- Synthesis of Dibenzyls by Nickel-Catalyzed Homocoupling of Benzyl Alcohols
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Dibenzyls are essential building blocks that are widely used in organic synthesis, and they are typically prepared by the homocoupling of halides, organometallics, and ethers. Herein, we report an approach to this class of compounds using alcohols, which are more stable and readily available. The reaction proceeds via nickel-catalyzed and dimethyl oxalate assisted dynamic kinetic homocoupling of benzyl alcohols. Both primary and secondary alcohols are tolerated.
- Pan, Feng-Feng,Guo, Peng,Huang, Xiaochuang,Shu, Xing-Zhong
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p. 3094 - 3100
(2021/04/23)
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- Reactions of benzyltriphenylphosphonium salts under photoredox catalysis
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The development of benzyltriphenylphosphonium salts as alkyl radical precursors using photoredox catalysis is described. Depending on substituents, the benzylic radicals may couple to form C-C bonds or abstract a hydrogen atom to form C-H bonds. A natural product, brittonin A, was also synthesized using this method.
- Boldt, Andrew M.,Dickinson, Sidney I.,Ramirez, Jonathan R.,Benz-Weeden, Anna M.,Wilson, David S.,Stevenson, Susan M.
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supporting information
p. 7810 - 7815
(2021/09/28)
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- Tandem Acceptorless Dehydrogenative Coupling-Decyanation under Nickel Catalysis
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The development of new catalytic processes based on abundantly available starting materials by cheap metals is always a fascinating task and marks an important transition in the chemical industry. Herein, a nickel-catalyzed acceptorless dehydrogenative coupling of alcohols with nitriles followed by decyanation of nitriles to access diversely substituted olefins is reported. This unprecedented C=C bond-forming methodology takes place in a tandem manner with the formation of formamide as a sole byproduct. The significant advantages of this strategy are the low-cost nickel catalyst, good functional group compatibility (ether, thioether, halo, cyano, ester, amino, N/O/S heterocycles; 43 examples), synthetic convenience, and high reaction selectivity and efficiency.
- Babu, Reshma,Balaraman, Ekambaram,Midya, Siba P.,Subaramanian, Murugan,Yadav, Vinita
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p. 7552 - 7562
(2021/06/28)
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- Coupling Photocatalysis and Substitution Chemistry to Expand and Normalize Redox-Active Halides
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Photocatalysis can generate radicals in a controlled fashion and has become an important synthetic strategy. However, limitations due to the reducibility of alkyl halides prevent their broader implementation. Herein we explore the use of nucleophiles that can substitute the halide and serve as an electron capture motif that normalize the variable redox potentials across substrates. When used with photocatalysis, bench-stable, commercially available collidinium salts prove to be excellent radical precursors with a broad scope.
- Rathnayake, Manjula D.,Weaver, Jimmie D.
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supporting information
p. 2036 - 2041
(2021/04/05)
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- Aryl dechlorination and defluorination with an organic super-photoreductant
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Direct excitation of the commercially available super-electron donor tetrakis(dimethylamino)ethylene (TDAE) with light-emitting diodes at 440 or 390 nm provides a stoichiometric reductant that is able to reduce aryl chlorides and fluorides. The method is very simple and requires only TDAE, substrate, and solvent at room temperature. The photoactive excited state of TDAE has a lifetime of 17.3 ns in cyclohexane at room temperature and an oxidation potential of ca. -3.4 V vs. SCE. This makes TDAE one of the strongest photoreductants able to operate on the basis of single excitation with visible photons. Direct substrate activation occurs in benzene, but acetone is reduced by photoexcited TDAE and substrate reduction takes place by a previously unexplored solvent radical anion mechanism. Our work shows that solvent can have a leveling effect on the photochemically available redox power, reminiscent of the pH-leveling effect that solvent has in acid-base chemistry.
- Glaser, Felix,Kerzig, Christoph,Larsen, Christopher B.,Wenger, Oliver S.
