- MASS SPECTROMETRY FOR INVESTIGATIONS OF GAS-PHASE RADICAL CATION CHEMISTRY. THE TWO STEP CYCLOADDITION OF THE BENZENE RADICAL CATION AND 1,3-BUTADIENE
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Mass spectrometric techniques are now used extensively for the study of gas-phase radical cation chemistry.The generation and structural properties, the unimolecular and bimolecular chemistry of some representative radical cation systems, and the methods of study are reviewed.The structure of the ionmolecule adduct produced in the reaction of the benzene radical cation and neutral 1,3-butadiene was investigated by collisionally stabilizing the adduct and then acquiring its collision-activated decomposition spectrum.The CAD spectrum of the adduct changes dramatically as a function of the degree of collisional stabilization.This observation is interpreted in terms of two distinct structures for the adduct.The species that is stabilized at 0.7 Torr has a CAD spectrum similar to the 2-phenyl-2-butene radical cation.The second structure, stabilized at 0.1 Torr, has a CAD similar to that of 1-methylindan.The results of these experiments are interpreted in terms of a two-step cycloaddition mechanism for the formation of the 1-methylindan radical cation.
- Holman, R. W.,Rozeboom, M. D.,Gross, M. L.,Warner, C. D.
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- Reductive Cyclization of o-(3-Butenyl)fluorobenzene at Mercury and Lead Cathodes
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The cathodic behavior of o-(3-butenyl)fluorobenzene (1) at mercury and lead cathodes in DMF was investigated.Cyclic voltammograms were recorded, and the products of preparative electrolyses were isolated and identified.The reduction products at either cathode were 1-methylindane (3) and 3-butenylbenzene (2), the first predominating in all experiments with dry solvent.The effects of various reaction conditions on the product composition were studied, and the highest yield of 3 was obtained at a lead cathode at 22 deg C (3/2 = 3.8).Dimethylpyrrolidinium (DMP+) was tested as a possible catalyst for the reduction of 1.It catalyzed the reaction and increased the proportionate amount of the cyclic product.However the mediated process at lead was very inefficient.The mechanism for the reductive cyclization of 1 at mercury and lead and the mediation by DMP+ are discussed.It is proposed that tetraalkylammonium-metals are involved in these processes.
- Loffredo, David M.,Swartz, James E.,Kariv-Miller, Essie
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- Exploiting the radical reactivity of diazaphosphinanes in hydrodehalogenations and cascade cyclizations
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The remarkable reducibility of diazaphosphinanes has been extensively applied in various hydrogenations, based on and yet limited by their well-known hydridic reactivity. Here we exploited their unprecedented radical reactivity to implement hydrodehalogenations and cascade cyclizations originally inaccessible by hydride transfer. These reactions feature a broad substrate scope, high efficiency and simplicity of manipulation. Mechanistic studies suggested a radical chain process in which a phosphinyl radical is generated in a catalytic cycle via hydrogen-atom transfer from diazaphosphinanes. The radical reactivity of diazaphosphinanes disclosed here differs from their well-established hydridic reactivity, and hence, opens a new avenue for diazaphosphinane applications in organic syntheses.
- Cheng, Jin-Pei,Yang, Jin-Dong,Zhang, Jingjing
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p. 4786 - 4790
(2020/06/18)
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- Computational Insight into 1,2-Diamine, -Diether, and -Amino Ether Chiral Ligand-Mediated Carbolithiation: A Case of Enantioinduction Reversal
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trans-1,2-Cyclohexanediamine, -diether, and -amino ether were compared as chiral inducers in the asymmetric intramolecular carbolithiation of olefinic aryllithiums. Switching from diamine to ethereal ligands inverts the sense of asymmetric induction. This reversal of stereoselectivity was investigated through density functional theory calculations. High enantioselectivities observed with diether and amino ether ligands arise from favorable weak interactions between the ligand and the substrate. The relative efficiency of the three ligands and sense of stereoinduction for the most efficient diether and amino ether ligands prove to be foreseeable by modeling the reaction with the parent achiral 1,2-bidentate additives and comparing the diastereomeric transition states stemming from the two half-chair conformations of their lithium chelate.
- Guyon, Hélène,Castanet, Anne-Sophie,Boussonnière, Anne
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p. 8933 - 8943
(2020/08/28)
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- Visible-Light-Induced, Base-Promoted Transition-Metal-Free Dehalogenation of Aryl Fluorides, Chlorides, Bromides, and Iodides
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We report a simple and efficient visible-light-induced transition-metal-free hydrogenation of aryl halides. The combined visible light and base system is used to initiate the desired radical-mediated hydrogenation. A variety of aryl fluorides, chlorides, bromides, and iodides could be reduced to the corresponding (hetero)arenes with excellent yields under mild conditions. Various functional groups and other heterocyclic compounds are tolerated.
- Ding, Ting-Hui,Qu, Jian-Ping,Kang, Yan-Biao
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supporting information
p. 3084 - 3088
(2020/04/10)
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- Competing dehalogenation versus borylation of aryl iodides and bromides under transition-metal-free basic conditions
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In this work, selectivity-controllable base-promoted transition-metal-free borylation and dehalogenation of aryl halides are described. Under the conditions of borylation, the dehalogenation which emerges as a competitive side reaction has been well-controlled by carefully controlling the borylation conditions. On the other hand, the dehalogenation using benzaldehyde as a hydrogen source has also been accomplished. The applications of direct radical borylation and dehalogenation of aryl halides demonstrate their synthetic practicability in pharmaceutical-oriented organic synthesis. Based on the experimental evidences, the tBuOK/1,10-Phen-triggered radical nature of both competitive reactions has been revealed.
