- Regioselective N-Functionalization of Tautomerizable Heterocycles through Methyl Trifluoromethanesulfonate-Catalyzed Substitution of Alcohols and Alkyl Group Migrations
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A catalytic synthetic strategy has been developed combining two protocols, such as, direct nucleophilic substitution of alcohols followed by X- to N- alkyl group migration (X=O, S) to access N-functionalized benzoxazolones, benzothiazolethiones, indolinone, benzoimidazolethiones, and pyridinones derivatives. Methyl trifluoromethanesulfonate (MeOTf) was found to catalyze the reaction, which revealed the catalytic property of MeOTf. A mechanism was established through experiments as well as DFT calculations wherein the ?OH group of alcohols were converted to the corresponding ?OMe groups and in situ generated TfOH. The ?OMe groups produced underwent TfOH catalyzed ?X alkylation (X=O, S) of the heterocycles followed by ?X- to ?N-alkyl group migrations in a single step. (Figure presented.).
- Biswas, Srijit,Biswas, Subrata,Duari, Surajit,Elsharif, Asma M.,Maity, Srabani,Mishra, Abhishek Kumar,Morgon, Nelson H.,Roy, Arnab,de Souza, Aguinaldo R.
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- Multiple Mechanisms Mapped in Aryl Alkyl Ether Cleavage via Aqueous Electrocatalytic Hydrogenation over Skeletal Nickel
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We present here detailed mechanistic studies of electrocatalytic hydrogenation (ECH) in aqueous solution over skeletal nickel cathodes to probe the various paths of reductive catalytic C-O bond cleavage among functionalized aryl ethers relevant to energy science. Heterogeneous catalytic hydrogenolysis of aryl ethers is important both in hydrodeoxygenation of fossil fuels and in upgrading of lignin from biomass. The presence or absence of simple functionalities such as carbonyl, hydroxyl, methyl, or methoxyl groups is known to cause dramatic shifts in reactivity and cleavage selectivity between sp3 C-O and sp2 C-O bonds. Specifically, reported hydrogenolysis studies with Ni and other catalysts have hinted at different cleavage mechanisms for the C-O ether bonds in α-keto and α-hydroxy β-O-4 type aryl ether linkages of lignin. Our new rate, selectivity, and isotopic labeling results from ECH reactions confirm that these aryl ethers undergo C-O cleavage via distinct paths. For the simple 2-phenoxy-1-phenylethane or its alcohol congener, 2-phenoxy-1-phenylethanol, the benzylic site is activated via Ni C-H insertion, followed by beta elimination of the phenoxide leaving group. But in the case of the ketone, 2-phenoxyacetophenone, the polarized carbonyl πsystem apparently binds directly with the electron rich Ni cathode surface without breaking the aromaticity of the neighboring phenyl ring, leading to rapid cleavage. Substituent steric and electronic perturbations across a broad range of β-O-4 type ethers create a hierarchy of cleavage rates that supports these mechanistic ideas while offering guidance to allow rational design of the catalytic method. On the basis of the new insights, the usage of cosolvent acetone is shown to enable control of product selectivity.
- Hegg, Eric L.,Jackson, James E.,Klinger, Grace E.,Saffron, Christopher M.,Zhou, Yuting
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p. 4037 - 4050
(2020/03/10)
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- Palladium-Catalyzed Alkoxycarbonylation of sec-Benzylic Ethers
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Herein, we report the palladium-catalyzed synthesis of 3-arylpropionate esters starting from secondary benzylic ethers. With this investigation it could be shown that ethers are suitable starting materials in addition to the established carbonylation reactions of olefins, alcohols, or aryl halides.
- Beller, Matthias,Jackstell, Ralf,Maes, Bert U. W.,Schneider, Carolin
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supporting information
(2020/02/25)
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- In Situ Generation of Br?nsted Acidity in the Pd-I Bifunctional Catalysts for Selective Reductive Etherification of Carbonyl Compounds under Mild Conditions
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Selective synthesis of ethers from biomass-derived carbonyl compounds is an important academic and industrial challenge. The existing processes based on strong acid or metallic catalysts cannot provide high selectivity to ethers due to the occurrence of side reactions. Hereby we propose a Pd-I bifunctional heterogeneous catalyst for the selective reductive etherification of aldehydes with alcohols. Extensive catalyst characterizations uncovered the presence of iodine species on the surface of Pd nanoparticles. Heterolytic dissociation of hydrogen on the I-Pd surface sites leads to the "in situ" generation of a Br?nsted acid, which promotes the reaction toward the corresponding ethers with extremely high selectivity under very mild reaction conditions.
- Wu, Dan,Hernández, Willinton Y.,Zhang, Songwei,Vovk, Evgeny I.,Zhou, Xiaohong,Yang, Yong,Khodakov, Andrei Y.,Ordomsky, Vitaly V.
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p. 2940 - 2948
(2019/04/13)
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- Auto-Tandem Catalysis with Frustrated Lewis Pairs for Reductive Etherification of Aldehydes and Ketones
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Herein we report that a single frustrated Lewis pair (FLP) catalyst can promote the reductive etherification of aldehydes and ketones. The reaction does not require an exogenous acid catalyst, but the combined action of FLP on H2, R-OH or H2O generates the required Br?nsted acid in a reversible, “turn on” manner. The method is not only a complementary metal-free reductive etherification, but also a niche procedure for ethers that would be either synthetically inconvenient or even intractable to access by alternative synthetic protocols.
