- Iron Catalyzed Double Bond Isomerization: Evidence for an FeI/FeIII Catalytic Cycle
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Iron-catalyzed isomerization of alkenes is reported using an iron(II) β-diketiminate pre-catalyst. The reaction proceeds with a catalytic amount of a hydride source, such as pinacol borane (HBpin) or ammonia borane (H3N?BH3). Reactivity with both allyl arenes and aliphatic alkenes has been studied. The catalytic mechanism was investigated by a variety of means, including deuteration studies, Density Functional Theory (DFT) and Electron Paramagnetic Resonance (EPR) spectroscopy. The data obtained support a pre-catalyst activation step that gives access to an η2-coordinated alkene FeI complex, followed by oxidative addition of the alkene to give an FeIII intermediate, which then undergoes reductive elimination to allow release of the isomerization product.
- Woof, Callum R.,Durand, Derek J.,Fey, Natalie,Richards, Emma,Webster, Ruth L.
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supporting information
p. 5972 - 5977
(2021/03/17)
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- Nitrogen-Doped Carbon-Encapsulated Nickel/Cobalt Nanoparticle Catalysts for Olefin Migration in Allylarenes
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Olefin migration in allylarenes is typically performed with precious-metal-based homogeneous catalysts. In contrast, very limited progress has been made with the use of cheap, Earth-abundant base metals as heterogeneous catalysts for these transformations—in spite of the obvious economic and environmental advantages. Herein, we report on the use of an easily prepared heterogeneous catalyst material for the migration of olefins, in particular, for allylarenes. The catalyst material consists of nickel/cobalt alloy nanoparticles encapsulated in nitrogen-doped carbon shells. The encapsulated nanoparticles are stable in air and are easily collected by centrifugation, filtration, or magnetic separation. Furthermore, we demonstrate that the catalysts can be reused several times and provide continuously high yields of the olefin-migration product.
- Kramer, S?ren,Mielby, Jerrik,Buss, Kasper,Kasama, Takeshi,Kegn?s, S?ren
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p. 2930 - 2934
(2017/08/14)
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- Nickel-Catalyzed Allylic C(sp2)–H Activation: Stereoselective Allyl Isomerization and Regiospecific Allyl Arylation of Allylarenes
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Stereoselective allyl isomerization and regiospecific allyl arylation reactions of allylarenes with a catalytic system comprising nickel(II) with an aryl Grignard reagent were studied. Both reactions are triggered by allylic internal C(sp2)–H activation by in-situ-formed Ni0, which is inserted into the C–H bond at the 2-position of the allyl moiety without a directing group. The isomerization of allylarene to 1-propenylarene favors the E isomer and proceeds with quantitative conversion. The arylation takes place through oxidative cross-coupling of allylarenes with excess Grignard reagent. It occurs regiospecifically at the position of C(sp2)–H activation and represents a new method for the synthesis of 1,1-disubstituted olefins. The results of deuterium labeling experiments reveal an alkenyl/alkyl mechanism involving allylic internal C(sp2)–H activation and multiple intermolecular 1,2-, 1,3-, and 2,3-hydride shifts. These methods represent new approaches to the functionalization of olefins, and the mechanistic investigations could be helpful for the discovery and design of new strategies for olefin functionalization.
- Wu, Qiang,Wang, Lanlan,Jin, Rizhe,Kang, Chuanqing,Bian, Zheng,Du, Zhijun,Ma, Xiaoye,Guo, Haiquan,Gao, Lianxun
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p. 5415 - 5422
(2016/11/22)
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- A facile and convenient sequential homobimetallic catalytic approach towards β-methylstyrenes. A one-pot Stille cross-coupling/isomerization strategy
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An efficient one-pot synthetic approach towards β-methylstyrenes is reported. The transformation, based on sequential homobimetallic catalysis, involves a Stille cross-coupling reaction between aryl halides and allyltributylstannane, followed by an in situ palladium-catalyzed conjugative isomerization. The reaction was optimized, and the best results were obtained with 10 mol% Pd(PPh3)2Cl2, 8.0 equiv. LiCl, and 0.5 equiv. PPh3 in diglyme at 130 °C for 12 h. It was demonstrated that the reaction tolerates a wide variety of functional groups. This journal is the Partner Organisations 2014.
- Simonetti, Sebastian O.,Larghi, Enrique L.,Kaufman, Teodoro S.
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p. 3735 - 3743
(2014/06/09)
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- Wittig reaction: Role of steric effects in explaining the prevalent formation of Z olefin from nonstabilized ylides
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For understanding the mechanism involved in the Wittig reaction, it is important to know the factors which influence the stability of 1,2-oxaphosphetane intermediates with pentacoordinate phosphorus; in these intermediates, the steric factor plays a predominant role. Studying the Wittig reaction between nonstabilized ylides and different aldehydes, we noted that the stereochemical outcome driving toward Z-olefin formation was influenced only by different steric factors. The proposed mechanism differs from those previously reported because it underlines the fundamental role of the two cis/trans oxaphosphetane intermediates with the oxygen atom in equatorial position.