- Niu, Yi-Jie,Sui, Guo-Hui,Zheng, Hong-Xing,Shan, Xiang-Huan,Tie, Lin,Fu, Jia-Le,Qu, Jian-Ping,Kang, Yan-Biao
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p. 10805 - 10813
(2019/09/30)
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- Remote, Diastereoselective Cobalt-Catalyzed Alkene Isomerization-Hydroboration: Access to Stereodefined 1,3-Difunctionalized Indanes
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The remote, diastereoselective hydroboration of 2- and 3-substituted indenes with a 2,2′:6′,2″-terpyridine cobalt alkyl precatalyst is described that maintains high regio- and stereoselectivity independent of the starting position of the alkene. Several 1,2- and 1,3-disubstituted indanyl boronate esters were obtained with exclusive (>20:1 dr) selectivity for the trans diastereomer including synthetically versatile, stereodefined diboron derivatives. Alkene isomerization by a putative cobalt hydride intermediate precedes carbon-boron bond formation, leading to the observed regioselectivity for boron incorporation at the unsubstituted C(sp3)-H benzylic site. The regio- and diastereoselectivity of the transformation were maintained independent of the starting position of the alkene, as demonstrated by hydroboration of three isomers of methyl-substituted indene. Deuterium-labeling experiments support rapid and reversible insertion and β-hydride elimination to isomerize 3-methylindene and 1-exo-methylene-indane, accounting for the isotopic distribution observed in the products. Mechanistic studies, including stoichiometric experiments, density functional theory calculations, and kinetic analysis, support a mechanism in which 2,3-alkene insertion into a cobalt hydride intermediate determines both the regio- and diastereoselectivity of the catalytic reaction. Synthetic applications of the indanyl boronate esters were demonstrated through the elaboration of the products to several examples of 1,3-disubstituted indanes, important carbocyclic structural motifs in both pharmacological and bioactive molecules.
- Léonard, Nadia G.,Palmer, W. Neil,Friedfeld, Max R.,Bezdek, Máté J.,Chirik, Paul J.
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p. 9034 - 9044
(2019/10/02)
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- Ligand-free nickel-catalyzed Kumada couplings of aryl bromides with tert-butyl Grignard reagents
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A ligand-free nickel-catalyzed Kumada cross-coupling of aryl bromides and tert-butyl Grignard reagents led to the formation of a series of tert-butyl aryls in moderate to good yields, excellent tBu/iBu ratios, and good functional group compatibility. A radical coupling process is indicated and a mechanism with a Ni(I)-Ni(III) catalytic cycle is proposed.
- Wu, Zhenghan,Si, Tengda,Xu, Guangqing,Xu, Bin,Tang, Wenjun
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supporting information
p. 597 - 600
(2019/01/05)
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- Air-Stable α-Diimine Nickel Precatalysts for the Hydrogenation of Hindered, Unactivated Alkenes
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Treatment of a mixture of air-stable nickel(II) bis(octanoate), Ni(O2CC7H15)2, and α-diimine ligand, iPrDI or CyADI (iPrDI = [2,6-iPr2-C6H3N=C(CH3)]2, CyADI = [C6H11N=C(CH3)]2) with pinacolborane (HBPin) generated a highly active catalyst for the hydrogenation of hindered, essentially unfunctionalized alkenes. A range of tri- and tetrasubstituted alkenes was hydrogenated and a benchtop procedure for the hydrogenation of 1-phenyl-1-cyclohexene on a multigram scale was demonstrated and represents an advance in catalyst activity and scope for the nickel-catalyzed hydrogenation of this challenging class of alkenes. Deuteration of 1,2-dimethylindene with the in situ-generated nickel catalyst with iPrDI exclusively furnished the 1,2-syn-d2-dimethylindane. With cyclic trisubstituted alkenes, such as 1-methyl-indene and methylcyclohexene, deuteration with the in situ generated nickel catalyst under 4 atm of D2 produced multiple deuterated isotopologues of the alkanes, signaling chain running processes that are competitive with productive hydrogenation. Stoichiometric studies, titration, and deuterium labeling experiments identified that the borane reagent served the dual role of reducing nickel(II) bis(carboxylate) to the previously reported nickel hydride dimer [(iPrDI)NiH]2 and increasing the observed hydrogenation activity. Performing the catalyst activation procedure with D2 gas and HBPin generated both HD and DBPin, establishing that the borane is involved in H2 activation as judged by 1H and 11B nuclear magnetic resonance spectroscopies.
- Léonard, Nadia G.,Chirik, Paul J.
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p. 342 - 348
(2018/01/17)
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- Transition-metal-free hydrogenation of aryl halides: From alcohol to aldehyde
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A transition-metal-and catalyst-free hydrogenation of aryl halides, promoted by bases with either aldehydes or alcohols, is described. One equivalent of benzaldehyde affords an equal yield as that of 0.5 equiv of benzyl alcohol. The kinetic study reveals that the initial rate of PhCHO is much faster than that of BnOH, in the ratio of nearly 4:1. The radical trapping experiments indicate the radical nature of this reaction. Based on the kinetic study, trapping and KIE experiments, and control experiments, a tentative mechanism is proposed. As a consequence, a wide range of (hetero)aryl iodides and bromides were efficiently reduced to their corresponding (hetero)arenes. Thus, for the first time, aldehydes are directly used as hydrogen source instead of other well-established alcohol-hydrogen sources.
