- Lewis acid-catalyzed ring-opening reactions of methylenecyclopropanes with alcoholic or acidic nucleophiles
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(matrix presented) Nu-H can be alcohols, thiols, phenols, carboxylic acids yield: 60%-100%. Methylenecyclopropanes can react with various nucleophiles such as alcohols, phenols, carboxylic acids, and thiols to give the corresponding homoallylic esters or
- Shi, Min,Xu, Bo
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Read Online
- Early main group metal catalysis: How important is the metal?
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Organocalcium compounds have been reported as efficient catalysts for various alkene transformations. In contrast to transition metal catalysis, the alkenes are not activated by metal-alkene orbital interactions. Instead it is proposed that alkene activation proceeds through an electrostatic interaction with a Lewis acidic Ca2+. The role of the metal was evaluated by a study using the metal-free catalysts: [Ph2N-Me4N+] and [Ph3C-][Me4N- ]. These "naked" amides and carbanions can act as catalysts in the conversion of activated double bonds (C=O and C=N) in the hydroamination of Ar-N=C=O and R-N=C=N=R (R=alkyl) by Ph2NH. For the intramolecular hydroamination of unactivated C=C bonds in H2C=CHCH2CPh2CH2NH2 the presence of a metal cation is crucial. A new type of hybrid catalyst consisting of a strong organic Schwesinger base and a simple metal salt can act as catalyst for the intramolecular alkene hydroamination. The influence of the cation in catalysis is further evaluated by a DFT study.
- Harder, Sjoerd,Penafiel, Johanne,Maron, Laurent
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Read Online
- Solvent Effects on the Singlet - Triplet Equilibrium and Reactivity of a Ground Triplet State Arylalkyl Carbene
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Results from intramolecular singlet and triplet specific reactivity in solvents of different polarity suggest that the spin state equilibrium of 1,2-diphenyl-1-butylidene, a triplet ground state carbene, is largely susceptible to solvent polarity.The results are consistent with stabilization of the zwitterionic singlet state in solvents of high polarity.
- Garcia-Garibay, Miguel A.,Theroff, Craig,Shin, Steve H.,Jernelius, Jesper
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Read Online
- Iron-Catalyzed Radical Cleavage/C?C Bond Formation of Acetal-Derived Alkylsilyl Peroxides
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A novel radical-based approach for the iron-catalyzed selective cleavage of acetal-derived alkylsilyl peroxides, followed by the formation of a carbon–carbon bond is reported. The reaction proceeds under mild reaction conditions and exhibits a broad substrate scope with respect to the acetal moiety and the carbon electrophile. Mechanistic studies suggest that the present reaction proceeds through a free-radical process involving carbon radicals generated by the homolytic cleavage of a carbon–carbon bond within the acetal moiety. A synthetic application of this method to sugar-derived alkylsilyl peroxides is also described.
- Shiozaki, Yoko,Sakurai, Shunya,Sakamoto, Ryu,Matsumoto, Akira,Maruoka, Keiji
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supporting information
p. 573 - 576
(2020/02/20)
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- Bromomethyl Silicate: A Robust Methylene Transfer Reagent for Radical-Polar Crossover Cyclopropanation of Alkenes
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A general protocol for visible-light-induced cyclopropanation of alkenes was developed with bromomethyl silicate as a methylene transfer reagent, offering a robust tool for accessing highly valuable cyclopropanes. In addition to α-aryl or methyl-substituted Michael acceptors and styrene derivatives, the unactivated 1,1-dialkyl ethylenes were also shown to be viable substrates. Apart from realizing the cyclopropanation of terminal alkenes, the methyl transfer reaction has been further demonstrated to be amenable to the internal olefins. The photocatalytic cyclopropanation of 1,3-bis(1-arylethenyl)benzenes was also achieved, giving polycyclopropane derivatives in excellent yields. With late-stage cyclopropanation as the key strategy, the synthetic utility of this transformation was also demonstrated by the total synthesis of LG100268.
