- Synthesis, solid-state structures, solution behaviour and catalysis studies of nickel complexes of bis(benzimidazolin-2-ylidene)pyridine pincer ligands
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N-Heterocyclic carbenenickel complexes with five- and four-coordinate geometries [(CNC)NiBr2] and [(CNC)NiBr]X (X=PF6 or BPh4) have been prepared with the pincer ligands 2,6-bis(N- octylbenzimidazolin-2-ylidene)pyridine and 2,6-bis(N-butyl-5,6- dimethoxybenzimidazolin-2-ylidene)pyridine. The addition of the n-octyl substituent significantly extends the solubility of the complexes and has allowed UV-vis solution studies of the complexes in dichloromethane and methanol. The four- and five-coordinate species exist in equilibrium in solution and this equilibrium has been explored by UV-vis studies. The complexes have also been characterized by NMR studies, and single crystal X-ray diffraction studies have been performed on [(CNC)NiBr2] (where CNC=2,6-bis(N-octylbenzimidazolin-2-ylidene)pyridine) and [(CNC)NiBr]BPh 4 (where CNC=2,6-bis(N-butyl-5,6-dimethoxybenzimidazolin-2-ylidene) pyridine).
- Magee, Karen D.M.,Travers, Guy,Skelton, Brian W.,Massi, Massimilliano,Payne, Alan D.,Brown, David H.
-
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Read Online
- Palladium-catalyzed anti-Markovnikov oxidative acetalization of activated olefins with iron(iii) sulphate as the reoxidant
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This paper discloses the efficient palladium-catalyzed anti-Markovnikov oxidative acetalization of activated terminal olefins with iron(iii) sulfate as the reoxidant. This methodology requires mild reaction conditions and shows high regioselectivity toward anti-Markovnikov products and compatibility with a wide range of functional groups. Iron(iii) sulphate was the sole reoxidant used in this method. Various olefins like vinylarenes, aryl-allylethers, aryl or benzyl acrylates and homoallylic alcohols all reacted well providing anti-Markovnikov acetals, some of which represent orthogonally functionalized 1,3- and 1,4-dioxygenated compounds.
- Fernandes, Rodney A.,Kumar, Praveen,Yadav, Sandhya S.
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p. 427 - 443
(2022/01/20)
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- Iron(II) and Copper(I) Control the Total Regioselectivity in the Hydrobromination of Alkenes
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A new method that allows the complete control of the regioselectivity of the hydrobromination reaction of alkenes is described. Herein, we report a radical procedure with TMSBr and oxygen as common reagents, where the formation of the anti-Markovnikov product occurs in the presence of parts per million amounts of the Cu(I) species and the formation of the Markovnikov product occurs in the presence of 30 mol % iron(II) bromide. Density functional theory calculations combined with Fukui's radical susceptibilities support the obtained results.
- Cruz, Daniel A.,Sinka, Victoria,De Armas, Pedro,Steingruber, Hugo Sebastian,Fernández, Israel,Martín, Víctor S.,Miranda, Pedro O.,Padrón, Juan I.
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supporting information
p. 6105 - 6109
(2021/08/18)
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- Application of Bifunctional 2-Amino-1,4-naphthoquinones in Visible-Light-Promoted Photocatalyst-Free Alkene Perfluoroalkyl-Alkenylation
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A simple and practical photochemical strategy for intermolecular perfluoroalkyl-alkenylation of alkenes with 2-amino-1,4-naphthoquinones and perfluoroalkyl iodides has been demonstrated under visible-light irradiation. Mechanistic studies reveal that easily available 2-amino-1,4-naphthoquinone substrates can serve as efficient photosensitizers to activate perfluoroalkyl iodides through a photoredox process. Therefore, the developed radical relay reaction proceeds smoothly without additional transition metals and photocatalysts.
- Tang, Lin,Yang, Fang,Yang, Zhen,Chen, Hanfei,Cheng, Hao,Zhang, Shuaifei,Zhou, Qiuju,Rao, Weihao
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supporting information
p. 519 - 524
(2021/02/03)
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- Organophotoredox/palladium dual catalytic decarboxylative Csp3-Csp3coupling of carboxylic acids and π-electrophiles
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A dual catalytic decarboxylative allylation and benzylation method for the construction of new C(sp3)-C(sp3) bonds between readily available carboxylic acids and functionally diverse carbonate electrophiles has been developed. The new process is mild, operationally simple, and has greatly improved upon the efficiency and generality of previous methodology. In addition, new insights into the reaction mechanism have been realized and provide further understanding of the harnessed reactivity.