- Zheng, Hong-Xing,Shan, Xiang-Huan,Qu, Jian-Ping,Kang, Yan-Biao
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p. 5114 - 5117
(2017/11/07)
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- Copper-Catalyzed Dicarbofunctionalization of Unactivated Olefins by Tandem Cyclization/Cross-Coupling
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We present a strategy that difunctionalizes unactivated olefins in 1,2-positions with two carbon-based entities. This method utilizes alkyl/arylzinc reagents derived from olefin-tethered alkyl/aryl halides that undergo radical cyclization to generate C(sp3)-Cu complexes in situ, which are intercepted with aryl and heteroaryl iodides. A variety of (arylmethyl)carbo- and heterocycles (N, O) can be synthesized with this new method.
- Thapa, Surendra,Basnet, Prakash,Giri, Ramesh
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supporting information
p. 5700 - 5703
(2017/05/04)
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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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- Readily Accessible 1,2-Amino Ether Ligands for Enantioselective Intramolecular Carbolithiation
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A new class of chiral 1,2-amino ether ligands, readily accessible from naturally occurring α-amino- or α-hydroxy acids, was found to provide high levels of both conversion and stereocontrol (up to 95:5 er) in intramolecular carbolithiation reactions, outperforming the benchmark ligand (?)-sparteine. The ligand could be used in a substoichiometric amount (0.25 equiv) without significant loss of enantioselectivity.
- Guyon, Hélène,Boussonnière, Anne,Castanet, Anne-Sophie
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p. 4949 - 4957
(2017/05/12)
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- The Manganese-Catalyzed Cross-Coupling Reaction and the Influence of Trace Metals
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The substrate scope of the MnCl2-catalyzed cross-coupling between aryl halides and Grignard reagents has been extended to several methyl-substituted aryl iodides by performing the reaction at elevated temperature in a microwave oven. A radical clock experiment revealed the presence of an aryl radical as an intermediate leading to the proposal of an SRN1 pathway for the coupling. The mechanistic information gave rise to suspicion about two previously published cross-coupling reactions catalyzed by manganese(II) salts. As a result, the coupling between aryl halides and organostannanes as well as between aryl halides and amines were revisited. Both reactions were found impossible to reproduce without the addition of small amounts of palladium or copper and are therefore not believed to be catalyzed by manganese.
- Santilli, Carola,Beigbaghlou, Somayyeh Sarvi,Ahlburg, Andreas,Antonacci, Giuseppe,Fristrup, Peter,Norrby, Per-Ola,Madsen, Robert
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p. 5269 - 5274
(2017/09/29)
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- Arylation of hydrocarbons enabled by organosilicon reagents and weakly coordinating anions
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Over the past 80 years, phenyl cation intermediates have been implicated in a variety of C-H arylation reactions. Although these examples have inspired several theoretical and mechanistic studies, aryl cation equivalents have received limited attention in organic methodology. Their high-energy, promiscuous reactivity profiles have hampered applications in selective intermolecular processes. We report a reaction design that overcomes these challenges. Specifically, we found that b-silicon-stabilized aryl cation equivalents, generated via silylium-mediated fluoride activation, undergo insertion into sp3 and sp2 C-H bonds. This reaction manifold provides a framework for the catalytic arylation of hydrocarbons, including simple alkanes such as methane. This process uses low loadings of Earth-abundant initiators (1 to 5 mole percent) and occurs under mild conditions (30° to 100°C).
- Shao, Brian,Bagdasarian, Alex L.,Popov, Stasik,Nelson, Hosea M.
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- Single-Electron-Transfer-Induced Coupling of Alkylzinc Reagents with Aryl Iodides
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Alkylzinc reagents prepared from an alkyllithium and zinc iodide were found to undergo coupling with aryl and alkenyl iodides in the presence of LiI in a mixed solvent consisting of THF and diglyme (1:1). Alkyllithiums, prepared by halogen–lithium exchange between an alkyl iodide and tert-butyllithium, are also converted to alkylarenes through alkylzinc reagents.
- Okura, Keisho,Shirakawa, Eiji
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supporting information
p. 3043 - 3046
(2016/07/14)
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- A New Generation of Smart Amine Donors for Transaminase-Mediated Biotransformations
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The application of ω-transaminase biocatalysts for the synthesis of optically pure chiral amines presents a number of challenges, including difficulties associated with displacing the challenging reaction equilibria. Herein, we report a highly effective approach using low equivalents of the new diamine donor, cadaverine, which enables high conversions of challenging substrates to the corresponding chiral amines in excellent ee. This approach paves the way for the design of self-sufficient fermentation processes combining transaminase biotransformations with existing strategies for cadaverine production by decarboxylation of endogenous lysine.
