- Reactivity of mixed organozinc and mixed organocopper reagents: 6. Nickel-catalyzed coupling of methylarylzincs with primary alkyl halides; An atom-economic aryl-alkyl coupling
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A nickel-catalyzed process for the cross-coupling of mixed arylzincs and primary alkyl halides has been developed. The reaction of a methylarylzinc with a primary alkyl halide in THF in the presence of NiCl2/PPh 3 takes place with selective aryl transfer at room temperature in moderate yields. This protocol provides an atom-economic alternative to aryl-primary alkyl coupling using diarylzincs.
- Pekel, ?zgen ?mür,Erdik, Ender
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- Photochemistry of substituted benzyl acetates and benzyl pivalates: A reinvestigation of substituent effects
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The photosolvolysis reactions, in methanol, of six substituted benzyl acetates (7a-f) and benzyl pivalates (8a-f) were studied. Five major benzylic products were formed from two critical intermediates. The ethers (9) were formed from the ion pair, 15, and all of the other products (10-14) were formed from the radical pair, 16. Quenching studies showed that only excited singlet state reactivity was important. The product yields were found to be highly substituent dependent. For instance, for the acetate esters, the yield of ether (9) varied from 2% for X = 4-OCH3 to 32% for X = 3-OCH3. Most of the differences in the yields could be attributed to ground state processes that occur after bond cleavage. The important competition is between electron transfer, converting the radical pair to the ion pair, and decarboxylation of RCO2*. The rates of electron transfer are shown to fit Marcus theory in both the normal and inverted regions. Direct heterolytic cleavage to form the ion pair is of minimal importance.
- Hilborn,MacKnight,Pincock,Wedge
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- SELECTIVE COUPLING OF FREE RADICALS VIA ORGANOCHROMIUM COMPLEXES.
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Free radicals can be coupled in high yield to give either symmetric dimers or cross coupling products by reacting chromous chloride in THF with alkyl halides.
- Sustmann, Reiner,Altevogt, Rudolf
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Read Online
- On the Mechanism of the Reduction of Primary Halides with Grignard Reagents in the Presence of (dppf)PdCl2 or (dppf)Pd(0)
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Reaction of primary alkyl halides with Grignard reagents in the presence (dppf)PdCl2 or (dppf)Pd(0) leads to reduction of the halide.The mechanism of the reduction is dependent on the solvent and the Grignard reagent.In tetrahydrofuran, reduction is independent of palladium.The alkyl halide is largely reduced by β-hydride transfer from the Grignard reagent.Competing with hydride transfer is a halogen-metal exchange reaction, which converts the alkyl halide into the corresponding Grignard reagent.Protonation of reaction mixture then gives the observed products.Grignard reagents that do not possess β-hydrogens undergo the halogen-metal exchange exclusively, but still lead to reduction of the alkyl halide.At subambient temperatures and in diethyl ether, reduction of primary alkyl halides with Grignard reagents in the absence of palladium catalysts is very slow.That reduction which does occur is almost exclusively the product of β-hydride transfer.The addition of (dppf)PdCl2 markedly accelerates the rate of reduction of alkyl halides in diethyl ether.The catalytic effect is proposed to occur through a catalytic cycle involving oxidative addition of the alkyl halide, hydride-transfer, and reductive-elimination steps.The order of the first two steps remains unclear.
- Yuan, Kaixu,Scott, William J.
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- Site-Specific Alkene Hydromethylation via Protonolysis of Titanacyclobutanes
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Methyl groups are ubiquitous in biologically active molecules. Thus, new tactics to introduce this alkyl fragment into polyfunctional structures are of significant interest. With this goal in mind, a direct method for the Markovnikov hydromethylation of alkenes is reported. This method exploits the degenerate metathesis reaction between the titanium methylidene unveiled from Cp2Ti(μ-Cl)(μ-CH2)AlMe2 (Tebbe's reagent) and unactivated alkenes. Protonolysis of the resulting titanacyclobutanes in situ effects hydromethylation in a chemo-, regio-, and site-selective manner. The broad utility of this method is demonstrated across a series of mono- and di-substituted alkenes containing pendant alcohols, ethers, amides, carbamates, and basic amines.
- Bartfield, Noah M.,Frederich, James H.,Law, James A.
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supporting information
p. 14360 - 14364
(2021/05/27)
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- Reductive Deamination with Hydrosilanes Catalyzed by B(C6F5)3
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The strong boron Lewis acid tris(pentafluorophenyl)borane B(C6F5)3 is known to catalyze the dehydrogenative coupling of certain amines and hydrosilanes at elevated temperatures. At higher temperature, the dehydrogenation pathway competes with cleavage of the C?N bond and defunctionalization is obtained. This can be turned into a useful methodology for the transition-metal-free reductive deamination of a broad range of amines as well as heterocumulenes such as an isocyanate and an isothiocyanate.