- Cartwright, Kaitie C.,Tunge, Jon A.
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p. 8167 - 8175
(2020/09/09)
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- Nickel-catalyzed removal of alkene protecting group of phenols, alcohols via chain walking process
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An efficient nickel-catalyzed removal of alkene protection group under mild condition with high functional group tolerance through chain walking process has been established. Not only phenolic ethers, but also alcoholic ethers can be tolerated with the retention of stereocenter adjacent to hydroxyl group. The new reaction brings the homoallyl group into a start of new type of protecting group.
- Meng, Chenkai,Niu, Haolin,Ning, Juehan,Wu, Wengang,Yi, Jun
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supporting information
(2020/02/04)
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- Linear Hydroaminoalkylation Products from Alkyl-Substituted Alkenes
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The regioselective conversion of alkyl-substituted alkenes into linear hydroaminoalkylation products represents a strongly desirable synthetic transformation. In particular, such conversions of N-methylamine derivatives are of great scientific interest, because they would give direct access to important amines with unbranched alkyl chains. Herein, we present a new one-pot procedure that includes an initial alkene hydroaminoalkylation with an α-silylated amine substrate and a subsequent protodesilylation reaction that delivers linear hydroaminoalkylation products with high selectivity from simple alkyl-substituted alkenes. For that purpose, new titanium catalysts have been developed, which are able to activate the α-C?H bond of more challenging α-silylated amine substrates. In addition, a direct relationship between the ligand structure of the new catalysts and the obtained regioselectivity is described.
- Warsitz, Michael,Doye, Sven
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supporting information
p. 15121 - 15125
(2020/10/23)
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- Reductive C-O, C-N, and C-S Cleavage by a Zirconium Catalyzed Hydrometalation/β-Elimination Approach
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A zirconium catalyzed reductive cleavage of Csp3 and Csp2 carbon-heteroatom bonds is reported that makes use of a tethered alkene functionality as a traceless directing group. The reaction is successfully demonstrated on C-O, C-N, and C-S bonds and proposed to proceed via a hydrozirconation/β-heteroatom elimination sequence of an in situ formed zirconium hydride catalyst. The positional isomerization of the catalyst further enables the cleavage of homoallylic ethers and the removal of terminal allyl and propargyl groups.
- Matt, Christof,K?lblin, Frederic,Streuff, Jan
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p. 6983 - 6988
(2019/09/09)
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- Tuning Regioselectivity of Wacker Oxidation in One Catalytic System: Small Change Makes Big Step
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A regioselectivity switchable aerobic Wacker-Tsuji oxidation has been developed using catalytic tert-butyl nitrite as a simple organic redox cocatalyst. By solely switching the solvent, either substituted aldehydes or ketones could be prepared under mild
- Hu, Kang-Fei,Ning, Xiao-Shan,Qu, Jian-Ping,Kang, Yan-Biao
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p. 11327 - 11332
(2018/09/06)
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- Radical Hydrodehalogenation of Aryl Bromides and Chlorides with Sodium Hydride and 1,4-Dioxane
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A practical method for radical chain reduction of various aryl bromides and chlorides is introduced. The thermal process uses NaH and 1,4-dioxane as reagents and 1,10-phenanthroline as an initiator. Hydrodehalogenation can be combined with typical cyclization reactions, proving the nature of the radical mechanism. These chain reactions proceed by electron catalysis. DFT calculations and mechanistic studies support the suggested mechanism.
- Hokamp, Tobias,Dewanji, Abhishek,Lübbesmeyer, Maximilian,Mück-Lichtenfeld, Christian,Würthwein, Ernst-Ulrich,Studer, Armido
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supporting information
p. 13275 - 13278
(2017/10/09)
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- Intermolecular Palladium-Catalyzed Oxidative Fluorocarbonylation of Unactivated Alkenes: Efficient Access to β-Fluorocarboxylic Esters
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A novel palladium-catalyzed intermolecular oxidative fluorocarbonylation of alkenes has been developed, in which employment of a cooperative process with electrophilic ArIF2-meidated alkenes activation and palladium-catalyzed carbonylation is c
- Qi, Xiaoxu,Yu, Feng,Chen, Pinhong,Liu, Guosheng
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supporting information
p. 12692 - 12696
(2017/10/06)
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- Visible-light-induced thiotrifluoromethylation of terminal alkenes with sodium triflinate and benzenesulfonothioates
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An unconventional reductive quenching cycle was developed to realize the visible-light-induced thiotrifluoromethylation of terminal alkenes. CF3SO2Na was used as an easy to handle CF3 radical source to afford the desired products in moderate to good yields. Mild reaction conditions and a broad substrate scope feature in this transformation.