- Gomm, Andrew,Lewis, William,Green, Anthony P.,O'Reilly, Elaine
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supporting information
p. 12692 - 12695
(2016/08/30)
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- Enantioselective Synthesis of Carbo- and Heterocycles through a CuH-Catalyzed Hydroalkylation Approach
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The enantioselective, intramolecular hydroalkylation of halide-tethered styrenes has been achieved through a copper hydride-catalyzed process. This approach allowed for the synthesis of enantioenriched cyclobutanes, cyclopentanes, indanes, and six-membered N- and O-heterocycles. This protocol was applied to the synthesis of the commercial serotonin reuptake inhibitor (ˉ)-paroxetine.
- Wang, Yi-Ming,Bruno, Nicholas C.,Placeres, ángel L.,Zhu, Shaolin,Buchwald, Stephen L.
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supporting information
p. 10524 - 10527
(2015/09/28)
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- Zinc-Catalyzed Dual C-X and C-H Borylation of Aryl Halides
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A zinc-catalyzed combined C-X and C-H borylation of aryl halides using B2pin2 (pin=OCMe2CMe2O) to produce the corresponding 1,2-diborylarenes under mild conditions was developed. Catalytic C-H bond activation occurs ortho to the halide groups if such a site is available or meta to the halide if the ortho position is already substituted. This method thus represents a novel use of a groupXII catalyst for C-H borylation. This transformation does not proceed via a free aryne intermediate, but a radical process seems to be involved. Two B or not two B: A novel catalytic system based on a ZnII-dtbpy precursor was developed for the preparation of 1,2-diborylarenes. This method represents a new type of catalytic process for diborylation of aryl halides via both C-X and C-H activation.
- Bose, Shubhankar Kumar,Deissenberger, Andrea,Eichhorn, Antonius,Steel, Patrick G.,Lin, Zhenyang,Marder, Todd B.
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supporting information
p. 11843 - 11847
(2015/10/05)
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- Gallium-assisted transfer hydrogenation of alkenes
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We report a rare case of alkene transfer hydrogenation using a main-group compound instead of a transition-metal complex as catalyst. We disclosed that 1, 4-cyclo-hexadiene can be used as H2 surrogate towards olefin reduction in the presence of [IPrGaCl2][SbF6]. Hydrogenative cycli-zations have also been carried out because this cationic gallium complex is also a potent hydroarylation catalyst.
- Michelet, Bastien,Bour, Christophe,Gandon, Vincent
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supporting information
p. 14488 - 14492
(2015/04/16)
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- ENANTIOPURE BASE-METAL CATALYSTS FOR ASYMMETRIC CATALYSIS AND BIS(IMINO)PYRIDINE IRON ALKYL COMPLEXES FOR CATALYSIS
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Disclosed herein are iron, nickel, or cobalt compounds having tridentate ligands, which can have at least one chiral moiety in the molecular structure thereof and the use of these compounds for the hydrogenation and transformation of olefins (preferably prochiral) and alkynes.
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Paragraph 0145; 0146; 0147
(2013/04/10)
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- Nickel-catalyzed hydrodehalogenation of aryl halides
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In the present study, the nickel-catalyzed dehalogenation of aryl and alkyl halides with iso-propyl zinc bromide or tert-butylmagnesium chloride has been examined in detail. With a straightforward nickel complex as pre-catalyst good to excellent yields and chemoselectivities were feasible for a variety of aryl and alkyl halides.
- Weidauer, Maik,Irran, Elisabeth,Someya, Chika I.,Haberberger, Michael,Enthaler, Stephan
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supporting information
p. 53 - 59
(2013/08/25)
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- Single electron transfer-induced Grignard cross-coupling involving ion radicals as exclusive intermediates
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The mechanism of the previously developed cross-coupling reaction of aryl Grignard reagents with aryl halides was explored in more detail. Single electron transfer from an aryl Grignard reagent to an aryl halide initiates a radical chain by giving an anion radical of the aryl halide. The following propagation cycle consists entirely of anion radical intermediates.
- Uchiyama, Nanase,Shirakawa, Eiji,Hayashi, Tamio
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p. 364 - 366
(2013/02/23)
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- Highly asymmetric synthesis of (+)-corsifuran A. Elucidation of the electronic requirements in the Ruthenium-NHC catalyzed hydrogenation of benzofurans
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A short and efficient synthesis of ent-corsifuran A by a highly asymmetric hydrogenation of a benzofuran precursor is reported. In addition, the electronic influence of the substituents on the asymmetric hydrogenation of benzofurans is provided. Whereas the hydrogenation of electron-deficient benzofurans was achieved under very mild conditions, the presence of electron-donating groups in the benzofuran required harsher reaction conditions for achieving full conversion to the 2,3-dihydrobenzofuran.
- Ortega, Nuria,Beiring, Bernhard,Urban, Slawomir,Glorius, Frank
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supporting information; experimental part
p. 5185 - 5192
(2012/07/31)
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- Enantiopure C1-symmetric bis(imino)pyridine cobalt complexes for asymmetric alkene hydrogenation
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Enantiopure C1-symmetric bis(imino)pyridine cobalt chloride, methyl, hydride, and cyclometalated complexes have been synthesized and characterized. These complexes are active as catalysts for the enantioselective hydrogenation of geminal-disubstituted olefins.
- Monfette, Sebastien,Turner, Zoe R.,Semproni, Scott P.,Chirik, Paul J.