- Fang, Huaquan,Oestreich, Martin
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supporting information
p. 11394 - 11398
(2020/05/25)
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- Carbonyl and olefin hydrosilylation mediated by an air-stable phosphorus(iii) dication under mild conditions
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The readily-accessible, air-stable Lewis acid [(terpy)PPh][B(C6F5)4]21 is shown to mediate the hydrosilylation of aldehydes, ketones, and olefins. The utility and mechanism of these hydrosilylations are considered.
- Andrews, Ryan J.,Chitnis, Saurabh S.,Stephan, Douglas W.
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supporting information
p. 5599 - 5602
(2019/05/21)
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- Mechanistic Characterization of (Xantphos)Ni(I)-Mediated Alkyl Bromide Activation: Oxidative Addition, Electron Transfer, or Halogen-Atom Abstraction
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Ni(I)-mediated single-electron oxidative activation of alkyl halides has been extensively proposed as a key step in Ni-catalyzed cross-coupling reactions to generate radical intermediates. There are four mechanisms through which this step could take place: oxidative addition, outer-sphere electron transfer, inner-sphere electron transfer, and concerted halogen-atom abstraction. Despite considerable computational studies, there is no experimental study to evaluate all four pathways for Ni(I)-mediated alkyl radical formation. Herein, we report the isolation of a series of (Xantphos)Ni(I)-Ar complexes that selectively activate alkyl halides over aryl halides to eject radicals and form Ni(II) complexes. This observation allows the application of kinetic studies on the steric, electronic, and solvent effects, in combination with DFT calculations, to systematically assess the four possible pathways. Our data reveal that (Xantphos)Ni(I)-mediated alkyl halide activation proceeds via a concerted halogen-atom abstraction mechanism. This result corroborates previous DFT studies on (terpy)Ni(I)- and (py)Ni(I)-mediated alkyl radical formation, and contrasts with the outer-sphere electron transfer pathway observed for (PPh3)4Ni(0)-mediated aryl halide activation. This study of a model system provides insight into the overall mechanism of Ni-catalyzed cross-coupling reactions and offers a basis for differentiating electrophiles in cross-electrophile coupling reactions.
- Diccianni, Justin B.,Katigbak, Joseph,Hu, Chunhua,Diao, Tianning
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supporting information
p. 1788 - 1796
(2019/01/26)
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- Photoredox-Assisted Reductive Cross-Coupling: Mechanistic Insight into Catalytic Aryl-Alkyl Cross-Couplings
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Here, we describe a photoredox-assisted catalytic system for the direct reductive coupling of two carbon electrophiles. Recent advances have shown that nickel catalysts are active toward the coupling of sp3-carbon electrophiles and that well-controlled, light-driven coupling systems are possible. Our system, composed of a nickel catalyst, an iridium photosensitizer, and an amine electron donor, is capable of coupling halocarbons with high yields. Spectroscopic studies support a mechanism where under visible light irradiation the Ir photosensitizer in conjunction with triethanolamine are capable of reducing a nickel catalyst and activating the catalyst toward cross-coupling of carbon electrophiles. The synthetic methodology developed here operates at low 1 mol % catalyst and photosensitizer loadings. The catalytic system also operates without reaction additives such as inorganic salts or bases. A general and effective sp2-sp3 cross-coupling scheme has been achieved that exhibits tolerance to a wide array of functional groups.
- Paul, Avishek,Smith, Mark D.,Vannucci, Aaron K.
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p. 1996 - 2003
(2017/02/26)
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- Decarboxylative Cross-Electrophile Coupling of N-Hydroxyphthalimide Esters with Aryl Iodides
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A new method for the decarboxylative coupling of alkyl N-hydroxyphthalimide esters (NHP esters) with aryl iodides is presented. In contrast to previous studies that form alkyl radicals from carboxylic acid derivatives, no photocatalyst, light, or arylmetal reagent is needed, only nickel and a reducing agent (Zn). Methyl, primary, and secondary alkyl groups can all be coupled in good yield (77% ave yield). One coupling with an acid chloride is also presented. Stoichiometric reactions of (dtbbpy)Ni(2-tolyl)I with an NHP ester show for the first time that arylnickel(II) complexes can directly react with NHP esters to form alkylated arenes.
- Huihui, Kierra M. M.,Caputo, Jill A.,Melchor, Zulema,Olivares, Astrid M.,Spiewak, Amanda M.,Johnson, Keywan A.,Dibenedetto, Tarah A.,Kim, Seoyoung,Ackerman, Laura K. G.,Weix, Daniel J.