- Luo, Wenping,Fang, Yewen,Zhang, Li,Xu, Tianhang,Liu, Yongjun,Li, Yan,Jin, Xiaoping,Bao, Jiakan,Wu, Xiaodong,Zhang, Zongyong
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p. 1778 - 1781
(2020/03/11)
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- Controllable Isomerization of Alkenes by Dual Visible-Light-Cobalt Catalysis
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We report herein that thermodynamic and kinetic isomerization of alkenes can be accomplished by the combination of visible light with Co catalysis. Utilizing Xantphos as the ligand, the most stable isomers are obtained, while isomerizing terminal alkenes over one position can be selectively controlled by using DPEphos as the ligand. The presence of the donor–acceptor dye 4CzIPN accelerates the reaction further. Transformation of exocyclic alkenes into the corresponding endocyclic products could be efficiently realized by using 4CzIPN and Co(acac)2 in the absence of any additional ligands. Spectroscopic and spectroelectrochemical investigations indicate CoI being involved in the generation of a Co hydride, which subsequently adds to alkenes initiating the isomerization.
- Meng, Qing-Yuan,Schirmer, Tobias E.,Katou, Kousuke,K?nig, Burkhard
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p. 5723 - 5728
(2019/04/03)
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- Conversion of Carbonyl Compounds to Olefins via Enolate Intermediate
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A general and efficient protocol to synthesize substituted olefins from carbonyl compounds via nickel catalyzed C—O activation of enolates was developed. Besides ketones, aldehydes were also suitable substrates for the presented catalytic system to produce di- or tri- substituted olefins. It is worth noting that this approach exhibited good tolerance to highly reactive tertiary alcohols, which could not survive in other reported routes for converting carbonyl compounds to olefins. This method also showed good regio- and stereo-selectivity for olefin products. Preliminary mechanistic studies indicated that the reaction was accomplished through nickel catalyzed C—O activation of enolates, thus offering helpful contribution to current enol chemistry.
- Cao, Zhi-Chao,Xu, Pei-Lin,Luo, Qin-Yu,Li, Xiao-Lei,Yu, Da-Gang,Fang, Huayi,Shi, Zhang-Jie
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supporting information
p. 781 - 785
(2019/06/24)
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- Palladium-Catalyzed C?H Alkenylation of Arenes with Alkynes: Stereoselective Synthesis of Vinyl Chlorides via a 1,4-Chlorine Migration
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A directing group-free, ligand-promoted palladium-catalyzed C?H arylation of internal alkynes with simple arenes was developed. Alkenyl chlorides resulting from a 1,4-chlorine migration or trisubstituted alkenes were produced in moderate to good yields depending on the type of alkyne.
- Li, Zhen,Duan, Wei-Liang
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supporting information
p. 16041 - 16045
(2018/11/23)
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- Ruthenium(II)-catalyzed olefination: Via carbonyl reductive cross-coupling
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Natural availability of carbonyl groups offers reductive carbonyl coupling tremendous synthetic potential for efficient olefin synthesis, yet the catalytic carbonyl cross-coupling remains largely elusive. We report herein such a reaction, mediated by hydrazine under ruthenium(ii) catalysis. This method enables facile and selective cross-couplings of two unsymmetrical carbonyl compounds in either an intermolecular or intramolecular fashion. Moreover, this chemistry accommodates a variety of substrates, proceeds under mild reaction conditions with good functional group tolerance, and generates stoichiometric benign byproducts. Importantly, the coexistence of KOtBu and bidentate phosphine dmpe is vital to this transformation.
- Wei, Wei,Dai, Xi-Jie,Wang, Haining,Li, Chenchen,Yang, Xiaobo,Li, Chao-Jun
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p. 8193 - 8197
(2017/11/27)
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- Nickel-Catalyzed Direct Synthesis of Aryl Olefins from Ketones and Organoboron Reagents under Neutral Conditions
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Nickel-catalyzed addition of arylboron reagents to ketones results in aryl olefins directly. The neutral condition allows acidic protons of alcohols, phenols, and malonates to be present, and fragile structures are also tolerated.