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p. 4561 - 4564
(2012/04/23)
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- Polarity reversal catalysis in radical reductions of halides by N-heterocyclic carbene boranes
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Otherwise sluggish or completely ineffective radical reductions of alkyl and aryl halides by N-heterocyclic carbene boranes (NHC-boranes) are catalyzed by thiols. Reductions and reductive cyclizations with readily available 1,3-dimethylimidazol-2-ylidene borane and a water-soluble triazole relative are catalyzed by thiophenol and tert-dodecanethiol [C9H 19C(CH3)2SH]. Rate constants for reaction of the phenylthiyl (PhS?) radical with two NHC-boranes have been measured to be ~108 M-1 s-1 by laser flash photolysis experiments. An analysis of the available evidence suggests the operation of polarity reversal catalysis.
- Pan, Xiangcheng,Lacote, Emmanuel,Lalevee, Jacques,Curran, Dennis P.
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supporting information; experimental part
p. 5669 - 5674
(2012/06/04)
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- Iron-catalyzed reductive dehydroxylation of benzylic alcohols using polymethylhydrosiloxane (PMHS)
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The combination of FeCl3 and PMHS is an efficient reducing system for the selective dehydroxylation of secondary benzylic alcohols, even in the presence of carbonyls, under very mild conditions. Georg Thieme Verlag Stuttgart · New York.
- Chan, Li Yan,Lim, Jazreel Seh Kai,Kim, Sunggak
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experimental part
p. 2862 - 2866
(2012/01/11)
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- Iridium-catalyzed asymmetric hydrogenation of olefins using TIQ phosphine-oxazoline ligands
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A novel family of tetrahydroisoquinoline (TIQ) phosphine-oxazoline ligands and four corresponding iridium complexes have been developed and applied to the asymmetric hydrogenation of unfunctionalized olefins. The results showed that the best conversion rates were observed in up to 99% with an enantiomeric excess of 91%.
- Chakka, Sai Kumar,Peters, Byron K.,Andersson, Pher G.,Maguire, Glenn E.M.,Kruger, Hendrik G.,Govender, Thavendran
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experimental part
p. 2295 - 2301
(2010/11/04)
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- Spurring radical reactions of organic halides with tin hydride and TTMSS using microreactors
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Tributyltin hydride-mediated radical reactions of organic halides were successfully carried out in a continuous flow system using a microreactor. The reactions proceeded within a very short period of time, coupled with quickly decomposing radical initiators such as V-65 and V-70. The continuous flow reaction system was applied to gram scale synthesis of a key intermediate for furofuran lignans.
- Fukuyama, Takahide,Kobayashi, Masahide,Rahman, Md Taifur,Kamata, Naoya,Ryu, Llhyong
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p. 533 - 536
(2008/04/05)
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- Radical chain reactions using THP as a solvent
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THP (tetrahydropyran) has been found to show an excellent stability towards autooxidation, compared with THF. Tributyltin hydride mediated radical cyclization, when conducted in THF as a solvent, suffers from competition of hydrogen abstraction from the solvent, whereas the use of THP resulted in the course to negligible degree. Tributyltin hydride, TTMSS, and hexanethiol mediated radical reactions were carried out successfully using THP as a solvent.
- Yasuda, Hiroshi,Uenoyama, Yoshitaka,Nobuta, Osamu,Kobayashi, Shoji,Ryu, Ilhyong
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p. 367 - 370
(2008/09/17)
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- An environmentally friendly synthesis of functionalized indanes using electrochemical cyclization of ortho-halo-substituted homoallyl ethers and esters
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The electrochemical cyclization of a series of ortho-halo-substituted homoallyl ethers and esters to functionalized indanes catalyzed by Ni(II) catalyst precursors derived from Ni(cyclam)Br2, (cyclam = 1,4,8,11-tetraazacyclotetradecane) and Ni(tmc)Br2, (tmc = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) is reported. The starting homoallyl ethers were synthesized using either a one-pot method for allylation of aldehydes or by direct allylation of the corresponding acetals using bismuth triflate as a catalyst. The remarkably low toxicity, low cost and ease of handling of bismuth salts coupled with the mild nature of the electrochemical procedure makes this approach to indane synthesis especially environmentally friendly and attractive. Georg Thieme Verlag Stuttgart.
- Olivero, Sandra,Perriot, Rodolphe,Du?ach, Elisabet,Baru, Ashvin R.,Bell, Eric D.,Mohan, Ram S.