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p. 5016 - 5019
(2016/05/19)
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- Nickel(0)/NaHMDS adduct-mediated intramolecular alkylation of unactivated arenes via a homolytic aromatic substitution mechanism
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A variety of polycycles can be synthesized via an intramolecular alkylation cyclization promoted by Ni(PPh3)4 and NaHMDS. Mechanistic investigations support the catalytic nature of Ni0 in the course of TEMPO scavenging experiments and its association with the substrate and NaHMDS to form an adduct by DOSY NMR.
- Beaulieu, Louis-Philippe B.,Roman, Daniela Sustac,Vallee, Frederic,Charette, Andre B.
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supporting information; scheme or table
p. 8249 - 8251
(2012/09/07)
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- Selective palladium-loaded MIL-101 catalysts
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Palladium nanoparticles (NPs) of different mean particle size have been synthesized in the host structure of the porous coordination polymer (or metal-organic framework: MOF) MIL-101. The metal-organic chemical vapor deposition method was used to load MIL-101 with the Pd precursor complex [(η5-C5H5)Pd(η3-C 3H5)]. Loadings higher than 50 wt.% could be accomplished. Reduction of the Pd precursor complex with H2 gave rise to Pd NPs inside the MIL-101 (Pd@MIL-101). The reduction conditions, especially the temperature, allows us to make size-conform (size of the Pd NPs correlates with the size of the cavities of the host structure of MIL-101) and undersized Pd NPs. The Pd@MIL-101 samples were characterized by X-ray diffraction, IR spectroscopy, Brauner-Emmett-Teller (BET) analysis, elemental analysis, and transmission electron microscopy (TEM). Catalytic studies, hydrogenation of ketones, were performed with selected Pd@MIL-101 catalysts. Activity, selectivity, and recyclability of the catalyst family are discussed.
- Hermannsdoerfer, Justus,Kempe, Rhett
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experimental part
p. 8071 - 8077
(2011/09/12)
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- The positional and structural izomerization equilibrium of branched pentylbenzenes
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The equilibrium of the positional and structural isomerization of branched monopentylbenzenes, pentyltoluenes, and pentyl-o-xylenes was studied. It was found that the 1,2-dimethylpropyl substituted derivatives prevail over the 1,1-dimethylpropyl substituted isomers in the equilibrium mixture of all of the examined groups of compounds. The thermodynamic characteristics of the structural isomerization of pentylbenzenes were calculated from the experimental data.
- Naumkin,Nesterova,Nesterov,Vodenkova,Golovin
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experimental part
p. 141 - 148
(2011/08/05)
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- Silver-catalyzed benzylation and allylation of tertiary alkyl bromides with organozinc reagents
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Silver salts catalyze the benzylation and allylation of tertiary alkyl bromides with organozinc reagents. The reactions create quaternary carbon centers efficiently. Treatment of gem-dibromoalkanes with benzylic or allylic zinc reagents under silver catalysis leads to dibenzylation or diallylation. The functional-group compatibility of the present reactions is wider than that of the previous reactions with Grignard reagents.
- Mitamura, Yukihiro,Asada, Yoshihiro,Murakami, Kei,Someya, Hidenori,Yorimitsu, Hideki,Oshima, Koichiro
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experimental part
p. 1487 - 1493
(2011/07/07)
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- Nickel-catalyzed reductive cross-coupling of aryl halides with alkyl halides
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(Chemical Equation Presented) The direct reductive cross-coupling of alkyl halides with aryl halides is described. The transformation is efficient (equimolar amounts of the starting materials are used), generally high-yielding (all but one between 55 and 88% yield), highly functional-group-tolerant [OH, NHBoc, NHCbz, Bpin, C(O)Me, CO2Et, and CN are all tolerated], and easy to perform (uses only benchtop-stable reagents, tolerates small amounts of water and oxygen, changes color when complete, and uses filtration workup). The reaction appears to avoid the formation of intermediate organomanganese species, and a synergistic effect was found when a mixture of two ligands was employed.
- Everson, Daniel A.,Shrestha, Ruja,Weix, Daniel J.
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supporting information; experimental part
p. 920 - 921
(2010/03/31)
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- Iron-catalyzed cross-coupling of alkyl sulfonates with arylzinc reagents
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Iron-catalyzed cross-coupling reactions of primary and secondary alkyl sulfonates with arylzinc reagents proceed smoothly In the presence of excess TMEDA and a concomitant magnesium salt. The arylzinc reagents are prepared from the corresponding aryllithium or magnesium reagents with ZnI2. The In situ formation of alkyl Iodides and consecutive rapid cross-coupling avoids discrete preparation of the unstable secondary alkyl halides and also achieves high product selectivity.