- Bakos, Mária,Gy?m?re, ádám,Domján, Attila,Soós, Tibor
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supporting information
p. 5217 - 5221
(2017/04/27)
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- Oxidation of Secondary Methyl Ethers to Ketones
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We present a mild way of converting secondary methyl ethers into ketones using calcium hypochlorite in aqueous acetonitrile with acetic acid as activator. The reaction is compatible with various oxygen- and nitrogen-containing functional groups and afforded the corresponding ketones in up to 98% yield. The use of this methodology could expand the application of the methyl group as a useful protecting group.
- Gilissen, Pieter J.,Blanco-Ania, Daniel,Rutjes, Floris P. J. T.
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supporting information
p. 6671 - 6679
(2017/07/15)
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- Cleavage of the lignin β-O-4 ether bond: Via a dehydroxylation-hydrogenation strategy over a NiMo sulfide catalyst
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The efficient cleavage of lignin β-O-4 ether bonds to produce aromatics is a challenging and attractive topic. Recently a growing number of studies have revealed that the initial oxidation of CαHOH to CαO can decrease the β-O-4 bond dissociation energy (BDE) from 274.0 kJ mol-1 to 227.8 kJ mol-1, and thus the β-O-4 bond is more readily cleaved in the subsequent transfer hydrogenation, or acidolysis. Here we show that the first reaction step, except in the above-mentioned pre-oxidation methods, can be a Cα-OH bond dehydroxylation to form a radical intermediate on the acid-redox site of a NiMo sulfide catalyst. The formation of a Cα radical greatly decreases the Cβ-OPh BDE from 274.0 kJ mol-1 to 66.9 kJ mol-1 thereby facilitating its cleavage to styrene, phenols and ethers with H2 and an alcohol solvent. This is supported by control experiments using several reaction intermediates as reactants, analysis of product generation and by radical trap with TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy) as well as by density functional theory (DFT) calculations. The dehydroxylation-hydrogenation reaction is conducted under non-oxidative conditions, which are beneficial for stabilizing phenol products.
- Zhang, Chaofeng,Lu, Jianmin,Zhang, Xiaochen,Macarthur, Katherine,Heggen, Marc,Li, Hongji,Wang, Feng
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p. 6545 - 6555
(2018/06/06)
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- Thermal hazard evaluation of cumene hydroperoxide-metal ion mixture using DSC, TAM III, and GC/MS
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Cumene hydroperoxide (CHP) is widely used in chemical processes, mainly as an initiator for the polymerization of acrylonitrile-butadiene-styrene. It is a typical organic peroxide and an explosive substance. It is susceptible to thermal decomposition and is readily affected by contamination; moreover, it has high thermal sensitivity. The reactor tank, transit storage vessel, and pipeline used for manufacturing and transporting this substance are made of metal. Metal containers used in chemical processes can be damaged through aging, wear, erosion, and corrosion; furthermore, the containers might release metal ions. In a metal pipeline, CHP may cause incompatibility reactions because of catalyzed exothermic reactions. This paper discusses and elucidates the potential thermal hazard of a mixture of CHP and an incompatible material's metal ions. Differential scanning calorimetry (DSC) and thermal activity monitor III (TAM III) were employed to preliminarily explore and narrate the thermal hazard at the constant temperature environment. The substance was diluted and analyzed by using a gas chromatography spectrometer (GC) and gas chromatography/mass spectrometer (GC/MS) to determine the effect of thermal cracking and metal ions of CHP. The thermokinetic parameter values obtained from the experiments are discussed; the results can be used for designing an inherently safer process. As a result, the paper finds that the most hazards are in the reaction of CHP with Fe2+. When the metal release is exothermic in advance, the system temperature increases, even leading to uncontrollable levels, and the process may slip out of control.
- You, Mei-Li
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- Cooperative Catalysis of Noncompatible Catalysts through Compartmentalization: Wacker Oxidation and Enzymatic Reduction in a One-Pot Process in Aqueous Media
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A Wacker oxidation using CuCl/PdCl2 as a catalyst system was successfully combined with an enzymatic ketone reduction to convert styrene enantioselectively into 1-phenylethanol in a one-pot process, although the two reactions conducted in aqueous media are not compatible due to enzyme deactivation by Cu ions. The one-pot feasibility was achieved via compartmentalization of the reactions. Conducting the Wacker oxidation in the interior of a polydimethylsiloxane thimble enables diffusion of only the organic substrate and product into the exterior where the biotransformation takes place. Thus, the Cu ions detrimental to the enzyme are withheld from the reaction media of the biotransformation. In this one-pot process, which formally corresponds to an asymmetric hydration of alkenes, a range of 1-arylethanols were formed with high conversions and 98-99% ee. In addition, the catalyst system of the Wacker oxidation was recycled 15 times without significant decrease in conversion.
- Sato, Hirofumi,Hummel, Werner,Gr?ger, Harald
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supporting information
p. 4488 - 4492
(2015/04/14)
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- Carbon-supported iron-ionic liquid: An efficient and recyclable catalyst for benzylation of 1,3-dicarbonyl compounds with alcohols
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The effect of the addition of ILs with non-coordinating anions on the iron-catalyzed benzylation of 1,3-dicarbonyl compounds with alcohols under solvent free conditions has been evaluated. Among them, the presence of those containing the bistriflimide anion was found to be crucial for selectivity towards the benzylated product in a homogenous reaction. Therefore, the catalytic activity of Fe(OTf)3-N4111NTf2 combination supported on carbon materials with different textural and chemical surface properties has been studied. In the heterogeneous phase, reaction selectivity was also enhanced by the addition of the IL. However, substantial differences between the activities of different Fe-IL/carbon material catalytic systems were observed, indicating the influence of carbon support properties. With regards to selectivity, the best results were obtained using carbon supports with low microporosity. Moreover, the presence of oxygen functional groups on the carbon surface improved catalyst recycling. the Partner Organisations 2014.