- Kong, Weiguang,An, Hejun,Song, Qiuling
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supporting information
p. 8968 - 8971
(2017/08/15)
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- Regioselective Alkoxycarbonylation of Allyl Phenyl Ethers Catalyzed by Pd/dppb under Syngas Conditions
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A simple and regioselective synthesis of phenoxy esters and phenylthio esters is reported. The products are obtained by selective alkoxycarbonylation catalyzed by Pd2(dba)3, 1,4-bis(diphenylphisphino)butane (dppb), and syngas (CO/H2) in chloroform/alcohol. This methodology affords bifunctional products in good yield with excellent n-selectivity and without the need to use additives.
- Amézquita-Valencia, Manuel,Alper, Howard
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p. 3860 - 3867
(2016/05/24)
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- Iron-catalyzed olefin hydrogenation at 1 bar H2 with a FeCl3-LiAlH4 catalyst
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The scope and mechanism of a practical protocol for the iron-catalyzed hydrogenation of alkenes and alkynes at 1 bar H2 pressure were studied. The catalyst is formed from cheap chemicals (5 mol% FeCl3-LiAlH4, THF). A homogeneous mechanism operates at early stages of the reaction while active nanoparticles form upon ageing of the catalyst solution. This journal is
- Gieshoff, Tim N.,Villa, Matteo,Welther, Alice,Plois, Markus,Chakraborty, Uttam,Wolf, Robert,Jacobi Von Wangelin, Axel
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supporting information
p. 1408 - 1413
(2015/03/18)
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- Synthesis and functionalization of inherently chiral tetraoxacalix[2] arene[2]pyridines
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Inherently chiral tetraoxacalix[2]arene[2]pyridines containing C 2 symmetry were synthesized efficiently from a macrocyclic condensation reaction of resorcinol derivatives with 2,6-dichloro-3- nitropyridine in a one-pot reaction manner, while tetraoxacalix[2]arene[2] pyridine with an ABCD-substitution pattern was prepared in a good yield by means of a stepwise fragment coupling approach. Postmacrocyclization chemical manipulations led to functionalized tetraoxacalix[2]arene[2]pyridines. A racemic sample was resolved into enantiopure (+)- and (-)-inherently chiral compounds.
- Pan, Shuai,Wang, De-Xian,Zhao, Liang,Wang, Mei-Xiang
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supporting information
p. 6254 - 6257
(2013/02/23)
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- Synthesis of (-)-astrogorgiadiol
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Astrogorgiadiol is a naturally occurring Vitamin D analogue that, in cell culture, downregulates the production of the cytokine osteopontin (OPN). OPN has been implicated in virulent asthma, and OPN knockout mice do not develop osteoporosis. As we have pursued whole animal studies with astrogorgiadiol, we have increased the scale of the synthesis. We report an improved preparation of the A-ring synthon and the scale-up of the diasteromerically pure D-ring/sidechain chiron.
- Taber, Douglass F.,Raciti, David M.
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experimental part
p. 10229 - 10233
(2012/02/03)
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- ISOXAZOLINES AS INHIBITORS OF FATTY ACID AMIDE HYDROLASE
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The present invention provides isoxazoline FAAH inhibitors of the formula (I): or pharmaceutically acceptable forms thereof, wherein each of G, Ra, Rb, Rc, and Rd are as defined herein. The present invention also provides pharmaceutical compositions comprising a compound of formula (I), or a pharmaceutically acceptable form thereof, and a pharmaceutically acceptable excipient. The present invention also provides methods for treating an FAAH-mediated condition comprising administering a therapeutically effective amount of a compound of formula (I), or pharmaceutically acceptable form thereof, to a subject in need thereof.
