- Transition-metal-free decarboxylative bromination of aromatic carboxylic acids
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Methods for the conversion of aliphatic acids to alkyl halides have progressed significantly over the past century, however, the analogous decarboxylative bromination of aromatic acids has remained a longstanding challenge. The development of efficient methods for the synthesis of aryl bromides is of great importance as they are versatile reagents in synthesis and are present in many functional molecules. Herein we report a transition metal-free decarboxylative bromination of aromatic acids. The reaction is applicable to many electron-rich aromatic and heteroaromatic acids which have previously proved poor substrates for Hunsdiecker-type reactions. In addition, our preliminary mechanistic study suggests that radical intermediates are not involved in this reaction, which is in contrast to classical Hunsdiecker-type reactivity. Overall, the process demonstrates a useful method for producing valuable reagents from inexpensive and abundant starting materials.
- Quibell, Jacob M.,Perry, Gregory J. P.,Cannas, Diego M.,Larrosa, Igor
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p. 3860 - 3865
(2018/04/26)
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- A novel mode of reactivity for gold(I): The decarboxylative activation of (hetero)aromatic carboxylic acids
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Gold(I) salts are found to mediate the decarboxylation of a variety of aromatic and heteroaromatic carboxylic acids at significatively lower temperatures (as low as 60°C) than the currently used copper(I) (180-190°C) and silver(I) (80-140°C) systems. In contrast to silver(I)- and copper(I)-mediated decarboxylations, the resulting aryl-gold(I) complexes are stable towards protodemetallation and can be readily isolated.
- Cornella, Josep,Rosillo-Lopez, Martin,Larrosa, Igor
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supporting information; experimental part
p. 1359 - 1366
(2011/06/26)
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- Efficient one-pot transformation of aminoarenes to haloarenes using halodimethylisulfonium halides generated in situ
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Halodimethylsulfonium halide 1, which is readily formed in situ from hydrohaloic acid and DMSO, is a good nucleophilic halide. This activated nucleophilic halide rapidly converts aryldiazonium salt prepared in situ by the same hydrohaloic acid and nitrite ion to aryl chlorides, bromides, or iodides in good yield. The combined action of nitrite ion and hydrohaloic acid in DMSO is required for the direct transformation of aromatic amines, which results in the production of aryl halides within 1 h. Substituted compounds with electron-donating or -withdrawing groups or sterically hindered aromatic amines are also smoothly transformed to the corresponding aromatic halides. The only observed by-product is the deaminated arene (usually 7%). The isolated aryldiazonium salts can also be converted to the corresponding aryl halides using 1. The present method offers a facile, one-step procedure for transforming aminoarenes to haloarenes and lacks the environmental pollutants that usually accompany the Sandmeyer reaction using copper halides.
- Baik, Woonphil,Luan, Wanqiang,Lee, Hyun Joo,Yoon, Cheol Hun,Koo, Sangho,Kim, Byeong Hyo
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p. 213 - 219
(2007/10/03)
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- Formation of 3-halobenzyne: Solvent effects and cycloaddition adducts
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Noncoordinating solvents permit the halogen-metal exchange-induced formation of benzyne (aryne) from di- and trihalobenzene precursors in the presence of cyclopentadiene to give 1,4-dihydro-1,4-methano-naphthalenes. Studies with mixed halide precursors and nonacidic Diels-Alder diene traps reveal that ethereal and hydrocarbon solvents influence the halide leaving group facility, resulting in a reversal of 3-halobenzyne regioselectivity.
- Coe, Jotham W.,Wirtz, Michael C.,Bashore, Crystal G.,Candler, John
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p. 1589 - 1592
(2007/10/03)
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- Method for producing tetrakis ( fluoroaryl) borate-magnesium compound
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Fluoroaryl magnesium halide is reacted with a boron compound so that a molar ratio of the fluoroaryl magnesium halide to the boron compound is not less than 3.0 and not more than 3.7, so as to produce a tetrakis (fluoroaryl) borate·magnesium compound. With this method, there occurs no hydrogen fluoride which corrodes a producing apparatus and requires troublesome waste water treatment.
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- Exploring Structural Opportunities: The Regioflexible Substitution of 1,3-Difluorobenzene
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To demonstrate the superiority of modern organometallic methods, the inexpensive starting material 1,3-difluorobenzene has been selectively converted into the three benzoic acids and all seven bromobenzoic acids containing the two fluorine atoms in homovicinal positions. The 2,6-difluorobenzoic acid (1) was prepared in a one-pot reaction consisting of direct metallation and carboxylation. The key step on the route to the bromobenzoic acid 4 was a deprotonation-triggered bromine migration from the 2- to the 4-position. All other products were attained through (2,6-difluorophenyl)triethylsilane (11). Consecutive deprotonation of the sites adjacent to the fluorine atoms, followed by appropriate electrophilic substitution, provided not only the acid 7 but also the dibromo and iodobromo derivatives 13 and 23. These in turn gave the isomers 14 and 24 upon base-mediated migration of the heaviest halogen, which made the acids 8 and 10 directly accessible. The regiocontrolled monodebromination of intermediate 14 afforded (4-bromo-2,6-difluoro)triethylsilane (15), which opened the route to the acids 3 and 5 (by carboxylation and protodesilylation) and to acid 9 (by carboxylation and bromodesilylation). Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.
- Schlosser, Manfred,Heiss, Christophe
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p. 4618 - 4624
(2007/10/03)
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- Electrophilic ipso substitution of trimethylsilyl groups in fluorobenzenes
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Using variants of literature methods 2,4- and 2,6- difluorophenyltrimethylsilanes have been bromodesilylated to the corresponding bromodifluorobenzenes in moderate to good yields, 3-bromo-2,6-difluorophenyltrimethylsilane afforded 1,3-dibromo-2,4-difluorobenzene whilst 1,3-difluoro-2,4-bis(trimethylsilyl)benzene yielded 3-bromo-2,6-difluorophenyltrimethylsilane. Application of either the Eaborn or Chvalovsky methods of nitrodesilylation to 4-fluorophenyltrimethylsilane, 2,4-difluorophenyltrimethylsilane and 2,6-difluorophenyltrimethylsilane afforded largely the corresponding desilylated products together with products associated with initial protodesilylation, followed by nitration of the resulting fluorobenzenes. The results obtained show that ipso desilylation in the fluoroaromatic series does follow the expected pattern previously obtained in the hydrocarbon analogues. They also show that in some cases the formation of unusually substituted fluoroarenes can be achieved more readily than by the methods previously used.
- Coe, Paul L.,Stuart, Alison M.,Moody, David J.
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