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p. 1035 - 1041
(2020/08/28)
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- "bulky-Yet-Flexible" α-Diimine Palladium-Catalyzed Reductive Heck Cross-Coupling: Highly Anti-Markovnikov-Selective Hydroarylation of Alkene in Air
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To pursue a highly regioselective and efficient reductive Heck reaction, a series of moisture-and air-stable α-diimine palladium precatalysts were rationally designed, readily synthesized, and fully characterized. The relationship between the structures of the palladium complexes and the catalytic properties was investigated. It was revealed that the"bulky-yet-flexible"palladium complexes allowed highly anti-Markovnikov-selective hydroarylation of alkenes with (hetero)aryl bromides under aerobic conditions. Further synthetic application of the present protocol could provide rapid and straightforward access to functional and biologically active molecules.
- Yang, Xu-Wen,Li, Dong-Hui,Song, A-Xiang,Liu, Feng-Shou
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p. 11750 - 11765
(2020/10/23)
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- Ni-Catalyzed Iterative Alkyl Transfer from Nitrogen Enabled by the in Situ Methylation of Tertiary Amines
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Current methods to achieve transition-metal-catalyzed alkyl carbon-nitrogen (C-N) bond cleavage require the preformation of ammonium, pyridinium, or sulfonamide derivatives from the corresponding alkyl amines. These activated substrates permit C-N bond cleavage, and their resultant intermediates can be intercepted to affect carbon-carbon bond-forming transforms. Here, we report the combination of in situ amine methylation and Ni-catalyzed benzalkyl C-N bond cleavage under reductive conditions. This method permits iterative alkyl group transfer from tertiary amines and demonstrates a deaminative strategy for the construction of Csp3-Csp3 bonds. We demonstrate PO(OMe)3 (trimethylphosphate) to be a Ni-compatible methylation reagent for the in situ conversion of trialkyl amines into tetraalkylammonium salts. Single, double, and triple benzalkyl group transfers can all be achieved from the appropriately substituted tertiary amines. Transformations developed herein proceed via recurring events: The in situ methylation of tertiary amines by PO(OMe)3, Ni-catalyzed C-N bond cleavage, and concurrent Csp3-Csp3 bond formation.
- Nwachukwu, Chideraa Iheanyi,McFadden, Timothy Patrick,Roberts, Andrew George
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p. 9979 - 9992
(2020/09/03)
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- Synthesis of dimeric molecules via ag-catalyzed electrochemical homocoupling of organic bromides paired with electrooxidation of urea
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We present a sacrificial anode-free approach to reductive homocoupling of organohalides that does not require a co-catalyst. In this approach, a divided electrochemical cell with aprotic and aqueous compartments separated by an anion exchange membrane enables coupling of the cathodic homocoupling reaction with anodic oxidation of urea. We show that, in contrast with traditional one-compartment cells relying on sacrificial anodes, the proposed cell configuration maintains stable cell voltage in the course of galvanostatic electrolysis. A synthetic potential of this method was assessed using a series of 13 organic bromides that demonstrated a strong dependence of the reaction outcome on the structure of the organic substrate, more specifically, the dissociation energy of the C–Br bond and the redox properties of formed radicals, which are discussed in detail. While not being suitable for the synthesis of byarylstructures, this method is excellent for C(sp3)-C(sp3) coupling to corresponding dimeric products with up to quantitative yields. Simultaneous electrochemical treatment of nitrogenous waste in the adjacent half-cell provides an additional incentive for wide adaptation of this sustainable synthetic approach.
- Klinkova, Anna,Krivoshapkina, Elena F.,Medvedev, Jury J.,Medvedeva, Xenia V.,Pivovarova, Yekaterina,Steksova, Yulia P.
