- Synthesis of Polysubstituted Meta-Halophenols by Anion-Accelerated 2π-Electrocyclic Ring Opening
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Disrotatory – thermally allowed – 2π-electrocyclic ring-opening reactions require high temperatures to proceed. Herein, we report the first anion-accelerated 2π-electrocyclic ring opening of 6,6-dihalobicyclo[3.1.0]hexan-2-ones at low temperature to give the corresponding meta-halophenols in good to high yields (18 examples, 29–92 % yield, average: 65 %). Many of the phenols have unconventional substitution patterns and are reported here for the first time. Furthermore, the strength of the methodology was shown by the total synthesis of the densely functionalized phenolic natural product caramboxin (isolated as the lactam dehydrate). The reaction mechanism underlying the anion-acceleration was investigated in an ab initio study, which concluded that base-mediated proton abstraction anti to the concurrently departing endo-bromine was the initiating step in an overall concerted reaction mechanism leading directly to the meta-halophenol.
- Staudt, Markus,S?lling, Theis,Bunch, Lennart
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supporting information
p. 10941 - 10947
(2021/06/16)
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- Nickel Hydride Catalyzed Cleavage of Allyl Ethers Induced by Isomerization
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This report discloses the deallylation of O - and N -allyl functional groups by using a combination of a Ni-H precatalyst and excess Bronsted acid. Key steps are the isomerization of the O - or N -allyl group through Ni-catalyzed double-bond migration followed by Bronsted acid induced O/N-C bond hydrolysis. A variety of functional groups are tolerated in this protocol, highlighting its synthetic value.
- Kathe, Prasad M.,Berkefeld, Andreas,Fleischer, Ivana
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supporting information
p. 1629 - 1632
(2021/02/09)
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- Highly efficient heterogeneous V2O5@TiO2 catalyzed the rapid transformation of boronic acids to phenols
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A V2O5@TiO2 catalyzed green and efficient protocol for the hydroxylation of boronic acid into phenol has been developed utilizing environmentally benign oxidant hydrogen peroxide. A wide range of electron-donating and the electron-withdrawing group-containing (hetero)aryl boronic acids were transformed into their corresponding phenol. The methodology was also applied successfully to transform various natural and bioactive molecules like tocopherol, amino acids, cinchonidine, vasicinone, menthol, and pharmaceuticals such as ciprofloxacin, ibuprofen, and paracetamol. The other feature of the methodology includes gram-scale synthetic applicability, recyclability, and short reaction time.
- Upadhyay, Rahul,Singh, Deepak,Maurya, Sushil K.
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supporting information
p. 3925 - 3931
(2021/08/24)
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- Highly efficient, recyclable and alternative method of synthesizing phenols from phenylboronic acids using non-endangered metal: Samarium oxide
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Oxidation of phenylboronic acid to phenol is one of the important industrial processes and it is generally employed in the plastic, explosive and drug manufacturing industries. Over the past decades, numerous efficient methods have been described for the generation of phenols from phenylboronic acids in the presence of oxidant. However, these methods suffered from various limitations, including the use of expensive, toxic reagents and sophisticated protocol to synthesise the phenols. Additionally, some of these reported literatures employed endangered metals, in which mankind is facing the risk of limited supply of these elements in 20 years’ time from now. As such, a viable alternative and green method for achieving organic synthesis is highly sought after by the chemists of today. Herein, we report for the first time a facile, efficient and alternative method in the preparation of phenols from phenylboronic acids using non-endangered metal as catalyst. In all cases, all phenols were afforded in satisfactory yields (81–96%) by employing column-free method. In the recyclability study, the Sm2O3 catalyst was found to possess good catalytic performance, even after being reused for five consecutive times (96–91%). In addition, SEM result revealed that the morphology of the recycled Sm2O3 catalyst was well preserved after five successive uses, which indicate no observable changes occurred in the recovered catalysts. As a final note, the current method is anticipated to be useful for industries manufacturing chemical intermediates as it provides an alternative method of catalysis by using a non-endangered metal in organic transformations.
- Yusoff, Hanis Mohd,Bala Chandran, Prasana Devi,Sayuti, Fatin Amira Binti,Kan, Su-Yin,Mohd Radzi, Siti Aisha,Yong, Fu-Siong Julius,Lee, Oon Jew,Chia, Poh Wai
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- Activity and specificity studies of the new thermostable esterase EstDZ2
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In this paper, we study the activity and specificity of EstDZ2, a new thermostable carboxyl esterase of unknown function, which was isolated from a metagenome library from a Russian hot spring. The biocatalytic reaction employing EstDZ2 proved to be an efficient method for the hydrolysis of aryl p-, o- or m-substituted esters of butyric acid and esters of secondary alcohols. Docking studies revealed structural features of the enzyme that led to activity differences among the different substrates.
- Myrtollari, Kamela,Katsoulakis, Nikolaos,Zarafeta, Dimitra,Pavlidis, Ioannis V.,Skretas, Georgios,Smonou, Ioulia
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supporting information
(2020/09/16)
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- Copper and L-(?)-quebrachitol catalyzed hydroxylation and amination of aryl halides under air
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L-(?)-Quebrachitol, a natural product obtained from waste water of the rubber industry, was utilized as an efficient ligand for the copper-catalyzed hydroxylation and amination of aryl halides to selectively give phenols and aryl amines in water or 95percent ethanol. In addition, the hydroxylation of 2-chloro-4-hydroxybenzoic acid was validated on a 100-g scale under air.