- Moriel,Garcia
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supporting information
p. 4306 - 4311
(2014/10/16)
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- Hydroalkoxylation of unactivated olefins with carbon radicals and carbocation species as key intermediates
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A unique Markovnikov hydroalkoxylation of unactivated olefins with a cobalt complex, silane, and N-fluoropyridinium salt is reported. Further optimization of reaction conditions yielded high functional group tolerance and versatility of alcoholic solvent employed, including methanol, i-propanol, and t-butanol. Use of trifluorotoluene as a solvent made the use of alcohol in stoichiometric amount possible. Mechanistic insight into this novel catalytic system is also discussed. Experimental results suggest that catalysis involves both carbon radical and carbocation intermediates.
- Shigehisa, Hiroki,Aoki, Tatsuya,Yamaguchi, Sumiko,Shimizu, Nao,Hiroya, Kou
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supporting information
p. 10306 - 10309
(2013/08/23)
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- CATALYTIC C-H BOND ACTIVATION FOR THE SYNTHESIS OF ETHERS AND THIOETHERS
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Disclosed is a method for the transition metal-mediated oxidation of C-H bonds to form C-0 or C-S bonds. The methods are useful for the formation of ethers (R-OR') from alcohols, R'OH, and sp3 -hybridized C-H bonds in substrates, R-H. Aryl or heteroaryl acetates may also be used for C-H to C-OAr bond formation. The methods are also useful in the preparation of C-S bonds from acetyl-protected thiols, MeC(0)SR, and disulfides, RSSR. Advantageously, the methods minimize reaction steps, the handling of oxidized intermediates, and environmental impact.
- -
-
Page/Page column 5-6; 51
(2014/01/08)
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- Novel gallium and indium salts of the 12-tungstophosphoric acid: Synthesis, characterization and catalytic properties
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The objective of this study was the preparation, characterization and testing of the catalytic properties of the GaPW12O40 and InPW12O40 salts of 12-tungstophosphoric heteropolyacid (HPW). The samples were characterized by XRD, IR, SEM, and 31P and 1H MAS NMR spectroscopy. The acid properties of the solids were directly accounted for by applying 1H MAS NMR. The salts were screened in the etherification of 1-phenylethanol with C1-C 4 alkanols in dichloromethane as a solvent to yield the corresponding C6H5CH(OR)CH3 unsymmetrical ethers. In comparison with pure HPW, the new salts revealed generally a higher selectivity of ethers formation at 65 °C.
- Filek, Urszula,Mucha, Dariusz,Hunger, Michael,Sulikowski, Bogdan
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- Iron-catalyzed N-alkylation using π-activated ethers as electrophiles
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A new method for the synthesis of diverse N-alkylation compounds was developed via an iron-catalyzed etheric Csp3-O cleavage with the C-N bond formation in the reaction of π-activated ethers with various nitrogen-based nucleophiles. In addition, the mechanism of this reaction was investigated. The Royal Society of Chemistry 2013.
- Fan, Xiaohui,Fu, Lin-An,Li, Na,Lv, Hao,Cui, Xiao-Meng,Qi, Yuan
-
supporting information
p. 2147 - 2153
(2013/04/10)
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- Methoxycarbonylation of styrene by palladium (II) complex containing the diphenylphosphinocyrhetrene ligand
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The palladium-catalyzed methoxycarbonylation of vinylarenes has been investigated for the first time using phosphinocyrhetrene [(ν5- C5H4PPh2Re(CO)3] a non-metallocenic organometallic ligand. The catalytic system trans -[(ν5-C 5H4PPh2Re(CO)3]PdCl 2(NCMe)/PPh3 (1:2 ratio), carbon monoxide and methanol, in the presence of HCl as acidic promoter, showed good catalytic activity, excellent regioselectivity to the branched products and chemoselectivity up to 94%.
- Zuniga, Cesar,Sierra, Diego,Oyarzo, Juan,Klahn, A. Hugo
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p. 1101 - 1103,3
(2020/08/24)
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- Chemical photocatalysis with 1-(N, N-dimethylamino)pyrene
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1-(N,N-Dimethylamino)pyrene was applied as chemical photocatalyst for two different organic reactions: Both the photocatalytically driven nucleophilic addition of methanol to 1,1-diphenylethylene and the photocatalytic deprotection of N-phenylsulfonylindole gave the corresponding products in good yields and in a highly sustainable way after short irradiation with high-power LED. This concept can potentially be transferred to other photochemical reactions. Copyright
- Penner, Alexander,B?tzner, Effi,Wagenknecht, Hans-Achim
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p. 2803 - 2807
(2013/02/22)
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- Catalytic hydroalkoxylation of alkenes by iron(III) catalyst
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Catalytic hydroalkoxylation of alkenes by iron(III) chloride in the presence of toluenesulfonic acid (TsOH) was developed in moderate to good yields up to 91%. Intramolecular cyclization of 5-hydroxyl pentene afforded 2-methyltetrahedronfuran in 63% yield.