- Ito, Shingo,Fujiwara, Yu-Ichi,Nakamura, Eiichi,Nakamura, Masaharu
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supporting information; experimental part
p. 4306 - 4309
(2009/12/26)
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- Silver-catalyzed benzylation and allylation reactions of tertiary and secondary alkyl halides with grignard reagents
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Treatment of alkyl halides, including tertiary alkyl bromides, with benzylic or allylic Grignard reagent in the presence of a catalytic amount of silver nitrate in ether yielded the corresponding cross-coupling products in high yields. The coupling reactions of tertiary alkyl halides provide efficient access to quaternary carbon centers.
- Someya, Hidenori,Ohmiya, Hirohisa,Yorimitsu, Hideki,Oshima, Koichiro
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scheme or table
p. 969 - 971
(2009/04/10)
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- Preparation, structure, and reactivity of nonstabilized organoiron compounds. Implications for iron-catalyzed cross coupling reactions
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A series of unprecedented organoiron complexes of the formal oxidation states -2, 0, +1, +2, and +3 is presented, which are largely devoid of stabilizing ligands and, in part, also electronically unsaturated (14-, 16-, 17- and 18-electron counts). Specifically, it is shown that nucleophiles unable to undergo β-hydride elimination, such as MeLi, PhLi, or PhMgBr, rapidly reduce Fe(3+) to Fe(2+) and then exhaustively alkylate the metal center. The resulting homoleptic organoferrate complexes [(Me4Fe)(MeLi)] [Li(OEt2)]2 (3) and [Ph4Fe][Li(Et 2O)2][Li(1,4-dioxane)] (5) could be characterized by X-ray crystal structure analysis. However, these exceptionally sensitive compounds turned out to be only moderately nucleophilic, transferring their organic ligands to activated electrophiles only, while being unable to alkylate (hetero)aryl halides unless they are very electron deficient. In striking contrast, Grignard reagents bearing alkyl residues amenable to β-hydride elimination reduce FeXn (n = 2, 3) to clusters of the formal composition [Fe(MgX)2]n. The behavior of these intermetallic species can be emulated by structurally well-defined lithium ferrate complexes of the type [Fe(C2H4) 4][Li(tmeda)]2 (8), [Fe(cod)2][Li(dme)] 2 (9), [CpFe(C2H4)2][Li(tmeda)] (7), [CpFe(cod)][Li(dme)] (11), or [Cp*Fe(C2H4) 2][Li(tmeda)] (14). Such electron-rich complexes, which are distinguished by short intermetallic Fe-Li bonds, were shown to react with aryl chlorides and allyl halides; the structures and reactivity patterns of the resulting organoiron compounds provide first insights into the elementary steps of low valent iron-catalyzed cross coupling reactions of aryl, alkyl, allyl, benzyl, and propargyl halides with organomagnesium reagents. However, the acquired data suggest that such C-C bond formations can occur, a priori, along different catalytic cycles shuttling between metal centers of the formal oxidation states Fe(+1)/Fe(+3), Fe(0)/Fe(+2), and Fe(-2)/Fe(0). Since these different manifolds are likely interconnected, an unambiguous decision as to which redox cycle dominates in solution remains difficult, even though iron complexes of the lowest accessible formal oxidation states promote the reactions most effectively.
- Fuerstner, Alois,Martin, Ruben,Krause, Helga,Seidel, Guenter,Goddard, Richard,Lehmann, Christian W.
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p. 8773 - 8787
(2008/12/23)
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- Cross-coupling of alkyl halides with aryl Grignard reagents catalyzed by a low-valent iron complex
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A striking reversal of the usual reactivity pattern of aryl Grignard reagents is observed for reactions in the presence of catalytic amounts of the "bare" ferrate complex [Li(tmeda)]2[Fe(C2H 4)4] (1). Highly reduced iron-magnesium clusters may play a decisive role in the exceptionally facile and chemoselective cross-coupling reaction with alkyl halides (see scheme).
