- Br?nsted Acid and H-Bond Activation in Boronic Acid Catalysis
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Boronic acid catalysis has emerged as a mild method for promoting a wide variety of reactions. It has been proposed that the mode of catalysis involves Lewis acid or covalent activation of hydroxyl groups by boron, but limited mechanistic evidence exists. In this work, representative boronic acid catalyzed reactions of alcohols and oximes have been reinvestigated. A series of control experiments with boronic and Br?nsted acids were interpreted along with correlations between their reactivity and their acidity measured by the Gutmann–Beckett method. Overall, it was concluded that the major modes of catalysis involve either dual H-bond catalysis or Br?nsted acid catalysis. Strong Br?nsted acids were shown to be generated in situ from covalent assembly of the boronic acids with hexafluoroisopropanol, explaining why the solvent had such a major impact on the reactivity. This new insight should guide the future development of boronic acid catalysis, where the diverse and solvent-specific nature of catalytic modes has been overlooked.
- Zhang, Shaofei,Leb?uf, David,Moran, Joseph
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supporting information
p. 9883 - 9888
(2020/06/10)
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- Green, Mild, and Efficient Friedel–Crafts Benzylation of Scarcely Reactive Arenes and Heteroarenes under On-Water Conditions
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Metal-free Friedel–Crafts benzylation (FCB) of scarcely reactive arenes and heteroarenes was performed under on-water conditions by an environmentally sustainable procedure. The catalytic strategy exploits the hydrophobicity of the resorcinarene macrocycle 1 a. The proposed mechanism is based on the activation of benzyl chloride by H-bonding interactions with catalyst 1 a. In fact, under on-water conditions the hydrophobic amplification of the strength of the H-bonding interactions between the OH groups of the resorcinarene catalyst and the chlorine atom of benzyl chloride leads to polarization of the C?Cl bond, which consequently promotes electrophilic attack of the π nucleophile. Thus, many arenes and heteroarenes were efficiently benzylated under mild on-water conditions by using resorcinarene 1 a as catalyst. The FCB of benzene is industrially relevant for the synthesis of diphenylmethane, and hence the on-water procedure was extended to the gram-scale synthesis of diphenylmethane, starting from benzene and benzyl chloride in the presence of resorcinarene catalyst 1 a.
- La Manna, Pellegrino,Soriente, Annunziata,De Rosa, Margherita,Buonerba, Antonio,Talotta, Carmen,Gaeta, Carmine,Neri, Placido
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p. 1673 - 1683
(2019/03/26)
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- Bisulfate Salt-Catalyzed Friedel-Crafts Benzylation of Arenes with Benzylic Alcohols
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We report here a method of direct Friedel-Crafts benzylation of arenes with benzylic alcohols using cheap and readily available bisulfate salt as the catalyst in hexafluoroisopropanol. The catalytic system is powerful with a quite diverse group of functionalized arenes and benzylic alcohols. These mild conditions provide a straightforward synthesis of a variety of unsymmetrical diarylmethanes in high yield with good to high regioselectivity. An SN1 mechanism involving activation of the hydroxy group through a hydrogen bond is proposed.
- Tang, Ren-Jin,Milcent, Thierry,Crousse, Benoit
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p. 14001 - 14009
(2018/11/23)
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- MoO3 supported on ordered mesoporous zirconium oxophosphate: An efficient and reusability solid acid catalyst for alkylation and esterification
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A series of molybdenum oxide supported on ordered mesoporous zirconium oxophosphate (MoO3/M-ZrPO) materials with different MoO3 loadings (0–20 wt%) and calcination temperatures (500–900 °C) have been designed, synthesized and employed as solid acid catalysts in alkylation and esterification. The XRD, TG-DSC, H2-TPR, N2-physisorption and TEM characterizations were taken to investigate the structural properties and states of introduced MoO3 species. The influence of MoO3 loadings and calcination temperatures in catalytic performance was detailedly investigated and optimal catalytic activity was reached at 10 wt% MoO3 loadings and treated at 700 °C. Moreover, MoO3/M-ZrPO catalysts exhibited outstanding catalytic performance in Friedel-Crafts alkylation of different aromatic compounds and esterification of levulinic acid with 1-butanol. Furthermore, it was noteworthy that the catalyst had superior reusability and no noticeable declines were observed in catalytic performance even after seven runs.
