- An Efficient and Remarkably Regioselective Synthesis of Benzocyclobutenones from Benzynes and 1,1-Dimethoxyethylene
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New efficient methodology for the synthesis of substituted benzocyclobutenones is presented that involves the cycloaddition of various substituted benzynes to 1,1-dimethoxyethylene followed by hydrolysis to the corresponding ketone.In most cases studied a high degree of regioselectivity was observed.These observations are consistent with a nonsynchronous mechanism wherein steric and inductive considerations can be used to account for the products observed.
- Stevens, Robert V.,Bisacchi, Gregory S.
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- Visible-Light-Enabled Carboxylation of Benzyl Alcohol Derivatives with CO2 Using a Palladium/Iridium Dual Catalyst
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A highly efficient carboxylation of benzyl alcohol derivatives with CO2 using a palladium/iridium dual catalyst under visible-light irradiation was developed. A wide range of benzyl alcohol derivatives could be employed to provide benzylic carboxylic acids in moderate to high yields. Mechanistic studies indicated that the oxidative addition of benzyl alcohol derivatives was possibly the rate-determining-step. It was also found that a switchable site-selective carboxylation between benzylic C?O and aryl C?Cl moieties could be achieved simply by changing the palladium catalyst.
- Iwasawa, Nobuharu,Jin, Yushu,Toriumi, Naoyuki
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- Visible-light photoredox-catalyzed selective carboxylation of C(sp3)?F bonds with CO2
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It is highly attractive and challenging to utilize carbon dioxide (CO2), because of its inertness, as a nontoxic and sustainable C1 source in the synthesis of valuable compounds. Here, we report a novel selective carboxylation of C(sp3)?F bonds with CO2 via visible-light photoredox catalysis. A variety of mono-, di-, and trifluoroalkylarenes as well as α,α-difluorocarboxylic esters and amides undergo such reactions to give important aryl acetic acids and α-fluorocarboxylic acids, including several drugs and analogs, under mild conditions. Notably, mechanistic studies and DFT calculations demonstrate the dual role of CO2 as an electron carrier and electrophile during this transformation. The fluorinated substrates would undergo single-electron reduction by electron-rich CO2 radical anions, which are generated in situ from CO2 via sequential hydride-transfer reduction and hydrogen-atom-transfer processes. We anticipate our finding to be a starting point for more challenging CO2 utilization with inert substrates, including lignin and other biomass.
- Bo, Zhi-Yu,Chen, Lin,Gao, Tian-Yu,Jing, Ke,Lan, Yu,Liu, Shi-Han,Luo, Shu-Ping,Yan, Si-Shun,Yu, Bo,Yu, Da-Gang
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supporting information
p. 3099 - 3113
(2021/11/16)
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- Macrolactam Synthesis via Ring-Closing Alkene-Alkene Cross-Coupling Reactions
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Reported herein is a practical method for macrolactam synthesis via a Rh(III)-catalyzed ring closing alkene-alkene cross-coupling reaction. The reaction proceeded via a Rh-catalyzed alkenyl sp2 C-H activation process, which allows access to macrocyclic molecules of different ring sizes. Macrolactams containing a conjugated diene framework could be easily prepared in high chemoselectivities and Z,E stereoselectivities.
- Goh, Jeffrey,Loh, Teck-Peng,Maraswami, Manikantha
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supporting information
p. 9724 - 9728
(2020/12/21)
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- Carboxylation of benzylic and aliphatic C-H bonds with CO2 induced by light/ketone/nickel
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A photoinduced carboxylation reaction of benzylic and aliphatic C-H bonds with CO2 is developed. Toluene derivatives capture gaseous CO2 at the benzylic position to produce phenylacetic acid derivatives when irradiated with UV light in the presence of an aromatic ketone, a nickel complex, and potassium tert-butoxide. Cyclohexane reacts with CO2 to furnish cyclohexanecar-boxylic acid under analogous reaction conditions. The present photoinduced carboxylation reaction provides a direct access from readily available hydrocarbons to the corresponding carboxylic acids with one carbon extension.