- Ke, Fang,Li, Zhengkai,Xiang, Haifeng,Zhou, Xiangge
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supporting information; experimental part
p. 318 - 320
(2011/02/26)
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- InI3/me3sii-catalyzed direct alkylation of enol acetates using alkyl acetates or alkyl ethers
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A combined Lewis acid of InI3 and Me3SiI was used to catalyze the direct coupling reactions of enol acetates with alkyl acetates or alkyl ethers without generating metal waste. The easily-handled alkylating reagents enlarged the application area of this coupling reaction. 2011 The Chemical Society of Japan.
- Onishi, Yoshiharu,Nishimoto, Yoshihiro,Yasuda, Makoto,Baba, Akio
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supporting information; experimental part
p. 1223 - 1225
(2011/11/29)
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- Indium(i)-catalyzed alkyl-allyl coupling between ethers and an allylborane
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An efficient method for alkyl-allyl cross-coupling between ethers and a 9-BBN-derived allylborane catalyzed by indium(i) triflate has been developed. The allylborane proved to be essential to obtain the desired products in high yields. The reaction displayed good substrate scope including high functional group tolerance. The Royal Society of Chemistry 2011.
- Dao, Hai Thanh,Schneider, Uwe,Kobayashi, Shu
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supporting information; experimental part
p. 692 - 694
(2011/03/22)
-
- Carbene-metal hydrides can be much less acidic than phosphine-metal hydrides: Significance in hydrogenations
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Acidities of iridium hydride intermediates were shown to be critical in some transformations mediated by the chiral analogues of Crabtree's catalyst, 1-3. To do this, several experiments were undertaken to investigate the acidities of hydrogenation mixtures formed using these iridium-oxazoline complexes. DFT calculations indicated that the acidity difference for Ir-H intermediates in these hydrogenations were astounding; iridium hydride from the N-heterocyclic carbene catalyst 1 was calculated to be around seven pK a units less acidic than those from the P-based complexes 2 and 3. Consistent with this, the carbene complex 1 was shown to be more effective for hydrogenations of acid-sensitive substrates. In deuteration experiments, less "abnormal" deuteration was observed, corresponding to fewer complications from acid-mediated alkene isomerization preceding the D 2-addition step. Finally, simple tests with pH indicators provided visual evidence that phosphine-based catalyst precursors give significantly more acidic reaction mixtures than the corresponding N-heterocyclic carbene ones. These observations indicate carbene-for-phosphine (and similar) ligand substitutions may impact the outcome of catalytic reactions by modifying the acidities of the metal hydrides formed.
- Zhu, Ye,Fan, Yubo,Burgess, Kevin
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scheme or table
p. 6249 - 6253
(2010/06/20)
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- A novel, chemoselective and efficient microwave-assisted deprotection of silyl ethers with Selectfluor
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A novel microwave-assisted, chemoselective and efficient method for the cleavage of silyl ethers (aliphatic and aromatic) catalyzed by Selectfluor is reported. A wide range of TBS-, TIPS-, and TBDPS-protected alkyl silyl ethers can be chemoselectively cleaved in high yield in the presence of aryl silyl ethers. The chemoselective deprotection of phenolic TBS ethers, and not the TIPS- or TBDPS-protected phenolic ethers, and the deprotection of silyl esters were also achieved under these reaction conditions. In addition, the transetherification and etherification of benzylic hydroxy groups in alcoholic solvents is observed.
- Shah, Syed Tasadaque A.,Singh, Surendra,Guiry, Patrick J.
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experimental part
p. 2179 - 2182
(2009/07/01)
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- Efficient addition of alcohols, amines and phenol to unactivated alkenes by AuIII or PdII stabilized by CuCl2
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The nucleophilic addition of alcohols, amines and phenol to unactivated alkenes catalyzed by cationic gold and palladium becomes limited due to the fast reduction into metallic gold under reaction conditions. The presence of CuCl2 retards the reduction of AuIII and PdII, strongly increasing the turnover number of gold and palladium catalysts. It is shown that new AuIII-CuCl2 and PdII-CuCl 2 catalysts are active and selective for the nucleophilic addition of alcohols, amines and phenol to unactivated alkenes. This journal is The Royal Society of Chemistry.
- Zhang, Xin,Corma, Avelino
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p. 397 - 403
(2008/09/17)
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- Hydrogen bonding lowers intrinsic nucleophilicity of solvated nucleophiles
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The relationship between nucleophilicity and the structure/environment of the nucleophile is of fundamental importance in organic chemistry. In this work, we have measured nucleophilicities of a series of substituted alkoxides in the gas phase. The functional group substitutions affect the nucleophiles through ion-dipole, ion-induced dipole interactions and through hydrogen bonding whenever structurally possible. This set of alkoxides serves as an ideal model system for studying nucleophiles under microsolvation settings. Marcus theory was applied to analyze the results. Using Marcus theory, we separate nucleophilicity into two independent components, an intrinsic nucleophilicity and a thermodynamic driving force determined solely by the overall reaction exothermicity. It is found that the apparent nucleophilicities of the substituted alkoxides are always much lower than those of the unsubstituted ones. However, ion-dipole, ion-induced dipole interactions, by themselves, do not significantly affect the intrinsic nucleophilicity; the decrease in the apparent nucleophilicity results from a weaker thermodynamic driving force. On the other hand, hydrogen bonding not only stabilizes the nucleophile but also increases the intrinsic barrier height by 3 to ~4 kcal mol-1. In this regard, the hydrogen bond is not acting as a perturbation in the sense of an external dipole but more directly affects the electronic structure and reactivity of the nucleophilic alkoxide. This finding offers a deeper insight into the solvation effect on nucleophilicity, such as the remarkably lower reactivities in nucleophilic substitution reactions in protic solvents than in aprotic solvents.