- Bao, Xuefei,Chen, Guoliang,Dong, Jinhua,Du, Fangyu,Li, Hui,Liang, Xinjie,Wu, Ying,Zhang, Yongsheng
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supporting information
(2020/08/03)
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- Quaternary ammonium hydroxide-functionalized g-C3N4 catalyst for aerobic hydroxylation of arylboronic acids to phenols
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A new and efficient metal-free approach toward the synthesis of phenols via an aerobic hydroxylation of arylboronic acids by using a novel quaternary ammonium hydroxide g-C3N4 catalyst has been described. The functionalized quaternary ammonium hydroxide (g-C3N4-OH) has been prepared from graphitic carbon nitride (g-C3N4) scaffold by converting the residual –NH2 and –NH groups to quaternary methyl ammonium iodide by performing a methylation reaction with methyl iodide followed by ion-exchange with 0.1 N KOH or anion exchange resin Amberlyst A26 (OH- form) by post-synthetic modification. The resultant g-C3N4-OH was characterized by XRD, FTIR, field-emission scanning electron microscope (FESEM), high-resolution transmission electron microscope (HRTEM), N2 adsorption/desorption isotherms, and acid–base titration. Tested as solid-base catalysts, the g-C3N4-OH showed excellent catalytic activity in the aerobic hydroxylation reaction by converting a variety of arylboronic acids to the corresponding phenols in high yields. More importantly, the g-C3N4-OH solid-base has been successfully reused four times with the minor loss of initial catalytic activity (10.5percent).
- Muhammad, Ibrahim,Mannathan, Subramaniyan,Sasidharan, Manickam
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p. 1470 - 1476
(2020/07/13)
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- A scalable and green one-minute synthesis of substituted phenols
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A mild, green and highly efficient protocol was developed for the synthesis of substituted phenols via ipso-hydroxylation of arylboronic acids in ethanol. The method utilizes the combination of aqueous hydrogen peroxide as the oxidant and H2O2/HBr as the reagent under unprecedentedly simple and convenient conditions. A wide range of arylboronic acids were smoothly transformed into substituted phenols in very good to excellent yields without chromatographic purification. The reaction is scalable up to at least 5 grams at room temperature with one-minute reaction time and can be combined in a one-pot sequence with bromination and Pd-catalyzed cross-coupling to generate more diverse, highly substituted phenols.
- Elumalai, Vijayaragavan,Hansen, J?rn H.
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p. 40582 - 40587
(2020/11/18)
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- Versatile catalysis of “natural extract”: oxidation of sulfides and alcohols and ipso-hydroxylation of arylboronic acids
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Abstract: In the present work, we have described the versatile applications of naturally available inexpensive citrous lemon juice as biocatalyst for controlled oxidation of sulfides and alcohols and ipso-hydroxylation of arylboronic acids using 30% H2O2 as a green oxidant. A series of structurally divergent sulfides and benzyl alcohols were oxidized to their corresponding sulfoxides and aldehydes, respectively, with good-to-excellent yields. Similarly, aryl and heteroaryl boronic acids were rapidly, often within minutes, transformed to their corresponding phenols at room temperature. Graphic abstract: [Figure not available: see fulltext.]
- Dutta, Apurba,Ali, Abdul Aziz,Sarma, Diganta
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p. 2379 - 2388
(2019/06/28)
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- Polymer-supported eosin Y as a reusable photocatalyst for visible light mediated organic transformations
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A novel polymer-supported recyclable photocatalyst has been developed for visible light mediated oxidation reactions. The organic dye eosin Y was loaded on macroporous commercially available Amberlite IRA 900 chloride resin and exploited as a photocatalyst for visible light mediated oxidation of thioethers to sulfoxides and phenylboronic acids to phenols under open atmospheric air. Varieties of functional groups were well tolerated during oxidation. The catalyst is recyclable for six cycles without significant loss in its efficiency. Furthermore, gram-scale oxidation of sulfides to sulfoxides has been demonstrated to prove the commercial viability of the method.
- Sridhar, Arunasalam,Rangasamy, Rajmohan,Selvaraj, Mari
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p. 17974 - 17979
(2019/12/02)
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- Potassium: Tert -butoxide mediated aerobic hydroxylation of arylboronic acids: An application towards the synthesis of (E)-phenoxy acrylates
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The first example of potassium tert-butoxide mediated aerobic hydroxylation of arylboronic acids is described. A variety of arylboronic acids bearing both electron donating and withdrawing substituents successfully participated in the reaction and furnished phenols in good yields. This strategy also provides access to one pot synthesis of (E)-3-phenoxy acrylates from arylboronic acids and propiolates. The solvent plays an important role and a binary solvent system comprising CH3CN/THF is found to be the best.
- Muhammad, Ibrahim,Balakrishnan, Madasamy Hari,Sasidharan, Manickam,Mannathan, Subramaniyan
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supporting information
p. 11065 - 11068
(2019/07/31)
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- Deprotection of durable benzenesulfonyl protection for phenols — efficient synthesis of polyphenols
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A robust protection method for phenol was demonstrated by the use of durable benzenesulfonyl group, which survives various harsh reaction conditions using Grignard reagent, organolithium reagent, metal alkoxide, phosgene, mineral, and Lewis acids. A facile deprotection condition utilizing pulverized KOH (5 equiv) and t-BuOH (10 equiv) in hot toluene makes this protocol as a practical method, which can be applied to the multistep synthesis of biologically and medicinally important polyphenol compounds.