- Ishida, Naoki,Masuda, Yusuke,Imamura, Yuuya,Yamazaki, Katsushi,Murakami, Masahiro
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supporting information
p. 19611 - 19615
(2019/12/24)
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- Visible-Light-Driven External-Reductant-Free Cross-Electrophile Couplings of Tetraalkyl Ammonium Salts
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Cross-electrophile couplings between two electrophiles are powerful and economic methods to generate C-C bonds in the presence of stoichiometric external reductants. Herein, we report a novel strategy to realize the first external-reductant-free cross-electrophile coupling via visible-light photoredox catalysis. A variety of tetraalkyl ammonium salts, bearing primary, secondary, and tertiary C-N bonds, undergo selective couplings with aldehydes/ketone and CO2. Notably, the in situ generated byproduct, trimethylamine, is efficiently utilized as the electron donor. Moreover, this protocol exhibits mild reaction conditions, low catalyst loading, broad substrate scope, good functional group tolerance, and facile scalability. Mechanistic studies indicate that benzyl radicals and anions might be generated as the key intermediates via photocatalysis, providing a new direction for cross-electrophile couplings.
- Liao, Li-Li,Cao, Guang-Mei,Ye, Jian-Heng,Sun, Guo-Quan,Zhou, Wen-Jun,Gui, Yong-Yuan,Yan, Si-Shun,Shen, Guo,Yu, Da-Gang
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p. 17338 - 17342
(2019/01/04)
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- Ruthenium-catalyzed umpolung carboxylation of hydrazones with CO2
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The first ruthenium-catalyzed umpolung carboxylation of hydrazones with CO2 to generate important aryl acetic acids is reported. Besides aldehyde hydrazones, a variety of ketone hydrazones, which have not been successfully applied in previous umpolung reactions with other reactive electrophiles, also show high reactivity and selectivity under mild conditions. Moreover, this operationally simple protocol features good functional group tolerance, is readily scalable, and offers easy derivation of important structures, including bioactive felbinac and adiphenine. Computational studies reveal that this umpolung reaction proceeds through the generation of a Ru-nitrenoid followed by concerted [4 + 2] cycloaddition with CO2.
- Yan, Si-Shun,Zhu, Lei,Ye, Jian-Heng,Zhang, Zhen,Huang, He,Zeng, Huiying,Li, Chao-Jun,Lan, Yu,Yu, Da-Gang
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p. 4873 - 4878
(2018/06/07)
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- Regio- and Stereoselective Oxidation of Styrene Derivatives to Arylalkanoic Acids via One-Pot Cascade Biotransformations
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Green and selective oxidation methods are highly desired in chemical synthesis and manufacturing. In this work, we have developed a biocatalytic method for the regio- and stereoselective oxidation of styrene derivatives into arylacetic and (S)-2-arylpropionic acids via a one-pot epoxidation–isomerization–oxidation sequence. This was done via the engineering of Escherichia coli (StyABC-EcALDH) coexpressing styrene monooxygenase (SMO), styrene oxide isomerase (SOI) and aldehyde dehydrogenase (EcALDH) as an active and easily available whole-cell catalyst. Regioselective oxidation of styrene and 11 substituted styrenes using the E. coli cells was performed in a one-pot set-up, producing 12 phenylacetic acids in both high conversion and high yield. Engineering of E. coli (StyABC-ADH9v1) coexpressing SMO, SOI and ADH9v1 (a mutated alcohol dehydrogenase) led to biocatalysts capable of regio- and stereoselective oxidation of α-methylstyrene derivatives to the corresponding chiral acids. One-pot asymmetric synthesis of 4 (S)-2-arylpropionic acids was achieved in good conversion and excellent ee with the E. coli cells. This is a new type of asymmetric alkene oxidation to give chiral acids with no chemical counterpart thus far. The cascade bio-oxidation operates under mild conditions, uses molecular oxygen, exhibits very high regio- and enantioselectivity, and gives high conversion, thus providing a green and efficient method for the synthesis of arylacetic acids and (S)-2-arylpropionic acids directly from easily available styrenes. (Figure presented.).