- Chen, Xin,Brauman, John I.
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scheme or table
p. 15038 - 15046
(2009/03/12)
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- Iridium-catalyzed asymmetric hydrogenation of vinyl ethers
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A carbene-oxazoline catalyst 1 proved to be an effective catalyst for reduction of an enol ether that the literature suggested could not be hydrogenated effectively by P,N-Ir catalysts. Thus, a series of ester and alcohol substrates were hydrogenated using catalyst 1. Good to excellent enantioselectivities and high conversions were obtained.
- Zhu, Ye,Burgess, Kevin
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supporting information; experimental part
p. 979 - 983
(2009/05/30)
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- Iodine catalyzed selective O-alkylation of alcohols with orthoesters
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In the present communication O-alkylation of a number of allylic and benzylic alcohols has been described.
- Kumar,Anjaneyulu,Joyasawal, Sipak,Pawan Chakravarthy,Naveen Kumar,Yadav
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p. 189 - 192
(2008/02/13)
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- Effective Au(III)-CuCl2-catalyzed addition of alcohols to alkenes
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Alkenes can be activated by Au(III) catalysts, and the effective addition of alcohols to alkenes can be carried out under mild conditions with Au(III), provided that catalytic amounts of CuCl2 are added, which significantly stabilize the cationic Au(III). The Royal Society of Chemistry.
- Zhang, Xin,Corma, Avelino
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p. 3080 - 3082
(2008/02/10)
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- Pd-catalysed methoxycarbonylation of vinylarenes using chiral monodentate phosphetanes and phospholane as ligands. Effect of substrate substituents on enantioselectivity
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Palladium complexes bearing phospholane 1 and phosphetane 2-4 ligands have been synthesised to be used as catalyst precursors in the asymmetric methoxycarbonylation of vinyl arenes. Single crystals of the complex [PdCl 2(2)2] II were obtained from a toluene solution and analysed by X-ray crystallography. Using these complexes, excellent regioselectivity (up to 99%) to the branched esters was obtained. Phosphetane ligands provide higher enantioselectivity than the phospholane under the same reaction conditions and an important influence of the substrate was observed. Enantioselectivity up to 50% was obtained using 4-methoxystyrene. The Royal Society of Chemistry.
- Munoz, Bianca K.,Godard, Cyril,Marinetti, Angela,Ruiz, Aurora,Benet-Buchholz, Jordi,Claver, Carmen
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p. 5524 - 5530
(2008/04/13)
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- NaIO4-mediated C-H activation of alkylbenzenes and alkanes with LiBr
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NaIO4 oxidizes lithium bromide efficiently under acidic conditions to functionalize alkylbenzenes and alkanes and produce the corresponding bromo and acetoxy derivatives in excellent yields. The protocol also demonstrates the direct conversion of cyclohexane into trans-1,2- dibromocyclohexane in moderate yield.
- Shaikh, Tanveer M.,Sudalai, Arumugam
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p. 5589 - 5592
(2007/10/03)
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- Efficient and selective formation of mixed acetals by Nafion-H SAC-13 silica nanocomposite solid acid catalyst
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Various types of hydroxy compounds can readily be converted to the corresponding mixed acetals with dialkoxymethanes in the presence of SAC-13 solid superacid. The transformation is almost instantaneous, product acetals are isolated in good to excellent yields, and the catalyst can be reused with minor loss of activity. Comparative studies were also carried out with p-toluenesulfonic acid and BF3·OEt2.
- Ledneczki, Istvan,Molnar, Arpad
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p. 3683 - 3690
(2007/10/03)
-
- Deoxygenative dimerization of benzylic and allylic alcohols, and their ethers and esters using lanthanum metal and chlorotrimethylsilane in the presence of a catalytic amount of iodine and copper(I) iodide
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Benzylic and allylic alcohols were deoxygenatively dimerized by a treatment with lanthanum metal and chlorotri-methylsilane in the presence of a catalytic amount of iodine, giving the corresponding coupling products, alkanes, in moderate-to-good yields. This dimerization reaction was dramatically accelerated by the addition of a catalytic amount of copper(I) iodide. Similarly, ethers and esters were deoxygenatively dimerized by La/Me3SiCl/cat.I2/cat.CuI system in the presence of a catalytic amount of H2O.
- Nishino, Toshiki,Nishiyama, Yutaka,Sonoda, Noboru
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p. 635 - 641
(2007/10/03)
-
- Oxidation of benzylic alcohols and ethers to carbonyl derivatives by nitric acid in dichloromethane
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Nitric acid in dichloromethane may be successfully employed for the oxidation of benzylic alcohols and ethers to the corresponding carbonyl compounds. The proposed method proved to be of general applicability, affording very good yields of aldehydes and ketones and showing interesting chemoselectivity in many instances, allowing competitive aromatic nitration to be avoided, as well as - in the case of aldehydes - any further oxidation to carboxylic acids. The reaction probably proceeds by a radical mechanism, the active species in the oxidation process being NO2. Competitive formation of nitro esters was observed in some cases, whereas poor results were obtained with allylic and non-benzylic substrates. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.
- Strazzolini, Paolo,Runcio, Antonio
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p. 526 - 536
(2007/10/03)
-
- Substitution of α-azido ethers with Grignard reagents and its use in combinatorial chemistry
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α-Azidobenzyl ethers were reacted with alkyl or arylGrignard reagents in toluene to produce α-alkylbenzyl or diarylmethyl ethers in 82-94% yield. α-Azidobenzyl ethers were also reacted with multicomponent Grignard reagents to produce libraries of α-alkylbenzyl ethers.