- Lei, Chuanhu,Yip, Yong Jie,Zhou, Jianrong Steve
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supporting information
p. 6086 - 6089
(2017/05/08)
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- Synthetic and Computational Studies on the Rhodium-Catalyzed Hydroamination of Aminoalkenes
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The influence of ligand structure on rhodium-catalyzed hydroamination has been evaluated for a series of phosphinoarene ligands. These catalysts have been evaluated in a set of catalytic intramolecular Markovnikov hydroamination reactions. The mechanism o
- Strom, Alexandra E.,Balcells, David,Hartwig, John F.
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p. 5651 - 5665
(2016/09/09)
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- N-heterocyclic carbene dichotomy in Pd-catalyzed acylation of aryl chlorides via C-H bond functionalization
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The first Pd-catalyzed intramolecular acylation of aryl chlorides via C-H bond functionalization is presented. The method allows for the synthesis of a variety of elusive benzocyclobutenones with a wide range of functional groups and substitution patterns. We demonstrate that a change in the ligand backbone dictates the selectivity pattern.
- Flores-Gaspar, Areli,Gutierrez-Bonet, Alvaro,Martin, Ruben
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supporting information
p. 5234 - 5237,4
(2012/12/12)
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- N-heterocyclic carbene dichotomy in Pd-catalyzed acylation of aryl chlorides via C-H bond functionalization
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The first Pd-catalyzed intramolecular acylation of aryl chlorides via C-H bond functionalization is presented. The method allows for the synthesis of a variety of elusive benzocyclobutenones with a wide range of functional groups and substitution patterns. We demonstrate that a change in the ligand backbone dictates the selectivity pattern.
- Flores-Gaspar, Areli,Gutierrez-Bonet, Alvaro,Martin, Ruben
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supporting information
p. 5234 - 5237
(2013/01/15)
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- Heteropolyacid-catalyzed direct deoxygenation of propargyl and allyl alcohols
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The combination of H3[PW12O40] ?nH2O (1 mol %) and Et3SiH led to the direct catalytic deoxygenation of propargyl alcohols, in which proper solvent selection Cl(CH2)2Cl vs CF3CH2OH was the key to obtaining better product yields. Under similar conditions, the deoxygenation of allyl alcohols proceeded to give thermodynamically stable alkenes with migration of the double bonds in good yields.
- Egi, Masahiro,Kawai, Takuya,Umemura, Megumi,Akai, Shuji
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scheme or table
p. 7092 - 7097
(2012/10/07)
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- Oxidative heck arylation for the stereoselective synthesis of tetrasubstituted olefins using nitroxides as oxidants
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One, two, and three! Nitroxides and dioxygen serve as oxidants in highly stereoselective oxidative Pd-catalyzed Heck arylations in which aryl boronic acids are used to synthesize triarylalkyl-substituted olefins. The reactions occur under very mild conditions at room temperature. As an example, the threefold sequential arylation of methyl acrylate is the crucial step in the stereoselective synthesis of Z-Tamoxifen.
- He, Zhiheng,Kirchberg, Sylvia,Froehlich, Roland,Studer, Armido
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p. 3699 - 3702
(2012/05/20)
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- A novel and efficient method for the olefination of carbonyl compounds with Grignard reagents in the presence of diethyl phosphite
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The widely available carbonyl compounds react with Grignard reagents in the presence of diethyl phosphite to give the corresponding olefins in good to excellent yields: A range of conjugated dienes, terminal olefins, multisubstituted-alkenes and conjugated enynes could be readily obtained by the method in mild conditions.
- Wang, Tongqiang,Hu, Yuanyuan,Zhang, Songlin
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supporting information; experimental part
p. 2312 - 2315
(2010/07/09)
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- Pd-catalyzed oxidative cross-coupling of N-tosylhydrazones with arylboronic acids
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The Pd-catalyzed reaction of N-tosylhydrazones and arylboronic acids provides olefin derivatives. This oxidative cross-coupling is suggested to proceed through a migratory insertion process of a Pd carbene intermediate.
