- Salt-Stabilized Silylzinc Pivalates for Nickel-Catalyzed Carbosilylation of Alkenes
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We herein report the preparation of solid and salt-stabilized silylzinc pivalates from the corresponding silyllithium reagents via transmetalation with Zn(OPiv)2. These resulting organosilylzinc pivalates show enhanced air and moisture stability and unique reactivity in the silylative difunctionalization of alkenes. Thus, a practical chelation-assisted nickel-catalyzed regioselective alkyl and benzylsilylation of alkenes has been developed, which provides an easy method to access alkyl silanes with broad substrate scope and wide functional group compatibility. Kinetic experiments highlight that the OPiv-coordination is crucial to improve the reactivity of silylzinc pivalates. Furthermore, late-stage functionalizations of druglike molecules and versatile modifications of the products illustrate the synthetical utility of this protocol.
- Chen, Kaixin,Dong, Shoucheng,Duan, Zhili,Li, Jie,Liu, Xingchen,Wang, Jixin
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supporting information
(2022/03/03)
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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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- 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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- Photo-catalytic preparation method of bibenzyl compounds
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The invention relates to a preparation method of bibenzyl compounds. A compound represented by a formula (A) and a compound represented by a formula (C) carry out reactions under the action of an organic tungsten catalyst and an alkali in the presence of light to generate bibenzyl compounds represented by the formula (B). The method is simple and is easy to operate. The yield is high, and the application range is wide. Moreover, the invention also provides an application of a tungsten complex in organic chemical reactions as a photocatalyst.
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Paragraph 0049-0053
(2020/02/27)
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- Luminescent tungsten(vi) complexes as photocatalysts for light-driven C-C and C-B bond formation reactions
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The realization of photocatalysis for practical synthetic application hinges on the development of inexpensive photocatalysts which can be prepared on a large scale. Herein an air-stable, visible-light-absorbing photoluminescent tungsten(vi) complex which can be conveniently prepared at the gram-scale is described. This complex could catalyse photochemical organic transformation reactions including borylation of aryl halides, such as aryl chloride, reductive coupling of benzyl bromides for C-C bond formation, reductive coupling of phenacyl bromides, and decarboxylative coupling of redox-active esters of alkyl carboxylic acid with high product yields and broad functional group tolerance.
- Chan, Kaai-Tung,Che, Chi-Ming,Du, Lili,Liu, Yungen,Phillips, David Lee,To, Wai-Pong,Tong, Glenna So Ming,Wu, Liang-Liang,Yu, Daohong
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p. 6370 - 6382
(2020/07/15)
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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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- Dual copper- and photoredox-catalysed C(sp2)-C(sp3) coupling
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The use of copper catalysis with visible light photoredox catalysis in a cooperative fashion has recently emerged as a versatile means of developing new C-C bond forming reactions. In this work, dual copper and photoredox catalysis is exploited to effect C(sp2)-C(sp3) cross-couplings between aryl boronic acids and benzyl bromides.
- McLean, Euan B.,Gauchot, Vincent,Brunen, Sebastian,Burns, David J.,Lee, Ai-Lan
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supporting information
p. 4238 - 4241
(2019/04/30)
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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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- 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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- 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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- Iron nanoparticle-promoted Cu (I)-catalysed homocoupling of arylmethyl halides for the synthesis of 1,2-diarylethanes
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Carbon-carbon bond formation is important in organic synthesis for the preparation of natural products, organic materials and polymers and so on. An efficient and mild reductive homocoupling of arylmethyl halides is now described. Treatment of various benzylic halides in the presence of zero valent iron nanoparticles (nZVI) and a catalytic amount of CuBr in air and water at room temperature afforded 1,2-diarylethanes in excellent yields.