- Baruah, Mukulesh,Bols, Mikael
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p. 509 - 512
(2007/10/03)
-
- Chemical equilibrium study in the reacting system of the (1-alkoxyethyl)benzene synthesis from alkanols and styrene
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The chemical equilibrium of the reactive system alkanol + styrene ? (1-alkoxyethyl)benzene (where alkyl is methyl, ethyl, propyl, and butyl) was studied in the liquid phase at 343-423 K using a cation exchanger as the heterogeneous catalyst. Enthalpies of reactions of (1-alkoxyethyl)benzene synthesis in the liquid phase were obtained from the temperature dependence of equilibrium constants measured in the reactive mixtures with an excess of alkanol and indicated a good agreement with those reaction enthalpies derived from values of the enthalpies of formation (liquid) of the reactions participants measured for (1-methoxyethyl)benzene and (1-butoxyethyl)benzene by combustion calorimetry. Isopropylbenzene was a relevant structural pattern of strain in the (1-alkoxyethyl)benzenes studied. Its strain enthalpy was a reflection of the intrinsic strain of the molecule due to steric repulsions of methyl tertiary carbon atom. No additional group additivity parameters or correction terms were required for the group contribution correlation for enthalpies of formation (gas) of (1-alkoxyethyl)benzenes.
- Verevkin, Sergey,Heintz, Andreas
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p. 984 - 990
(2007/10/03)
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- Asymmetric nucleophilic substitution of acetals
-
Benzaldehyde dimethylacetal (1) and 2-aryl-1,3-dioxolanes 5 react with organolithium reagents 2 in the presence of chiral ligands such as sparteine (3), 1-alkoxy-2-aminoethanes, or 1,2-dialkoxyethanes and BF3 to afford monosubstitution products in high yields and in up to 81% enantiomeric excess. The enantioselectivity is strongly influenced by steric effects in the acetal and in the reagent. The highest ee was achieved with 2-(2-isopropyl)-1,3-dioxolane (5c) on treatment with 2-ethylphenyllithium (2i) in the presence of sparteine. The approach was applied to the synthesis of enantioenriched (S)-(-)-neobenodine (17) with 49% ee.
- Mueller, Paul,Nury, Patrice,Bernardinelli, Gerald
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p. 4137 - 4147
(2007/10/03)
-
- Reduction of acetals with samarium diiodide in acetonitrile in the presence of Lewis acids
-
Transformation of acetals into ethers by partial reduction using a samarium diiodide-Lewis acids-acetonitrile system is described. The reaction with aromatic acetals occurred in good yields in the presence of aluminum chloride (2 eq) whereas the corresponding aliphatic, vinylic, and alkynyl derivatives did not afford ethers under the same conditions, β-Elimination to give an enol ether becomes predominant when aliphatic acetals that possess a hydrogen at the 2-position are treated with iodotrimethylsilane in the presence of SmI2 or SmI3.
- Kunishima,Nakata,Sakuma,Kono,Sato,Tani
-
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- Tri-n-butylstannyl chloride-sodium cyanoborohydride mediated regioselective reductive demethoxylation of alkyl methyl ketals
-
A regioselective reductive demethoxylation of alkyl methyl ketals employing sodium cyanoborohydride in the presence of a catalytic amount of tri-n-butyltin chloride as Lewis acid is described.
- Srikrishna,Viswajanani
-
p. 621 - 625
(2007/10/03)
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- New chiral auxiliaries for highly stereoselective asymmetric methoxyselenenylations
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Replacement of the 2-keto group of readily available di(endo-3-camphoryl) diselenide with oxime or O-benzoyloxime substituents, followed by conversion into the corresponding selenenyl triflates, produced highly effective chiral selenium electrophiles for
- Back, Thomas G.,Moussa, Ziad
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p. 3007 - 3009
(2007/10/03)
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- BiBr3, an efficient catalyst for the benzylation of alcohols: 2-Phenyl- 2-propyl, a new benzyl-type protecting group
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The benzylation of aliphatic alcohols with various benzylic alcohols has been achieved in the presence of BiBr3 under mild conditions. 2- Phenylpropan-2-ol proved to be the most efficient and can be considered as a novel protecting group. (C) 2000 Elsevier Science Ltd.
- Boyer, Bernard,Keramane, El-Mehdi,Roque, Jean-Pierre,Pavia, André A.
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p. 2891 - 2894
(2007/10/03)
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- Excited Precursor Reactivity, Fast 1,2-H Shifts, and Diffusion-Controlled Methanol Insertion in 1,2-Diphenylalkylidenes
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The photochemistry of several arylalkyldiazo compounds has been investigated by steady-state direct and triplet sensitized irradiations and by nanosecond laser flash photolysis. Steady-state photolyses in methanol yielded methyl ethers and alkenes as the only significant products. Ethers were formed by denitrogenation of the diazo compound followed by carbene insertion into the MeO-H bond, and alkenes were obtained by 1,2-R (R = H,Ph) migrations both in the free carbene and in the singlet excited state of the diazo precursor. Evidence for the exited-state precursor reaction came from differences in product yields as a function of excitation wavelength and excited-state multiplicity. The yields of methyl ethers increased with increasing excitation wavelengths and were greatest upon triplet-state sensitization but were never the sole products formed despite expected diffusion-controlled insertion rates. Accordingly, the formation of pyridine ylides analyzed by laser flash photolysis in the presence of high concentrations of the base yielded relatively modest transient absorptions. The kinetics of the 1,2-H reaction, analyzed by time-resolved detection of stilbene in the case of 1,2-diphenylethylidenes, displayed fast and slow components. The fast component was attributed to stilbene that formed from the excited-state precursor and from the originally formed singlet carbene within the 20 ns pulse. The long-lived component was attributed to a spin-state equilibrated carbene with a lifetime of 70-80 ns in fluorocarbon solvents. Analysis of the long-lived component by a Stern-Volmer treatment upon addition of MeOH gave a lower limit for the reaction rate constant with a value of k1,2-H > 5 × 109 s-1 in a mixed Freon-methanol solvent. It is concluded that the combined effect of phenyl substituents at the carbon bearing the migrating group and high solvent polarity can lead to intramolecular 1,2-H shifts and 1,2-Ph migrations that are fast enough to compete with diffusion-controlled intermolecular MeO-H insertion in concentrated MeOH solutions.