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- Ni(II)/Al(0) mediated benzylic Csp 3 - Csp 3 coupling in aqueous media
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Abstract : The reaction of benzyl bromides and chlorides with aluminium metal powder or foil (1.2 eqv.) in the presence of catalytic nickel nitrate (10 mol%) in water at room temperature resulted in homocoupling to the corresponding bibenzyl products which were isolated in moderate to good yields. In sharp contrast, the same reaction in organic solvents like dichloromethane, dimethylformamide, acetonitrile, methanol and toluene yielded only a trace amount of the desired product. The scope of the reaction was tested with substituents on the aromatic ring such as Me-, Cl-, CN-, F-, NO 2-, Ph- as well as 2 ° benzyl halides. Graphical abstract: The reagent combination of aluminium metal and catalytic Ni(NO3)2 promotes the homocoupling of benzyl bromides and chlorides giving rise to the corresponding bibenzyl products in good to excellent yields. The reaction is greatly facilitated in water and showed good functional group tolerance. Besides the mild reaction condition and bench-friendliness, the present reaction constitutes the first example of aluminium-mediated homocoupling of a halide in water. [Figure not available: see fulltext.].
- Nayak, Mukesh Kumar,Mukhi, Priyabrata,Mohanty, Anuradha,Rana, Sohel Samim,Arora, Rajat,Narjinari, Himani,Roy, Sujit
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- Visible-Light-Driven Self-Coupling of Methylarenes Catalyzed by Ni2P?Cd0.5Zn0.5S Nanoparticles
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The Ni2P?Cd0.5Zn0.5S nanoparticles photocatalyzed self-coupling of p-xylene was reported here, and the corresponding coupling product 1,2-di-p-tolylethane was obtained. The reaction could be extended to toluene derivatives with electron-donating and electron-withdrawing substituents. Ni2P?Cd0.5Zn0.5S nanoparticles had already been characterized by XRD, ICP-AES, SEM, TEM, UV/Vis, FL, XPS. The Mott–Schottky curves of Ni2P?Cd0.5Zn0.5S were made through electrochemical methods. An active carbon free-radical was captured through ESR measurement under irradiation. The research demonstrated this photocatalytic system feasible for the self-coupling reaction of toluene derivatives.
- Yang, Dan-Dan,Hu, Jia-Jun,Zhang, Hong,Lv, Xiao-Jun,Chen, Yong,Fu, Wen-Fu
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p. 1384 - 1392
(2020/01/08)
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- Photoredox-Catalysis-Modulated, Nickel-Catalyzed Divergent Difunctionalization of Ethylene
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Divergent synthesis that enables a catalytic reaction to selectively produce different products from common substrates will allow the charting of wider chemical space and the unveiling of distinct mechanistic paradigms. A common strategy for it employs different ligands to modulate organometallic catalysts. Dramatic developments in photocatalysis have enabled previously inaccessible transformations. In particular, photoredox catalysis modulates the oxidation state of transition-metal complexes, offering enormous opportunities for methodology development. Herein, we developed a photo-mediated divergent ethylene difunctionalization via modulating oxidation states of the nickel catalyst by using different photoredox catalysts. This work will inspire new perspectives for value-added chemical synthesis using ethylene as a feedstock and shed light on photoredox-catalyst-based divergent synthesis, which fundamentally differs from ligand-controlled transition-metal catalysis.Divergent synthesis represents a powerful strategy for directly accessing different molecular scaffolds originating from the same starting materials. Access to different end products via transition-metal catalysis is conventionally achieved by ligand control. We herein demonstrate the use of ethylene feedstock and commercially available aryl halides to accomplish the divergent synthesis of 1,2-diarylethanes, 1,4-diarylbutanes, or 2,3-diarylbutanes in a highly selective fashion through the synergistic combination of nickel and photoredox catalysis. Mechanistic studies suggest that the observed selectivity was due to different active states of Ni(I) and Ni(0) modulated by Ru- and Ir-based photoredox catalysts, respectively. The ability to access different organometallic oxidation states via photoredox catalysis promises to inspire new perspectives for synergistic transition-metal-catalyzed divergent synthesis.Functionalization of ethylene without polymerization is challenging under photo-irradiation conditions. We have demonstrated that the photo-transformation of ethylene can be controllable by merging photoredox and transition-metal catalysis. In our study, the use of different photoredox catalysts was able to modulate the oxidation state of the nickel catalyst. Through different oxidation states, the nickel-catalyzed couplings proceeded via distinct pathways to generate divergent ethylene difunctionalization products selectively from the same feedstock.
