- Iodine-catalyzed tandem oxidative aromatization for the synthesis of meta-substituted alkoxybenzenes
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A rapid method for the synthesis of meta-substituted alkoxybenzenes is achieved by oxidation of cyclohexenones. This one-pot transformation is catalyzed by molecular iodine with DDQ as an oxidant in the presence of alcohols. Diverse cyclohexenones with aryl or alkyl substitutes are well tolerated to the mild oxidative conditions affording desired products in up to 92% yield. These oxidizing processes were applicable to the efficient synthesis of useful meta-substituted phenolic products which are difficult to obtain by traditional electrophilic substitutions.
- Jiang, Dahong,Jia, Xicheng,Zhang, Shuhua,Zhang, Zhihua,Li, Lei,Qiao, Yanhui
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supporting information
(2021/06/12)
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- A new alkylation of aryl alcohols by boron trifluoride etherate
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The ethylation of aryl alcohols by an ethyl moiety of boron trifluoride etherate is described. The reaction proceeded cleanly and afforded good yields of the corresponding aryl ethyl ethers. It tolerated the presence of functional groups such as aryl, alkyl, halogens, nitro, nitrile, and amino. However, the presence of amino or nitro groups ortho to a hydroxyl group of an aryl compound drastically reduced the yields of the anticipated products due to the chelation of the aforementioned functional groups with boron trifluoride etherate. A nitrogen atom in the aromatic ring system, as exemplified by hydroxypyridine and 8-hydroxyquinoline, completely inhibited the reaction. Resorcinol, hydroquinone, and aryl alcohols with aldehyde functions decomposed under the reaction conditions.
- Jumbam, Ndze Denis,Maganga, Yamkela,Masamba, Wayiza,Mbunye, Nomthandazo I.,Mgoqi, Esethu,Mtwa, Sphumusa
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- Solvent-free Williamson synthesis: An efficient, simple, and convenient method for chemoselective etherification of phenols and bisphenols
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Etherification of phenols with dimethyl- and diethylsulfates and benzyl chloride was performed efficiently in the presence of a suitable solid base, NaHCO3 or K2CO3, under solvent-free conditions. The reaction proceeded rapidly at low temperature, and the corresponding ethers were obtained with high purity and excellent yield. Selective etherification of electron-poor phenols in the presence of electron-rich ones and also selective mono-etherification of bisphenols are the noteworthy advantages of this method. This method is environmentally friendly. Copyright Taylor & Francis Group, LLC.
- Massah, Ahmad R.,Mosharafian, Masumeh,Momeni, Ahamad R.,Aliyan, Hamid,Naghash, H. Javaherian,Adibnejad, Mohamad
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p. 1807 - 1815
(2008/02/02)
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- Facile and regioselective dealkylation of alkyl aryl ethers using niobium(V) pentachloride
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A simple and facile method for the cleavage of carbon-oxygen bonds promoted by niobium pentachloride(V) is described. Excellent yields and regioselectivities were observed with various alkyl aryl ethers to give the phenols. NMR studies revealed the formation of monoaryloxy niobium salt(V), and a neighboring-group effect may play a significant role in the regioselectivity. Wiley-VCH Verlag GmbH & Co. KGaA, 2006.
- Sudo, Yukinori,Arai, Shigeru,Nishida, Atsushi
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p. 752 - 758
(2007/10/03)
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- pH effects on ethanolysis of some arenediazonium ions: Evidence for homolytic dediazoniation proceeding through formation of transient diazo ethers
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The effects of pH on the observed rate constants (kobsd.) and on the solvolytic dediazoniation product distributions of ethanolysis of 2-, 3-, and 4-methylbenzenediazonium ions (2MBD, 3MBD, and 4MBD, respectively) were determined by a combination of spectrophotometric (UV/Vis) and Chromatographic (HPLC) techniques. The variation of both kobsd. and product yields with pH follow S-shaped curves with inflection points at pH ≈ 3.6, depending on solvent composition. With increasing pH, kobsd. values increase by factors of up to about 4 (2MBD), about 3 (3MBD), and about 50 (4MBD) with respect to the kobsd. values at low pH. HPLC analyses of the reaction mixtures show that only heterolytic products are obtained at low pH, indicating that solvolytic dediazoniation takes place through an ionic mechanism, but an increase in pH favors homolytic dediazoniation, with quantitative conversion into the reduction product toluene being obtained at pH ≥ 6 (4MBD), indicating that a turnover from the heterolytic to the homolytic mechanisms is taking place under experimental conditions under which insignificant amounts of EtO- or OH- should be present in solution. The obtained S-shaped profiles suggest that the initiation process of the homolytic pathway is the result of the formation of a highly unstable transient diazo ether complex and not by direct electron transfer from the solvent (EtOH) to the arenediazonium ions as is currently believed. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.