- Miao, Zhichao,Li, Zhenbin,Zhao, Jinping,Si, Weijiang,Zhou, Jin,Zhuo, Shuping
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- Benzylation with Benzyl Alcohol Catalyzed By [ChCl][TfOH]2, a Br?nsted Acidic DES with Reaction Control Self-Separation Performance
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Abstract: A deep eutectic solvent with strong Br?nsted acidity was prepared easily by choline chloride and trifluoromethanesulfonic acid. The obtained [ChCl][TfOH]2 catalyst which was characterized by FT-IR, 1H NMR and TG, possessed greatly enhanced stability than trifluoromethanesulfonic acid, and exhibited excellent catalytic performance in benzylation with benzyl alcohol. Especially, the prepared [ChCl][TfOH]2 catalyst could dissolve into the reactants to realize homogeneous catalysis, and then self-separate from the organic phase after reaction due to the entire consumption of benzyl alcohol. As a result, the catalyst could be recovered and reused simply for six-runs without noticeable loss of catalytic performance. Graphical Abstract: [Figure not available: see fulltext.].
- Yuan, Bing,Li, Yinglian,Yu, Fengli,Li, Xiaoqiang,Xie, Congxia,Yu, Shitao
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p. 2133 - 2138
(2018/05/29)
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- Mild Friedel–Crafts Reactions inside a Hexameric Resorcinarene Capsule: C?Cl Bond Activation through Hydrogen Bonding to Bridging Water Molecules
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A novel catalytic feature of a hexameric resorcinarene capsule is highlighted. The self-assembled cage was exploited to promote the Friedel–Crafts benzylation of several arenes and heteroarenes with benzyl chloride under mild conditions. Calculations showed that there are catalytically relevant hydrogen-bonding interactions between the bridging water molecules of the capsule and benzyl chloride, which is fundamental for the activation of the C?Cl bond. The capsule controls the reaction outcome. Inside the inner cavity of the capsule, N-methylpyrrole is preferentially benzylated in the unusual β-position while mesitylene reacts faster than 1,3-dimethoxybenzene despite the greater π-nucleophilicity of the latter compound.
- La Manna, Pellegrino,Talotta, Carmen,Floresta, Giuseppe,De Rosa, Margherita,Soriente, Annunziata,Rescifina, Antonio,Gaeta, Carmine,Neri, Placido
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p. 5423 - 5428
(2018/04/09)
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- A surprising substituent effect provides a superior boronic acid catalyst for mild and metal-free direct Friedel-Crafts alkylations and prenylations of neutral arenes
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The development of more general and efficient catalytic processes for Friedel-Crafts alkylations is an important objective of interest toward the production of pharmaceuticals and commodity chemicals. Herein, 2,3,4,5-tetrafluorophenylboronic acid was identified as a potent air- and moisture-tolerant metal-free catalyst that significantly improves the scope of direct Friedel-Crafts alkylations of a variety of slightly activated and neutral arenes, including polyarenes, with allylic and benzylic alcohols. This method also provides a simple alternative for the direct installation of prenyl units commonly found in naturally occurring arenes. Alkylations with benzylic alcohols occur under exceptionally mild conditions.
- Ricardo, Carolynne L.,Mo, Xiaobin,McCubbin, J. Adam,Hall, Dennis G.