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p. 2021 - 2026
(2008/02/05)
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- Radical clocks and electron transfer. Comparison of crown ether effects on the reactivity of potassium and magnesium towards 1-bromo-2-(3-butenyl)benzene. the incidence of homogeneous versus heterogeneous electron transfer on selectivity
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The reaction of the title precursor of the aryl radical clock 1-bromo-2-(3-butenyl)benzene, 1Br, towards potassium and magnesium in THF was studied in the presence and absence of various additives, at ambient and low temperatures. The additives were cis-dicyclohexano-18-crown-6 or tert-butyl alcohol; the first one to render soluble potassium by forming its alkalide, the second to distinguish carbanionic from radical cyclization. The addition of 1Br to a THF stirred suspension of potassium pieces yields remarkably low amounts of products resulting from radical cyclization, in contrast to the amounts reported by Bunnett and Beckwith's group for the reaction in 67% ammonia-33% tert-butyl alcohol medium. The amount of cyclized products obtained with potassium pieces in THF is in the same range as that observed in the reaction of magnesium with 1Br in THF. This similarity allows us to discard the earlier triad hypothesis that we proposed to account for the unexpectedly low amounts of cyclized products of aryl halides radical clocks in Grignard reagent formation. The addition of crown ethers to the THF reaction medium induces contrasting effects for potassium and magnesium. A distinctive increase in the radical cyclization is observed for potassium, whereas the addition of crown inhibits the formation of Grignard reagent more efficiently when the solvent is diethyl ether than when it is THF. The observed effects are explained by putting in perspective the metal reactive dissolution with elementary steps occurring in the vicinity of a cathode. The reaction of potassium pieces or magnesium turnings is comparable to the heterogeneous electron transfer occurring at a cathode whereas the reaction of potassium in the presence of crown ether is comparable to homogeneous conditions of electron transfer obtained in redox catalysis. A discussion of the dianion hypothesis for the Grignard reaction of aryl halides is provided and the importance of considering the reactivity of reactive metal dissolution (or organic corrosion) in the framework of recent progress made in the modelling of electrode reactivity is emphasized. This paper shows that caution should be taken when radical clocks are used to study reactions at the metal-solution interface. More specifically, the non-bservation of rearranged products from the radical clock (even for the very rapid ones) under these conditions does not necessary imply that there is no radical intermediate along the dominant reaction channel. This pattern of reactivity strongly contrasts with that usually observed when radical clocks are used in homogeneous media. The leading parameters in the rearranged/unrearranged products ratio seem to be the time that the reactive species (radical anions) created by the first electron transfer spend in the close vicinity of this surface, the rate constant of rearrangement of the radical formed by the cleavage of the radical anion and the redox properties of this radical. Copyright
- Hazimeh, Hassan,Mattalia, Jean-Marc,Marchi-Delapierre, Caroline,Barone, Rene,Nudelman, Norma S.,Chanon, Michel
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p. 1145 - 1160
(2007/10/03)
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- Olefins turned alkylating agents: Diastereoselective intramolecular Zr-catalyzed olefin alkylations
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(Equation Presented) 62% yield; 12 : 1 syn : anti The first examples of intramolecular Zr-catalyzed electrophilic alkylation of aryl olefins are disclosed. Substituted carbo-and heterocycles are prepared efficiently and diastereoselectively.
- Cesati III, Richard R.,De Armas, Judith,Hoveyda, Amir H.
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p. 395 - 398
(2007/10/03)
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- Alkylation of alkyl aromatic hydrocarbons over metal oxide-alkali metal superbasic catalysts
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The alkylation of toluene, ethylbenzene, cumene, and o-, m-, and p-xylenes with ethylene, propylene, and 1,2-diphenylethylene was studied over superbasic MgO-K and γ-Al2O3-K catalysts and over model systems of the electron donor acceptor complex type. The ethylation and propylation of alkylbenzenes indicated that the donor power and the concentration of the one-electron donor centers were not the only factors, which determined the activity (depicted by the initial reaction rate, turnover number, or alkylbenzene conversion) and selectivity of the catalytic system. In the series of reactions, a higher total conversion of alkyl aromatic hydrocarbons to their ethylation or propylation products was achieved over γ-Al2O3-K systems. The reaction chemoselectivity (mono- or difunctionalization of alkylbenzenes) depended on the nature of the alkyl aromatic reactant and alkylating alkene, on the reaction temperature, and on the used catalyst.
- Kijenski,Radomski,Fedorynska
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p. 407 - 425
(2007/10/03)
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- Fast interconversion of C4H7+ cations in the gas phase and in a gaseous microsolvated environment
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The equilibration of cyclobutyl 1 and 1′ and the cyclopropylmethyl cation (2) has been studied in the gas phase by utilizing FT-ICR mass spectrometry and high-pressure radiolytic techniques. A suitable gaseous nucleophile, C6X6 (X = H,D), was used to sample the equilibration of C4H7+ ions, produced from both cyclobutanol and cyclopropylmethanol. These are either dispersed in the bulk gas or confined within a C4H7+/C6X6 complex that contains a molecule of solvent (H2O). The analysis of the products shows that, irrespective of their source and of the intermolecular or intracomplex nature of the process, the C4H7+ ions undergo equilibration before they are trapped. The equilibrium (1+1′)/2 ratio is very close to unity at 300 K, and the results from the intracomplex trapping experiment show that equilibration occurs within a time interval ≤ 10-10 s.
- Cacace, Fulvio,Chiavarino, Barbara,Crestoni, M. Elisa
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p. 2024 - 2031
(2007/10/03)
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- Functional-Group-Directed Diastereoselective Hydrogenation of Aromatic Compounds
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Diastereoselective liquid phase hydrogenation of a series of monosubstituted indane and tetralin substrates was studied on supported rhodium catalysts. Predominantly the cis-cis diastereomer, obtained by hydrogenation from the diastereoface opposite the substituent (at the stereogenic center), and the cis-trans diastereomer, obtained by hydrogenation from the diastereoface on the same side as the substituent, were formed. The diastereoselectivity between the two isomers was dependent on the steric repulsion or the electronic attraction of the substituent with the surface of the catalyst. The hydroxyl group did not exhibit a strong attraction (haptophilicity), and the cis-cis diastereomer was obtained as the major product. The amino group exhibited a very high haptophilicity, yielding primarily the cis-trans diastereomer. The diastereoselectivity obtained in the hydrogenation of all the substrates was influenced on addition of bases to the reaction mixture. In the case of alcoholic substrates, the selectivity to the cis-trans diastereomer could be substantially increased with alkaline hydroxide additives.
