- Mixed Alkyl/Aryl Diphos Ligands for Iron-Catalyzed Negishi and Kumada Cross Coupling Towards the Synthesis of Diarylmethane
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Mixed alkyl/aryl diphos ligands have been prepared and their application in iron-catalyzed cross coupling of benzylic chlorides with diaryl zinc (Negishi) or aryl Grignard reagents (Kumada) towards the synthesis of diarylmethane has been evaluated. The iron?diphos catalytic system exhibited the enhanced activity and selectivity in the two coupling reactions. The electron-rich mixed PPh2/PCy2 ligands outperformed their symmetrical PPh2 congeners, and led to decreased homocoupling byproduct formation. It indicates that the electronic effect of the ligands plays an important role in the catalytic performance. The Fe catalyst supported by L8 bearing an electron-rich PCy2 substituent and a sterically demanding tert-butyl on ethene backbone exhibited the best catalytic performance and good functional group tolerance in the two cross coupling reactions.
- Ma, Xufeng,Wang, Han,Liu, Yao,Zhao, Xing,Zhang, Jun
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p. 5134 - 5140
(2021/11/16)
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- Skeletal editing through direct nitrogen deletion of secondary amines
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Synthetic chemistry aims to build up molecular complexity from simple feedstocks1. However, the ability to exert precise changes that manipulate the connectivity of the molecular skeleton itself remains limited, despite possessing substantial potential to expand the accessible chemical space2,3. Here we report a reaction that ‘deletes’ nitrogen from organic molecules. We show that N-pivaloyloxy-N-alkoxyamides, a subclass of anomeric amides, promote the intermolecular activation of secondary aliphatic amines to yield intramolecular carbon–carbon coupling products. Mechanistic experiments indicate that the reactions proceed via isodiazene intermediates that extrude the nitrogen atom as dinitrogen, producing short-lived diradicals that rapidly couple to form the new carbon–carbon bond. The reaction shows broad functional-group tolerance, which enables the translation of routine amine synthesis protocols into a strategy for carbon–carbon bond constructions and ring syntheses. This is highlighted by the use of this reaction in the syntheses and skeletal editing of bioactive compounds.
- Kennedy, Sean H.,Dherange, Balu D.,Berger, Kathleen J.,Levin, Mark D.
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p. 223 - 227
(2021/05/19)
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- Nickel-Catalyzed Electrochemical C(sp3)?C(sp2) Cross-Coupling Reactions of Benzyl Trifluoroborate and Organic Halides**
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Reported here is the redox neutral electrochemical C(sp2)?C(sp3) cross-coupling reaction of bench-stable aryl halides or β-bromostyrene (electrophiles) and benzylic trifluoroborates (nucleophiles) using nonprecious, bench-stable NiCl2?glyme/polypyridine catalysts in an undivided cell configuration under ambient conditions. The broad reaction scope and good yields of the Ni-catalyzed electrochemical coupling reactions were confirmed by 50 examples of aryl/β-styrenyl chloride/bromide and benzylic trifluoroborates. Potential applications were demonstrated by electrosynthesis and late-stage functionalization of pharmaceuticals and natural amino acid modification, and three reactions were run on gram-scale in a flow-cell electrolyzer. The electrochemical C?C cross-coupling reactions proceed through an unconventional radical transmetalation mechanism. This method is highly productive and expected to find wide-spread applications in organic synthesis.
- Luo, Jian,Hu, Bo,Wu, Wenda,Hu, Maowei,Liu, T. Leo
-
supporting information
p. 6107 - 6116
(2021/02/01)
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- Visible Light-Driven α-Alkylation of N-Aryl tetrahydroisoquinolines Initiated by Electron Donor-Acceptor Complexes
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The visible light-driven α-alkylation of N-aryl tetrahydroisoquinolines was initiated through electron donor-acceptor complex photochemistry. The reaction can proceed smoothly without the addition of any photocatalysts, transition-metal catalysts, or additional oxidants. The proposed mechanism was supported by various mechanistic studies, and the reactive open-shell alkyl radicals were generally produced from an alkylamine and underwent radical coupling for alkylating a wide range of N-aryl tetrahydroisoquinolines.