- Li, Jiesheng,Luo, Yixin,Cheo, Han Wen,Lan, Yu,Wu, Jie
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supporting information
p. 192 - 203
(2019/01/21)
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- Nondirecting Group sp3 C?H Activation for Synthesis of Bibenzyls via Homo-coupling as Catalyzed by Reduced Graphene Oxide Supported PtPd@Pt Porous Nanospheres
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The use of heterogeneous bimetallic Pd-based nanocatalyst for directing the inactivated sp3 C?H coupling has been scarcely explored. This work reported the formation of symmetrical C?C bonds from the inactivated sp3 C?H bonds catalyzed by employing reduced graphene oxide supported PtPd@Pt porous nanospheres. The reaction of sp3 C?H activation proceeded under mild conditions without any solvent, ligand or directing group. It is a higher atom-, step- and cost-effectiveness strategy for developing heterogeneous catalysts in the synthesis of bibenzyls with various functional groups (e. g. aryl, alkyl, methoxyl, halogen, ester, and pyridyl). (Figure presented.).
- Wang, Zheng-Jun,Lv, Jing-Jing,Yi, Rong-Nan,Xiao, Min,Feng, Jiu-Ju,Liang, Zhi-Wu,Wang, Ai-Jun,Xu, Xinhua
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supporting information
p. 932 - 941
(2018/01/05)
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- Dimerization of Benzyl and Allyl Halides via Photoredox-Mediated Disproportionation of Organozinc Reagents
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Benzyl and allyl halides undergo homocoupling when treated with zinc in the presence of a catalytic amount of a cationic iridium(III) complex under irradiation with 400 nm light-emitting diodes. The reaction proceeds through the intermediate formation of an organozinc reagent, which disproportionates to a free radical and elemental zinc under photoredox conditions.
- Levin, Vitalij V.,Agababyan, Daniil P.,Struchkova, Marina I.,Dilman, Alexander D.
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p. 2930 - 2935
(2018/05/28)
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- A Zinc Catalyzed C(sp3)?C(sp2) Suzuki–Miyaura Cross-Coupling Reaction Mediated by Aryl-Zincates
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The Suzuki–Miyaura (SM) reaction is one of the most important methods for C?C bond formation in chemical synthesis. In this communication, we show for the first time that the low toxicity, inexpensive element zinc is able to catalyze SM reactions. The cross-coupling of benzyl bromides with aryl borates is catalyzed by ZnBr2, in a process that is free from added ligand, and is compatible with a range of functionalized benzyl bromides and arylboronic acid pinacol esters. Initial mechanistic investigations indicate that the selective in situ formation of triaryl zincates is crucial to promote selective cross-coupling reactivity, which is facilitated by employing an arylborate of optimal nucleophilicity.
- Procter, Richard J.,Dunsford, Jay J.,Rushworth, Philip J.,Hulcoop, David G.,Layfield, Richard A.,Ingleson, Michael J.
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p. 15889 - 15893
(2017/10/24)
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- Cobalt-Catalyzed Csp3?Csp3Homocoupling
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An efficient and easy method for Csp3?Csp3homocoupling was developed using cobalt bromide as catalyst. A series of functionalized alkyl bromides and alkyl chlorides were coupled in high yields under mild conditions. This reaction seems to involve a radical intermediate. (Figure presented.).
- Cai, Yingxiao,Qian, Xin,Gosmini, Corinne
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supporting information
p. 2427 - 2430
(2016/08/16)
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- A well-defined low-valent cobalt catalyst Co(PMe3)4 with dimethylzinc: a simple catalytic approach for the reductive dimerization of benzyl halides
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Herein, we report the first catalytic version of a cobalt-catalysed reductive homocoupling of benzyl halides which proceeds with low catalyst loadings (0.5 to 5 mol%). By synthetizing each cobalt intermediate we demonstrate that reaction proceeds through two single electron transfers (SET) and that dimethylzinc is only involved in the regeneration of the catalytic species.