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supporting information
p. 4218 - 4223
(2015/03/14)
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- Unsymmetrical diarylmethanes by ferroceniumboronic acid catalyzed direct friedel-crafts reactions with deactivated benzylic alcohols: Enhanced reactivity due to ion-pairing effects
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The development of general and more atom-economical catalytic processes for Friedel-Crafts alkylations of unactivated arenes is an important objective of interest for the production of pharmaceuticals and commodity chemicals. Ferroceniumboronic acid hexafluoroantimonate salt (1) was identified as a superior air- and moisture-tolerant catalyst for direct Friedel-Crafts alkylations of a variety of slightly activated and neutral arenes with stable and readily available primary and secondary benzylic alcohols. Compared to the use of classical metal-catalyzed alkylations with toxic benzylic halides, this methodology employs exceptionally mild conditions to provide a wide variety of unsymmetrical diarylmethanes and other 1,1-diarylalkane products in high yield with good to high regioselectivity. The optimal method, using the bench-stable ferroceniumboronic acid salt 1 in hexafluoroisopropanol as cosolvent, displays a broader scope compared to previously reported catalysts for similar Friedel-Crafts reactions of benzylic alcohols, including other boronic acids such as 2,3,4,5-tetrafluorophenylboronic acid. The efficacy of the new boronic acid catalyst was confirmed by its ability to activate primary benzylic alcohols functionalized with destabilizing electron-withdrawing groups like halides, carboxyesters, and nitro substituents. Arene benzylation was demonstrated on a gram scale at up to 1 M concentration with catalyst recovery. Mechanistic studies point toward the importance of the ionic nature of the catalyst and suggest that factors other than the Lewis acidity (pKa) of the boronic acid are at play. A SN1 mechanism is proposed where ion exchange within the initial boronate anion affords a more reactive carbocation paired with the non-nucleophilic hexafluoroantimonate counteranion.
- Mo, Xiaobin,Yakiwchuk, Joshua,Dansereau, Julien,Adam McCubbin,Hall, Dennis G.
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supporting information
p. 9694 - 9703
(2015/08/18)
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- Iron-catalyzed arylation of aromatic ketones and aldehydes mediated by organosilanes
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A simple and efficient iron-catalyzed method for arylation of aromatic carbonyl compounds is reported. The use of 4-% FeCl3 or Fe(acac) 3 as the catalyst, in combination with a slight excess of chlorotrimethylsilane and triethylsilane, chlorination of benzylic ketones and aldehydes with subsequent Friedel-Crafts alkylation of arenes is achieved. Although the method is limited by the general constraints associated with Friedel-Crafts alkylation reactions, robust applications for the synthesis of pharmaceutical intermediates and so on can be envisioned. A robust one-pot, iron-catalyzed chlorination Friedel-Crafts alkylation reaction of benzylic carbonyl compounds, mediated by chlorotrimethylsilane and triethylsilane, has been developed to yield substituted diaryl and triaryl building blocks. Copyright
- Savela, Risto,Majewski, Marcin,Leino, Reko
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p. 4137 - 4147
(2014/07/08)
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- Benzylation of arenes with benzyl ethers promoted by the in situ prepared superacid BF3-H2O
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An efficient and environmentally friendly benzylation of arenes with benzyl ethers as benzyl donors using BF3-Et2O to generate in situ the superacid BF3-H2O as an efficient promotor has been described. A wide variety of functional groups have been investigated and found to be compatible to give the desired diarylmethanes in yields of up to 99%. The crucial role of the moisture content in this transformation has been demonstrated by detailed investigations. This journal is the Partner Organisations 2014.
- Li, Yu,Xiong, Yan,Li, Xueming,Ling, Xuege,Huang, Ruofeng,Zhang, Xiaohui,Yang, Jianchun
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p. 2976 - 2981
(2014/06/10)
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- Transition metal-free domino sequential synthesis of (E)-stilbenes, biaryl methanes and biaryl ethers using Et2AlCl as a Lewis acid
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A transition metal-free domino process has been developed, for the first time, to synthesize (E)-stilbenes, biaryl methanes and biaryl ethers from substituted α,β-unsaturated ketones, benzyl acetones and phenacyl ethers, respectively, in moderate to good yields at room temperature using diethyl aluminium chloride (Et2AlCl) as a Lewis acid. The Royal Society of Chemistry 2013.