- Pazo-Llorente, Roman,Bravo-Diaz, Carlos,Gonzalez-Romero, Elisa
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p. 3221 - 3226
(2007/10/03)
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- Solvolysis of some arenediazonium salts in binary EtOH/H2O mixtures under acidic conditions
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We have determined the product distribution, the rate constants for dediazoniation product formation, and the solvolytic rate constants for 2-, 3-, and 4-methylbenzenediazonium ions (2-, 3-, and 4-MBD, respectively) loss in acidic ethanol/water mixtures over the whole composition range by a combination of spectrophotometric (UV/Vis) and high performance liquid chromatography (HPLC) measurements. The observed rate constants (kobs) for substrate loss are equal to those for product formation, and they remain essentially constant (2-MBD) with changing solvent composition but increase by a factor of ≈2 (4MBD) on going from water to 100% EtOH. Up to four dediazoniation products - cresols (ArOH), chlorotoluene (ArCl), methylphenetole (ArOEt), and toluene (ArH) - were detected, depending on the solvent composition; the major dediazoniation products were the ArOH and ArOEt derivatives. The product selectivity (S) of the reaction towards nucleophiles is low and essentially constant with changing solvent composition, and good linear correlations between log kobs and Yc1 (solvent ionizing power) were observed for the three ArN2+ ions. All data are consistent with the rate-determining formation of an aryl cation, which reacts immediately with available nucleophiles. The data suggest that the distribution of neutral and anionic nucleophiles in the neighborhood of the ground state arenediazonium ion remains essentially unchanged upon dediazoniation, the observed product distribution reflecting the concentrations of nucleophiles in their immediate environment (i.e., in the first solvation shells of the arenediazonium ions). Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.
- Pazo-Llorente, Roman,Bravo-Diaz, Carlos,Gonzalez-Romero, Elisa
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p. 3421 - 3428
(2007/10/03)
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- A product analytical study of the thermal and photolytic decomposition of some arenediazonium salts in solution
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Products of thermal and photochemical reactions of eleven arenediazonium tetrafluoroborates in various solvents have been analyzed. All compounds in most solvents undergo unimolecular heterolysis to give singlet aryl cations which are captured by solvent. This mechanism is dominant for arenediazonium ions without electron-withdrawing substituents in all solvents, and the only reaction observed in water. Additionally, appreciable yields of fluoroarenes are obtained by fluoride abstraction by the aryl cation from fluorinated solvents and from tetrafluoroborate in fluorinated solvents. Yields from photochemical processes are very similar to those from thermal reactions indicating that the main reactions proceed through common or very similar intermediates. Aryl cations formed from ion-paired diazonium ions may react with the counterion, but fragmentation of dissociated diazonium ions leads only to solvent-derived product. Some arenediazonium ions in some solvents undergo an alternative radical reaction leading principally to hydrodediazoniation. It is proposed that this reaction involves initial rate-limiting electron transfer from ethanol to the arenediazonium ion followed rapidly by homolysis of the resultant aryldiazenyl radical. Within the same solvent cage, the aryl radical then either abstracts an α-hydrogen from the ethanol radical cation generated in the first step to give the reduction product and protonated acetaldehyde, or combines with it at the oxygen to give a protonated aryl ethyl ether.
- Canning, Peter S. J.,Maskill, Howard,McCrudden, Katharine,Sexton, Brian
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p. 789 - 800
(2007/10/03)
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- New Oxidative Aromatization of α,β-Unsaturated Cyclohexenones with Iodine-Cerium(IV) Ammonium Nitrate in Alcohol
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The reaction of 2-cyclohexen-1-one derivatives with iodine-cerium(IV) ammonium nitrate in alcohols (methanol, ethanol, 1-propanol, 2-propanol, and 1-butanol) under refluxing, gave the corresponding alkyl phenyl ethers in good yields.In the case of diol (ethylene glycol, 1,3-propanediol, and 1,4-butanediol), phenoxyalkanol derivatives were obtained.The present method was also applicable to oxidative rearrangement of isophorone.
- Horiuchi, C. Akira,Fukunishi, Hirotada,Kajita, Mika,Yamaguchi, Akihisa,Kiyomiya, Hiroshi,Kiji, Shinji
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p. 1921 - 1924
(2007/10/02)
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- A New Rearrangement of Alkoxybenzyl Anions
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Alkyl groups migrate from oxygen to carbon in alkyl aryl ethers which have been metalated in benzylic positions. 2,6-Dimethylanisole provides a variety of 2,6-dialkylphenols and their ethers in 45-80percent yields.Rearrangement products are obtained in 10-30percent yields from other dimethylanisoles and from methylanisoles.The reactions appear to proceed, like Wittig rearrangements, by homolytic cleavage of the alkyl-oxygen bond followed by recombination of the resulting radical pair in a different way.The rearrangements can be avoided by using methyl ethers and working at or below room temperature.
- Bates, Robert B.,Siahaan, Teruna J.,Suvannachut, Kessara
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p. 1328 - 1334
(2007/10/02)
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- Preparation and Reactions of Dianions from the Cresols
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With n-BuLi/KO-t-Bu, protons are removed from the hydroxyl and methyl groups of cresols 5 to give dianions 6 in yields of 85percent (ortho), 95percent (meta), and 42percent (para).These dianions react with alkyl halides, Me3SiCl, Bu3SnCl, CO2, and oxidizing agents at carbon only and with dialkyl sulfates at both carbon and oxygen.Thus phenol derivatives bearing primary alkyl groups can be prepared from the corresponding methylphenols via dianions 6.
- Bates, Robert B.,Siahaan, Teruna J.
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p. 1432 - 1434
(2007/10/02)
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- Aryl Radical Departure Aptitudes in Reactions of Diaryliodonium Fluoroborates with Sodium Ethoxide
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Several unsymmetrical diaryliodonium fluoroborates have been prepared and subjected to reaction with sodium ethoxide in ethanol solution at 71 deg C.From quantitative determinations of products, it has been possible to calculate apparent departure aptitudes of several common aryl radical cations of type 6.These results are compared with similar data obtained from thermolysis reactions of hydroxytetraarylstiboranes.
- Lubinkowski, Jacek J.,Arrieche, Cecilia Gimenez,McEwen, William E.
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p. 2076 - 2079
(2007/10/02)
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