- Wu, Shuke,Zhou, Yi,Seet, Daniel,Li, Zhi
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p. 2132 - 2141
(2017/06/23)
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- Nickel-Catalyzed Carboxylation of Benzylic C-N Bonds with CO2
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A user-friendly Ni-catalyzed reductive carboxylation of benzylic C-N bonds with CO2 is described. This procedure outperforms state-of-the-art techniques for the carboxylation of benzyl electrophiles by avoiding commonly observed parasitic pathways, such as homodimerization or β-hydride elimination, thus leading to new knowledge in cross-electrophile reactions.
- Moragas, Toni,Gaydou, Morgane,Martin, Ruben
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supporting information
p. 5053 - 5057
(2016/04/26)
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- Photogenerated α,n-didehydrotoluenes from chlorophenylacetic acids at physiological pH
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Aromatic diradicals are recognized as promising intermediates for DNA cleavage, but their formation has thus far been limited to the Bergman and Myers-Saito cycloaromatizations. We report here the phototriggered generation of all isomers of the potential DNA-cleaving α,n-didehydrotoluene diradicals at physiological pH, accomplished by the irradiation of chlorophenylacetic acids under mild conditions. The desired diradicals were formed upon photolysis of the chosen aromatic in aqueous phosphate buffer solution (pH = 7.3), with the consecutive elimination of biologically compatible chloride ion and carbon dioxide. Theoretical simulations reveal that the efficient decarboxylation of the primarily generated phenyl cations involves a previously not known diradical structure.
- Ravelli, Davide,Protti, Stefano,Fagnoni, Maurizio
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supporting information
p. 852 - 858
(2015/03/05)
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- Ni-catalyzed carboxylation of C(sp2)- and C(sp3)-O bonds with CO2
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In recent years a significant progress has been made for the carboxylation of aryl and benzyl halides with CO2, becoming convenient alternatives to the use of stoichiometric amounts of well-defined metal species. Still, however, most of these processes require the use of pyrophoric and air-sensitive reagents and the current methods are mostly restricted to organic halides. Therefore, the discovery of a mild, operationally simple alternate carboxylation that occurs with a wide substrate scope employing readily available coupling partners will be highly desirable. Herein, we report a new protocol that deals with the development of a synergistic activation of CO2 and a rather challenging activation of inert C(sp2)-O and C(sp3)-O bonds derived from simple and cheap alcohols, a previously unrecognized opportunity in this field. This unprecedented carboxylation event is characterized by its simplicity, mild reaction conditions, remarkable selectivity pattern and an excellent chemoselectivity profile using air-, moisture-insensitive and easy-to-handle nickel precatalysts. Our results render our method a powerful alternative, practicality and novelty aside, to commonly used organic halides as counterparts in carboxylation protocols. Furthermore, this study shows, for the first time, that traceless directing groups allow for the reductive coupling of substrates without extended π-systems, a typical requisite in many C-O bond-cleavage reactions. Taking into consideration the limited knowledge in catalytic carboxylative reductive events, and the prospective impact of providing a new tool for accessing valuable carboxylic acids, we believe this work opens up new vistas and allows new tactics in reductive coupling events.
- Correa, Arkaitz,Leon, Thierry,Martin, Ruben
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supporting information
p. 1062 - 1069
(2014/02/14)
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- Direct addition of functionalized organozinc reagents to carbon dioxide, ketones, and aldehydes in the presence of MgCl2
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A variety of functionalized organozinc reagents undergo smooth addition reactions at ambient temperature to carbon dioxide, ketones, and aldehydes in the presence of stoichiometric amounts of MgCl2. Several reactions were performed on a 20 mmol scale. Georg Thieme Verlag Stuttgart · New York.