- Motschiedler, Krista,Gudmundsdottir, Anna,Toscano, John P.,Platz, Matthew,Garcia-Garibay, Miguel A.
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p. 5139 - 5147
(2007/10/03)
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- Secondary deuterium kinetic isotope effects in irreversible additions of hydride and carbon nucleophiles to aldehydes: A spectrum of transition states from complete bond formation to single electron transfer
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The competitive kinetics of hydride and organometallic additions to benzaldehyde-H and -D were determined at -78 °C using LiAlH4, LiBEt3H, NaBH4, LiBH4, LiAl(O-tert-butoxy)3H, NaB(OMe)3H, NaB(OAc)3H (at 20°C). methyl, phenyl, and allyl Grignard, and methyl-, phenyl-, n-butyl-, tert- butyl-, and allyllithium. The additions of hydride were found to have an inverse secondary deuterium kinetic isotope effects in all cases, but the magnitude of the effect varied inversely with the apparent reactivity of the hydride. In the additions of methyl Grignard reagent and of methyllithium and phenyllithium, inverse secondary deuterium isotope effects were observed; little if any isotope effect was observed with phenyl Grignard or n-butyl- and tert-butyllithium. With allyl Grignard and allyllithium, a normal secondary deuterium kinetic isotope effect was observed. The results indicate that rate-determining single-electron transfer occurs with allyl reagents, but direct nucleophilic reaction occurs with all of the other reagents, with the extent of bond formation dependent on the reactivity of the reagent. In the addition of methyllithium to cyclohexanecarboxaldehyde, a less inverse secondary deuterium kinetic isotope effect was observed than that observed in the addition of methyllithium to benzaldehyde, and allyllithium addition to cyclohexanecarboxaldehyde had a kinetic isotope effect near unity. The data with organometallic additions, which are not incompatible with observations of carbonyl carbon isotope effects, suggest that electrochemically determined redox potentials which indicate endoergonic electron transfer with energies less than ca. 13 kcal/mol allow electron-transfer mechanisms to compete well with direct polar additions to aldehydes, provided that the reagent is highly stabilized, like allyl species. Methyl-and phenyllithium and methyl and phenyl Grignard reagents are estimated to undergo electron transfer with endoergonicities greater than 30 kcal/mol with benzaldehyde, so these react by direct polar additions. A working hypothesis is that butyllithium reagents undergo polar additions, despite redox potentials which indicate less than 13 kcal/mol endoergonic electron transfer, because of the great exoergonicity associated with the two-electron addition, which is responsible for a low barrier for polar reactions.
- Gajewski, Joseph J.,Bocian, Wojciech,Harris, Nathan J.,Olson, Leif P.,Gajewski, John P.
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p. 326 - 334
(2007/10/03)
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- Catalytic carbonylation of α-(6-methoxyl-2-naphthyl)ethanol to methyl esters of naproxen using PdCl2-CuCl2-PPh3-acid catalyst system
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α-(6-Methoxyl-2-naphthyl)ethanol was carbonylated into methyl ester of α-(6-methoxyl-2-naphthyl)propionic acid (Naproxen) in up to 100% yield and 100% selectivity using PdCl2-CuCl2-PPh3-p-Ts catalyst system without any halogen promoter or other extreme condition.
- Zhou, Hongying,Cheng, Jing,Lu, Shijie,Fu, Hongxiang,Wang, Hanqing
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p. 239 - 242
(2007/10/03)
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- Metalation of arylmethyl alkyl ethers
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Arylmethyl alkyl ethers 1a-11 were metallated with n-BuLi or sec-BuLi in THF at different temperatures, affording α-alkoxy-substituted arylmethyllithium derivatives. At low temperature, the organometallics derived from methyl and isopropyl ethers are suff
- Azzena, Ugo,Pilo, Luciano,Sechi, Alessandra
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p. 12389 - 12398
(2007/10/03)
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- The β-heteroatom effect on carbenes
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The β-thiophosphinoyl carbene PhCCH2P(S)Ph2 (5) has been prepared by irradiation of the corresponding diazo compound. The relative rates for insertion into the OH bond of methanol and for addition to the double bond of 2-methyl-2-but
- Lambert, Joseph B.,Liu, Xiaoyang
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p. 9989 - 9996
(2007/10/03)
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- Anodic oxidation of 3-phenylpropionic acid
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The electrochemical oxidation of 3-phenylpropionic acid has been performed on platinum, graphite and PtO2/Ti anodes. Two types of products have been obtained, either formed by one-electron oxidation, or by two-electron oxidation. The influence of the anode material, current density and solvent nature on the products distribution has been studied. The electrochemical oxidations of 3-(p-t-butylphenyl)propionic, 3,3-d-3-phenylpropionic and 2,2-d-3-phenylpropionic acids have been studied in order to get information concerning the carbonium-type intermediate in the two-electron oxidation. Unlike the chemical generation, the 2-phenylethyl carbocation formed by two-electron oxidation stabilises, leading mainly to rearranged products. The obtained results are in agreement with the assumption that either phenyl or σC-H bond assists the carbocation formation.