- Ranade, Vidyadhar S.,Consiglio, Giambattista,Prins, Roel
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p. 8862 - 8867
(2007/10/03)
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- The Barrier to Rotation about the Double Bond in Methylenecyclopropane
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Activation parameters have been determined in the gas phase for the geometrical isomenzation of the double bonds in two phenyl-substituted methylenecyclopropanes (2 and 8). Comparison with the analogous values for three sterically non-restricted styrene derivatives (15, 16 and 17) shows that the enthalpies of activation for the methylenecyclopropanes are lower by 3.7 kcal mol-1. This value, which is an upper limit to the amount of strain energy released by pyramidalization of the ring carbon atom in the orthogonal diradical transition state when undergoing geometrical isomerization, is considerably smaller than the value of 12-14 kcal mol-1 by which the strain energy of methylenecyclopropane is larger relative to that of cyclopropane. Our kinetics experiments thus show that the angle strain, associated with incorporating a trigonal carbon atom into the three-membered ring, is not responsible for the majority of the additional strain energy of methylenecyclopropane, relative to that of cyclopropane.
- Roth, Wolfgang R.,Quast, Michael
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p. 763 - 768
(2007/10/03)
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- The Photochemistry of Conformationally Rigid Benzylic Esters: 2,2-Dimethyl-1-indanyl Acetates and Pivalates
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The photochemistry, in methanol, of substituted 2,2-dimethyl-1-indanyl acetates 9a-c and pivalates 10a-c has been studied.In agreement with previous studies on benzylic esters, the results show that the substituents change the yield of products derived from the ion pair.The mechanistic conclusion reached is that the substituents change the oxidation potential of the indanyl radicals and thus the rate constant of electron transfer for converting the radical pair to the ion pair.The results also reveal two other substituent effects.First, substituents can increase the overall efficiency of the photoreaction by enhancing homolytic cleavage.The second effect is conformational.In compounds where the bond that is cleaving is conformationally mobile, such as the C-O bond in benzylic esters, substituents on the ring can change the population of the reactive conformer and thus the overall efficiency of the reaction.For the indanyl acetate esters, the difference in excited-state reaction rate between the m- and p-methoxy substituted ester is 15:1.For the m- and p-methoxy substituted benzyl acetates, this difference in reaction rate is 48:1.The larger difference in reaction rate for the conformationally mobile benzylic esters is attributed to a higher population of the unreactive conformer for the p-methoxy substituted ester.
- Pincock, J. A.,Wedge, P. J.
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p. 4067 - 4076
(2007/10/02)
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- Characterization of New Methyl-Substituted Tetralins and Indans by 13C NMR Spectroscopy
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In order to perform the analysis of the components contained in fossil fuels, carbon assignments of new methylated derivatives of tetralin and indan were obtained.Their chemical shifts were calculated by applying additivity rules. - Keywords: NMR; 13C NMR; tetralins; indans
- Laurens, T.,Schmit-Quiles, F.,Nicole, D.
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p. 523 - 528
(2007/10/02)
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- BINAP-Ru(II) and BINAP-Rh(I)-catalyzed asymmetric hydrogenation of olefins without heteroatom-functionalities
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Asymmetric hydrogebation of 1,1'-disubstituted olefins which have no heteroatom functionalities to allow additional interactions with catalyst centers, have been investigated by use of Ru(II) and Rh(I) complexes of BINAP as catalysts.Enantioselectivities and the sense of asymmetric induction are highly dependent on the structure of substrates and the nature of catalysts.Hydrogenation of 1-methyleneindan (1a), a five-membered methylenecycloalkane, gave the highest optical yield (78percent) when Ru(OAc)2((R)-binap) was used as catalyst, while the use of the catalyst system 2/(R)-BINAP afforded the highest ees (71-82percent) for six-membered analogs, 1-methylenetetralin (4a) and its derivatives.In ciontrast, hydrogenation of seven-membered analog 7 and acyclic olefins 10 resulted in only moderate enantioselectivities by use of these catalysts.The BINAP-Ru(II) catalyzed hydrogenation exhibited a remarkable dependence of enantioselectivities on solvents, while a large anionic ligand effect was observed for the reaction with the BINAP-Rh(I) system.Based on these experimental results, mechanistic aspects of these asymmetric hydrogenation have been discussed.Keywords: Ruthenium; Rhodium; BINAP; Assymetric hydrogenation; Simple olefins; Catalysis
- Ohta, Tetsuo,Ikegami, Hiroshi,Miyake, Tsutomu,Takaya, Hidemasa
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p. 169 - 176
(2007/10/02)
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- Potassium hydroxide as a promoter for the potassium-metal catalyzed side-chain alkylation of toluene
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Potassium hydroxide acts synergistically with catalyst supports such as alumina, diatomaceous earth, or potassium carbonate to promote the potassium-metal catalyzed side-chain alkylation of toluene with propene.Carrying out the reaction with wet toluene to generate KOH in situ is a particularly effective method for promoting the reaction.The catalyst supports are not inert in the absence of the promoter, because they alter alkylation regiochemistry and increase the formation of methylindan by-products.As a mechanistic probe, the amounts of benzylpotassium that formare compared with propylation reaction rates.This is the first report concerning the amount of benzylpotassium that forms under side-chain alkylation conditions.From this and other data, a previously unrecognized mechanism for the promotion of side-chain alkylation is identified.
