- Photochemical Reductive C–C Coupling with a Guanidine Electron Donor
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The metal-free photoinduced reductive C–C coupling reactions of a number of substituted benzyl halides (15 examples) with the organic electron-donor 2,3,5,6-tetrakis(tetramethylguanidino)pyridine are evaluated. Depending on the substituents at the benzyl group, a C–C coupling product yield in the range 50–95 % is achieved. The photochemical benzyl-radical formation by homolytic N–C bond cleavage of the initially formed benzyl-pyridinium salts is the rate-determining step of these reactions. Electron-withdrawing as well as -donating substituents at the phenyl group increase the reaction rate. Quantum chemical computations did not reveal any correlation between either the enthalpy or Gibbs free energy of the N–C bond cleavage step and the experimentally determined first-order rate constants. Instead, the structural difference between the excited state generated by irradiation and the electronic ground state of the pyridinium ions could be used to rationalize the differences in the reaction rates.
- Wiesner, Sven,Walter, Petra,Wagner, Arne,Kaifer, Elisabeth,Himmel, Hans-J?rg
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p. 5045 - 5054
(2016/10/26)
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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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- A clean and selective radical homocoupling employing carboxylic acids with titania photoredox catalysis
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A titania photoredox catalysis protocol was developed for the homocoupling of C-centered radicals derived from carboxylic acids. Intermolecular reactions were generally efficient and selective, furnishing the desired dimers in good yields under mild neutral conditions. Selective cross-coupling with two acids proved unsuccessful. An intra-molecular adaptation enabled macrocycles to be prepared, albeit in modest yields. (Chemical Equation Presented).
- Manley, David W.,Walton, John C.
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supporting information
p. 5394 - 5397
(2015/02/19)
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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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- Ti-catalyzed homolytic opening of ozonides: A sustainable C-C bond-forming reaction
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The unprecedented homolytic opening of ozonides promoted and catalyzed by titanocene(III) is reported. This novel reaction proceeds at room temperature under neutral, mild conditions compatible with many functional groups and provides carbon radicals suitable to form C-C bonds via both homocoupling and cross-coupling processes. The procedure has been advantageously exploited for the straightforward synthesis of the natural product brittonin A.
- Rosales, Antonio,Munoz-Bascon, Juan,Lopez-Sanchez, Cristobal,Alvarez-Corral, Miriam,Munoz-Dorado, Manuel,Rodriguez-Garcia, Ignacio,Oltra, J. Enrique
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p. 4171 - 4176
(2012/06/18)
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- Benzyl bromide addition to pentafluorobenzaldehyde by Zaitsev-Barbier reaction promoted with complex systems underlain by iron pentacarbonyl
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Iron pentacarbonyl promots addition of benzyl bromide to benzaldehydes by Zaitsev-Barbier reaction only in the presence of nucleophilic additives [HMPT or (S)-N-benzoyl-2-methoxycarbonylpyrrolidine].
- Terent'Ev,Vasil'Eva,Ambartsumyan,Chakhovskaya,Mysova,Kochetkov
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experimental part
p. 1181 - 1184
(2009/12/05)
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- Kolbe carbon-carbon coupling electrosynthesis using solid-supported bases
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(Chemical Equation Presented) We have developed a novel electrolytic system for Kolbe carbon-carbon coupling electrosynthesis based on the acid-base reaction between carboxylic acids as a substrate and solid-supported bases. On the basis of the electrolytic system, Kolbe electrolysis of various carboxylic acids was successfully carried out to provide the corresponding homocoupling products in moderate to excellent yields.