- Alam, Mohammad Shariful,Koo, Sangho
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supporting information
p. 247 - 254
(2018/01/08)
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- Synthesis of Phenols: Organophotoredox/Nickel Dual Catalytic Hydroxylation of Aryl Halides with Water
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A highly effective hydroxylation reaction of aryl halides with water under synergistic organophotoredox and nickel catalysis is reported. The OH group of the resulting phenols originates from water, following deprotonation facilitated by an intramolecular base group on the ligand. Significantly, aryl bromides as well as less reactive aryl chlorides served as effective substrates to afford phenols with a wide range of functional groups. Without the need for a strong inorganic base or an expensive noble-metal catalyst, this process can be applied to the efficient preparation of diverse phenols and enables the hydroxylation of multifunctional pharmaceutically relevant aryl halides.
- Yang, Liu,Huang, Zhiyan,Li, Gang,Zhang, Wei,Cao, Rui,Wang, Chao,Xiao, Jianliang,Xue, Dong
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supporting information
p. 1968 - 1972
(2018/02/06)
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- Green Photoorganocatalytic Synthesis of Phenols from Arylboronic Acids
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A green and cheap protocol for the photocatalytic hydroxylation of arylboronic acids is presented. 2,2-Dimethoxy-2-phenylacetophenone proved to be the best photoinitiator, among a range of organocatalysts in promoting this reaction. This photocatalytic protocol can be expanded into a wide substrate scope of aromatic boronic acids bearing various functional groups, leading to the corresponding phenols in good to high yields under mild reaction conditions, which include water as solvent, light irradiation provided from standard light-bulbs at room temperature.
- Sideri, Ioanna K.,Voutyritsa, Errika,Kokotos, Christoforos G.
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supporting information
p. 1324 - 1328
(2017/12/06)
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- Method for continuous flow synthesis of phenol-based compound
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The present invention provides a method for continuous flow synthesis of a phenol-based compound represented by a formula (III), wherein the method is performed in two static mixers, a tubular reactor and an oil-water separator, wherein the two static mixers, the tubular reactor and the oil-water separator are sequentially connected in series. The method comprises that an acid solution and an aniline compound represented by a formula (I) are pumped into the static mixer A; the mixture of the acid solution and the compound represented by the formula (I) flows out from the static mixer A and flows into the static mixer B connected to the static mixer A; a sodium nitrite solution is pumped into the static mixer B, and a reaction is performed to produce a diazonium salt solution represented by a formula (II); and the solution represented by the formula (II) flows out from the static mixer B, is pumped into the tubular reactor connected to the static mixer B, and then into the oil-water separator connected to the tubular reactor, and the water phase is separated to obtain the compound represented by the formula (III). According to the present invention, the method has characteristics of short reaction time, solvent saving and high yield, and can well solve the problems in the synthesis of the phenol-based compound through diazotization hydrolysis in the intermittent kettle type reactor. The formulas (I), (II) and (III) are defined in the specification.
- -
-
Paragraph 0051; 0052
(2017/07/21)
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- Photoinduced Vitamin B12-Catalysis for Deprotection of (Allyloxy)arenes
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Vitamin B12 is a natural cobalt complex that, while reduced to the "supernucleophilic" Co(I) form, can easily react with electrophiles via an SN2 mechanism. It is also shown to react via an SN2′ mechanism with allylic compounds allowing for photochemical deprotection of (allyloxy)arenes. A sustainable alternative to commonly used noble metal-catalyzed deprotection reactions is presented.
- Giedyk, Maciej,Turkowska, Joanna,Lepak, Sandra,Marculewicz, Marcin,ó Proinsias, Keith,Gryko, Dorota
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supporting information
p. 2670 - 2673
(2017/05/24)
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- Chemoselective oxidation of aryl organoboron systems enabled by boronic acid-selective phase transfer
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We report the direct chemoselective Brown-type oxidation of aryl organoboron systems containing two oxidizable boron groups. Basic biphasic reaction conditions enable selective formation and phase transfer of a boronic acid trihydroxyboronate in the presence of boronic acid pinacol (BPin) esters, while avoiding speciation equilibria. Spectroscopic investigations validate a base-promoted phase-selective discrimination of organoboron species. This phenomenon is general across a broad range of organoboron compounds and can also be used to invert conventional protecting group strategies, enabling chemoselective oxidation of BMIDA species over normally more reactive BPin substrates. We also demonstrate the selective oxidation of diboronic acid systems with chemoselectivity predictable a priori. The utility of this method is exemplified through the development of a chemoselective oxidative nucleophile coupling.
- Molloy, John J.,Clohessy, Thomas A.,Irving, Craig,Anderson, Niall A.,Lloyd-Jones, Guy C.,Watson, Allan J. B.
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p. 1551 - 1559
(2017/02/10)
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- A dinuclear iron(II) complex bearing multidentate pyridinyl ligand: Synthesis, characterization and its catalysis on the hydroxylation of aromatic compounds
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A dinuclear iron(II) complex Fe2L2(μ2-Cl)2Cl2 (L = N,N-bis(pyridin-2-ylmethyl)prop-2-yn-1-amine) was prepared and fully characterized by UV–Vis spectroscopy, elemental analysis, electrochemical analysis and X-ray single crystal diffraction analysis. The catalytic activity of the complex was assessed for the hydroxylation of aromatic compounds by using aqueous H2O2 as an oxidant in acetonitrile. The catalytic system was applicable in a wide range of substrates including aromatic compounds with both electron-donating and electron-withdrawing substituents and showed moderate to good catalytic activity and selectivity in the oxidation reactions. Particularly, in the case of benzene the selectivity of phenol achieve to 74% with the reaction conversion of 24.8%.