- Fallon, Brendan J.,Corcé, Vincent,Amatore, Muriel,Aubert, Corinne,Chemla, Fabrice,Ferreira, Franck,Perez-Luna, Alejandro,Petit, Marc
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p. 9912 - 9916
(2016/12/07)
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- An unprecedented oxidative intermolecular homo coupling reaction between two sp3C–sp3C centers under metal-free condition
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An unprecedented formation of benzylic sp3C–sp3C coupled dibenzylic products has been illustrated. The reactions have been carried out in the presence of three oxidizing reagents, i.e., diacetoxy-iodobenzene (IBDA), N-fluorobenzenesulfonimide (NFSI), and pyridine (Py) using toluene derivatives.
- Sahoo, Santosh K.
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supporting information
p. 3476 - 3480
(2016/07/15)
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- Alkyne Semihydrogenation with a Well-Defined Nonclassical Co-H2 Catalyst: A H2 Spin on Isomerization and E-Selectivity
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The reactivity of a CoI-H2 complex was extended toward the semihydrogenation of internal alkynes. Under ambient temperatures and moderate pressures of H2, a broad scope of alkynes were semihydrogenated using a CoI-N2 precatalyst, resulting in the formation of trans-alkene products. Furthermore, mechanistic studies using 1H, 2H, and para-hydrogen induced polarization (PHIP) transfer NMR spectroscopy revealed cis-hydrogenation of the alkyne occurs first. The Co-mediated alkene isomerization afforded the E-selective products from a broad group of alkynes with good yields and E/Z selectivity.
- Tokmic, Kenan,Fout, Alison R.
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supporting information
p. 13700 - 13705
(2016/10/31)
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- Mechanism and Applications of the Photoredox Catalytic Coupling of Benzyl Bromides
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The photoredox catalytic coupling of halomethyl arenes to bibenzyl derivatives has been demonstrated. The catalytic protocol employed the Hantzsch ester, potassium phosphate, and a photoactive cyclometalated IrIIIcomplex catalyst. A photochemical quantum yield as high as 20 % was obtained. The catalytic mechanism was investigated in detail by performing photophysical and electrochemical measurements, as well as by quantum chemical calculations. The results suggest that two-electron mediation might be responsible for the improved photon economy. The reaction protocol was compatible with halomethyl arenes that contain a variety of functional groups. Finally, the synthetic utility of our protocol was demonstrated by the preparation of a natural dihydrostilbenoid, brittonin A.
- Park, Gyurim,Yi, Seung Yeon,Jung, Jaehun,Cho, Eun Jin,You, Youngmin
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p. 17790 - 17799
(2016/11/28)
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- Two dimensional inorganic electride-promoted electron transfer efficiency in transfer hydrogenation of alkynes and alkenes
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A simple and highly efficient transfer hydrogenation of alkynes and alkenes by using a two-dimensional electride, dicalcium nitride ([Ca2N]+·e-), as an electron transfer agent is disclosed. Excellent yields in the transformation are attributed to the remarkable electron transfer efficiency in the electride-mediated reactions. It is clarified that an effective discharge of electrons from the [Ca2N]+·e- electride in alcoholic solvents is achieved by the decomposition of the electride via alcoholysis and the generation of ammonia and Ca(OiPr)2. We found that the choice of solvent was crucial for enhancing the electron transfer efficiency, and a maximum efficiency of 80% was achieved by using a DMF mixed isopropanol co-solvent system. This is the highest value reported to date among single electron transfer agents in the reduction of C-C multiple bonds. The observed reactivity and efficiency establish that electrides with a high density of anionic electrons can readily participate in the reduction of organic functional groups.
- Kim, Ye Ji,Kim, Sun Min,Cho, Eun Jin,Hosono, Hideo,Yang, Jung Woon,Kim, Sung Wng
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p. 3577 - 3581
(2015/05/27)
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- Csp3-Csp3 homocoupling reaction of benzyl halides catalyzed by rhodium
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A highly reactive alkylrhodium complex was formed from Me2Zn and RhCl(PPh3)3 and effectively catalyzed a Csp 3-Csp3 homocoupling reaction of benzyl halides. A Csp 3-Csp3 coupling reaction using Rh catalyst has not been reported up to now. The reaction proceeded under very mild conditions and gave the corresponding homocoupling products even if they had reactive substituents such as an uncovered formyl or hydroxymethyl group.