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Page/Page column 196
(2010/12/18)
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- Copper(I)-catalyzed aryl bromides to form intermolecular and intramolecular carbon-oxygen bonds
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(Chemical Equation Presented) A highly efficient Cu-catalyzed C-O bond-forming reaction of alcohol and aryl bromides has been developed. This transformation was realized through the use of copper(I) iodide as a catalyst, 8-hydroxyquinoline as a ligand, and K3PO4 as a base. A variety of functionalized substrates were found to react under these reaction conditions to provide products in good to excellent yields.
- Niu, Jiajia,Guo, Pengran,Kang, Juntao,Li, Zhigang,Xu, Jingwei,Hu, Shaojing
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supporting information; experimental part
p. 5075 - 5078
(2009/10/17)
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- An efficient Ullmann-type C-O bond formation catalyzed by an air-stable copper(I)-bipyridyl complex
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(Chemical Equation Presented) An efficient O-arylation of phenols and aliphatic alcohols with aryl halides was developed that uses an air-stable copper(I) complex as the catalyst. This arylation reaction can be performed in good yield in the absence of Cs2CO3. A variety of functional groups are compatible with these reaction conditions with low catalyst loading levels.
- Niu, Jiajia,Zhou, Hua,Li, Zhigang,Xu, Jingwei,Hu, Shaojing
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p. 7814 - 7817
(2008/12/22)
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- Iron-catalyzed cross-coupling of alkyl halides with alkenyl Grignard reagents
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(Chemical Equation Presented) Cheap and safe: An iron-catalyzed cross-coupling reaction between alkyl halides and alkenyl Grignard reagents is described. This C-C bond coupling reaction is promoted by the cheap and nontoxic FeCl3 and displays good tolerance against various functional groups.
- Guerinot, Amandine,Reymond, Sebastien,Cossy, Janine
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p. 6521 - 6524
(2008/09/16)
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- Anions from dihydro substituted ethyl benzoates and quinoline. New hydrogen donors for tin-free radical chemistry
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The anions of substituted dihydro ethyl benzoates and quinoline are very good hydrogen donors to radicals in liquid ammonia and DMSO. With 4-substituted dihydro ethyl benzoates the rate of hydrogen transfer decreases and excellent yields of products are obtained by 6-exo ring closure reaction followed by reduction.
- Bardagí, Javier I.,Vaillard, Santiago E.,Rossi, Roberto A.
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p. 3149 - 3152
(2007/10/03)
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- Thionation using fluorous Lawesson's reagent
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Thionation of amides, 1,4-diketones, N-(2-oxoalkyl)amides, N,N-acylhydrazines, and acyl-protected uridines with the use of a fluorous analogue of the Lawesson's reagent leads to thioamides, thiophenes, 1,3-thiazoles, 1,3,4-thiadiazoles, and acyl-protected 4-thiouridines. The isolation of the final products in high yields is achieved in most cases by a simple filtration (fluorous solid-phase extraction).
- Kaleta, Zoltan,Makowski, Brian T.,Soos, Tibor,Dembinski, Roman
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p. 1625 - 1628
(2007/10/03)
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- Photo-induced radical cyclization of aromatic halides with sodium borohydride
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Direct UV irradiation of ortho-allyloxy- and ortho-but-3-enyloxy-iodo- and bromo-benzenes in the presence of NaBH4 or NaBH3CN gave radical cyclization products in high yield. Georg Thieme Verlag Stuttgart.
- Liu, Qiang,Han, Bing,Zhang, Wei,Yang, Li,Liu, Zhong-Li,Yu, Wei
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p. 2248 - 2250
(2007/10/03)
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- Exploring SmBr2-, SmI2-, and YbI2-mediated reactions assisted by microwave irradiation
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The use of microwave heating in lanthanide(II) halide (LnX2 = SmBr2, SmI2, and YbI2) mediated reduction and coupling reactions has been investigated for a variety of functional groups including α,β-unsaturated esters, aldehydes, ketones, imines, and alkyl halides. Good to quantitative transformations were obtained within a few minutes without the addition of any co-solvents, such as hexamethyl phosphoramide (HMPA). The redox potential of YbI2 in tetrahydrofuran (THF) has been determined as -1.02± 0.05 V (versus Ag/AgNO3) by cyclic voltammetry. A large selectivity difference in various reactions was observed depending on the redox potential of the LnX2 reagent. The more powerful reductant, SmBr2, afforded mainly pinacol-coupling products of ketones whereas the weaker reductant YbI2 afforded mainly reduction products. The results indicate that the reducing power of LnX 2 has a large impact on not only the pinacol coupling/reduction product ratio of ketones but also on other substrates in which there are competing coupling and reduction reactions. The use of in situ generated LnX2 has also been explored and proven useful in many of these reactions.