- Shekarriz, Marzieh,Adib, Mehdi,Biabani, Tayebe,Taghipoor, Sohrab
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experimental part
p. 29 - 30
(2012/04/04)
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- Synthesis and in vitro activity of dicationic bis-benzimidazoles as a new class of anti-MRSA and anti-VRE agents
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A new class of novel bis-benzimidazole diamidine compounds have been synthesized and evaluated for in vitro antibacterial activities, including drug-resistant bacterial strains. Anti-MRSA and anti-VRE activities of the most potent compound 1 were more act
- Hu, Laixing,Kully, Maureen L.,Boykin, David W.,Abood, Norman
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body text
p. 1292 - 1295
(2009/10/15)
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- Facile synthesis of bibenzyl by reductive homocoupling of benzyl halides in aqueous media
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A facile synthesis of bibenzyl derivatives by reductive homocoupling reaction is described. Treatment of benzyl halides with metallic iron powder in the presence of a catalytic amount of cuprous salt in aqueous media gives bibenzyls in good yields. Copyright Taylor & Francis Group, LLC.
- Liu, Jian,Li, Bin
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p. 3273 - 3278
(2008/02/12)
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- Reactions of organocobaloximes with aryldisulfonyl chlorides
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Photochemical reactions of benzyl, heteroaromaticmethyl and allylcobaloximes with aryldisulfonyl chlorides yield symmetrical disulfones. Allyl cobaloximes yield allyldisulfones as the major product whereas bibenzyl is the major product in benzylcobaloximes. A time dependent 1H NMR studies show that bibenzyl is formed from O -benzyldimethylglyoxime - a predominant product in the initial stage of the reaction.
- Gupta,Vijaikanth
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p. 1102 - 1109
(2007/10/03)
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- Generation of Sulfur Ylides from Sulfonium Salts and Their Reactions. Comparative Study of Electrochemical Reduction with the Base Method and Mechanism Elucidation by the MO Method
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The cathodic reduction of sulfonium salts in acetonitrile in the presence and absence of benzaldehyde was carried out. Results were compared with results of the base method. In the presence of benzaldehyde, the electrochemical reduction gave epoxides as a result of the Corey-Chaykovsky reaction, thus confirming ylide formation. The electrochemical reduction of sulfonium salts without benzaldehyde yielded rearrangement products in high yield. On the contrary, upon base treatment of sulfonium salts without benzaldehyde, symmetrical epoxides derived from the benzyl group of the sulfonium salt are obtained as main products as a result of the auto oxidation of the sulfur ylide. The reaction mechanisms were elucidated based on the results obtained by a semi-empirical molecular orbital method.
- Okazaki, Yuichi,Ando, Fumio,Koketsu, Jugo
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p. 2155 - 2165
(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
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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.
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- Antifungal activity of dicationic molecules
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Methods of treating fungal infections comprise administering a therapeutically effective amount of a compound described by Formulas [(I)-(VI)]. Examples of fungal infections include Candida albicans, Cryptococcus neoformans, Aspergillus fumigatus, Fusariu
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- Benzylic Manganese Halides, Sulfonates, and Phosphates: Preparation, Coupling Reactions, and Applications in Organic Synthesis
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The use of highly active manganese, prepared by the Rieke method, for the direct preparation of benzylic manganese reagents was investigated. The oxidative addition of the highly active manganese (Mn*) to benzylic halides was easily completed under mild conditions. More importantly, 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. The majority of these reactions were carried out in the absence of any transition metal catalyst under mild conditions. This approach also provided a facile synthetic route to the preparation of resorcinolic lipids.
- Kim, Seung-Hoi,Rieke, Reuben D.
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p. 2322 - 2330
(2007/10/03)
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- Co-C bond cleavage in the reactions of alkyl, benzyl and heteroaromaticmethyl cobaloximes with arene sulfenyl chloride: Homolytic and heterolytic pathways
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The reactions of arene sulfenyl chlorides, ArSCl, (Ar=Ph, C6Cl5, 2,4 (NO2)2C6H3) with organocobaloximes, RCo(dmgH)2Py, (R=alkyl, benzyl and heteroaromaticmethyl) were carried out under thermal and photochemical conditions. A variety of organic and organometallic products are formed depending upon the substrate cobaloxime. For 3-methoxybenzyl and heteroaromaticmethyl cobaloximes the results suggest that they represent a unique class of cobaloximes whereby both the aromatic ring as well as the Co-C bond are highly activated towards attack by the arene sulfenyl chloride. Both homolytic as well as heterolytic pathways are operative.