- Sato, Kazuyuki,Inoue, Yuichi,Mori, Tomohisa,Sakaue, Atsushi,Tarui, Atsushi,Omote, Masaaki,Kumadaki, Itsumaro,Ando, Akira
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supporting information
p. 3756 - 3759
(2014/08/05)
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- An amphiphilic, catalytically active, vitamin B12 derivative
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We performed the reaction of vitamin B12 with N,N-dimethylformamide dimethyl acetal for primary amide activation, and added MeOH as a nucleophile, to afford cobalester, the first amphiphilic cobalamin derivative. The unique combination of redox properties and solubility represents an asset for its use as a catalyst in C-C bond forming reactions. This journal is the Partner Organisations 2014.
- Giedyk,Fedosov,Gryko
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supporting information
p. 4674 - 4676
(2014/05/06)
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- Straightforward synthesis of substituted dibenzyl derivatives
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The C-C bond formation by homogeneous catalysis is a powerful tool in organic synthesis. The replacement of noble metal by cheaper one for already reported methodologies is of interest for an economical purpose. The attractivity of such replacement is also enhanced if a first raw transition metal is found to be active in several processes. This work demonstrates that a common nickel complex can be used for a two-step cross-coupling procedure, namely a homocoupling reaction of benzyl derivatives and a subsequent Suzuki reaction. These consecutive reactions permit the synthesis of new polyfunctionalized dibenzyl compounds.
- Mboyi, Clève D.,Gaillard, Sylvain,Mabaye, Mbaye D.,Pannetier, Nicolas,Renaud, Jean-Luc
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p. 4875 - 4882
(2013/06/26)
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- Homocoupling of benzyl halides catalyzed by POCOP-nickel pincer complexes
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Two types of POCOP-nickel(II) pincer complexes were prepared by mixing POCOP pincer ligands and NiX2 in toluene at reflux. The resulting nickel complexes efficiently catalyze the homocoupling reactions of benzyl halides in the presence of zinc. The coupled products were obtained in excellent to quantitative yields.
- Chen, Tao,Yang, Limin,Li, Liang,Huang, Kuo-Wei
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experimental part
p. 6152 - 6157
(2012/08/29)
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- Catalytic double C-Cl bond activation in CHlby iron(III) salts with grignard reagents
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Cross-coupling of Grignard reagents with dichloromethane is achieved using iron(III) catalysts. Aryl- and benzylmagnesium bromides show a range of activity toward double C-Cl bond activation resulting in the insertion of methylene fragments between two equivalents of the nucleophilic partner. Georg Thieme Verlag Stuttgart.
- Qian, Xin,Kozak, Christopher M.
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experimental part
p. 852 - 856
(2011/06/21)
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- Kinetics and mechanism of the reaction of benzyl bromide with copper in hexamethylphosphoramide
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The reaction of copper with benzyl bromides in hexamethylphosphoramide has been studied. The kinetic and thermodynamic parameters of the reaction have been obtained. Hammett plots of log (script k sign/script k sign°) vs the substituent constant σ gave good correlations (ρ = 0.15, S ρ = 0.02, r = 0.954). The structure of the organic group has little effect on the rate of reaction of benzyl bromide with copper. In the absence of atmospheric oxygen, the oxidative dissolution of copper occurred by the mechanism of single-electron transfer with the formation of 1,2-diphenylethane and copper(I) complexes. The stereochemistry and intermediates compound was also investigated. The reaction mechanism is discussed.
- Egorov, Anatoly M.,Matyukhova, Svetlana A.,Anisimov, Alexander V.