- Bernhardt, Sebastian,Metzger, Albrecht,Knochel, Paul
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experimental part
p. 3802 - 3810
(2011/01/12)
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- Synthesis of phenylacetic acids under rhodium-catalyzed carbonylation conditions
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Benzyl halides are efficiently carbonylated to phenylacetic acids in the presence of a catalytic amount of the dimer of chloro(1,5-cyclooctadiene)rhodium(I) in formic acid. Under these reaction conditions, sensitive functionalities such as esters and nitriles are tolerated and the phenylacetic acids are obtained in good to high yields. (C) 2000 Elsevier Science Ltd.
- Giroux,Nadeau,Han
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p. 7601 - 7604
(2007/10/03)
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- The effect of an alkoxy group on the kinetic and thermodynamic acidity of benzene and toluene
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2-, 3- and 4-Methoxytoluene can be selectively metalated at an O-adjacent ortho position when butyllithium or tert-butyllithium in the presence of sodium (potassium) tert-butoxide or N,N,N',N'',N''-pentamethyldiethylenetriamine are employed as reagents. In contrast, lithium diisopropylamide or lithium 2,2,6,6-tetramethylpiperidide deprotonate the benzylic α-position of 2- and 3-methoxytoaluene exclusively and of 4-methoxytoluene preferentially. These relative reactivities can be rationalized by an interplay of transition state stabilizing and destabilizing forces (dipole matching and metal coordination vs. lone pair repulsion).
- Schlosser, Manfred,Maccaroni, Paola,Marzi, Elena
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p. 2763 - 2770
(2007/10/03)
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- Thermodynamic and nuclear magnetic resonance study of the reactions of α- and β-cyclodextrin with acids, aliphatic amines, and cyclic alcohols
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Titration calorimetry was used to determine equilibrium constants and standard molar enthalpy, Gibbs energy, and entropy changes for the reactions of a series of acids, amines, and cyclic alcohols with α- and β-cyclodextrin. The results have been examined in terms of structural features in the ligands such as the number of alkyl groups, the charge number, the presence of a double bond, branching, and the presence of methyl and methoxy groups. The values of thermodynamic quantities, in particular the standard molar Gibbs energy, correlate well with the structural features in the ligands. These structural correlations can be used for the estimation of thermodynamic quantities for related reactions. Enthalpy-entropy compensation is evident when the individual classes of substances studied herein are considered, but does not hold when these various classes of ligands are considered collectively. The NMR results indicate that the mode of accommodation of the acids and amines in the α-cyclodextrin cavity is very similar, but that the 1-methyl groups in 1-methylhexylamine and in 1-methylheptylamine and the N-methyl group in N-methylhexylamine lie outside the α-cyclodextrin cavity. This latter finding is consistent with the calorimetric results. Many of the thermodynamic and NMR results can be qualitatively understood in terms of van der Waals forces and hydrophobic effects.
- Rekharsky, Mikhail V.,Mayhew, Martin P.,Goldberg, Robert N.,Ross, Philip D.,Yamashoji, Yuko,Inoue, Yoshihisa
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- p-Hydroxyphenacyl ATP: A new phototrigger
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A new photoactivated 'caged' ATP, p-hydroxyphenacyl ATP (4), is introduced to replace the o-nitrophenethyl and desyl analogues as a more efficient, rapid release phototrigger for ATP.
- Givens, Richard S.,Park, Chan-Ho
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p. 6259 - 6262
(2007/10/03)
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- A Practical O2-Oxidation of Functionalized Alcohols Producing Carboxylic Acids Catalyzed by the Pd-C/Pb(OAc)2 System
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The Pd-C/Pb(OAc)2 system catalyzes selective O2-oxidation of ArCH(R)CH2OH to ArCH(R)COOH (useful intermediates for drug synthesis) in high yields without contamination of ArCOOH.The turnover number (substrate/Pd) is improved to 85 and > 1800 by recycling the catalyst and using a special reactor, respectively.Alkanols are also efficiently oxidized to alkanoic acids by the title catalyst system.