- Martin, Ruben,Fuerstner, Alois
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p. 3955 - 3957
(2007/10/03)
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- Cobalt-catalyzed cross-coupling reactions of alkyl halides with allylic and benzylic grignard reagents and their application to tandem radical cyclization/cross-coupling reactions
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Details of cobalt-catalyzed cross-coupling reactions of alkyl halides with allylic Grignard reagents are disclosed. A combination of cobalt(II) chloride and 1,2-bis(diphenylphosphino)ethane (DPPE) or 1,3-bis(diphenylphosphino)propane (DPPP) is suitable as a precatalyst and allows secondary and tertiary alkyl halides-as well as primary ones-to be employed as coupling partners for allyl Grignard reagents. The reaction offers a facile synthesis of quaternary carbon centers. which has practically never been possible with palladium, nickel, and copper catalysts. Benzyl, methallyl, and crotyl Grignard reagents can all couple with alkyl halides. The benzylation definitely requires DPPE or DPPP as a ligand. The reaction mechanism should include the generation of an alkyl radical from the parent alkyl halide. The mechanism can be interpreted in terms of a tandem radical cyclization/cross-coupling reaction. In addition, serendipitous tandem radical cyclization/cyclopropanation/carbonyl allylation of 5-alkoxy-6-halo-4-oxa-1-hexene derivatives is also described. The intermediacy of a carbon-centered radical results in the loss of the original stereochemistry of the parent alkyl halides, creating the potential for asymmetric cross-coupling of racemic alkyl halides.
- Ohmiya, Hirohisa,Tsuji, Takashi,Yorimitsu, Hideki,Oshima, Koichiro
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p. 5640 - 5648
(2007/10/03)
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- Pinacol reduction-cum-rearrangement. A re-examination of the reduction of aryl alkyl ketones by zinc-aluminum chloride
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Reduction of alkyl phenyl ketones by zinc and aluminum chloride in acetonitrile results in pinacol condensation followed by rearrangement. The phenyl group migrates in every instance.
- Grant, Anya A.,Allukian, Myron,Fry, Albert J.
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p. 4391 - 4393
(2007/10/03)
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- Alkylation of Benzene with Alkanes in the Presence of Modified Aluminum Chloride
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The use of new catalytic systems based on promoted aluminum halides, instead of pure aluminum chloride, in benzene alkylation with alkanes provides a 1.5-4.4-fold higher yield of alkylbenzenes. An effect of various promotors (Br2, C2H5Cl, CCl4, Ph3CCl) on the alkylation process is revealed. The quantitative composition of the alkylbenzene fraction produced by the alkylation of benzene with 2-methylbutane is determined, and a mechanism of this reaction is proposed.
- Polubentseva,Pikerskii,Duganova,Chenets
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p. 1613 - 1617
(2007/10/03)
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- Use of Catalytic Systems Based on Aluminum Chloride in Alkylation of Benzene
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Catalytic action of supported catalysts AlCl3-MeX/SiO2, where MeX is a salt of a metal with variable valence, in alkylation of benzene with isoamyl bromide is studied for various temperatures and contact times. Binary catalytic systems are more active (with respect to the yield of amylbenzenes) than straight SiO2-supported catalysts. To a certain extent, the catalytic activity of binary systems is due to the presence of modifiers: water of crystallization and alkyl halides. The support influences the activity and selectivity of the catalysts owing to interaction between the components. Supported catalysts AlCl3-MeX/SiO2 surpass AlCl3 in selectivity and the yield of target products and suppress side processes that accompany alkylation. A mechanism is proposed for alkylation of benzene with isoamyl bromide on the catalysts prepared.
- Polubentseva,Duganova,Mikhailenko
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p. 607 - 613
(2007/10/03)
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- A modified Clemmensen reduction procedure for conversion of aryl ketones into aryl alkenes
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Aryl alkenes can be prepared from aryl ketones through reduction by refluxing with amalgamated zinc in a mixture of formic acid and ethanol.
- Hiegel, Gene A.,Carney, John R.
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p. 2625 - 2631
(2007/10/03)
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- PHOTOSTIMULATED REACTIONS OF NEOPENTYL IODIDES WITH CARBANIONS IN DMSO BY THE SRN1 MECHANISM
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Neopentyl iodide, 1, reacted under photostimulation with several carbanionic nucleophiles in DMSO.With acetone enolate ion only reduction and dimerization occured, but good yields of substitution products have been obtained with acetophenone, 5, and anthrone, 9, anions as nucleophiles.Nitromethane anion, 7, does not react with 1 under irradiation, but good yields of the substitution products are obtained when the photostimulated reaction is carried out in the presence of acetone enolate ions (entrainment reaction).Inhibition experiments by p-dinitrobenzene and by the radical trap TEMPO, suggest that these reactions occur by the SRN1 mechanism of nucleophilic substitution.The photostimulated reaction of 1,3-diiodo-2,2-dimethylpropane, 15, with 5 gave the disubstitution product 17 and the reduced monosubstitution product 18.It has been found that the monosubstitution product 16 (in which iodine is retained) is not an intermediate of these reactions. 1-iodoadamantane, 12, is more reactive (ca. 4.9 times) than 1 in competitive experiments toward 5 and under photostimulation.
- Penenory, Alicia B.,Rossi, Roberto A.