- Dai, Peng,Deng, Hongping,Li, Yufei,Wang, Xinmin,Xia, Qing,Zhang, Wei-Hua
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supporting information
p. 7290 - 7294
(2020/10/12)
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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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- Iodine-catalysed transfer hydrogenation of a carbon-carbon σ-bond with water
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Iodine catalysed the transfer hydrogenation of a benzylic C-C σ-bond in [2.2]paracyclophane with water to yield 4,4′-dimethylbibenzyl. The C-C σ-bond was first cleaved by homolytic substitution with iodine radicals to produce a 4,4′-diiodomethylbibenzyl i
- Yang, Wu,To, Ching Tat,Chan, Kin Shing
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p. 6757 - 6761
(2019/07/22)
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- Copper(II)-Catalyzed Asymmetric Photoredox Reactions: Enantioselective Alkylation of Imines Driven by Visible Light
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Asymmetric photoredox catalysis offers exciting opportunities to develop new synthetic approaches to chiral molecules through novel reaction pathways. Employing the first-row transition metal complexes as the chiral photoredox catalysts remains, however, a formidable challenge, although these complexes are economic, environmentally friendly, and often exhibit special reactivities. We report in this Article the development of one class of highly efficient asymmetric/photoredox bifunctional catalysts based on the copper(II) bisoxazoline complexes (CuII-BOX) for the light-induced enantioselective alkylation of imines. The reactions proceed under very mild conditions and without a need for any other photosensitizer. The simple catalytic system and readily tunable chiral ligands enable a significantly high level of enantioselectivity for the formation of chiral amine products bearing a tetrasubstituted carbon stereocenter (36 examples, up to 98% ee). Overall, the CuII-BOX catalysts initiate the radical generation, and also govern the subsequent stereoselective transformations. This strategy utilizing chiral complexes comprised of a first-row transition metal and a flexible chiral ligand as the asymmetric photoredox catalysts provides an effective platform for the development of green asymmetric synthetic methods.
- Li, Yanjun,Zhou, Kexu,Wen, Zhaorui,Cao, Shi,Shen, Xiang,Lei, Meng,Gong, Lei
-
supporting information
p. 15850 - 15858
(2018/11/23)
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- Dimerization of Benzyl and Allyl Halides via Photoredox-Mediated Disproportionation of Organozinc Reagents
-
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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- Postsynthetic bromination of UiO-66 analogues: Altering linker flexibility and mechanical compliance
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A new member of the UiO-66 series of zirconium metal-organic frameworks (MOFs) is reported, and the postsynthetic bromination of its integral alkene moeities in a single-crystal to single-crystal manner is fully characterised. Nanoindentation is used to p
- Marshall, Ross J.,Richards, Tom,Hobday, Claire L.,Murphie, Colin F.,Wilson, Claire,Moggach, Stephen A.,Bennett, Thomas D.,Forgan, Ross S.
-
supporting information
p. 4132 - 4135
(2016/03/12)
-
- 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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- 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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- Cyclopentadienyl nickel(ii) N, C-chelating benzothiazolyl NHC complexes: Synthesis, characterization and application in catalytic C-C bond formation reactions
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Cyclopentadienyl (Cp) Ni(ii) complexes [CpNiL][PF6] containing hybrid N,C chelating benzothiazolyl NHC ligands (L1 = 1-(2-benzothiazolyl)-3-methylimidazol-2-ylidene, 3a; L2 = 1-(2-benzothiazolyl)-3-allylimidazol-2-ylidene, 3b; L3 = 1-(2-benzothiazolyl)-3-benzylimidazol-2-ylidene, 3c) have been synthesized and fully characterized. The catalytic activity of 3a-3c in some C-C bond formation reactions has been examined. They are efficient catalysts for the homo-coupling of benzyl bromide in the presence of MeMgCl at r.t. with good functional group tolerance. Complex 3a is active in the catalytic oxidative homo-coupling of Grignard reagents with 1,2-dichloroethane as an oxidant at r.t.