- Sarkar, Satinath,Jana, Manoranjan,Tadigoppula, Narender
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p. 18755 - 18758
(2013/10/22)
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- Synthesis of diarylmethanes via a Friedel-Crafts benzylation using arenes and benzyl alcohols in the presence of triphenylphosphine ditriflate
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Triphenylphosphine ditriflate (TPPD) was found to be an efficient promoter for the Friedel-Crafts benzylation of arenes with benzyl alcohols in CH 2Cl2 at room temperature. The good yields, the 1:1 molar ratio of arene and benzyl alcohol, the benzylation of chlorobenzene as a nonactivated aromatic compound at room temperature, and no by-product formation are the main advantages of this procedure.
- Khodaei, Mohammad Mehdi,Nazari, Ehsan
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experimental part
p. 5131 - 5135
(2012/09/22)
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- Tin exchanged heteropoly tungstate: An efficient catalyst for benzylation of arenes with benzyl alcohol
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The partial exchange of tin with the protons of 12-tungstophosphoric acid (TPA) results in a highly active heterogeneous catalyst for benzylation of arenes with benzyl alcohol as benzylating agent. The catalysts were characterized by X-ray diffraction, Laser-Raman and FT-IR of pyridine adsorption. The catalytic activity depends significantly on the extent of tin exchanged with the protons of heteropoly tungstate. The characterization results suggest the presence of Lewis acidic sites by the exchange of tin. The catalyst with partial exchange of Sn showed high benzylation activity, which in turn related to variation in acidity of the catalysts. The catalyst is highly active for benzylation reaction irrespective of the nature of substituted arenes and benzyl alcohols. These catalysts are highly active compared to other acid catalysts used for benzylation of different arenes. The catalyst is easy to separate from reaction mixture and exhibit consistent activity upon reuse. The plausible reaction mechanism based on the role of both Lewis and Bronsted acid sites of the catalyst was discussed.
- Ramesh Kumar, Ch.,Rao, K.T. Venkateswara,Sai Prasad,Lingaiah
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experimental part
p. 17 - 24
(2011/04/21)
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- Iron oxide nanoparticles grown on carboxy-functionalized graphite: An efficient reusable catalyst for alkylation of arenes
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Here we report a simple procedure for the synthesis of a novel hybrid catalyst by growing iron oxide nanoparticles on carboxy-functionalized graphite. This hybrid catalyst demonstrated superior catalytic activity towards the alkylation of arenes with alkyl halides in contrast to commercial graphite or unsupported iron oxide nanoparticles in terms of yields and general applicability. The catalyst can be reused up to five times with a minimal loss of catalytic activity. Georg Thieme Verlag Stuttgart.
- Rajpara, Vikul,Banerjee, Subhash,Sereda, Grigoriy
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experimental part
p. 2835 - 2840
(2010/10/04)
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- Synthesis of early-transition-metal carbide and nitride nanoparticles through the urea route and their use as alkylation catalysts
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The use of urea as either a carbon or a nitrogen source enabled the synthesis of various early-transition-metal nitride and carbide nanoparticles (TiN, NbN, Mo2N, 2N, NbCxN1-x, Mo2 C and WC). The abil
- Yao, Weitang,Makowski, Philippe,Giordano, Cristina,Goettmann, Frederic
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scheme or table
p. 11999 - 12004
(2010/05/19)
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- Benzylation of arenes through FeCl3-catalyzed Friedel-Crafts reaction via C-O activation of benzyl ether
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Various benzyl ethers were converted to benzyl arenes via a FeCl3-catalyzed Friedel-Crafts alkylation reaction under mild condition in good yields. This method also offered a simple and practical approach to synthesize di- or tri-aryl methanes and aryl heteroaryl methanes through the activation of C-O bonds.
- Wang, Bi-Qin,Xiang, Shi-Kai,Sun, Zuo-Peng,Guan, Bing-Tao,Hu, Ping,Zhao, Ke-Qing,Shi, Zhang-Jie
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p. 4310 - 4312
(2008/09/21)
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- Molecular iodine-catalyzed benzylation of arenes with benzyl alcohols
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A novel molecular iodine-catalyzed benzylation of arenes with benzyl alcohols has been developed. The reaction can be carried out under mild conditions to afford a series of diarymethane derivatives in high yields and good regioselectivities.