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p. 296 - 305
(2007/10/03)
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- Flash vacuum pyrolysis over magnesium. Part 1 - Pyrolysis of benzylic, other aryl/alkyl and aliphatic halides
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Flash vacuum pyrolysis over a bed of freshly sublimed magnesium on glass wool results in efficient coupling of benzyl halides to give the corresponding bibenzyls. Where an ortho halogen substituent is present further dehalogenation gives some dihydroanthracene and anthracene. Efficient coupling is also observed for halomethylnaphthalenes and halodiphenylmethanes while chlorotriphenylmethane gives 4,4′-bis(diphenylmethyl)biphenyl. By using α,α′-dihalo-o-xylenes, benzocyclobutenes are obtained in good yield, while the isomeric α,α′-dihalo-p-xylenes give a range of high thermal stability polymers by polymerisation of the initially formed p-xylylenes. Other haloalkylbenzenes undergo largely dehydrohalogenation where this is possible, in some cases resulting in cyclisation. Deoxygenation is also observed with haloalkyl phenyl ketones to give phenylalkynes as well as other products. With simple alkyl halides there is efficient elimination of HCl or HBr to give alkenes. For aliphatic dihalides this also occurs to give dienes but there is also cyclisation to give cycloalkanes and dehalogenation with hydrogen atom transfer to give alkenes in some cases. For 5-bromopent-1-ene the products are those expected from a radical pathway but for 6-bromohex-1-ene they are clearly not. For 2,2-dichloropropane and 1,1-dichloropropane elimination of HCl occurs but for 1,1-dichlorobutane, -pentane and -hexane partial hydrolysis followed by elimination of HCl gives E, E-, E,Z- and Z,Z- isomers of the dialk-1-enyl ethers and fully assigned 13C NMR data are presented for these. With 6-chlorohex-1-yne and 7-chlorohept-1-yne there is cyclisation to give methylenecycloalkanes and -cycloalkynes. The behaviour of 1,2-dibromocyclohexane and 1,2-dichlorocyclooctane under these conditions is also examined. Various pieces of evidence are presented that suggest that these processes do not involve generation of free gas-phase radicals but rather surface-adsorbed organometallic species.
- Aitken, R. Alan,Hodgson, Philip K.G.,Morrison, John J.,Oyewale, Adebayo O.
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p. 402 - 415
(2007/10/03)
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- Silver catalyzed zinc Barbier reaction of benzylic halides in water
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Benzylic chlorides react in aqueous dibasic potassium phosphate under silver catalysis with aromatic aldehydes in the presence of zinc dust to give 1,2-diaryl alcohols in moderate to good yields. Dimerization to bibenzyls and reduction of the halide are important side reactions. A wide range of substituted aromatic and heteroaromatic aldehydes and of substituted benzylic chlorides can be used. Aliphatic aldehydes and ketones are unreactive. A mechanism of two SET on the metal surface is discussed.
- Bieber, Lothar W.,Storch, Elisabeth C.,Malvestiti, Ivani,Da Silva, Margarete F.
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p. 9393 - 9396
(2007/10/03)
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- Mechanism of the Solution-Phase Reaction of Alkyl Sulfides Atomic Hydrogen. Reduction via a 9-S-3 Radical Intermediate
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The low selectivity of benzyl alkyl sulfide fragmentation subsequent to its reaction with atomic hydrogen is indicative of a reaction that proceeds via an early transition state. The competitive reduction of a series of substituted-benzyl alkyl sulfides was insensitive to the substituent on the aromatic ring (ρ = -0.13, r = 0.99). The relative rates of fragmentation of a series of the substituted-benzyl alkyl sulfides gave a V-shaped Hammett plot. Both electron-donating and electron-withdrawing groups destabilized the transition state (ρ = +0.99, r = 0.999; ρ = -0.82, r = 0.992). Since the relative rates of disappearance of the alkyl benzyl sulfides are not substituent dependent, but the relative rates of fragmentation are, a 9-S-3 intermediate is preferred as the structure leading to products.
- Tanner, Dennis D.,Koppula, Sudha,Kandanarachchi, Pramod
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p. 4210 - 4215
(2007/10/03)
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- Dehalogenation of organic halides by flash vacuum pyrolysis over magnesium: A versatile synthetic method
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Flash vacuum pyrolysis over magnesium at 600°C results in efficient dehalogenation of a variety of organic halides and provides a preparatively useful method for C-C bond formation and other reactions.