- Teo, Wei Jie,Wang, Zhe,Xue, Fei,Andy Hor,Zhao, Jin
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p. 7312 - 7319
(2016/06/01)
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- Reversed electron apportionment in mesolytic cleavage: The reduction of benzyl halides by SmI2
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The paradigm that the cleavage of the radical anion of benzyl halides occurs in such a way that the negative charge ends up on the departing halide leaving behind a benzyl radical is well rooted in chemistry. By studying the kinetics of the reaction of substituted benzylbromides and chlorides with SmI2 in THF it was found that substrates para-substituted with electron-withdrawing groups (CN and CO2Me), which are capable of forming hydrogen bonds with a proton donor and coordinating to samarium cation, react in a reversed electron apportionment mode. Namely, the halide departs as a radical. This conclusion is based on the found convex Hammett plots, element effects, proton donor effects, and the effect of tosylate (OTs) as a leaving group. The latter does not tend to tolerate radical character on the oxygen atom. In the presence of a proton donor, the tolyl derivatives were the sole product, whereas in its absence, the coupling dimer was obtained by a SN2 reaction of the benzyl anion on the neutral substrate. The data also suggest that for the para-CN and CO2Me derivatives in the presence of a proton donor, the first electron transfer is coupled with the proton transfer. Reverse breakup: In the mesolytic cleavage of the radical anions of benzyl halides that are para-substituted by CN or CO2Me groups, the halogen departs, counterintuitively, as a radical and the benzyl system carries the negative charge (see figure).
- Yitzhaki, Offir,Hoz, Shmaryahu
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p. 9242 - 9248
(2015/06/16)
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- NaBH3CN: A janus substitute for tin-free radical-based reactions
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Beside showing that thermal radical reactions (reduction, Giese reaction) are efficient if bromo-/iodosugars are treated with NaBH3CN and 2,2″-azobisisobutyronitrile, we explored new initiation conditions on the basis of CuI salts (≤0.5 equiv.) supposed to produce radicals from organobromides through a set. This was confirmed, as at about 50 C under an inert atmosphere acetobromoglucose was reduced to the rearranged 2-deoxyglucose and as N-allyl α-bromoamides reacted, depending on the conditions, either by reductive cyclization or atom-transfer radical cyclization. A related cyclization occurred upon using Cu(OAc)2. This and other assays showed the reduction by NaBH3CN of CuII salts, either added or formed in situ. Having both ionic and radical reactivity, NaBH 3CN appears as a Janus reagent that may be useful for tin-free radical chemistry under mild and very simple conditions. Copyright
- Guiard, Julie,Rahali, Yaniss,Praly, Jean-Pierre
-
supporting information
p. 4461 - 4466
(2014/08/05)
-
- Csp3-Csp3 homocoupling reaction of benzyl halides catalyzed by rhodium
-
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
-
supporting information
p. 3756 - 3759
(2014/08/05)
-
- Straightforward synthesis of substituted dibenzyl derivatives
-
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)
-
- HEPATITIS C VIRUS INHIBITORS
-
This disclosure concerns novel compounds of Formula (I) as defined in the specification and compositions comprising such novel compounds. These compounds are useful antiviral agents, especially in inhibiting the function of the NS5A protein encoded by Hepatitis C virus (HCV). Thus, the disclosure also concerns a method of treating HCV related diseases or conditions by use of these novel compounds or a composition comprising such novel compounds
- -
-
Page/Page column 65
(2012/04/10)
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- Synthesis and structure-activity analysis of new phosphonium salts with potent activity against African trypanosomes
-
A series of 73 bisphosphonium salts and 10 monophosphonium salt derivatives were synthesized and tested in vitro against several wild type and resistant lines of Trypanosoma brucei (T. b. rhodesiense STIB900, T. b. brucei strain 427, TbAT1-KO, and TbB48). More than half of the compounds tested showed a submicromolar EC50 against these parasites. The compounds did not display any cross-resistance to existing diamidine therapies, such as pentamidine. In most cases, the compounds displayed a good selectivity index versus human cell lines. None of the known T. b. brucei drug transporters were required for trypanocidal activity, although some of the bisphosphonium compounds inhibited the low affinity pentamidine transporter. It was found that phosphonium drugs act slowly to clear a trypanosome population but that only a short exposure time is needed for irreversible damage to the cells. A comparative molecular field analysis model (CoMFA) was generated to gain insights into the SAR of this class of compounds, identifying key features for trypanocidal activity.
- Taladriz, Andrea,Healy, Alan,Flores Pérez, Eddysson J.,Herrero García, Vanessa,Ríos Martínez, Carlos,Alkhaldi, Abdulsalam A. M.,Eze, Anthonius A.,Kaiser, Marcel,De Koning, Harry P.,Chana, Antonio,Dardonville, Christophe
-
supporting information; experimental part
p. 2606 - 2622
(2012/06/01)
-
- Synthesis of 3,7-disubstituted imipramines by palladium-catalysed amination/cyclisation and evaluation of their inhibition of monoamine transporters
-
We describe a novel approach for the synthesis of a series of 3,7-difunctionalised symmetric and unsymmetrical analogues of the tricyclic antidepressant (TCA) imipramine, which uses a key palladium-catalysed amination/cyclisation of an ester-functionalise
- Christensen, Helle,Schjoth-Eskesen, Christina,Jensen, Marie,Sinning, Steffen,Jensen, Henrik H.