- Gu, Erxing,Zhong, Wei,Ma, Hongxia,Xu, Beibei,Wang, Hailong,Liu, Xiaoming
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p. 159 - 165
(2018/03/29)
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- Copper-Catalyzed Hydroxylation of (Hetero)aryl Halides under Mild Conditions
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The combination of Cu(acac)2 and N,N′-bis(4-hydroxyl-2,6-dimethylphenyl)oxalamide (BHMPO) provides a powerful catalytic system for hydroxylation of (hetero)aryl halides. A wide range of (hetero)aryl chlorides bearing either electron-donating or -withdrawing groups proceeded well at 130 °C, delivering the corresponding phenols and hydroxylated heteroarenes in good to excellent yields. When more reactive (hetero)aryl bromides and iodides were employed, the hydroxylation reactions completed at relatively low temperatures (80 and 60 °C, respectively) at low catalytic loadings (0.5 mol % Cu).
- Xia, Shanghua,Gan, Lu,Wang, Kailiang,Li, Zheng,Ma, Dawei
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supporting information
p. 13493 - 13496
(2016/10/31)
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- Ruthenium(II)-catalyzed protocol for preparation of diverse α,β- and β,β-Dihaloenones from diazodicarbonyls
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Efficient one-step syntheses of α,β- and β,β-dihaloenones were achieved by ruthenium(II)- catalyzed reactions between cyclic or acyclic diazodicarbonyl compounds and oxalyl chloride or oxalyl bromide in moderate to good yields. This methodology offers sev
- Magar, Krishna Bahadur Somai,Lee, Yong Rok
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p. 3422 - 3432
(2015/02/02)
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- Triethanolamine as an inexpensive and efficient ligand for copper-catalyzed hydroxylation of aryl halides in water
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The CuI/triethanolamine catalyst system efficiently promotes the direct hydroxylation of aryl iodides and bromides in water to provide the corresponding phenols in good to excellent yields. Moreover, the procedure avoids the use of toxic organic solvents and tolerates many functional groups. The CuI/triethanolamine catalyst system efficiently promotes the direct hydroxylation of aryl iodides and bromides in water to afford the corresponding phenols in good to excellent yields. Copyright
- Wang, Deping,Kuang, Daizhi,Zhang, Fuxing,Tang, Siping,Jiang, Wujiu
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supporting information
p. 315 - 318
(2014/01/23)
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- Triethanolamine as an Inexpensive and Efficient Ligand for Copper-Catalyzed Hydroxylation of Aryl Halides in Water
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The CuI/triethanolamine catalyst system efficiently promotes the direct hydroxylation of aryl iodides and bromides in water to provide the corresponding phenols in good to excellent yields. Moreover, the procedure avoids the use of toxic organic solvents and tolerates many functional groups.
- Wang, Deping,Kuang, Daizhi,Zhang, Fuxing,Tang, Siping,Jiang, Wujiu
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supporting information
p. 315 - 318
(2015/10/05)
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- Preparation of phenolic compounds through catalyst-free ipso-hydroxylation of arylboronic acids
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A novel method for the preparation of phenolic compounds through ipso-hydroxylation of the corresponding widely available arylboronic acid precursors is described. Through application of a novel PEG400-H 2O2 reactant system, a variety of substituted phenols and other aromatic analogues have been prepared in excellent yields at room temperature in the absence of any catalyst.
- Gohain, Mukut,Du Plessis, Maretha,Van Tonder, Johannes H.,Bezuidenhoudt, Barend C.B.
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p. 2082 - 2084
(2014/04/03)
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- Antimony(V) chloride as an efficient reagent for deprotection of methyl ethers
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This paper proposes a new and efficient method for the deprotection of methyl ethers using antimony pentachloride at ambient temperature. The procedure described here is a facile and practical method for the removal of the methyl group from aryl and benzyl methyl ethers. High selectivity was observed for the removal of the methyl group from dimethoxyarenes. The notable advantages of this protocol are mild reaction conditions, high yields, and the facility of workup procedure. The mechanism of the ether cleavage is proposed to explain this new reaction. Georg Thieme Verlag Stuttgart New York.
- Saadati, Fariba,Meftah-Booshehri, Hamid
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p. 1702 - 1706
(2013/09/02)
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- Efficient cleavage of alkyl aryl ethers using an ionic liquid under microwave irradiation
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A highly reliable dealkylation protocol of alkyl aryl ethers, whose alkyl groups are longer than methyl group, has been developed. We report that various ethyl, n-propyl, and benzyl aryl ethers are successfully cleaved using an ionic liquid, 1-n-butyl-3-methylimidazolium bromide, [bmim][Br], under microwave irradiation. Despite many characteristics such as lower cost and less toxicity of the alkylating agents, and greater hydrophobicity of the products, longer alkyl ethers have been significantly less exploited than methyl ethers, probably due to more difficulty in the deprotection step. Since it has the same advantages as the demethylation method developed by this group including mild conditions, short reaction time, and small use of the ionic liquids, the dealkylation protocol can greatly encourage the broader use of longer alkyl groups in the protection of phenolic groups. As with our previous study of demethylation using [bmim][Br], the microwave irradiation is crucial for the deprotection of longer alkyl aryl ethers. Unlike the conventional heating, which causes either low conversion or decomposition, the microwave irradiation seems to more effectively provide energy to cleave the ether bonds and therefore suppresses the undesired reactions.