- Smith, R. Scott,Ihrman, Kryn G.,LeBlanc, Monica B.
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p. 333 - 343
(2007/10/02)
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- Carbon-Oxygen Bond-Cleavage Reactions by Electron Transfer. 3. Electrochemical Formation and Decomposition of the Diphenyl Ether Radical Anion
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The electrochemical reduction of diphenyl ether to its unstable radical anion was observed at -2.95 V vs.SCE in dry N,N-dimethylformamide.Kinetic studies by cyclic voltammetry and homogeneous redox catalysis techniques resulted in a first-order rate constant of 4*E5 s-1 for the decomposition of the radical anion of diphenyl ether.Controlled-potential electrolysis of diphenyl ether resulted in carbon-oxygen bond cleavage with quantitative formation of phenol and benzene.Electroreduction of diphenyl ether in the presence of D2O produced 15percent monodeuterium incorporation on benzene.The intermediacy of the phenyl radical in the cleavage pathway was tested by deploying an intramolecular radical trap, an o-(3-butenyl) substituent, on diphenyl ether.Electrochemical reduction of o-(3-butenyl)phenoxybenzene (1) in the absence of and in the presence of D2O confirmed the presence of the o-(3-butenyl)phenyl radical in the cleavage mechanism of the radical anion.Electroreduction of 1 in the presence of sodium isopropylate, a hydrogen atom donor, changed the product distribution ratio of 1-methylindan-(3-butenyl)benzene.The rate constant of the intramolecular cyclization reaction of the o-(3-butenyl)phenyl radical was estimated to be 1.5*E8 s-1.
- Thornton, Todd A.,Woolsey, Neil F.,Bartak, Duane E.
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p. 6497 - 6502
(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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- Photosolvolysis of 2-Allylated Anilines to 2-Indanols
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It is shown that 2-allylated anilines (cf.Schemes 2-4,7, and 8) on irradiation in protic solvents such as H2O.MeOH, and EtOH in the presence of H2SO4 undergo a novel photosolvolysis reaction to yield specifically trans-2-hydroxy- and trans-2-alkoxy-1-methylindanes.Intermediates are presumably tricyclo1,8>nona-2,4-dienes formed in an intramolecular cycloaddition reaction (cf.Scheme 7).On the other hand, N,N,N-trimethyl-2-(1'-methylallyl)anilinium salts 18 (Scheme 6) and 2-(3'-butenyl)-N,N-dimethylaniline (17) lose on irradiation in MeOH or H2SO4/MeOH the ammonium group reductively to yield (1-methylallyl)benzene (19) and 1-methylindane (20), respectively.
- Scholl, Bernhard,Jolidon, Synese,Hansen, Hans-Juergen
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p. 184 - 194
(2007/10/02)
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- Electrosynthesis of Organic Compounds, VII. Electrochemical Oxidation of Selected Arylalkyl Halides
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Anodic oxidation of selected arylalkyl halides was carried out in methanol containing 0.05 mol.l-1 Ba(ClO4)2, as electrolyte on a platinum anode at + 1.7 V vs SCE.The compounds electrochemically oxidized were benzyl bromide (1), 2-phenylethyl bromide (2), 3-phenylpropyl bromide (3), 4-phenylbutyl chloride (4), 1-methyl-3-phenylpropyl chloride (5) and 1,1-dimethyl-3-phenylpropyl chloride (6).The principal products isolated were the corresponding alkylbenzenes, alkenylbenzenes, dimers, ethers and cyclic products.Mechanisms were suggested.Also, kinetic studies were carried out on carbon-halogen bond cleavage of the compounds investigated (1-6).Current-potential curves were drawn, and discharge oxidation potentials were determined from these.
- Ismail, M. T.,Abdel-Wahab, A. A.,El-Khawaga, A. M.,Mohamed, O. S.,Khalaf, A. A.
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- The Question of Cyclic Versus Acyclic Ions: The Structure of +. Gas Phase Ions
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The extent of isomerization of acyclic and cyclic gas phase radical cations of composition +. has been investigated by using collisionally activated dissociation spectroscopy.Both electron and charge exchange ionization were employed to form the ions with various internal energies.The +. ions investigated consisted of ionized phenylbutenes, ring-substituted methyl derivatives of allylbenzene and phenylpropene, 1-methyl-isopropenylbenzene, benzylcyclopropane, phenylcyclobutane, tetralin and 1-methylindan.The 1-methylindan and tetralin radical cations are the most stable of the C10H12 isomeric radical ions.The +. formed from acyclic olefins having the double bond in conjugation with the aromatic ring retain the initial structure to a significant extent.However, ions derived from olefins with the double bond out of conjugation with the benzene ring preferentially cyclize to stable five- and six-membered cyclic ions.Ring opening of small-ring cyclic ions, such as ionized benzylcyclopropane and phenylcyclobutane, occurs, followed by ring closure to the tetralin radical cation.
- Dass, Chhabil,Gross, Michael L.
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