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p. 605 - 610
(2007/10/03)
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- The Reaction of 2,2,5,5-Tetramethyl-3,4-diphenylhexane with D2. Stereochemical Effects in a High-Temperature Reaction
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The thermolysis of 2,2,5,5-tetramethyl-3,4-diphenylhexane was carried out at temperatures above 300 deg C in the absence and presence of D2 (14 MPa).The presence of D2 results in a greatly increased yield of the major product, neopentylbenzene.However, at higher concentrations of starting material, up to 50percent of the neopentylbenzene formed avoids deuterium incorporation, an outcome belived to result partly from participation of the phenylneopentyl radical in radical disproportionation reactions.The meso-isomer of starting material produces a substantial yield of stilbene in both the absence and presence of D2.Under D2, 1,2-diphenylethane is produced, and it is belived that stilbene and other alkenes present serve as D atom traps producing radicals which then participate in termination by disproportionation.Remarkably, the d,l-diastereomer gives a different product distribution than the meso-isomer, giving very little stilbene or other products of tert-butyl group loss.However, both systems produce 1-phenyl-2-methyl-2-propene by methyl radical loss from the phenylneopentyl radical.The formation of such alkenes and the path to termination they provide is blamed for the absence of efficient kinetic chains involving D atoms.
- Guthrie, Robert D.,Sharipov, Rustem V.,Ramakrishnan, Sreekumar,Shi, Buchang,Davis, Burton H.
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p. 4504 - 4509
(2007/10/02)
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- Carbanions 27. Rearrangements of (9-alkyl-9-fluorenyl)-methyllithium (or cesium) and 2,2-diphenyl-3,3-dimethyl-butyllithium
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A study has been made upon the products from warming various (9-alkyl-9-fluorenyl)methyllithium (or cesium) compounds in THF to near 0°C followed by carbonation. When the 9-alkyl group is ethyl, the result is chiefly the protonated product (9-alkyl-9- fluorenyl)methane; a similar product evidently is formed when the 9-alkyl group is 1-norbornyl. When the 9-alkyl group is tert-butyl, the minor product is 9-neopentylfluorene-9-carboxylic acid from a [1,2]-migration of the tert-butyl group while the major product is 9-methylfluorene-9-carboxylic acid from an intramolecular elimination as shown by deuterium labeling. When the 9-alkyl is neopentyl, the major product is 9-neopentyl-9,10-dihydro-phenanthrene-9-carboxylic acid along with some 9-neopentylphenanthrene which becomes the major product in diethyl ether solution at 35°C. 2,2-Diphenyl-3,3-dimethylbutyllithium undergoes predominantly [1,2]-phenyl migration in THF at 0°C. From an x-ray crystal study upon 9-tert-butyl-9-(chloromethyl)fluorene and 9-neopentyl-9-(chloromethyl) fluorene, it is concluded that steric acceleration is responsible for the unusual reactions of (9-alkyl-9-fluorenyl)methyllithiums when the 9-alkyl groups are tert-butyl and neopentyl.
- Grovenstein Jr., Erling,Singh, Jagvir,Patil, Bhalchandra B.,VanDerveer, Don
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p. 5971 - 5998
(2007/10/02)
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- Nickel-Mediated Cross-Coupling of Unactivated Neopentyl Iodides with Organozincs
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(dppf)NiCl2 catalyzes the cross-coupling of unactivated primary neopentyl iodides with diorganozinc reagents.The zinc nucleophiles are formed by the treatment of ZnCl2*dioxane with 2 mol equiv of a Grignard reagent in an etheral solvent.The cross-coupling works optimally for diorganozincs formed from aryl chlorides or CH3MgCl.Use of aryl bromides can cause reduction and/or reductive dimerization of the electrophile.The analogous reaction with (CH3)2CuMgCl in either the presence or the absence of Group 10 metal catalysts failed to afford reasonable yields of cross-coupled products.The diorganozinc methodology overcomes many of the side reactions observed with the (dppf)NiCl2-mediated cross-coupling of Grignard reagents.
- Park, Kwangyong,Yuan, Kaixu,Scott, William J.
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p. 4866 - 4870
(2007/10/02)
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- Nickel-catalyzed cross-coupling of unactivated neopentyl iodides with Grignard reagents
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Primary neopentyl iodides react with aryl Grignard reagents in the presence of 10 mol% (dppf)NiCl2 to give the cross-coupled product.