- Baccolini, Graziano,Delpivo, Camilla,Micheletti, Gabriele
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p. 1291 - 1302
(2012/11/13)
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- Efficient double bond migration of allylbenzenes catalyzed by Pd(OAc) 2-HFIP system with unique substituent effect
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A novel catalyst system of Pd(OAc)2-HFIP induces double-bond migration of allylbenzenes under mild conditions with low catalytic loading to afford 1-propenylbenzenes. The reaction shows a unique substituent effect that is highly dependent on the distance of substituents from the allylic moiety. Thus, the reactivity of substrates bearing a methyl group is ordered in para > meta > ortho, whereas it is entirely reversed as ortho > meta > para for methoxy and chloro substituents.
- Nishiwaki, Nagatoshi,Kamimura, Ryuichiro,Shono, Kimihiro,Kawakami, Toshihiko,Nakayama, Katsuhisa,Nishino, Kohei,Nakayama, Takayuki,Takahashi, Keisuke,Nakamura, Aki,Hosokawa, Takahiro
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supporting information; experimental part
p. 3590 - 3592
(2010/08/19)
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- Catalytic asymmetric epoxidation
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A compound and method for producing an enantiomerically enriched epoxide from an olefin using a chiral ketone and an oxidizing agent is disclosed.
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Page column 29
(2010/01/30)
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- Flash vacuum pyrolysis of stabilised phosphorus ylides. Part 12. Extrusion of Ph3P from sulfonyl ylides and reactivity of the resulting sulfonyl carbenes
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Twelve sulfonyl stabilised phosphorus ylides have been prepared and their behaviour upon flash vacuum pyrolysis at 600°C has been examined. Examples with an arylsulfonyl substituent undergo loss of Ph3PO to give intractable products but those with an arylmethylsulfonyl substituent separately lose Ph3P and SO2 to give products consistent with the intermediacy of sulfonyl carbenes. X-Ray structure determinations of one ylide from each series show a more significant P-O non-bonding interaction in the first case, providing some explanation for the different thermal reactivity.
- Aitken, R. Alan,Drysdale, Martin J.,Ferguson, George,Lough, Alan J.
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p. 875 - 880
(2007/10/03)
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- An efficient catalytic asymmetric epoxidation method
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This article describes a highly effective catalytic asymmetric epoxidation method for olefins using,potassium peroxomonosulfate (Oxone, Dupont) as oxidant and a fructose-derived ketone(l) as catalyst. High enantioselectivies have been obtained-for trans-disubstituted and trisubstituted olefins which can bear functional groups such as tributylsilyl ether, acetal, chloride, and ester. The enantiomeric excesses cis-olefins and terminal olefins are not high yet. The current epoxidation shows that the catalyst efficiency is enhanced dramatically-upon raising the pH. Mechanitic studies show that the epoxidation mainly proceeds via a spiro transition state, which provides a model for predicting the stereochemical outcome of the reaction. The planar transition state, likely to be the main competing pathway. The extent of the involvement of the planar mode is subject to the steric of the alkyl groups on the olefins.
- Wang, Zhi-Xian,Tu, Yong,Frohn, Michael,Zhang, Jian-Rong,Shi, Yian
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p. 11224 - 11235
(2007/10/03)
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- Regiochemistry and Stereochemistry of Nickel-Promoted, Carbon-Carbon Bond-Forming Reactions of Cyclic Sulfur Compounds
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Reaction of methylmagnesium iodide and phenylmagnesium bromide with thianaphthene, dibenzothiophenone, thianthrene, and 2,3-dihydrothiapyran in the presence of nickel dichloride have been shown to yield, regioselectively in most cases, ring-opened products in which the carbon-sulfur bonds have been replaced by carbon-carbon bonds.Stereospecific carbon-carbon bond formation has taken place in the reactions of thianaphthene and 2,3-dihydrothiapyran, the products having maintained the cis-olefin configuration of the starting sulfur compounds.Isomerization into the more stable compounds has been observed in some cases.
- Tiecco, Marcello,Tingoli, Marco,Wenkert, Ernest
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p. 3828 - 3831
(2007/10/02)
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- Intramolecular Reactions of o-Alkoxy- and o-Alkylthio-benzyl Radicals
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We report new gas-phase reactions of o-substituted benzyl radicals produced by flash vacuum pyrolysis of 2,3-dihydro-1,3,2-benzoxazaphosph(V)oles (4)-(6), dibenzyl sulphone (8), and dibenzyl oxalates (9)-(11).Both o-ethoxy- and o-methoxy-benzyl radicals rearrange to o-tolualdehyde via intramolecular hydrogen transfer, as shown by experiments using 2-methoxybenzyl radicals. o-Methylthiobenzyl radicals do not give the corresponding thioaldehyde, but produce a mixture of benzocyclobutene and isomeric dihydrobenzothiophens by novel rearrangement reactions. o-Ethylthio- and o-propylthio-benzyl radicals give o-methylstyrene and o-propenyltoluenes respectively as major products.
- Cadogan, J. I. G.,Husband, James B.,McNab Hamish
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p. 697 - 702
(2007/10/02)
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