- Akada, Mitsuo,Nakano, Shinji,Sugiyama, Toshiyuki,Ichitoh, Kazumoto,Nakao, Hiroki,et al.
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p. 1511 - 1515
(2007/10/02)
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- Photolysis of the 1-naphthylmethyl ester of substituted phenylacetic acids: intramolecular charge transfer and rates of decarboxylation of arylacyl radicals
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The photolysis of esters 6 and 8 in methanol leads to products resulting from both naphthylmethyl cations and radicals.The product distribution is nearly independent of X for the esters 6 except when X equals methoxy.A mechanism involving initial homolytic cleavage of the carbon-oxygen bond in the excited singlet state of the ester is proposed.Competition between electron transfer in the radical pair to form the ion pair and decarboxylation of the arylacyloxy radical allows calculations of the rates of this decarboxylation process.The ρ values versus ? is close to zero.When X equals methoxy, intramolecular electron transfer occurs with the naphthalene ring serving as the acceptor and the methoxyaromatic as the donor.This exciplex fragments to carbon dioxide and 1-(1-naphthyl)-2-arylethane. Key words: acyloxy radical, decarboxylation, photolysis of benzylic esters.
- Hilborn, James W.,Pincock, James A.
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p. 992 - 999
(2007/10/02)
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- Convenient Preparation of Arylacetic Acids by Tetracarbonylcobaltate Anion Catalysed Carbonylation
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Tetracarbonylcobaltate catalyst -, has been prepared in 6 hr by pressure carbonylation of cobalt salt in aq alkaline solution containing cyanide catalyst.Carbonylation of arylchloromethyl derivatives in aq methanolic solutions using this catalyst affords arylacetic acids in good yields.
- Rao, B. Nageswara,Adapa, Srinivas R.,Pardhasaradhi, M.
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- CATALYTIC PHASE TRANSFER CARBONYLATION OF BENZYL HALIDES WITH IRON PENTACARBONYL.
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Benzyl halides are readily carbonylated to arylacetic acids in a two-phase system (aqueous sodium hydroxide (1M), tetrabutylammonium sulfate ; organic phase (CH2Cl2 or C6H6 or C6H5CH3)), using a catalytic amount of the cheap, easy to handle iron pentacarbonyl under carbon monoxide atmosphere.
- Tanguy, Guy,Weinberger, Berndt,Abbayes, Herve des
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p. 4005 - 4008
(2007/10/02)
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- Esters of α-Arylalkanoic Acids from 'Masked' α-Halogenoalkyl Aryl Ketones and Silver Salts: Synthetic, Kinetic, and Mechanistic Aspects
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A method for the synthesis of alkyl esters of α-arylalkanoic acids is given based on silver-ion-assisted (AgBF4, AgOSO2CF3, AgSbF6, AgNO3) solvolysis of alkyl acetals of primary and secondary α-halogenoalkyl aryl ketones (Hal = I, Br, Cl) in an alcoholic medium (methanol, ethanol).The reaction is quite selective and alkyl esters are the only reaction products; ethers, which are possible substitution products, are not found.The importance of masking the carbonyl as the acetal is emphasised.The reaction is found to be first-order in AgBF4 and in the primary α-halogeno acetal.A three-point Hammett correlation (ρ = -3.29) between ?+ and the rate constants suggests a large cationic contribution as well as strong aryl participation in the transition state.The role payed by the oxygen of the acetal group in the specificity of the reaction is discussed in comparison with the reactivity of analogous compounds with saturated skeletons and of α-halogenoalkyl aryl ketones.
- Giordano, Claudio,Castaldi, Graziano,Casagrande, Francesco,Belli, Aldo
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p. 2575 - 2582
(2007/10/02)
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