- Zhao, Xia,Jing, Jing,Lu, Kui,Zhang, Yan,Wang, Jianbo
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supporting information; experimental part
p. 1724 - 1726
(2010/07/06)
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- A 1,3-sp2,sp3-hybridized dilithio intermediate by direct lithiation of cyclopropylidene diphenylmethane
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The reaction of cyclopropylidene diphenylmethane 1 with an excess of lithium and a catalytic amount of naphthalene (5 mol %) at -20°, followed by addition of an electrophile [E = H2O, D2O, t-BuCHO, Me2CO, Et2CO,
- Lillo, Victor J.,Gomez, Cecilia,Yus, Miguel
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experimental part
p. 29 - 44
(2010/08/20)
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- Suzuki-miyaura coupling of NHC-Boranes: A new addition to the C-C coupling toolbox
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Complexes of triaryl- and trialkylboranes with N-heterocyclic carbenes (NHCs) participate In Suzuki-Miyaura cross-coupling reactions and provide coupled products In good yields under base-free conditions. The reaction can be applied to Csp2-Csp
- Monot, Julien,Makhlourbrahmi, Malika,Ueng, Shau-Hua,Robert, Carine,Murr, Marine Desage-E.I.,Curran, Dennis P.,Malacria, Max,Fensterbank, Louis,Lacote, Emmanuel
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supporting information; experimental part
p. 4914 - 4917
(2010/01/06)
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- Intramolecular cycloisomerization of aryl-substituted alkylidenecyclopropanes via NHC palladium-catalyzed cascade C-C bond cleavage/C-H activation/C-C bond formation
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A well-defined N-heterocyclic carbene (NHC) palladium-catalyzed intramolecular cyclization reaction of aryl-substituted alkylidenecyclopropanes (ACP) to 1-aryl dihydronaphthalenes is described. The NHC salts were found to suppress β-hydride elimination from the homoallylpalladium intermediate, which may lead to unwanted alkene formation. A plausible mechanism for the cycloisomerization was proposed. Georg Thieme Verlag Stuttgart.
- Yang, Yewei,Huang, Xian
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scheme or table
p. 1366 - 1370
(2009/04/06)
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- Facile synthesis of multisubstituted buta-1,3-dienes via Suzuki-Miyaura and Kumada cross-coupling strategy of 2,4-diiodo-buta-1-enes with arylboronic acids and Grignard reagents
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One-pot Suzuki-Miyaura-type and Kumada-type cross-coupling reactions of 2,4-diiodo-buta-l-enes with arylboronic acids and alkyl/aryl magnesium bromides were carried out in the presence of accessibly simple catalysts under mild conditions. As a result, some 1,1,2-trisubstituted buta-1,3-dienes were obtained including the Tamoxifen-type, which have potential adjuvant therapy in women who have suffered from breast cancer and cyclooxygenase-2-type (COX-2-type) inhibitors, some of which have been proved to elicit efficient anti-inflammatory analgesic activities and less adverse gastrointestinal side effects and to be very useful in the prophylactic treatment of a wide variety of cancers and neurodegenerative disorders. The Royal Society of Chemistry 2005.