- Sun, Gaojun,Wang, Zhiyong
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p. 4929 - 4932
(2008/09/21)
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- An efficient synthesis of unsymmetrical diarylmethanes from the dehydration of arenes with benzyl alcohols using InCl3·4H2O/acetylacetone catalyst system
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An efficient and practical synthesis of unsymmetrical diarylmethanes has been achieved from the dehydration of arenes with benzyl alcohols in the presence of catalytic amount of InCl3·4H2O/acetylacetone.
- Sun, Hong-Bin,Li, Biao,Chen, Songjie,Li, Jie,Hua, Ruimao
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p. 10185 - 10188
(2008/02/13)
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- Versatile mesoporous carbonaceous materials for acid catalysis
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Starbon mesoporous materials were synthesized after pyrolysis of expanded starch and subsequently functionalised with sulfonated groups, providing highly active and reusable materials in various acid catalysed reactions. The Royal Society of Chemistry.
- Budarin, Vitaly L.,Clark, James H.,Luque, Rafael,Macquarrie, Duncan J.
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p. 634 - 636
(2007/10/03)
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- An efficient and inexpensive catalyst system for friedel-crafts alkylation of aromatic compounds with benzyl and allyl alcohols
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An new strategy that uses Ce2(SO4)3 as an effective catalyst for Friedel-Crafts alkylation of aromatic compounds with benzyl and allyl alcohols is presented. In the presence of 1 to 10 mol% of Ce2(SO4)3, Friedel-Crafts alkylation with both benzyl alcohols, including primary and secondary benzyl alcohols, and allyl alcohol were carried out smoothly and efficiently. Moreover, the catalyst was recovered and reused three times without significant loss of activity.
- Li, Jin-Heng,Liu, Wen-Jie,Yin, Du-Lin
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p. 3161 - 3165
(2007/10/03)
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- Friedel-Crafts Benzylation and Phenethylation Reactions Using Benzyl and Phenethyl Benzothiazol-2-yl Carbonate Derivatives
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Friedel-Crafts benzylation and phenethylation reactions of several aromatic compounds with benzyl and phenethyl benzothiazol-2-yl carbonate derivatives were carried out in the presence of scandium triflate (Sc(OTf) 3) as a catalyst. Suitable combinations of the leaving group of carbonates and acid promoters that generate cationic alkyl species were examined.
- Mukaiyama, Teruaki,Kamiyama, Hiroaki,Yamanaka, Hiroyuki
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p. 814 - 815
(2007/10/03)
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- Ruthenium complex-catalyzed novel transformation of alkyl formates
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The following ruthenium-catalyzed novel transformations of alkyl formates have been developed: (1) selective decarbonylation of alkyl formates to the corresponding alcohols; (2) alkylation of arenes and alkenes using alkyl formates as an alkylating reagent via decarboxylation.Also the ruthenium-catalyzed addition of alcohols to alkenes has been developed as an appendant reaction, providing an effective method for the protection of alcohols.Keywords: Ruthenium; Catalysis; Alkyl; Arene; Alkene; Alcohol
- Kondo, Teruyuki,Kajiya, Satoshi,Tantayanon, Supawan,Watanabe, Yoshihisa
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- Hafnium(IV)Trifluoromethanesulfonate, An Efficient Catalyst for the Friedel-Crafts Acylation and Alkylation Reactions
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Hafnium(IV) trifluoromethanesulfonate (hafnium(IV) triflate, Hf(OTf)4) was synthesized from hafnium tetrachloride and trifluoromethanesulfonic acid.The triflate thus prepared was found to be effective in the catalytic Friedel-Crafts acylation reactions of various substituted benzenes with acid anhydrides in lithium perchlorate-nitromethane (LiClO4-MeNO2).Lithium perchlorate-nitromethane is an excellent solvent system, and the catalytic activity of the Lewis acid was much improved in this medium.The product was obtained in up to 250000percent molar amounts baaed on the catalyst.Hafnium(IV) triflate was also found to be quite effective in the catalytic Friedel-Crafts alkylation reactions of aromatic compounds with alkyl chlorides.The reactions proceeded smoothly in the presence of 5percent molar amount of Hf(OTf)4 and 50percent molar amount of LiClO4 by using a slow addition procedure.
