- Direct Nucleophilic Substitution of Alcohols Using an Immobilized Oxovanadium Catalyst
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Direct nucleophilic substitution of alcohols with thiols or carbon nucleophiles was achieved using a mesoporous silica-supported oxovanadium catalyst (VMPS4). Benzyl and allyl alcohols were compatible in this reaction under mild conditions, affording the products in high yields. The VMPS4 catalyst showed excellent chemoselectivity toward alcohols in the presence of acid-labile functional groups, which is in contrast to that observed for the commonly used Lewis acid catalysts, which exhibit poor selectivity. The VMPS4 catalyst could be recycled by simple centrifugation, and the catalytic activity was maintained over seven cycles.
- Nishio, Tomoya,Yoshioka, Shin,Hasegawa, Kai,Yahata, Kenzo,Kanomata, Kyohei,Akai, Shuji
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p. 4417 - 4422
(2021/07/16)
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- Continuous-Flow Dynamic Kinetic Resolution of Racemic Alcohols by Lipase–Oxovanadium Cocatalysis
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A continuous-flow dynamic kinetic resolution of racemic secondary alcohols was carried out using a single column reactor packed with a mixture of immobilized lipase and an immobilized oxovanadium species, VMPS4. As a result, optically pure esters were produced in 88–92 % yields. Problems encountered in this study were overcome by using fillers that efficiently maintained the initial distribution of the catalysts in the reactor and by using a packing method in which the mixing ratio of the two catalysts was varied in a stepwise fashion. The flow process led to an increased turnover number of each catalyst compared to those of batch reactions.
- Adebar, Niklas,Akai, Shuji,Gr?ger, Harald,Higashio, Koichi,Kühn, Franziska,Katsuragi, Satoko,Kundu, Dhiman,Plass, Carmen
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supporting information
p. 1961 - 1967
(2020/04/09)
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- Iodine-catalyzed transformation of aryl-substituted alcohols under solvent-free and highly concentrated reaction conditions
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Iodine-catalyzed transformations of alcohols under solvent-free reaction conditions (SFRC) and under highly concentrated reaction conditions (HCRC) in the presence of various solvents were studied in order to gain insight into the behavior of the reaction intermediates under these conditions. Dimerization, dehydration and substitution were the three types of transformations observed with benzylic alcohols. Dimerization and substitution reactions were predominant in the case of primary- and secondary alcohols, whereas dehydration prevailed in the case of tertiary alcohols. The relative reactivity of substituted 1-phenylethanols in I2-catalyzed dimerization under SFRC provided a good Hammett plot ρ+ = -2.8 (r2 = 0.98), suggesting the presence of electron-deficient intermediates with a certain degree of developed charge in the rate-determining step.
- Jereb, Marjan,Vra?i?, Dejan
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p. 747 - 762
(2018/01/17)
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- Ether formation through reductive coupling of ketones or aldehydes catalyzed by a mesoionic carbene iridium complex
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An iridium(iii) Cp? complex containing a triazolylidene-pyridyl C,N-bidentate-coordinating ligand is a very powerful catalyst for the transformation of ketones and aldehydes into symmetrical ethers. This highly efficient reductive coupling proceeds immediately at room temperature and at a low catalyst loading (0.1 mol%) when Ph2SiH2 is used as an additive. Aromatic carbonyl substrates react faster than aliphatic ketones or aldehydes, and the substrate scope suggests some functional group tolerance. Likewise, the condensation of alcohols to symmetrical ethers is catalyzed by this triazolylidene iridium complex, though ether formation is an order of magnitude slower than when starting from the analogous ketone or aldehyde as a substrate, suggesting that alcohols are not potential intermediates in the reductive coupling process. Prolonged reactions or modification of the silane additive lead to ether cleavage and dehydration, thus affording the corresponding olefin. Mechanistic insights and in particular the different reactivities of alcohols and ketones have been exploited to develop a synthetic methodology for the iridium-catalyzed formation of unsymmetrical methyl ethers (R-OMe) in good yields.
- Petronilho,Vivancos,Albrecht
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p. 5766 - 5774
(2017/12/07)
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- Selective synthesis of thioethers in the presence of a transition-metal-free solid Lewis acid
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The synthesis of thioethers starting from alcohols and thiols in the presence of amorphous solid acid catalysts is reported. A silica alumina catalyst with a very low content in alumina gave excellent results in terms of both activity and selectivity also under solvent-free conditions. The reaction rate follows the electron density of the carbinol atom in the substrate alcohol and yields up to 99% and can be obtained for a wide range of substrates under mild reaction conditions.