- Park, Se Kyung,Battsengel, Oyunsaikhan,Chae, Junghyun
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supporting information
p. 174 - 178
(2013/08/24)
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- Twofold unsymmetrical C-H functionalization of PyrDipSi-substituted arenes: A general method for the synthesis of substituted meta-halophenols
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And the world is your oyster Sequential halogenation/oxygenation reactions of 2-diisopropylsilylpyrimidine-substituted arenes provide a general and efficient synthesis of substituted meta-halophenols from simple aryl iodides (see scheme; Piv=pivaloyl). The products are poised to undergo diverse C-C, C-N, and C-O bond-forming reactions that enable the transformation of their framework and the introduction of valuable functionalities. Copyright
- Sarkar, Dhruba,Melkonyan, Ferdinand S.,Gulevich, Anton V.,Gevorgyan, Vladimir
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supporting information
p. 10800 - 10804
(2013/10/22)
-
- Base-catalyzed dehydration of 3-substituted benzene cis -1,2-dihydrodiols: Stabilization of a cyclohexadienide anion intermediate by negative aromatic hyperconjugation
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Evidence that a 1,2-dihydroxycyclohexadienide anion is stabilized by aromatic "negative hyperconjugation" is described. It complements an earlier inference of "positive" hyperconjugative aromaticity for the cyclohexadienyl cation. The anion is a reactive intermediate in the dehydration of benzene cis-1,2-dihydrodiol to phenol. Rate constants for 3-substituted benzene cis-dihydrodiols are correlated by σ- values with = 3.2. Solvent isotope effects for the reactions are kH2O/kD 2O = 1.2-1.8. These measurements are consistent with reaction via a carbanion intermediate or a concerted reaction with a "carbanion-like" transition state. These and other experimental results confirm that the reaction proceeds by a stepwise mechanism, with a change in rate-determining step from proton transfer to the loss of hydroxide ion from the intermediate. Hydrogen isotope exchange accompanying dehydration of the parent benzene cis-1,2-dihydrodiol was not found, and thus, the proton transfer step is subject to internal return. A rate constant of ～1011 s-1, corresponding to rotational relaxation of the aqueous solvent, is assigned to loss of hydroxide ion from the intermediate. The rate constant for internal return therefore falls in the range 1011-1012 s -1. From these limiting values and the measured rate constant for hydroxide-catalyzed dehydration, a pKa of 30.8 ± 0.5 was determined for formation of the anion. Although loss of hydroxide ion is hugely exothermic, a concerted reaction is not enforced by the instability of the intermediate. Stabilization by negative hyperconjugation is proposed for 1,2-dihydroxycyclohexadienide and similar anions, and this proposal is supported by additional experimental evidence and by computational results, including evidence for a diatropic ("aromatic") ring current in 3,3-difluorocyclohexadienyl anion.
- Kudavalli, Jaya Satyanarayana,Rao, S. Nagaraja,More Oferrall, Rory A.,Bean, David E.,Fowler, Patrick W.,Sharma, Narain D.,Boyd, Derek R.,Kamerlin, Shina Caroline Lynn,Keeffe, James R.,Gronert, Scott
-
supporting information
p. 14056 - 14069,14
(2020/08/31)
-
- Mild and rapid hydroxylation of aryl/heteroaryl boronic acids and boronate esters with N-oxides
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Aryl and heteroaryl boronic acids and boronate esters are rapidly, often within minutes, transformed into the corresponding phenols by N-oxides in an open flask at ambient temperature. This transformation has broad compatibility with a variety of functional groups.
- Zhu, Chen,Wang, Rui,Falck
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supporting information; experimental part
p. 3494 - 3497
(2012/08/28)
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- Demethylation of aromatic methyl ethers using ionic liquids under microwave irradiation
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An efficient demethylation reaction for aromatic methyl ethers has been developed. Deprotection reactions give high yields with butylpyridinium bromide under microwave irradiation. Basic and acidic functional groups are tolerated if the reaction is performed under acidic conditions.
- Passiniemi, Mikko,Myllymaeki, Mikko J.,Vuokko, Juha,Koskinen, Ari M.P.
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scheme or table
p. 48 - 52
(2012/04/10)
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- Microwave-assisted demethylation of methyl aryl ethers using an ionic liquid
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An efficient demethylation of methyl aryl ethers using an ionic liquid, 1-n-butyl-3-methylimidazolium bromide ([bmim][Br]) has been developed. Methyl aryl ethers are successfully cleaved by the halide anion of [bmim][Br], without aid of any other activating agents. In this reaction, microwave irradiation was found to be crucial for the effective conversion. The newly developed protocol is a very attractive green chemical process as it utilizes minimal amount of cleaving reagents and does not require additional activating agents or solvents. Under the conditions described herein, a broad range of methyl aryl ethers were converted to the corresponding phenolic compounds in moderate to excellent yields in a short time. Georg Thieme Verlag Stuttgart New York.
- Park, Jiyeon,Chae, Junghyun
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experimental part
p. 1651 - 1656
(2010/08/22)
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- Aromatic Hydroxylation at a Non-Heme Iron Center: Observed Intermediates and Insights into the Nature of the Active Species
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Mechanism of substrate oxidations with hydrogen peroxide in the presence of a highly reactive, biomimetic, iron aminopyridine complex, [Fe II(bpmen)(CH3CN)2][ClO4] 2 (1; bpmen=N,N'-dimethyl-N,N'-bis(2-pyridylmethyl)ethane-1,2- diamine), is elucidated. Complex 1 has been shown to be an excellent catalyst for epoxidation and functional-group-directed aromatic hydroxylation using H2O2, although its mechanism of action remains largely unknown.1, 2 Efficient intermolecular hydroxylation of unfunctionalized benzene and substituted benzenes with H2O2 in the presence of 1 is found in the present work. Detailed mechanistic studies of the formation of iron(III)-phenolate products are reported. We have identified, generated in high yield, and experimentally characterized the key FeIII(OOH) intermediate (Imax=560 nm, rhombic EPR signal with g=2.21, 2.14, 1.96) formed by 1 and H2O2. Stopped-flow kinetic studies showed that FeIII(OOH) does not directly hydroxylate the aromatic rings, but undergoes rate-limiting self-decomposition producing transient reactive oxidant. The formation of the reactive species is facilitated by acid-assisted cleavage of the O-O bond in the iron-hydroperoxide intermediate. Acid-assisted benzene hydroxylation with 1 and a mechanistic probe, 2-Methyl-1-phenyl-2-propyl hydroperoxide (MPPH), correlates with O-O bond heterolysis. Independently generated FeIV=O species, which may originate from O-O bond homolysis in FeIII(OOH), proved to be inactive toward aromatic substrates. The reactive oxidant derived from 1 exchanges its oxygen atom with water and electrophilically attacks the aromatic ring (giving rise to an inverse H/D kinetic isotope effect of 0.8). These results have revealed a detailed experimental mechanistic picture of the oxidation reactions catalyzed by 1, based on direct characterization of the intermediates and products, and kinetic analysis of the individual reaction steps. Our detailed understanding of the mechanism of this reaction revealed both similarities and differences between synthetic and enzymatic aromatic hydroxylation reactions.