- Kurihara, Hitoshi,Fuchigami, Toshio,Tajima, Toshiki
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p. 6888 - 6890
(2008/12/22)
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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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- Reductive transformations of organofluorine compounds: II. Hydrodechlorination of chloropolyfluoroarenes by the action of zinc
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Polyfluoroarenes containing chlorine atoms in the aromatic ring and/or in the benzylic position undergo hydrodechlorination by the action of zinc in aqueous dimethylformamide. The use of Zn/Cu and addition of salts (NaCl, Na2SO4, NH4Cl) favor reductive dechlorination of the Carom - Cl bond. Polyfluorobenzotrichlorides react with excess zinc to give the corresponding CH3-substituted derivatives, otherwise CH2Cl- and CHCl2-containing compounds are formed. The reduction of C6F5CCl3 and C6F5CH2Cl with zinc in the presence of copper provides lower yields of the hydrodechlorination products and leads to formation of 1,2-bis(pentafluorophenyl)ethane.
- Krasnov,Platonov
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p. 1488 - 1499
(2007/10/03)
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- Chemistry of bis(pentafluorobenzyl) phosphines and phosphine oxides. Single-crystal X-ray diffraction study of η6-mesitylene-dichloro-[bis(pentafluorobenzyl)phosphinous acid]-ruthenium(II) and of 1,2-bis(pentafluorophenyl)ethane
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The reaction of pentafluorobenzyl magnesium bromide with phosphorus trichloride in a 2:1 molar ratio led to the disubstituted product, bis(pentafluorobenzyl)bromophosphine 1, which, upon reaction with lithium aluminium hydride, was converted to bis-(penta
- Krafczyk, Roland,Thoennessen, Holger,Jones, Peter G.,Schmutzler, Reinhard
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p. 159 - 166
(2007/10/03)
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- THE SYNTHESIS AND REARRANGEMENT REACTIONS OF 2,3,4,5,6-PENTAFLUOROBENZYL METHYL SULPHOXIDE AND 1,1-BIS(PENTAFLUOROPHENYL)METHYL METHYL SULPHOXIDE
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2,3,4,5,6-Pentafluorobenzyl methyl sulphoxide (6) and 1,1-bis(pentafluorophenyl)methyl sulphoxide (9) were synthesised from hexafluorobenzene and sodium methylsulphinylmethide.Flash vapour phase thermolysis of (6) at 410 degC gave 2,2',3,3'4,4',5,5'6,6'-decafluorodibenzyl (11) whereas static vapour phase thermolysis at 140-190 deg C gave (11), 2,3,4,5,6-pentafluorobenzyl alcohol (12) and 2,2'3,3'4,4'5,5'6,6'-decafluorodibenzyl disulphide (13).Decaflourobenzophenone (14) and bis(pentafluorophenyl)methanol (15) are thermolysis products of compound (9) at 115-122 deg C, accompanied by 4-methanoyl-nonafluorobenzophenone (16) formed by the thermolysis of (19), the unisolated material derived from (9) by nucleophilic substitution of one para-fluorine by CH3SOCH2-.Central to the formation of (12), (13), (14), (15) and (16) are sulphenate esters formed by '1,2'-rearrangements, while homolysis of the C-SO(CH3) bond in (6) and dimerisation of the radical gives (11).
- Brooke, Gerald M.,Ferguson, J. A. K. Jamie
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p. 263 - 276
(2007/10/02)
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- Determination of D by the toluene carrier method
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The pyrolysis of C6F5CH2Br has been studied by the toluene carrier technique over the temperature range 727-800 deg C.Rate constants are based on analysis for residual parent compound by gas chromatography using an internal standard technique.In selected runs a material balance of 100+/-2percent was obtained for bromine based on C6F5CH2Br plus HBr.Within the limits of the experimental technique the process appears to be first order and homogeneous.In addition to HBr the order major products of the thermal decomposition are C6F5CH3, (C6F5CH2)2, C6F5CH2CH2C6H5, and (C6H5CH2)2.The Arrhenius equation obtained is log k1 (s-1) = 14.54+/-0.42 - (225000+/-6000)/19.1T.The log A value is very close to the value of 14.6 recommended by Benson and O'Neal for the decomposition of C6H5CH2Br.The activation energy, 225+/-6 kJ mol-1, should be a reasonable estimate of D.
- Kominar, R. John,Krech, Michael J.,Price, Stanley James W.
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p. 1906 - 1908
(2007/10/02)
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