yields.
- Marzi, Elena,Mongin, Florence,Spitaleri, Andrea,Schlosser, Manfred
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p. 2911 - 2915
(2007/10/03)
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- A kinetic study into the hydrolysis of the ochratoxins and analogues by carboxypeptidase A
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The hydrolyses of the ochratoxins and analogues by carboxypeptidase A were assessed. This was done by measuring the amount of phenylalanine formed with liquid chromatography coupled to tandem electrospray mass spectrometry. The kinetic data of ochratoxin A, ochratoxin B, and the synthetic bromo-ochratoxin B were compared to the values of a number of synthesized structure analogues, namely, ochratoxin A methyl ester, ochratoxin B methyl ester, N-(2-hydroxybenzoyl)phenylalanine, N-(5-chloro-2-hydroxybenzoyl)phenylalanine, N-(5-bromo-2-hydroxybenzoyl)phenylalanine, and N-(5-fluoro-2-hydroxybenzoyl)phenylalanine. The halogen-containing analogues had lower turnovers than their des-halo analogues. There are no substantial differences in the kinetic data between the different halogen-containing analogues.
- Stander,Steyn,Van der Westhuizen,Payne
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p. 302 - 304
(2007/10/03)
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- Synthesis of 5-fluoro salicylic acid
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A short synthesis of 5-fluoro salicylic acid starting from 4- fluorophenol is reported.
- Sharma,Ilangovan,Lavanya
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p. 397 - 405
(2007/10/03)
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- Facile preparation of aromatic fluorides by deaminative fluorination of aminoarenes using hydrogen fluoride combined with bases
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One-pot deaminative fluorination of aminoarenes including heteroaromatics, namely, diazotization of aminoarenes followed by in situ fluoro-dediazoniation of the corresponding diazonium ions, was successfully accomplished to produce fluoroarenes in high yields by using hydrogen fluoride combined with base solutions. The diazotization stage has been found to play the most important part in yielding fluoroarenes effectively. It was greatly influenced by the composition of the HF solution and enhanced by employing appropriate amounts of bases such as pyridine under carefully controlled conditions. The fluoro-dediazoniation stage was effectively accelerated photochemically to afford fluoroarenes having polar substituents such as hydroxyl, nitro and so on in high yields.
- Yoneda,Fukuhara
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- The Preparation of p-Fluorophenols from p-Aminophenols: Diazotization and Fluorodiazoniation in Pyridine-HF.
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A facile preparation of p-fluorophenols is described by the diazotization of p-aminophenols and fluorodediazoniation in situ using HF in a pyridine solution (pyridine-HF) under carefully controlled conditions.
- Fukuhara, Tsuyoshi,Yoneda, Norihiko,Takamura, Kouki,Suzuki, Akira
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p. 299 - 304
(2007/10/02)
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- Benzamide derivatives
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Benzamide derivatives of the formula:- STR1 wherein R1 represents a fluorine, chlorine or bromine atom, or an alkyl, alkoxy, alkylthio, alkylsulphonyl, alkanoylamino, alkylamino or alkylsulphamoyl group, each such group containing from 1 to 6 carbon atoms, a dialkylsulphamoyl, dialkylamino or dialkylcarbamoyl group (wherein the two alkyl groups may be the same or different and each contains from 1 to 4 carbon atoms), an alkanoyl, alkoxycarbonyl, alkoxycarbonylamino or alkylcarbamoyl group containing from 2 to 6 carbon atoms, or a hydroxy, formyl, nitro, trifluoromethyl, aryl, benzyloxycarbonylamino, amino, sulphamoyl, cyano, tetrazol-5-yl, carboxy, carbamoyl or aroyl group, and n represents an integer 1, 2 or 3, are new compounds possessing pharmacological properties, in particular properties of value in the treatment of respiratory disorders manifested by the interaction of tissue-fixed antibodies with specific antigens.
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