- Makhlynets, Olga V.,Rybak-Akimova, Elena V.
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supporting information; scheme or table
p. 13995 - 14006
(2011/04/12)
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- Methylation of phenolic hydroxyl group and demethylation of anisoles
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A mild methylation of phenolic hydroxyl groups with iodomethane was enabled in the presence of sodium bis(trimethylsilyl)amide at room temperature. The reverse reaction, namely demethylation of methyl phenyl ethers, was easily achieved by microwave heating with neat iodotrimethylsilane.
- Sato, Nobuhiro,Endo, Hiroyuki
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experimental part
p. 229 - 230
(2009/12/03)
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- Regioselective synthesis of phenols and halophenols from arylboronie acids using solid poly(N-vinylpyrrolidone)/hydrogen peroxide and poly(4-vinylpyridine) /hydrogen peroxide complexes
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Solid hydrogen peroxide complexes based on poly(N-vinylpyrrolidone) and poly(4-vinylpyridine) were prepared and used as solid hydroxylating reagents. These solid hydrogen peroxide equivalents are found to be much safer, convenient and efficient reagent systems for the ipso-hydroxylation of arylboronie acids to the corresponding phenols in high yields at a faster rate. The versatility of the reagents has been further expanded for the one-pot synthesis of halophenols. Density functional theory calculations were carried out on hydrogen peroxide complexes of N-ethylpyrrolidone and 4-ethylpyridine as models to get a better understanding of structure and behavior of hydrogen peroxide complexes of the polymers poly(N-vinylpyrrolidone) and poly(4-vinylpyridine) compared to aqueous hydrogen peroxide.
- Prakash, G. K. Surya,Chacko, Sujith,Panja, Chiradeep,Thomas, Tisa Elizabeth,Gurung, Laxman,Rasul, Golam,Mathew, Thomas,Olah, George A.
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experimental part
p. 1567 - 1574
(2011/02/25)
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- Halophenol rearrangement in Lewis acid-catalyzed Friedel-Crafts conditions: Evidence of competitive initial protonation and acylation
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Halogen rearrangement was observed during the Lewis acid-catalyzed Friedel-Crafts reaction of phthalic anhydride with bromophenols or bromoanisole. Further investigation revealed that 2-, 3-, and 4-bromophenols undergo rearrangement into other isomers under these reaction conditions. Product distribution from these reactions suggested that halogen rearrangement takes place during the s-complex intermediate of the condensation step. Furthermore, iodophenol undergoes hydrodeiodination rapidly rather than rearrangement, whereas chlorophenol does not undergo rearrangement at all. CSIRO 2008.
- Saha, Koushik,Lajis, Nordin H.,Abas, Faridah,Naji, Nabil Ali,Hamzah, A. Sazali,Shaari, Khozirah
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p. 821 - 825
(2008/12/22)
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- Process for the synthesis of biologically active oxygenated compounds by dealkylation of the corresponding alkylethers
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Alkoxy aromatic compounds are conveniently dealkylated to the corresponding phenolic compounds by treatment with aluminum chloride/N,N-dimethyl aniline complex. Aromatic poly O-demethylation is a unique feature of this invention. This process is applicable to the manufacture of polyphenols such as Resveratrol, Oxyresveratrol, Gnetol.
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Page/Page column 6
(2008/06/13)
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- 2-(Diethylamino)ethanethiol, a new reagent for the odorless deprotection of aromatic methyl ethers
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A new reagent for the deprotection of aromatic methyl ethers, 2-(diethylamino)ethanethiol, is reported. This compound, commercially available as its HCl salt, affords the corresponding phenols in good to excellent yields on a wide variety of substrates. A clear advantage of this method over the use of more common thiols, such as ethanethiol, is the easy extraction of both the deprotecting reagent and the byproduct 2-(diethylamino)ethyl methyl sulfide into the aqueous phase by quenching with dilute acid, which allows an essentially odorless workup.
- Magano, Javier,Chen, Michael H.,Clark, Jerry D.,Nussbaumer, Thomas
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p. 7103 - 7105
(2007/10/03)
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- Direct hydroxylation of substituted benzenes to phenols with air and CO using molybdovanadophosphates as a key catalyst
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A direct synthetic method of cresols from toluene by hydroxylation with air using CO as a reducing agent was developed. The reaction of toluene with air (15 atm) and CO (5 atm) in the presence of catalytic amounts of H 4PMo11VO40·31H2O and Pd/C in aqueous acetic acid at 120°C for 2 h afforded a mixture of o-, m-, and p-cresols in 9.9% yield at 83% selectivity. Cresols were obtained in 19% yield by recharging air and CO under these conditions. A variety of substituted benzenes were hydroxylated by this method to give the corresponding phenol derivatives in higher selectivity.