- Hachiya, Iwao,Moriwaki, Mitsuhiro,Kobayashi, Shu
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p. 2053 - 2060
(2007/10/02)
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- Perfluorooctanesulfonic acid catalyzed Friedel-Crafts alkylation with alkyl halides
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A new procedure to prepare superacid perfluorooctanesulfonic acid (POSA) is reported. POSA catalyzed Friedel-Crafts alkylation of aromatic compounds with alkyl halides in liquid-phase reactions. Alkylation gave higher total yields than the corresponding reactions with Nafion-H, without the need of any complex decomposition or work-up. The reactions do not need to be carried out under absolutely anhydrous condition. The catalyst POSA can be easily separated from the reaction mixture and reused or recovered. The reactivity of the alkylation reagents and the mechanism of the reaction are discussed.
- Fu,He,Lei,Luo
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p. 1273 - 1279
(2007/10/02)
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- RUTHENIUM COMPLEX CATALYZED BENZYLATION OF ARENES WITH BENZYL FORMATES; DECARBONYLATION AND DECARBOXYLATION OF ALKYL FORMATES
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Ru3(CO)12-(CH3)3NO*2H2O showed high catalytic activity for the decarbonylation of alkyl formates to the corresponding alcohols at 150 -200 deg C under an argon atmosphere.Decarbonylation of β-phenetyl formate afforded β-phenetyl alcohol in 82 percent yield.On the other hand, when decarbonylation of benzyl formate was performed in the absence of (CH3)3NO*2H2O, benzylation of arenes, which were employed as a solvent, proceeded via catalytic decarboxylation of benzyl formate.For the reaction of toluene with benzyl formate, phenyltolylmethane (o-, m-, and p-mixture) was obtained in total 77 percent yield.
- Kondo, Teruyuki,Tantayanon, Supawan,Tsuji, Yasushi,Watanabe, Yoshihisa
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p. 4137 - 4140
(2007/10/02)
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- ACTIVATION BY PdCl2(PhCN)2 OF THE ALCOHOLIC BENZYLIC FUNCTION TO NUCLEOPHILIC ALIPHATIC AS WELL AS ELECTROPHILIC AROMATIC SUBSTITUTIONS. A ONE STEP SYNTHESIS OF A CHROMANE STRUCTURE
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Benzylic alcohols react, by activation with PdCl2(PhCN)2, under mild conditions with alkanols and enols to give the corresponding benzylic ethers, and, under the same conditions, with aromatic substrates to give the corresponding phenylmethanes.As an example, a one-step synthesis of a chromane structure is reported.
- Mincione, Enrico,Bovicelli, Paolo
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p. 437 - 440
(2007/10/02)
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- PREPARATION OF SOME TRIMETHYL- AND METHYLETHYLBIPHENYLS AND REACTIVITY OF AROMATIC HYDROCARBONS IN THE GOMBERG REACTION
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Trimethyl- and methylethylbiphenyls with the alkyl groups in the both phenyl rings have been prepared by the Gomberg reaction and identified by the capillary gas-liquid chromatography.Depending on choice of the aromatic hydrocarbon either individual isomers or their mixtures (three at the most) have been obtained which were contaminated with compounds of diarylmethane type in many cases.The methylethylbiphenyls have only been prepared as mixtures contaminated with diarylmethanes.These side products have been prepared by independent syntheses.A method has been developed for isolation and separation of mixtures of trimethyl- and methylethylbiphenyls from the reaction products containing tarry products.The method is suitable for preparation of small amounts of some analytical standards.The HMO method has been used for calculation of values of the radical superdelocalizabilities at individual centres in the molecules of o-, m- and p-xylene, toluene and ethylbenzene, and these values have been compared with composition of the Gomberg reaction products from these hydrocarbons.The competitive technique has been used for comparison of the reactivities of the mentioned aromatic substrates in the Gomberg reactions.
- Novrocik, Jan,Novrocikova, Marta,Titz, Milos
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p. 3140 - 3149
(2007/10/02)
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