- Ro?ca, Sorin,Ungureanu, Mihaela,Stan, Raluca
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- Metalation of Arylmethyl Methyl Ethers and Connection with Their Reductive Electrophilic Substitution
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Stable α-methoxy arylmethyl carbanions can be generated by metalation of arylmethyl methyl ethers, 1, with n-BuLi in THF at -40 degC, avoiding Wittig rearrengement to the corresponding alkoxides 2.Reaction of these carbanions with various electrophiles afforded the expected products 3 in satisfactory yields.Connection between the metalation procedure and the reductive electrophilic substitution of arylmethyl methyl ethers allowed the transformation of compounds 1 into 2-arylpropanoic acids, 5.
- Azzena, Ugo,Demartis, Salvatore,Fiori, Maria Giovanna,Melloni, Giovanni,Pisano, Luisa
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p. 5641 - 5644
(2007/10/02)
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- Hydroesterification of Olefins Catalyzed by Pd(OAc)2 Immobilized on Montmorillonite
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Palladium acetate immobilized on montmorillonite is an efficient catalyst for the hydroesterification of olefins with carbon monoxide and methanol, in the presence of triphenylphosphine and an acid promoter, affording branched chain esters.The reaction is regiospecific for aryl olefins as well as for vinyl benzoate and regioselective for aliphatic olefins.
- Lee, Chul Woo,Alper, Howard
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p. 250 - 252
(2007/10/02)
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- The Mechanism of RuO4-Mediated Oxidations of Ethers: Isotope Effects, Solvent Effects and Substituent Effects
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The mechanism of the RuO4-mediated oxidation of ethers to esters has been investigated.Oxidation of cyclopropylmethyl methyl ether gave methyl cyclopropanecarboxylate.No rearranged products were observed.On RuO4 oxidation of benzyl methyl ether and p-methoxybenzyl methyl ether in CCl4 with NaIO4 as stoichiometric oxidant, no chlorinated products were observed.A series of 4-substituted benzyl methyl ethers was oxidized with RuO4-NaIO4.A correlation of the rate of the reaction with Hammett ?-values gave a ρ of -1.7, indicating only a moderate charge separation in the transition state (TS).Benzyl methyl ether (1) was oxidized in a series of acetone-water mixtures.From these experiments, a Grunwald-Winstein m-value of 0.11 was obtained, indicating a non-polar TS for the reaction.PhCHDOCH3 (2) and PhCD2OCH3 (3) were oxidized and two deuterium isotipe effects, one of 6.1+/-0.4 and another of 1.3+/-0.1 were obtained.If one assumes a one-step reaction mechanism, the value of 1.3 would be a large α-secondary isotope effect, indicating a change in the hybridization of the benzylic carbon during the reaction. α-Methylbenzyl methyl ether (4) was oxidized at a seventh of the rate of 1, despite the fact that 4 would have given a more stable carbocation than 1.These conflicting pieces of evidence are difficult to rationalise with a hydride or hydrogen abstraction mechanism.Instead it is proposed that the reaction proceeds by either a concerted reaction or by a reversible oxidative addition of the ether to RuO4 followed by a slow concerted step to give the product.
- Bakke, Jan M.,Froehaug, Astrid E.
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p. 615 - 622
(2007/10/02)
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- The Competition between Cross-coupling and the Exchange Reaction in the Photoreduction of Aromatic Ketones
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Four aromatic ketones K with different reduction potentials and a series of hydrogen atom donors AH2 with different oxidation potentials of AH were irradiated in pairs and the product composition analyzed.Based on the product analysis the rate kex of the exchange reaction K + AH -> KH + A, was characterized as slow, medium fast or fast, respectively, relative to the radical-radical coupling reactions of K and AH.The results clearly point to the value of a knowledge of the oxidation potential of the AH radicals and the reduction potential of the ketones for the prediction of the outcome of the photoreduction of a ketone by an alcohol or another hydrogen atom donor.
- Lund, Torben,Lundgren, Birger,Lund, Henning
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p. 755 - 761
(2007/10/02)
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- Nucleophilic Substitution Reaction of 1-Phenylethyl Chlorides in Methanol
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Nucleophilic substitution reactions of 1-(Y-phenyl)ethyl chlorides with X-anilines have been investigated in methanol at 65.0 deg C.An isokinetic point is obtained at ?Y+ = ca. -0.23 with ρX = 0; the sign of ρX changes at this point from positive for the relatively strong electron donating Y substituents to negative for the more electron withdrawing Y substituents. The magnitude of the cross-interaction constant, ρXY, between the substituents X and Y is unusually large with the relatively small magnitude of ρXo resulting in an observable isokinetic point at .These results are interpreted in terms of a transition state (TS) structure in which nearly complete bond formation between the nucleophile and cation formed in an ion-pair preequilibrium is coupled with a TS imbalance phenomenon.The results of kinetic isotope effect studies involving deuteriated anilines and methanol are also in line with this mechanism.
- Lee, Ikchoon,Lee, Won Heui,Lee, Hai Whang,Bentley, T. W.
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p. 141 - 146
(2007/10/02)
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