- Dahlen, Anders,Prasad, Edamana,Flowers II, Robert A.,Hilmersson, Goeran
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p. 3279 - 3284
(2007/10/03)
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- Diastereoselective intramolecular SmI2-H2O-amine mediated couplings
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The effectiveness of SmI2-H2O-amine mixture for intramolecular couplings was discussed. Diastereoselectivities in the coupling of O-cyclohexanyliodophenol derivatives were provided into heterocycles. The amount of coupled product improved significantly as SmI2, the substrate and amine were premixed followed by a gradual addition of water.
- Dahlen, Anders,Petersson, Annika,Hilmersson, Goeran
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p. 2423 - 2426
(2007/10/03)
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- Reactivity of aryl and vinyl radicals: Abstraction of hydrogen atom or reaction with a nucleophile
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The reactivities of aryl and vinyl radicals, two fundamental transient intermediates, have been investigated with respect to two elementary processes: H-atom abstraction and reaction with a nucleophile (Y-, in the SRN1 reaction). The radicals of interest were generated from haloarene or haloethene precursors, either by use of the Bu3SnH/AIBN system or by photostimulated electron transfer from a nucleophile, and the partition of the intermediate radical between competing pathways was investigated. Use both of indirect methods (such as the study of the reaction products in competition experiments; use of a radical-clock probe) and of direct ones (such as the detection of the radicals by flash photolysis experiments) enabled the following rate constants to be obtained (all values in m-l.s-1 at 25 °C). For phenyl type radicals, the rate constants for H abstraction (kH) from the solvents Me2SO (2.8.106) and CH3CN (6.7.106) and the rate constant for combination with a nucleophile (ky) such as Me3CCOCH2- ion (3.3.109) were determined. For vinyl radical Ph2C=C(.)Ph (7.), the kH values from Me2SO (1.1.105), CH3CN (1.2.105), Bu3SnH(7.5-108), and (Me3Si)3SiH (1.6.109) and the ky values with Me3CCOCH2- (3.9.107), (EtO)2PO(2.8.106), and PhS- (1.9.107) ions were determined. Semiempirical calculations confirmed a stabilization of radical 7.by the α-Ph substituent (ca. 8 kcal/mol), and provided the BDE of the C-Y bond for the vinylic substitution products of 7.. Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002).
- Branchi, Barbara,Galli, Carlo,Gentili, Patrizia
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p. 2844 - 2854
(2007/10/03)
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- Substituent effects on the rate constants for the photo-claisen rearrangement of allyl aryl ethers
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The photochemistry of 11 substituted allyl 4-X- and 3-X-aryl ethers 3 (ArOCH2-CH=CH2) has been examined in both methanol and cyclohexane as solvents. The ethers react by the photo-Claisen rearrangement to give allyl substituted phenols as the major primary photoproducts, as expected from the well-established radical pair mechanism. The excited singlet state properties (absorption spectra, fluorescence spectra, fluorescence quantum yields, and singlet lifetimes) were compared with a parallel set of unreactive 4-X- and 3-X-anisoles 4. The excited-state properties of three substituted 4-X-aryl 4-(1-butenyl) ethers 14 (ArOCH2CH2-CH=CH2) were also examined. The model compounds 4 and the reactive allyl ethers 3 have essentially identical rate constants for the excited-state processes with the exception of khoms, the rate constant for homolytic cleavage from S1 of the allyl ethers to give the radical pair. The difference between the fluorescence quantum yields and/or singlet lifetimes for 3 and 4 were used to obtain values of khoms for all of the allyl ethers. These values exhibit a large substituent effect, spanning almost 2 orders of magnitude with electron-donating groups (CH3O, CH3) accelerating the reaction and electron-withdrawing ones (CN, CF3) slowing it down. The parallel range of rate constants observed in both methanol and cyclohexane indicates that ion pairs are not important intermediates in these rearrangements. Quantum yields of reaction (Φr) for several of the more reactive ethers demonstrate that neither these values nor rate constants of reaction (khomr) derived from them are reliable measures of the actual excited-state process. In fact, the khomr values are significantly lower than the khoms ones, indicating that the radical pairs undergo recombination to generate starting material. Finally, the khoms rate constants were found to parallel a trend for the change in bond dissociation energy (ΔBDE) for the O-C (allyl) bond of the allyl ethers, indicating that other possible substituent effects are of minor importance.