- Mita, Shuichi,Sakamoto, Takao,Yamada, Shingo,Sakaguchi, Satoshi,Ishii, Yasutaka
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p. 7729 - 7732
(2007/10/03)
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- Protease-mediated enzymatic hydrolysis and activation of aryl phosphoramidate derivatives of stavudine
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Several proteases are capable of hydrolyzing the aryl substituted phosphoramidate derivatives of stavudine resulting in the formation of the active metabolite, alaninyl d4T monophosphate. Subtilisin Protease A, Subtilisin Griseus, Subtilisin Carlsberg, Papaya, Bacillus were amongst the most effective proteases in hydrolyzing stavudine derivatives and specificity of their activity was confirmed using several protease inhibitors to block the hydrolysis of these phosphoramidate derivatives. We found that these proteases exhibit chiral selectivity at the phosphorus center of stavudine derivatives. Our results indicate that cellular proteases may be responsible for the activation of these phosphoramidate derivatives. In addition, we show that the enzymatic hydrolysis takes place at the carboxymethyl ester side chain of these pro-drugs and the direct attack on the phosphorus center by these enzymes does not occur. Finally, we describe a novel activation pathway hitherto unknown for the activation and viral inhibitory characteristic shown by these phosphoramidate derivatives of stavudine.
- Venkatachalam,Samuel,Qazi,Uckun
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p. 452 - 466
(2007/10/03)
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- Enantioselective hydrogenation of α-aryloxy α,β- unsaturated acids. Asymmetric synthesis of α-aryloxycarboxylic acids
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(Chemical Equation Presented) A facile preparation of chiral α-aryloxy carboxylic acids via asymmetric hydrogenation of the corresponding unsaturated acids has been discovered. A number of catalysts have been identified that give high product enantioselectivity, and the scope of the reaction has been examined with respect to substitution on the aromatic ring and olefin.
- Maligres, Peter E.,Krska, Shane W.,Humphrey, Guy R.
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p. 3147 - 3150
(2007/10/03)
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- Mild cleavage of aryl mesylates: Methanesulfonate as potent protecting group for phenols
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A mild protocol for the chemoselective deprotection of aryl methanesulfonates is described. The transformation can be conducted on highly functionalized substrates and renders the methanesulfonate a useful, previously underutilized protecting group for phenols.
- Ritter, Tobias,Stanek, Kyrill,Larrosa, Igor,Carreira, Erick M.
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p. 1513 - 1514
(2007/10/03)
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- Dealkylation of alklyl and aryl ethers with AlCl3-NaI in the absence of solvent
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A facile synthetic procedure, for dealkylation of alkyl and aryl ethers with AlCl3-NaI in the absence of solvent is developed. We have been able to deprotect different methyl ethers in excellent yields.
- Ghiaci, Mehran,Asghari, Jila
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p. 973 - 979
(2007/10/03)
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- Kinetics of oxidation of phenoxyacetic acids by pyridinium hydrobromide perbromide
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The oxidation of several monosubstituted phenoxyacetic acids by pyridinium hydrobromide perbromide (PHPB) was studied in aqueous acetic acid. The reaction is first order with respect to PHPB. Michaelis-Menten-type kinetics are observed with respect to phenoxyacetic acids. The oxidation of [2,2-2H2]phenoxyacetic acid exhibits a substantial kinetic isotopic effect. The effect of solvent composition indicates that the transition state is more polar than the reactants. The formation constants of the intermediate phenoxyacetic acid-PHPB complexes and the rates of their decomposition were determined at different temperatures. The rates of oxidation of para- and meta-substituted phenoxyacetic acids were correlated with Hammett's substituent constants. The ρ value is -2.59 at 35 °C. The rates of oxidation of ortho-substituted compounds are correlated with Charton's triparametric equation. A mechanism involving transfer of a hydride ion from the substrate to the oxidant is proposed.
- Karunakaran,Elango
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p. 105 - 110
(2007/10/03)
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- Concise synthesis of taxol A-ring components: Remote diastereoselective additions of alkenyl lithiums to aldehydes
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The acid chloride 6 provides access to 7 (R,S and S,S) which upon bromine-lithium exchange undergoes remarkably highly diastereoselective additions to aldehydes; 7 is also readily elaborated into the acetal 10.
- Frost, Christopher,Linnane, Patrick,Magnus, Philip,Spyvee, Mark
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p. 9139 - 9142
(2007/10/03)
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- Novel Chlorotrimethylsilane Catalyzed Stereoselective Deconjugation of β-Bromo (or Iodo) Substituted α,β-Unsaturated Acyclic Ketone
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TMSCl catalyzed stereoselective isomerization (deconjugation) of β-substituted α,β-unsaturated ketones to the corresponding (Z)-β,γ-unsaturated ketones and its mechanism studies are described.
- Luo, Fen-Tair,Hsieh, Li-Chen
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p. 9585 - 9588
(2007/10/02)
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- Mechanism of Arene Hydroxylation by Vanadium Picolinato Peroxo Complexes
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The mechanism of the reaction of VO(O2)PIC(H2O)2 (PIC = picolinic acid anion) with benzene and substituted benzenes in CH3CN, affording the corresponding phenols together with dioxygen, has been further investigated.The reaction is a radical chain process whose initiation produces the actual oxidant which may be described as a radical anion derived from the peroxovanadium complex, possessing, however, a marked electrophilic character.In the propagation steps such species react either with the original peroxo complex yielding dioxygen or with the aromatic substrates affording phenols via the formation of an intermediate.