- Shao, Li-Xiong,Shi, Min
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p. 1828 - 1831
(2007/10/03)
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- Stereoselective cis-addition of aromatic C - H bonds to alkynes catalyzed by dinuclear palladium complexes
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Reactions of alkynes with arenes proceeded in the presence of dinuclear palladium complexes and trialkylboranes to yield alkyne hydroarylation products with high stereoselectivity. In the reactions of monosubstituted benzenes, meta and para products were
- Tsukada, Naofumi,Mitsuboshi, Tomohiro,Setoguchi, Hiroyuki,Inoue, Yoshio
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p. 12102 - 12103
(2007/10/03)
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- Kinetics and equilibrium constants for reactions of α-phenyl- substituted cyclopropylcarbinyl radicals
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Laser-flash photolysis methods were used to determine Arrhenius functions for cyclizations of the 4,4-diphenyl-3-butenyl (2) and trans-4- phenyl-3-butenyl (5) radicals to the 1,1-diphenylcyclopropylcarbinyl (1) and 1-phenylcyclopropylcarbinyl (4) radicals, respectively. At 20 °C, the cyclization rate constants are 1.7 x 107 and 5.4 x 106 s-1. Equilibrium constants for the two processes were estimated and evaluated with thermochemical data and via computational methods, and Arrhenius functions for the ring-opening reactions of the cyclopropylcarbinyl radicals were calculated. The cyclization reactions of 2 and 5 are strongly enthalpy controlled. Production of radicals 1 and 2 from the corresponding tert- butylperoxy esters in the presence of Et3SnH gave diphenylcyclopropylmethane and 1,1-diphenyl-1-butene from H-atom trapping of radicals 1 and 2 and 4- phenyl-1,2-dihydronaphthalene which derives from the product radical formed by addition of the radical moiety in 2 to the cis-phenyl group. Rate constants for the latter cyclization of 2 and for reactions of radicals 1 and 2 with Et3SnH were obtained from the indirect kinetic studies.
- Halgren, Thomas A.,Roberts, John D.,Horner, John H.,Martinez, Felix N.,Tronche, Christopher,Newcomb, Martin
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p. 2988 - 2994
(2007/10/03)
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- Cationic and neutral diphenyldiazomethanerhodium(I) complexes as catalytically active species in the C-C coupling reaction of olefins and diphenyldiazomethane
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Cationic rhodium(I) complexes cis-[Rh(acetone)2(L)(L')]+ (2: L=L'=C8H14; 3: L=C8H14; L'=PiPr3; 4: L= L'=PiPr3), prepared from [{RhCl-(C8H14)
- Werner, Helmut,Schneider, Michael E.,Bosch, Marco,Wolf, Justin,Teuben, Jan H.,Meetsma, Auke,Troyanov, Sergei I.
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p. 3052 - 3059
(2007/10/03)
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- Free radical reactions to generate alkenes and/or ionic reactions to generate hydroximoyl chlorides when β-nitrostyrenes react with triethylaluminium or diethylaluminium chloride
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β-Nitrostyrenes 1 react with triethylaluminium or diethylaluminium chloride in diethyl ether solution and under nitrogen or argon to generate the alkenes 2 and the hydroximoyl chlorides 3 after work-up with ice-cold, cone, hydrochloric acid. The formation of the alkenes 2 is proposed to be a free-radical reaction via NO2/alkyl substitution since the yields of the alkenes 2 are increased in the presence of benzoyl peroxide (Bz2O2) and decreased in the presence of galvinoxyl. Only the alkenes 2 are produced with a high stereoselectivity for the E isomers when β-nitrostyrenes react with triethylaluminium in the presence of one to two equivalents of Bz2O2 as free-radical initiator. The mechanism of the generation of the hydroximoyl chlorides 3 is proposed to proceed through a 1,4-addition pathway to produce nitronates A, then the protonated nitronates B or the nitroso cations C are trapped by chloride ion to form the final products. The yields of compounds 3 are also improved by the presence of Lewis acids such as MgCl2. Medium to high yields of the hydroximoyl chlorides 3 and traces or low yields of the alkenes 2 are generated when triethylaluminium or diethylaluminium chloride react with β-nitrostyrenes in the presence of three equivalents of MgCl2 under argon.