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supporting information; experimental part
p. 10618 - 10627
(2011/11/14)
-
- HEPATITIS C VIRUS INHIBITORS
-
This disclosure concerns novel compounds of Formula (I) as defined in the specification and compositions comprising such novel compounds. These compounds are useful antiviral agents, especially in inhibiting the function of the NS5A protein encoded by Hepatitis C virus (HCV). Thus, the disclosure also concerns a method of treating HCV related diseases or conditions by use of these novel compounds or a composition comprising such novel compounds.
- -
-
Page/Page column 62-63
(2010/11/03)
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- Couplings of benzylic halides mediated by titanocene chloride: Synthesis of bibenzyl derivatives
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Titanocene monochloride catalyzes the homocoupling of benzylic halides and benzylic gem-dibromides to give the corresponding bibenzyl and stilbenyl systems. Exposure of benzylic bromides to Ti(III) in the presence of aldehydes gave rise to the Barbier-type products. Examples of the utility of the herein described processes are included.
- Barrero, Alejandro F.,Herrador, M. Mar,Del Moral, Jose F. Quilez,Arteaga, Pilar,Akssira, Mohammed,El Hanbali, Fadwa,Arteaga, Jesus F.,Dieguez, Horacio R.,Sanchez, Elena M.
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p. 2251 - 2254
(2007/10/03)
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- Direct preparation of benzylic manganese reagents from benzyl halides, sulfonates, and phosphates and their reactions: Applications in organic synthesis
-
The use of highly active manganese (Mn)*, prepared by the Rieke method, was investigated for the direct preparation of benzylic manganese reagents. The oxidative addition of the highly active manganese to benzylic halides was easily completed under mild conditions. Moreover, benzylic manganese sulfonates and phosphates were prepared by direct oxidative addition of Mn* to the carbon-oxygen bonds of benzylic sulfonates and phosphates. The resulting benzylic manganese reagents were found to undergo cross-coupling reactions with a variety of electrophiles. Most of these reactions were carried out in the absence of any transition metal catalyst under mild conditions. In addition, the use of highly active manganese was also studied for preparation of homo-coupled products of functionalized benzyl halides without transition metal catalysts. These useful approaches provided not only a facile synthetic route to the preparation of resoricinolic lipids but a facile synthesis of functionalized 4-benzylpyridines by regioselective and chemo selective γ-addition of benzylic group to N-alkoxycarbonylpyridinum salts.
- Suh, YoungSung,Lee, Jun-Sik,Kim, Seoung-Hoi,Rieke, Reuben D.
-
-
- Regioselective Chlorocarbonylation of Polybenzyl Cores and Functionalization Using Dendritic and Organometallic Nucleophiles
-
Regiospecific chlorocarbonylation of the polybenzyl cores PhCH2CH2Ph, C6(CH2CH2Ph)6, 7, and {CH(CH2Ph)2}4-1,2,4,5-C6H 2, 8, in the para position of the benzyl groups gives the chlorocarbonyl derivatives 2, 9, and 10, respectively, in good yields. The octachlorocarbonyl derivative 10 reacts with Newkome's aminotripod NH2C(CH2OCH2CH2CN)3 to give the 24-nitrile dendrimer 13 which is characterized by its molecular peak in the MALDITOF mass spectrum and with (5-aminopentyl)-1-ferrocene to give the octaferrocene complex 14. Reactions of 2, 9, and 10 with sodium methanolate in methanol gives the methyl esters 3, 15, and 16 which are reduced by LiAlH4 to the primary alcohols 4, 17, and 18; reactions of these alcohols with NaI and BF3·Et2O yield the iodomethyl derivatives 5, 19, and 20. The organoiron nucleophile [FeIICp(η5-C6Me5CH 2)], 1, reacts with 5, 19, and 20 leading to C-C bond formation and recovery of the aromatic structure of the ligand. This reaction with 5 yields a soluble complex, [FeIICp(η6-C6Me5CH 2CH2C6H4CH2-)] 2, 6, in which the two redox groups, separated by 14 carbon atoms, are independent, being reversibly reduced at approximately the same potential in an overall two-electron wave recorded by cyclic voltammetry. The analogous reaction with 19 and 20, however, gave almost insoluble hexa- and octa-iron complexes 21 and 22 with mediocre purities.