- Gupta,Dixit, Vandana,Das, Indira
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- Structure-in vitro activity relationships of pentamidine analogues and dication-substituted bis-benzimidazoles as new antifungal agents
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Twenty analogues of pentamidine, 7 primary metabolites of pentamidine, and 30 dicationic substituted bisbenzimidazoles were screened for their inhibitory and fungicidal activities against Candida albicans and Cryptococcus neoformans. A majority of the com
- Del Poeta, Maurizio,Schell, Wiley A.,Dykstra, Christine C.,Jones, Susan,Tidwell, Richard R.,Czarny, Agnieszka,Bajic, Miroslav,Bajic, Marina,Kumar, Arvind,Boykin, David,Perfect, John R.
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p. 2495 - 2502
(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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- Reactivity of the acids of trivalent phosphorus and their derivatives. Part VI. The reaction of the >P-O- anions with benzyl bromides para-substituted in the phenyl ring
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The reaction of p-substituted benzyl bromides with the >P-O- ions in THF, alcohols and toluene as the solvents is described. According to the reduction potential of the p-substituted benzyl bromides and the solvent used the formation of the P-C bond, debromination and/or dimerization occur. The principal process is believed to be X-philic substitution, the dimers are formed through a secondary process via SET from the p-substituted benzyl anions into the p-substituted benzyl bromides.
- Witt, Dariusz,Rachon, Janusz
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p. 169 - 187
(2007/10/03)
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- Substituent effects on the photocleavage of benzyl-sulfur bonds. Observation of the "Meta effect"
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Benzyl phenyl sulfide has been used to investigate the photocleavage mechanism for benzyl-sulfur bonds. Four experiments have shown that the reaction goes through a radical intermediate. First, the photoproducts observed can all be justified by radical mechanisms. Second, the radical intermediate was trapped with a five hexenyl tether. Third, UV analysis of analogs for the 4-NO2 derivative indicate no exciplex or electron transfer pathway. Fourth, no strong correlation is observed between a values and the quatum yields for loss of substituted benzyl phenyl sulide. The effect of oxygen on quantum yields is best observed after samples are thoroughly outgassed with consecutive freeze-pump-thaw cycles. It is shown that oxygen diminishes the substituent effect. Upon photolysis of the outgassed samples, the meta-substituted derivatives showed more significant variances than the para derivatives. The meta derivatives are most efficiently cleaved in the following order: 3-CN > 3-NO2 > 3-CF3 > 3-CH3 > 3-OCH3. These findings are justified by an increase in electron density of the radical ipso to the forming benzyl radical for the 3-OCH3 derivative and a decrease in the electron density of the radical ipso to the forming benzyl radical for the 3-CN derivative.
- Fleming, Steven A.,Jensen, Anton W.
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p. 7040 - 7044
(2007/10/03)
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- Photoinduced Electron Transfer Reaction of Cyclopropanone Acetals with Arylmethyl Methanesulfonate: Generation of β-Keto Radical Species and Application to C-C Bond Formation
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The photoinduced electron transfer reaction of the cyclopropanone acetals 1 with arylmethyl methanesulfonates 4 or 10 as electron acceptors was found to generate a transient pair of radicals, the β-keto radical 3 and the arylmethyl radical, which underwent a novel carbon-carbon formation reaction at the sterically hindered β-position of the esters.
- Abe, Manabu,Oku, Akira
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p. 1673 - 1674
(2007/10/02)
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- Homolytic displacement at saturated carbon in organocobaloximes: Part VI - Synthesis of benzyl sulphones
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The reactions of thiophene-2-sulphonyl chloride with benzyl and para-substituted benzyl cobaloximes under anaerobic and photochemical conditions at 0 deg C give benzyl sulphones and bibenzyls in variable yields.However, the reactions with heteroaromatic methyl cobaloximes give the corresponding sulphones as the exclusive organic products.The reactions are interpreted in terms of SH2 mechanism.