- Santoro, Federica,Mariani, Matteo,Zaccheria, Federica,Psaro, Rinaldo,Ravasio, Nicoletta
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supporting information
p. 2627 - 2635
(2017/01/09)
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- Competition of C-H and C-O fragmentation in substituted p-methoxybenzyl ether radical cations generated by photosensitized oxidation
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Laser and steady-state photolysis, sensitized by 2,4,6-triphenylpyrylium tetrafluoroborate (TPP+BF4-), of 4-methoxybenzyl ethers [4-CH3O-C6H4CH(OR 1)R, 1a: R = H, R1 = CH3; 1b: R = H, R 1 = C(CH3)3; 1c: R = CH3, R 1 = C(CH3)3; 1d: R = 4-CH3O-C 6H4, R1 = CH3] was carried out in CH3CN in the presence of oxygen. In particular, steady-state irradiation of 1a, b and d produced benzylic alcohols (together with a small amount of acetamide for 1a and 1b) and the oxidation carbonyl compounds (esters and ketones); 4-methoxy-α-methylbenzyl alcohol was the only product observed with 1c. Time-resolved investigations of 1c and 1d gave evidence of the intermediate benzylic carbocation, coming from the ether radical cation formed within the laser pulse by an electron transfer process from the ether to the TPP+ excited state. These results suggested that, besides the deprotonation of the benzyl carbon, the cleavage of the C-OR1 bond is also operative in the reaction pathways of the ether radical cation. The comparison of these results with those obtained in the photolysis of 1c with the uncharged 9,10-dicyanoanthracene (DCA) upholds a particular behavior of TPP+BF4-, probably due to the specific electrostatic interactions of BF4- with the radical cation. This is also supported by quantum mechanical calculation results performed at the B3LYP/6-31G(d) level to obtain the charge and spin density distributions of radical cations, free and complexed with BF4 -.
- Carlotti, Benedetta,Del Giacco, Tiziana,Elisei, Fausto
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p. 489 - 499
(2013/07/11)
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- Mesoporous nickel-aluminosilicate nanocomposite: A solid acid catalyst for ether synthesis
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Mesoporous nickel aluminosilicate, a solid acid catalyst prepared by sol-gel technique was utilized as a heterogeneous catalyst for the synthesis of symmetrical ethers by dehydro-condensation of alcohols. The prepared catalysts were characterized by Fourier-transform infra red spectroscopy (FT-IR), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), N2 adsorption-desorption analysis, temperature programmed desorption of ammonia (TPD) and X-ray photoelectron spectroscopic techniques. The presence of the catalyst assisted the etherification reaction in 30 minutes. Ethers formed in these reactions were quantified by gas chromatography (GC) and the identities of few of them were confirmed by nuclear magnetic resonance spectral data (NMR). Copyright
- Neelakandeswari,Karvembu,Dharmaraj
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p. 2853 - 2863
(2013/08/25)
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- Sodium bisulfite: An efficient catalyst for ether formation via dehydration of aromatic/aliphatic alcohol
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Straightforward etherification of benzyl alcohols (1) via intermolecular dehydration can be efficiently catalyzed by sodium bisulfite under solvent-free conditions. In the presence of 0.3 mol% or 0.6 mol% amount of sodium bisulfite, symmetric and unsymmetric ethers are prepared from the corresponding alcohols in high yields (up to 95%). Etherification of benzhydryl alcohols is also discussed. Copyright
- Wang, Hui,Zhu, Xingfei,Lu, Yangning,Li, Yue,Gao, Xiang
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p. 1180 - 1184
(2012/04/23)
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- Dual behavior of alcohols in iodine-catalyzed esterification under solvent-free reaction conditions
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The dual behavior phenomenon of alcohols in iodine-catalyzed esterification under solvent-free reaction conditions (SFRCs) is described; the governing factor is the stability of the carbonium ion generated from the alcohol; high concentration reaction conditions (HCRCs) or dilute solutions are much less suitable. In the case of benzylic alcohols, loss of optical activity was noted, whereas alkyl alcohols furnished a product with retention of stereochemistry.
- Jereb, Marjan,Vra?i?, Dejan,Zupan, Marko
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scheme or table
p. 2347 - 2352
(2009/09/06)
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- Anomalous reactivity of radical cations produced by photosensitized oxidation of 4-methoxybenzyl alcohol derivatives: Role of the sensitizer
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Steady-state and nanosecond laser flash photolysis measurements of 4-methoxybenzyl alcohol (1a), 4-methoxy-α-methylbenzyl alcohol (1b), 4,4′-dimethoxydiphenylmethanol (1c) and 4-methoxy-α,α′- dimethylbenzyl alcohol (1d) were carried out in air-equilibrated CH 2Cl2 and CH3CN solutions, in the presence of 9,10-dicyanoanthracene (DCA) and N-methylquinolinium tetrafluoroborate (NMQ +BF4-) as sensitizers. In particular, steady-state irradiation with DCA produced carbonyl compounds and, with NMQ +BF4-, carbonyl compounds, ethers (substrates 1a-c) and styrene (substrate 1d) while time-resolved investigations gave evidence of charged species produced upon irradiation. The effect of solvent polarity on the reactivity was investigated; in the case of DCA, the reactivity increased with the solvent polarity, while the opposite was obtained when NMQ+BF4- was used. Quantum mechanical calculations at semiempirical (INDO/1-CI) and DFT (B3LYP/6-311G(d)) levels were used to support transient assignments and to obtain the charge and spin density distributions, respectively. The different photooxidation mechanisms operative with the neutral and charged sensitizer were rationalized in terms of the reactivity of free and complexed radical cations, respectively. the Owner Societies.