- Valerio, Christine,Moulines, Francoise,Ruiz, Jaime,Blais, Jean-Claude,Astruc, Didier
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p. 1996 - 2002
(2007/10/03)
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- Stilbenes from Sulfur-Mediated Dehydrodimerization of Substituted Toluenes
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When provision is made for removal of coproduct hydrogen sulfide, the reaction of sulfur with methyl p-toluate (MPT; 1) at 280 deg C leads to 70+percent yields of the product dimethyl trans-4,4'-stilbenedicarboxylate (DMSC, 2) if conversion of the MPT is restricted to ca 10percent.Diphenyl ether or excess MPT serves as the reaction solvent.Other products of the reaction include dimethyl 4,4'-bibenzyldicarboxylate (DBD, 3), 1,2,3-tris(4-carbomethoxyphenyl)propane (4), 1,2,3-tris(4-carbomethoxyphenyl)propene (5; mixture of E and Z isomers), and 2,3,4,5-tetrakis(4-carbomethoxyphenyl)thiophene (6).The products are consistent with the reversible formation of 4-carbomethoxybenzyl radicals from sulfur and MPT where removal of the hydrogen sulfide drives the reaction forward.
- Sickle, Dale E. Van
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p. 3263 - 3267
(2007/10/02)
-
- Le composes d'insertion du graphite comme precurseurs de metaux finement divises I. Couplage d'halogenures benzyliques
-
The reduction of a nickel salt by the intercalation compound KC8, results in highly dispersed nickel on graphite, which has been used as a coupling reagent for benzyl chloride.The yield and the selectivity of the reaction were slightly improved when nickel-copper bimetallic clusters were used.The properties of these mixtures are illustrated by the coupling of various substituted benzyl halides.Functional groups such as methoxy-, chloro-, bromo-, nitro-, cyano-, trifluoromethyl- and alkoxy-carbonyl groups, on the aromatic ring, were not affected by the conditions employed.
- Marceau, P.,Beguin, F.,Guillaumet, G.
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p. 137 - 142
(2007/10/02)
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- OXIDATIVE COUPLING THE TOLUIC ACID DIANION SYSTEM
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The behavior of all three toluic acid isomers upon treatment with two equivalents of base followed by the addition of iodide-containing reagents is described.
- Belletire, J. L.,Spletzer, E. G.
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p. 575 - 584
(2007/10/02)
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- REDUCTIVE COUPLING OF BENZYL HALIDES USING NICKEL(0)-COMPLEX GENERATED IN SITU IN THE PRESENCE OF TETRAETHYLAMMONIUM IODIDE, A SIMPLE AND CONVENIENT SYNTHESIS OF BIBENZYLS
-
Zerovalent nickel complex generated in situ by reduction of NiBr2(PPh3)2 with zinc powder in the presence of Et4NI was found to be an effective catalyst for homo-coupling of benzyl halides.The catalytic reactions proceeded smoothly in various solvents under mild conditions to afford dehalogenative-coupling products in good to high yields.
- Iyoda, Masahiko,Sakaitani, Masahiro,Otsuka, Hiroki,Oda, Masaji
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p. 127 - 130
(2007/10/02)
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- Highly Reactive Metallic Nickel: Reductive Homocoupling Reagent for Benzylic Mono- and Polyhalides
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Metallic nickel, prepared by the reduction of nickel halides with lithium in glyme using naphthalene as an electron carrier, was found to be a useful reagent for the homocoupling of benzylic mono- and polyhalides.Benzyl halides reacted with metallic nickel at room temperature to give the corresponding 1,2-diarylethanes in good to high yields and functional groups on the aromatic ring such as methoxy, chloro, bromo, nitro, cyano, and alkoxycarbonyl groups were not affected under the conditions employed.Benzylic monohalides (1-(chloromethyl)- or 2-(bromomethyl)naphthalene, chlorodiphenylmethane, and 9-bromofluorene) also underwent coupling reactions with metallic nickel at room temperature to give the corresponding ethane derivatives.On the other hand, benzylic di- and trihalides such as α,α-dibromotoluene and α,α,α-trichlorotoluene yielded mixtures of cis and trans isomers of substituted ethenes.The intermediate of the reaction, benzylnickel complex, was trapped with electron deficient olefins such as methyl acrylate and acrylonitrile.