- Aitken, R. Alan,Hodgson, Philip K. G.,Oyewale, Adebayo O.,Morrison, John J.
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p. 1163 - 1164
(2007/10/03)
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- A Superior Procedure for Generation of Substituted Benzyllithiums from the Corresponding Chlorides
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The use of diethyl ether-tetrahydrofuran-light petroleum (b.p. 30-40 deg C) (4:3:1) as solvent for the reaction of substituted benzyl chlorides with lithium naphthalenide at low temperature gives useful yields of the corresponding benzyllithium compounds, which react with electrophiles such as iodomethane and water to yield the expected reaction products.
- Smith, Keith,Hou, Daunjie
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p. 185 - 186
(2007/10/02)
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- Photolysis of (Arylmethyl)triphenylphosphonium Salts. Substituent, Counterion, and Solvent Effects on Reaction Products
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Quaternary (arylmethyl)phosphonium salts of the general formula ArCH2-PR3(+)Y(-) (Ar = substituted phenyl or 1-naphthyl; R = phenyl, ferrocenyl, or butyl; Y(-) = BF4(-) or halide) have been photolyzed in acetonitrile or in methanol.Photolysis involved the cleavage of the P-CH2 bond and the products derived from both, the arylmethyl radical and the carbocation, were formed.The proportion of the radical- and carbocation-derived products was determined as a function of substituents in group Ar, of groups R, counterions Y(-), and the solvent.For the nonoxidizable counterion (BF4(-), the proposed mechanism of the reaction involves initial homolysis, followed by the escape of the radical products from a solvent cage, or by the electron transfer from carbon to phosphorus, yielding the corresponding arylmethyl carbocation.The latter can either react with the solvent to form the observed carbocation-derived product or can undergo recombination with the tertiary phosphine formed to yield the starting phosphonium ion.Some indication of the "inverted substituent effect" resulting from the inhibition of single electron transfer from an easily oxidized radical was obtained.For the oxidizable counterions (halides), an additional pathway is suggested, that involves electron transfer from the anion, yielding the arylmethyl radical and the phosphine, thus decreasing the ionic/radical products ratio.
- Imrie, C.,Modro, T. A.,Rohwer, E. R.,Wagener, C. C. P.
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p. 5643 - 5649
(2007/10/02)
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- The Effect of Substituents on the Photochemical Reaction between Naphtalenedicarbonile and Methylbenzenes
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The photochemical reaction between 1,4-naphtalenedicarbonile (NDN) and toluene in acetonitrile is extended to bibenzyl (4), 3- and 4-fluorotoluene (8, 7), and 3- and 4-methoxytoluene (9, 10).The product distribution obtained with compounds 4, 7 and 10 is
- Albini, Angelo,Fasani, Elisa,Montessoro, Ezio
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p. 1409 - 1415
(2007/10/02)
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- Photochemical Transformations. 26. Sensitized and Unsensitized Photoreactions of Some Benzyl Chlorides in tert-Butyl Alcohol
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Benzyl chloride and a variety of meta- and para-substituted derivatives have been irradiated in tert-butylalcohol at 254 nm or in acetone-tert-butyl alcohol mixtures at 300 nm.Quantum and chemical yields of photosolvolysis products (benzyl tert-butyl ether and/or benzyl alcohol), photohomolysis products (bibenzyl and 4-phenyl-2-methyl-2-butanol), and corresponding products from substituted benzylchlorides have been measured as functions of substrate concentration and medium composition.Sensitized reactions favor bond heterolysis, but direct irradiations favor homolysis, although reactions are not clean in either case.There is no correlation between quantum yields for photosolvolysis and Hammett ? or Brown ?+ constants, and no salt effects of added lithium perchlorate were observed, in either direct or sensitized reactions.
- Cristol, Stanley J.,Bindel, Thomas H.
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p. 951 - 957
(2007/10/02)
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