- Del Giacco, Tiziana,Faltoni, Annalisa,Elisei, Fausto
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p. 200 - 210
(2008/09/20)
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- A general method for the preparation of ethers using water-resistant solid lewis acids
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(Chemical Equation Presented) This most ethereal of cascades: Water-resistant single isolated Lewis acids within the framework of molecular sieves act as excellent general catalysts for the synthesis of ethers (see scheme). On this basis, an environmentally friendly process has been developed for the preparation of fine chemicals that involves a one-pot Meerwein-Ponndorf-Verley reduction/etherification cascade.
- Corma, Avelino,Renz, Michael
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p. 298 - 300
(2008/02/08)
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- Metal triflate-catalyzed cationic benzylation and allylation of 1,3-dicarbonyl compounds
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(Chemical Equation Presented) The rare earth metal and hafnium triflate-catalyzed secondary benzylation and allylation of 1,3-diketones, ketoesters, and ketoamides are described. The procedure was carried out under non-anhydrous conditions. Various 1-phenylethyl cations were generated from substituted 1-phenylethanols using 0.5 mol % of the metal triflates in CH 3NO2. The cations reacted with 1,3-diketones and ketoesters to give benzylated products in high yields. Following the GC analysis, the reaction conditions were easily optimized by the selection of catalysts based on the Lewis acidity of the triflates and reaction temperature. A tertiary-alkylated diketone and a corresponding ketoester were also benzylated to afford products with a quaternary carbon atom in 57-84% yield. The ketoamide reactions required stronger Lewis acids than those used in the diketone and ketoester reactions. The reactions of benzylic alcohols possessing various substituents on the aromatic ring and dibenzoylmethane (2b) as a diketone were examined in the presence of Hf(OTf)4. Electron-rich benzylic alcohols reacted with 2b in 86-96% yield, and electron-deficient alcohol gave the desired product in 79-65% yield. Despite possessing a strong electron-withdrawing group, the reaction of 1-(4-nitrophenyl)ethanol gave the corresponding product in 61% yield. It was also possible to use allylic alcohols directly for the allylation of diketone 2b. The catalyst can be recovered by water extraction and reused up to five times.
- Noji, Masahiro,Konno, Yosuke,Ishii, Keitaro
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p. 5161 - 5167
(2008/02/07)
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- Zirconium tetrachloride catalysed synthesis of symmetric and unsymmetric ethers from secondary benzylic alcohols
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Secondary benzylic alcohols are coupled in the presence of zirconium tetrachloride to afford the corresponding symmetrical ethers in good yields. Unsymmetric ethers are obtained with good selectivity by condensation of two different secondary benzylic alcohols under the action of the same catalyst.
- Das, Biswanath,Krishnaiah, Maddeboina,Veeranjaneyulu, Boyapati,Srinivas, Yallamalla,Rao, Yerra Koteswara
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p. 717 - 719
(2008/09/20)
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- ANOMALOUS REDUCTION OF ALIPHATIC-AROMATIC KETONES BY THE COMPLEX HYDRIDES OF BORON
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During the reduction of XC6H4COCH3 by the action of sodium borohydride or potassium borohydride in a water-methanol medium the ethers XC6H4CH(OCH3)CH3 and not the corresponding alcohols were obtained.The formation of the ethers indicates that the O-Calkyl (and not O-B) bond is broken in the intermediate tetraalkoxyborate if a stable carbocation of the benzylic type, further stabilized by an electron-donor group at the ortho or para position of the benzene ring, is formed.
- Dem'yanovich, V.M.,Khlebnikov, V.A.
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p. 255 - 259
(2007/10/02)
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- Reactivity-Selectivity in the Swern Oxidation of Alcohols Using Dimethyl Sulfoxide-Oxalyl Chloride
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The competitive oxidation of a mixture of two alcohols by less than an equivalent amount of oxidant under the conditions developed by Swern (reaction of the alcohol at -60 deg C with Me2SCl+Cl- (4) generated from (COCl)2 and Me2SO in CH2Cl2 followed by re
- Marx, Michael,Tidwell, Thomas T.
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p. 788 - 793
(2007/10/02)
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