- Inaba, Shin-ichi,Matsumoto, Hideyuki,Rieke, Reuben D.
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p. 2093 - 2098
(2007/10/02)
-
- Temperature and Substituent Effects on Regioselectivity in the Insertion of Arylcarbene into Alcohols
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Photolysis of aryldiazomethanes in methanol, ethanol, and 2-propanol gave OH insertion products along with small amounts of CH insertion products at ambient temperature.However, the CH insertion products increased significantly at the expense of the ether as the temperature was lowered.The attempted sensitized decomposition of the diazomethane did not lead to an increase in the CH insertion products presumably because of a rapid singlet-triplet equilibrium.The key intermediate leading to the CH insertion is suggested to be ground-state triplet arylcarbene, based on the accumulated spectroscopic as well as chemical evidence for the intervention of the triplet arylcarbene in the low-temperature photolysis of aryldiazomethanes.Substituents on the phenyl ring also have an appreciable effect on the insertion selectivity.At room temperature, the OH/CH insertion selectivity increased with the electron-donating ability of the substituents.This is interpreted in terms of the substituent effect on the transition state of OH insertion, where there is a deficiency of electrons at the benzylic carbon atom, rather than on the stability of singlet carbene.At low temperature, both electron-donating and -withdrawing substituents facilitate OH insertion, indicating the change in substituents induces a concomitant change in the insertion mechanism, presumably due to decreasing nucleophilicity of carbene with increasing electron-withdrawing ability as well as decreasing proton-donor activity of alcohol with decreasing temperature.This may also reflect the effect of the substituent on the singlet-triplet energy gap.
- Tomioka, Hideo,Suzuki, Shinji,Izawa, Yasuji
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p. 3156 - 3162
(2007/10/02)
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- Flash Pyrolysis of Selenides. Syntheses of Bibenzyls, Olefins, and Related Compounds
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Pyrolyses of a series of selenides and diselenides were studied. Selenides and diselenides bound with an active methylene group like benzyl gave a variety of substituted bibenzyls and related ethane derivatives in high yields. Other diselenides were easily caused to cleave to give various aromatic and aliphatic olefins in good yields together with elemental selenium. Lepidopterene, paracyclophane, and benzocyclobutene were prepared by thermal cleavage of their corresponding phenylselenomethyl-substituted compounds as an application of the pyrolysis concerned.
- Higuchi, Hiroyuki,Otsubo, Tetsuo,Ogura, Fumio,Yamaguchi, Hachiro,Sakata, Yoshiteru,Misumi, Soichi
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p. 182 - 187
(2007/10/02)
-
- NEW SYNTHETIC METHOD OF PARACYCLOPHANE, BENZOCYCLOBUTENE, AND LEPIDOPTRENE: PYROLYSIS OF ARYLMETHYL PHENYL SELENIDES
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The flash vacuum pyrolysis of benzyl phenyl selenides gave bibenzyls and diphenyl diselenide in excellent yields.This type of reaction was successfully applied to the synthesis of the title compounds.
- Higuchi, Hiroyuki,Sakata, Yoshiteru,Misumi, Soichi,Otsubo, Tetsuo,Ogura, Fumio,Yamaguchi, Hachiro
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p. 627 - 630
(2007/10/02)
-
- Electro-organic Reactions. Part 16. The Preparative-scale Cathodic Hydrogenolysis and Coupling of Benzyl-, Allyl-, Cinnamyl-, and Polyenylphosphonium salts
-
An investigation of the cathodic reduction of benzyltriphenylphosphonium nitrate confirms that optimum yields of the product of coupling (bibenzyl) are formed at an aluminium cathode using high current densities and in dimethylformamide or hexamethylphosphoramide solution.The cathodic reduction of allylphosphonium salts gives mainly cleavage; e.g. α-farnesene (5) is obtained in 32percent yield from the corresponding farnesylphosphonium salt.Moderately efficient coupling (ca. 30percent) is observed for the electro-reduction of trans-cinnamyltriphenylphosphonium nitrate (6) and a C15 polyenylphosphonium salt (7).The products of coupling have been fully characterised; the relative proportions of positional isomers are apparently dictated by steric factors.
- Utley, James H. P.,Webber, Andrew
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p. 1154 - 1160
(2007/10/02)
-