- Pincock, Alexandra L.,Pincock, James A.,Stefanova, Roumiana
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p. 9768 - 9778
(2007/10/03)
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- Determination of rate constants for the reaction of aryl radicals with enolate ions
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The rate of ring closure (kC) of o-(ω-alkenyl)aryl radicals by means of an intramolecular attack of the intermediate phenyl-type radical at the tethered double bond was found to be 4.2 × 108 S-1 (for 1?) and 7.6×107 S-1 (for 8?), both being 6-exo-trig processes, and 9.6 × 109 S-1 for the 5-exo-trig process of 3?. The kC rate constant of these radicals was calibrated with respect to a known rate of H-atom abstraction (kH). The photostimulated SRN1 reactions of radical clock precursor 1 with anions PhS- and (EtO)2PO- in Me2SO at 25 °C provided the rates of addition of these nucleophiles (kY) to intermediate 1? (3.2 × 108 and 2.5 × 109 M-1 S-1, respectively). In contrast, the analogous reaction of a ketone enolate ion with precursor 1 did not take the expected SRN1 course; instead an elimination reaction was favoured. Similarly, the reactions of radical clock precursors 3 or 8 with the enolate ion failed. However, investigation of the distribution of 9-anthracenyl (11?) or 1-naphthyl (12?) radicals between two competing reactions, namely combination with a nucleophile and H abstraction from the solvent (Me2SO), was successful and eventually enabled us to find the kY values for the addition of the enolate ion to these two aryl radical intermediates (4.4 × 108 and 2.9 × 109 M-1 S-1, respectively).
- Annunziata, Alfonso,Galli, Carlo,Marinelli, Manuela,Pau, Tullia
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p. 1323 - 1329
(2007/10/03)
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- Intramolecular triplet energy transfer in flexible molecules: Electronic, dynamic, and structural aspects
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Exothermic intramolecular triplet energy transfer (TET) rate constants in various flexible bichromophoric systems D-(CH2)n-O-A (D = benzoyl, 4-methylbenzoyl; A = 2-naphthyl, 4-, 3-, 2-biphenyl; n = 3-14) have been determined from steady-state quenching and quantum yield measurements. The magnitude of the rate constants in molecules where n = 3 is comparable to those in molecules with a rigid spacer between chromophores, so that a through-bond mechanism is presumed to remain important. A very gradual drop in TET rate constants as the connecting polymethylene chain becomes longer indicates that through-space interactions compete and apparently provide the only mechanism responsible for transfer when n ≥ 5. Rate constants in long molecules (n = 11-14) remain remarkably high (~108 s-1) - lower than in those with four-atom tethers by only 1 order of magnitude. This effect is explained on the basis of rapid conformational equilibria always keeping a sufficient fraction of the molecules coiled so that the two chromophores are close enough to interact within 10 ns, the time required for the competing γ-hydrogen abstraction used to monitor triplet lifetimes. Energy transfer accounts for 40-75% of triplet decay for the longer molecules. This high efficiency indicates that only a small fraction involves static quenching in ground-state conformers with the two ends within 4 A. The majority must represent a combination of rate-determining bond rotations to such geometries and equilibrated conformations with their ends farther apart but still able to undergo energy transfer within 10 ns. Thus, the measured rate constants are, in fact, a weighted average of three different conformational mechanisms. The decrease in rate constant with tether length is not monotonic: a relative increase in rate for medium-chain-length molecules is explained by a larger number of favorable conformers and further, in biphenyl derivatives, by a rotation along the terminal O-C bond between the tether and the aromatic ring. As was expected, replacement of the polymethylene tether with poly(ethylene oxide) promotes better flexibility and thus higher transfer rates. Rate constants were found to be lower by a factor of ~2 when biphenyl rather than naphthyl is the acceptor, in agreement with earlier bimolecular measurements. With the 4-methylbenzoyl group (π,π* lowest triplet) as donor instead of benzoyl (n,π* lowest triplet), a small (~1.5x) but consistent rate increase occurred for all tether lengths.