- Gupta, B. D.,Das, Indira,Dixit, Vandana
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p. 762 - 766
(2007/10/02)
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- Photocleavage of Benzyl-Sulfide Bonds
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The nucleoside transport inhibitor 6--9-(β-D-ribofuranosyl)purine, NBMPR, has been used successfully in photoaffinity labeling.We have studied the mechanism for photocleavage of the benzyl-sulfur bond by using substituted benzyl phenyl sulfides as analogues of NBMPR.This has enabled us to enhance the photoreactivity of the benzyl-sulfur bond.We have also performed "radical clock" studies with a hexenyl side chain to trap reactive intermediates.The mechanistic interpretation from the substituent and side chain studies is that the benzyl-sulfur moiety is photocleaved via a homolytic pathway.
- Fleming, Steven A.,Jensen, Anton W.
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p. 7135 - 7137
(2007/10/02)
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- ?-Acceptor Induced Reactions: Radicals vs. Ions in Thermally Induced Ether Cleavage Reactions
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The reactions of benzyl ether (1a) and 4,4'-dicyanobenzyl ether (1b) with a wide range of ?-acceptors in acetonitrile at 190 deg C have been studied.The ?-acceptors were chosen in order to systematically vary the ΔG0 for hydride or electron transfer from the ethers to the ?-acceptors.The products of thermal activation of the bond cleavage reaction are the aldehyde and the alcohol derived from the starting ethers.A linear free energy correlation of the two relative thermal reaction rates of 1a and 1b with the reduction potentials of the quinones was obtained.This relationship indicates that the rate of radical pair separation becomes increasingly important relative to the rate of the second electron transfer and subsequent product formation through the hydride transfer intermediate as the electron affinity of the quinone decreases.
- Penn, John H.,Deng, Dao-Li
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p. 4823 - 4830
(2007/10/02)
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- Homolytic Displacement at Saturated Carbon in Organocobalamines. Part 4
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Benzyl and para-substituted benzylcobaloximes react with substituted arenesulphonyl chlorides under photochemical and anaerobic conditions at 0 deg C to give a variety of products including the sulphones, bibenzyls, and benzyl ethers of dimethylglyoxime in variable yields.However, when the reactions are carried out in the presence of a 1 mol excess of pyridine, the yield of sulphones is increased by at least 20percent in each case.The corresponding yield of bibenzyls is decreased and no trace of the benzyl ether of dimethylglyoxime is formed.On the other hand, the reaction of heteroaromatic methyl cobaloximes with arenesulphonyl chlorides form the corresponding sulphones as the exclusive organic product in good yield and with no side products.The reactions are interpreted in terms of a direct attack of the arenesulphonyl radical on the α carbon of the benzyl and heteroaromatic methyl ligand.
- Gupta, B. Dass,Roy, Maheswar,Roy, Sujit,Kumar, Manoj,Das, Indira
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p. 537 - 543
(2007/10/02)
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- Le composes d'insertion du graphite comme precurseurs de metaux finement divises I. Couplage d'halogenures benzyliques
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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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- Antiparasitic Agents: Part VII - Synthesis of 1,2-Bis(3,4-substituted phenyl)ethanes and 1,3-Bis(4-amidinophenyl)propene and Their Biological Activity
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1,2-Bis(3-substituted 4-amidinophenyl)ethanes (11-13), 1,3-bis(4-amidinophenyl)propene (20), 3,9-dicyano-12,13-dihydrodibenzotriazepine (14) and 1,3-bis(amidinophenyl)propanone (23) have been synthesised.The compounds 11, 12 and 13 when tested for an
- Chauhan, P. M. S.,Iyer, R. N.,Bhakuni, D. S.
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p. 144 - 147
(2007/10/02)
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- Photochemistry of Some Group V Onium Salts. Effect of Magnetic Nuclei on In-Cage Radical Coupling Reactions
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A series of group V arylammonium, arylphosphonium, and arylarsonium salts have been synthesized and their photochemical behaviour investigated.Direct irradiation of the onium salts in acetonitrile provided photoproducts that were dependent on the magnitude of the nuclear hyperfine coupling constant of the heteroatom rather than spin-orbit coupling.The ammonium and phosphonium salts provided only out-of-cage coupling products while the arsonium salt provided both in-cage and out-of-cage coupling products.
- Breslin, David T.,Saeva, Franklin D.