- Bonchio, Marcella,Conte, Valeria,Di Furia, Fulvio,Modena, Giorgio,Moro, Stefano
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p. 6262 - 6267
(2007/10/02)
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- Acid-catalysed Aromatisation of Benzene cis-1,2-dihydrodiols: a Carbocation Transition State poorly stabilised by Resonance
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Acid-catalysed dehydration of 3-substituted benzene cis-1,2-dihydrodiols exhibits a Hammett plot with ρ=-8.2, consistent with reaction via a benzenonium ion-like intermediate; however, correlation of +M resonance substituents such as Me and MeO by ?p rather than ?+ constants indicates a marked imbalance between resonance and inductive stabilisation of the transition state.
- Boyd, Derek R.,Blacker, John,Byrne, Briege,Dalton, Howard,Hand, Mark V.,et al.
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p. 313 - 314
(2007/10/02)
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- Substituted alkylamine derivatives
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The substituted alkylamine derivatives represented by formula (I) STR1 wherein R1 represents (a) substituted or unsubstituted C2-6 alkenyl group, (b) substituted or unsubstituted C3-6 cycloalkenyl group, (c) substituted or unsubstituted C2-6 alkynyl group, (d) substituted or unsubstituted aryl group, (e) substituted or unsubstituted heterocyclic group, (f) fused heterocyclic group which may be substituted, or (g) group represented by the formula Ru11 -Ar wherein R11 is a heterocyclic group and Ar is a 5- or 6-membered aromatic ring which may contain a hetero N, O or S atom, and which may be substituted; STR2 represents a 5- or 6-membered aromatic ring which may contain a hetero N, O or S atom, and may be substituted by R7, X and Y are linking groups, R2 is H or lower alkyl, R3 is hydrogen, lower alkyl, lower alkenyl, lower alkynyl or lower cycloalkyl, R4 and R5 are independently hydrogen or halogen atoms, R6 represents (a) substituted or unsubstituted acyclic hydrocarbon group which may be unsaturated, (b) substituted or unsubstituted cycloalkyl group, or (c) substituted or unsubstituted phenyl group, or non-toxic salts thereof. (E)-N-(6-6-dimethyl-2-hepten-4-ynyl)-N-ethyl-3-[4-(3-thienyl)-2-thienyl-methyloxy]benzylamine hydrochloride is a representative example. The substituted alkylamine derivatives are useful as pharmaceuticals, particularly for the treatment and prevention of hypercholesterolemia, hyperlipemia and arteriosclerosis.
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- Structural Requirements for Glyme Catalysis in Butylaminolysis of Aryl Acetates in Chlorobenzene. Identification of -OCH2CH2OCH2CH2OCH2CH2O- as the Optimal Subunit for Catalysis
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The catalytic behavior of linear (open-chain) polyethers (glymes) in butylaminolysis of 4-nitrophenyl acetate carried out in chlorobenzene has been reexamined (J.Am.Chem.Soc. 1980, 102, 2865-2866).The observation of a break in a plot of the catalytic rate constant vs chain length indicates that four oxygens in a -OCH2CH2OCH2CH2OCH2CH2O- subunit are necessary for optimal catalysis.The break, occuring at four oxygens in the profile (corresponds to triglyme), has been verified by a Hammett analysis, which employed four additional aryl acetates (3-chlorophenyl, 3-bromphenyl, 3-cyanophenyl, and 4-cyanophenyl).This break was missed in a previous study (J.Am.Chem.Soc. 1980, 102, 2865-2866) because differing amounts of impurities in the glymes increased the experimental scatter of the data.The Hammett study supports the conclusions of others that breakdown of the zwitterionic tetrahedral intermediate is rate-limiting.The break in the polyether plot implies a specific structure for a glyme-zwitterionic tetrahedral intermediate complex, which contains an ammonium ion that hydrogen bonds to the ether oxygens.
- Hogan, John C.,Gandour, Richard D.
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p. 2821 - 2826
(2007/10/02)
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- Reactions of Carbonyl Compounds in Basic Solutions. Part 13. The Mechanism of the Alkaline Hydrolysis of 3-(3-Substituted Phenoxy)phthalides, -3-methylphthalides, -3-phenylphthalides, naphthalides, -3-phenylnaphthalides, and Phenanthralides, and of 3-Substituted 3-Methoxyphthalides
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Rate coefficients have been measured for the alkaline hydrolysis of 3-(3-substituted phenoxy)phthalides, -3-methylphthalides, -3-phenylphthalides, naphthalides, -3-phenylnaphthalides, and phenanthralides at 30.0 and 50.0 deg C and for a series of methyl pseudo-2-acylbenzoates at several temperatures in 70percent (v/v) dioxane-water.The enthalpies and entropies of activation have been evaluated.The effects of substitution on the phenoxy esters have been assessed by means of the Hammett equation.The results for the methyl esters are related to the steric effect of substituentsusing the Taft equation.All the pseudo-esters are hydrolysed with rate-determining attack by hydroxide anion at the carbonyl group, followed by rapid ring fission to form the carboxylate anion of the corresponding acid as the product.Reactivity-selectivity is not shown over the whole range of the six series of the phenyl pseudo-esters.These results are discussed in terms of the structure of the transition state and the steric, stereochemical and polar factors influencing reactivity.
- Anvia, Fredrick,Bowden, Keith,Kaissi, Faiq A. El,Saez, Victoria
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p. 1809 - 1814
(2007/10/02)
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- 16-Substituted polyunsaturated hexadecanoic fatty acids
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Sixteen carbon atom carboxylic acids having 16-phenoxy or 16-phenylthio substituents, and 0, 1, or 4 triple bonds, methods of preparing them, and pharmaceutical preparations containing them. These compounds are useful as lipoxygenase inhibitors.
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