- Yuan,Scott
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p. 189 - 192
(2007/10/02)
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- Zinc-Promoted Reactions. 2. Ionic and Nonionic Pathways in the Reduction of Acetophenone and 2,2-Dimethyl-1-phenylpropan-1-one
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The Clemmensen reduction of acetophenone and related substrates (PhCHXCH3, X = Cl, OH, OAc) was investigated in anhyd AcOH and in the presence of LiCl, HCl, or TFA.Ethylbenzene, 1-acetoxy-1-phenylethane, 2,3-diphenyl-2,3-butanediol, and 2,3-diphenyl-2-butene were formed in yields strongly dependent on the experimental conditions.The formation of the hydrocarbon was favored in neat AcOH and in AcOH/HCl/LiCl.Ionic and nonionic pathways were recognized.In the presence of Cl-, the proposed mechanism involves the intermediacy of PhCH(CH3)Cl.The process may proceed via *- and the carbon radical PhC*(CH3)OZnX.The second SET may lead to a carbanion, quenched by the acid to give PhCH(CH3)OZnX, a precursor of PhCHXCH3 (X = OAc, Cl).Coupling reactions, involving different radical species, account for the formation of the dimeric compounds.In the reduction of 2,2-dimethyl-1-phenylpropan-1-one, the preponderance of addition reactions, mainly involving Cl-, can be explained by the difficult approach of zinc metal to the hindered carbonyl group.Only traces of neopentylbenzene were obtained, the main product being 2-methyl-3-phenyl-2-butene.The proposed mechanism requires that the first SET occurs on adduct PhCCl(OH)C(CH3)3 to produce 2,2-dimethyl-1-phenylpropan-1-ol, the precursor of the alkene.
- Luchetti, Luciana,Rosnati, Vittorio
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p. 6836 - 6839
(2007/10/02)
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- Radical Substitution on the Sulphur of Thioester Group
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Intermolecular reaction of an organo-radical with thioester gives the sulphide, which is formed by the sulphur centred substitution of acyl groups with a nucleophilic organo-radical, but no displacement of S-alkyl groups with the organo-radical takes place.
- Tada, Masaru,Uetake, Tomohiro,Matsumoto, Mitsuhiro
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p. 1408 - 1409
(2007/10/02)
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- Electrochemical Reduction of (1-bromo-2,2-dimethylpropyl)benzene in Dimethylformamide on Carbon Electrodes
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Products from the electrochemical reduction of (1-bromo-2,2-dimethylpropyl)benzene (4a) on carbon electrodes in dimethylformamide containing lithium perchlorate were found to depend upon the electrolysis potential.At relatively positive potentials the products are derived primarily from the coupling of two benzylic radicals, wheres at more negative potentials the products are derived from the corresponding carbanions.This establishes for the first time the mechanism of bibenzyl formation in the electrochemical reduction of benzyl bromides at nonmetallic electrodes.It has also been found that the meso-dl ratios of the 1,2-di-tert-butyl-1,2-diphenylethane products are dependent upon electrolysis potential and that head-to-head coupling of 1-phenyl-2,2-dimethylpropyl radicals is sterically restricted.
- Fry, Albert J.,Powers, Thomas J.
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p. 2498 - 2501
(2007/10/02)
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- Dramatic Reversal of Diastereoselectivity in an N-Acyliminium Ion Cyclization Leading to Hexahydropyrroloisoquinolines. A Case of Competing Steric Interactions
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The N-acyliminium ion cyclization 1 -> 2 + 3 (eq 1) with various aliphatic substituents (R = ethyl, cyclohexyl, and tert-butyl) was carried out, as an extension of our work in ref 2.The following 2:3 ratios were obtained: 39:61, 12:88, and 15:85, respecti
- Maryanoff, Bruce E.,McComsey, David F.,Almond, Harold R.,Mutter, Martin S.,Bemis, Guy W.,et al.
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p. 1341 - 1346
(2007/10/02)
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- Rearrangement of Benzylically Lithiated Methylaryl Alkyl Sulfones
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Lithiathion of appropriate methylaryl alkyl sulfones is followed by migration of the alkyl group from sulfur to the benzylic carbon.Product studies, relative reactivities, and crossover experiments are consistent with a radical-radical anion chain process for this rearrangement.
- Madaj, Edmund J.,Snyder, Donald M.,Truce, William E.
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p. 3466 - 3469
(2007/10/02)
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- THE REACTION OF CARBANIONS WITH TERT-BUTYL RADICALS
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The SRNl free radical chain reaction of Me3CHgCl with nitronate -O2N=C(R1)(R2)> and phenone enolate -)=C(R1)(R2)> anions yields the C-alkylation products 1)(R2)NO2, PhCOC(R1)(R2)CMe3>.Competitive reactions between pairs of anions demonstrate that as the basicity of the anion increases the reactivity toward Me3Cat first increases and then decreases.An inverted reactivity order is also observed with phenylacetonitrile anions.In early transition state reactions, the nucleophilic character of the tert-butyl radical apparently controls the reactivity by virtue of a transition state involving transfer of the electron from radical to the LUMO of the resonance stabilized anion.