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p. 713 - 715
(2007/10/02)
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- Highgly Reactive Magnesium and Its Application to Organic Syntheses
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A method for producing highly reactive magnesium slurries is presented, along with a brief comparison to other methods of activation.Reactions of the activated magnesium with a variety of functional groups are examined, including ethers, tosylates, and nitriles.Attempts were made to form Grignard reagents which contained ketone, ester, and nitrile functionality.The Grignard reagent from 8-bromooctane-1-nitrile was succesfully prepared in moderate yield.
- Burns, Timothy P.,Rieke, Reuben D.
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p. 3674 - 3680
(2007/10/02)
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- Investigations about the Reducing Properties of Dimeric Dihydropyridines
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The reaction of a series of bis- derivatives P2 with some benzyl halides, trans-1,2-dibromoethane and several heteroaromatic cations Q+ was investigated in acetonitrile/toluene with electrochemical and kinetic methods.For substrates with a reduction potential between -0.9 and -1.5 V the reaction occurs via the ratedetermining dissociation of P2 into free radicals P. as the real reducing agents, which transform the benzyl halides into the corresponding 1,2-diarylethanes and Q+ into the corresponding dimeric product Q2.For thereduction of trans-1,2-dibromocyclohexane to cyclohexene a simultaneous transfer of two electrons to the substrate combined with the dissociation of P2 into two pyridinium ions P+ is proposed.In the case of a reduction potential more positive than -0.9 V (e.g. nitro substituted benzyl halides) P2 itself can act as the reducing agent with an increased reaction rate.With pyrylium ions Q+ a product P-Q was detected by voltammetry and mass spectroscopy.In this case an electrophilic attack onto P2 instead of the electron transfer from P2 to Q+ cannot be excluded.
- Pragst, F.,Santrucek, M.
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- HOMOLYTIC DISPLACEMENT AT SATURATED CARBON CENTRE: SYNTHESIS OF BENZYLSULPHONES
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The reactions of benzyl cobaloximes with p-substitued benzene sulphonyl chlorides under photochemical conditions from benzyl sulphones by novel SH2 process.
- Gupta, B. D.,Kumar, Manoj,Das, Indira,Roy, M.
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p. 5773 - 5776
(2007/10/02)
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- Electron Transfer in Competition with Loss of Nitrogen in Photochemical Reactions of Aryldiazomethane with Diethylamine
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The photolysis of aryldiazomethanes was studied as a function of aryl substituents and the p-nitro group was found to exert a special effect of product distribution.
- Tomioka, Hideo,Tabayashi, Kazuo,Izava, Yasuji
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p. 906 - 907
(2007/10/02)
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- THE EFFECT OF ARYL SUBSTITUENTS ON ARYLCARBENE REACTIVITY
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Substituted (p-MeO, p-Me, H, p-Cl, p-Br, m-Br, m-MeO, 3,4-Cl2, p-CO2Me, m-CN and p-CN) monophenylcarbenes are generated in a binary mixture of substrates (methanol, cis-4-methyl-2-pentene and cyclohexane) and the relative rate of O - H insertion into methanol to stereospecific cyclopropanation of the olefin to C - H insertion into cyclohexane are calculated from the ratios of products and substrates.It is found (i) that the reactivities of the substrates decrease in the order of methanol, olefin and cyclohexane and (ii) that electron-donating substituents generally lead to reaction with the more reactive substrates while the reaction with the less reactive substrates is favoured in the case of electron-withdrawing substituents.These results are interpreted in terms of the change in the electrophilicity of the singlet arylcarbene by the substituents rather than the change in the singlet-triplet equilibrium.
- Tomioka, Hideo,Tabayashi, Kazuo,Ozaki, Yasuji,Izawa, Yasuji
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p. 1435 - 1440
(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
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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)
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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)
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- 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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- METALLIC NICKEL AS A REAGENT FOR THE COUPLING OF AROMATIC BENZYLIC HALIDES
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The oxidative addition of aromatic and benzylic halides to activated metallic nickel occured under mild conditions to give the corresponding dehalogenative coupled products in good yields.
- Inaba, Shin-ichi,Matsumoto, Hideyuki,Rieke, Reuben D.
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p. 4215 - 4216
(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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- 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)
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