- Wagner, Peter J.,Klan, Petr
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p. 9626 - 9635
(2007/10/03)
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- Auxiliary accelerated reactions: Towards the use of catalytic chiral auxiliaries
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In competition experiments, the acceleration of reactivity of alkenes tethered to pyridyl groups compared with the corresponding alkenes tethered to phenyl groups in the presence of transition metals was demonstrated for two reaction types: Diels-Alder cycloaddition of enoate esters and catalytic hydrogenation of allylic and homoallylic ethers. The rate accelerations observed are of crucial importance in the development of a new concept for asymmetric catalysis: chiral auxiliaries which can function in a catalytic manner.
- Westwell, Andrew D.,Williams, Jonathan M. J.
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p. 13063 - 13078
(2007/10/03)
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- Intramolecular ortho and meta photocycloadditions of 3-alkyl-4-phenoxybut-1-enes
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Upon irradiation of 3-alkyl-4-phenoxybut-1-enes 1a-d at 254 nm in cyclohexane, ortho and meta photocycloadditions occur. The ortho photocycloadducts rearrange readily, while the meta photocycloaddition involves the 2′,6′-positions of the arene as directed
- Van Der Eycken, Erik,De Keukeleire, Denis,De Bruyn, Andre
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p. 3573 - 3576
(2007/10/02)
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- Cobalt-mediated Radical Reactions in Organic Synthesis. Oxidative Cyclisations of Aryl and Alkyl Halides leading to Functionalised Reduced Heterocycles and Butyrolactones
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Reactions between the CoI species derived from cobalt(III) salen (11) or cobalt(II) salophen (12) and (O-allyl) or (O-but-3-enyl) iodophenols lead to isolatable cobalt complexes, viz. (16) and (27), which can be converted into substituted benzofurans, i.e. (17) and (23), and benzopyrans, i.e. (28) and (34); similarly, interaction between compound (36) and Co1 salen led in one step to 1,3-dimethylindole (37).Radical cyclisation of the acetal (38a) in the presence of Co1 cobaloxime leads to the cis-ring-fused alkyl cobalt complex (42), which can be converted in a preparative manner into lactone (44) following 1,2-elimination and hydrolysis/oxidation, and into lactone (53) following insertion of molecular oxygen , reduction and hydrolysis/oxidation.
- Bhandal, Harcharan,Patel, Vinod F.,Pattenden, Gerald,Russell, Jamie J.
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p. 2691 - 2701
(2007/10/02)
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- Rate Constants for the Cyclisation of Some Aryl Radicals bearing Unsaturated ortho-Substituents
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Rate constants and Arrhenius parameters have been determined for ring-closure of o-alkenyl- and o-alkenyloxy-aryl radicals, and for deuterium atom transfer from tributyltin deuteride.
- Abeywickrema, Anil N.,Beckwith, Athelstan L. J.
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p. 464 - 465
(2007/10/02)
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- HOMOLYTIC REDUCTIVE DEHALOGENATION OF ARYL HALIDES BY SODIUM BOROHYDRIDE
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Aryl iodides and some bromides, but not chlorides or fluorides, undergo efficient dehalogenation by UV photostimulated reduction with sodium borohydride and a free radical initiator in dimethylformamide.
- Abeywickrema, Anil N.,Beckwith, Athelstan L.J.
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p. 109 - 112
(2007/10/02)
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- SYNTHESIS OF BENZOFURANS, INDOLES AND BENZOPYRANS VIA OXIDATIVE FREE RADICAL CYCLISATIONS USING COBALT SALEN COMPLEXES.
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Reactions between the Co(I) species derived from cobalt(III) 'salen'(1), and (O-allyl) or (O-but-3-enyl)iodophenol, leads to isolatable cobalt complexes, viz (2), (13), which can be converted into substituted benzofurans, i.e. (5), (6) and benzopyrans, i.e. (14), (15); similarly interaction between (18) and Co(I) 'salen' led, in one step, to the 3-methylindole (19).
- Patel, Vinod F.,Pattenden, Gerald,Russell, Jamie J.
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p. 2303 - 2306
(2007/10/02)
-