- Russell, Glen A.,Khanna, Rajive K.
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p. 4133 - 4146
(2007/10/02)
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- Thermolabile Hydrocarbons, XVIII. 1-Substituted Neopentyl radicals and their Dimers
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Five 3,4-diaryl-2,2,5,5-tetramethylhexanes 1a - e were prepared as pure meso- and DL-isomers.According to the NMR spectra, x-ray analyses for meso- and DL-1e (with an (FB)2E conformation as energy minimum for DL-1e), and force field calculations the diastereomers have distinctly different minimum energy conformations, rotational potentials, and strain enthalpies.Also the activation parameters for the thermal dissociation into 1-arylneopentyl radicals 2 are typically differing.From an entropy discussion it is concluded that sandwich-like diastereomeric radical complexes are formed in these reactions as first intermediates.Their tightness influences ΔS%.The recombinations of the radicals 2 likewise take place stereoselectively.Their substituent effects on the selectivity can also be understood by primary formation of diastereomeric complexes of radical pairs.
- Eichin, Karl-Heinz,Beckhaus, Hans-Dieter,Hellmann, Siegried,Fritz, Hans,Peters, Eva-Maria,et al.
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p. 1787 - 1821
(2007/10/02)
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- Chemistry of the tert-Butyl Radical: Polar Character, ρ Value for Reaction with Toluenes, and the Effect of Radical Polarity on the Ration of Benzylic Hydrogen Abstraction to Addition to Aromatic Rings
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We have reexamined the reactions of tert-butyl radicals with toluenes and have obtained a ρ value of 0.49 +/- 0.04 at 80 deg C.The new, independent system involves the quantification of all of the principal products from the reaction of tert-butyl radicals with mixtures of toluene and substituted toluene.Five major products contain benzyl fragments and are formed in significant yields: two symmetrical bibenzyls, the cross bibenzyl, and the two neopentylbenzenes that result from combination of tert-butyl and the two benzyl radicals.Attack on the side chain is a major reaction of free tert-butyl radicals and is the only significant reaction that they undergo other than cage and termination reactions. tert-Butyl radicals do not add to the ring of toluenes.Data on the relative rates of addition to benzenes and hydrogen abstraction from toluenes are collected for a series of radicals including hydrogen atoms; methyl, isopropyl, and tert-butyl radicals; and p-nitrophenyl, p-bromophenyl, and phenyl radicals.The data demonstrate that more electrophilic radicals have a larger tendency to add to rings whereas more nucleophilic radicals have a larger tendency to abstract benzylic hydrogens.
- Pryor, William A.,Tang, Felicia Y.,Tang, Robert H.,Church, Daniel F.
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p. 2885 - 2891
(2007/10/02)
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- Electrophilic Aromatic Substitution. Part 30. The Effects of the p-Bicyclooctan-1-yl, Adamantan-1-yl, exo-and endo-Norbornan-2-yl,and Neopentyl Substituents in Detritiation. Steric Acceleration of Hyperconjugation
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Rate coefficients have been measured for detritiation of compounds (p-3H)C6H4R by anhydrous trifluoracetic acid at 70 deg C, and lead to the following partial rate factors(R=): bicyclooctan-1-yl, 2650; adamantan-1-yl, 2000; exo-norbornan-2-yl, 175
- Archer, William J.,Morteza, A. Hossaini,Taylor, Roger
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p. 181 - 186
(2007/10/02)
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- Ketone-derived Peroxides. III. Decompositions of Cyclic Diperoxides derived from Dialkyl Ketones
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The decompositions of diperoxides from acetone, pentan-3-one, 1,5-diphenylpentan-3-one, pinacolone, benzyl methyl ketone and dibenzyl ketone have been studied.The yield of ketone decreases in this series, from 68percent with acetone to 1-2percent with dibenzyl ketone, i.e. with the increasing stability of the more stable radical fragment.The major products from the decompositions of diperoxides from the dibenzyl ketone and di(p-methylbenzyl) ketone were bibenzyl and 4,4'-dimethylbibenzyl respectively formed through coupling of benzyl radicals; crossover experiments showed that this was primarily an out-of-cage process.Most of the peroxides gave significant yields (5-20percent) of esters formed by an in-cage reaction between the alkyl radical and diacyl peroxide generated from decomposition of the biradical formed in the initial O-O bond homolysis of the peroxide.
- McCullough, Kevin J.,Morgan, Alistair R.,Nonhebel, Derek C.,Pauson, Peter L.
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p. 651 - 676
(2007/10/02)
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