- Chu, Cheng-Ming,Liu, Ju-Tsung,Lin, Wen-Wei,Yao, Ching-Fa
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- Convenient preparation method of β-silylated olefins by hydrosilylation of methylenecyclopropanes over Rh(I) complexes
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The catalytic hydrosilylation of methylenecyclopropanes with various substituents at the double bond in the presence of Rh(I) complexes occurs selectively with the cleavage of the cyclopropane ring. This is a convenient route to β-silicon-substituted olef
- Bessmertnykh,Donskaya,Tveritinova,Beletskaya
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p. 799 - 808
(2007/10/03)
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- Magnesium alkylidene carbenoids: Generation from 1-halovinyl sulfoxides with Grignard reagents and studies on their property, mechanism, and some synthetic uses
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Magnesium alkylidene carbenoids were generated from 1-halovinyl sulfoxides, derived from ketones and aryl halomethyl sulfoxide, through the ligand exchange reaction of sulfoxides with Grignard reagents. The generated magnesium alkylidene carbenoids were found to be stable at -78 °C for over 30 min. The carbenoids reacted with aldehydes to give the adducts in moderate yields; however, they were found to be relatively unreactive to usual electrophiles. The generated magnesium alkylidene carbenoid exists in equilibrium between an α-halo alkenyl Grignard reagent and an alkylidene carbene-magnesium halide complex. Halogen exchange and geometrical isomerization of the alkylidene carbenoids were observed. 1-Chlorovinyl sulfoxides reacted with excess aryl Grignard reagents to give alkenyl Grignard reagents having an aryl group. These Grignard reagents reacted with several electrophiles to give tetra-substituted olefins in moderate to good yields.
- Satoh, Tsuyoshi,Takano, Koji,Hiroyuki, Ota,Someya, Hideaki,Matsuda, Kenji,Koyama, Mai
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p. 5557 - 5574
(2007/10/03)
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- Free-Radical Reactions of Trialkylboranes with β-Nitrostyrenes to Generate Alkenes
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β-Nitrostyrenes 1 react with trialkylboranes under a nitrogen atmosphere to generate high yields of alkenes 2. The mechanism is proposed to be a free-radical reaction via NO2/alkyl substitution since the reaction is stimulated by the presence of a trace of oxygen in the nitrogen or tert-butyl peroxide or by photolysis and is retarded or inhibited by the addition of galvinoxyl to the solution.
- Yao, Ching-Fa,Chu, Cheng-Ming,Liu, Ju-Tsung
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p. 719 - 722
(2007/10/03)
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- Generation of magnesium alkylidene carbenoids from 1-halovinyl sulfoxides with Grignard reagent - Their property and some synthetic uses
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The first example of magnesium alkylidene carbenoids is described. 1-Halovinyl sulfoxides 3 (X = F, Cl, Br) were synthesized from ketones and aryl halomethyl sulfoxides in three steps in moderate to good overall yields. Ligand exchange reaction of the sulfoxides of 3 with ethylmagnesium halide in THF at low temperature afforded a magnesium alkylidene carbenoid, which reacted with several electrophiles to give new alkylidene compounds.
- Satoh,Takano,Someya,Matsuda
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p. 7097 - 7100
(2007/10/02)
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- Selective Alkylation and Allylation of Allylic Halides by Tetraorganoidates: Regio- and Stereo-selective Synthesis of Rosefuran and Sesquirosefuran
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Tetraalkylindanes regioselectively alkylate allylic bromides at the α-carbon.In this way, 1,5-dienes have been regio- and stereo-selectively synthesized by the allyl-allyl coupling of allylic bromides and allylic indates, including rosefuran 1 and sequirosefuran 3.
- Araki, Shuki,Jin, Shun-Ji,Butsugan, Yasuo
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p. 549 - 552
(2007/10/02)
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- Polylithiumorganic compounds -19. Regioselective carbon-carbon σ-bond scission followed by a 1,6-proton shift upon the reductive metalation of benzylidenecyclopropane derivatives with lithium metal
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Depending on the substituent α-substituted benzylidenecyclopropanes (32) react more or less readily with lithium dust (2% sodium) in diethyl ether whereby a regioselective scission of only the cyclopropane σ-bond cis to the phenyl ring takes place. Upon raising the temperature the primarily formed 1,3-dilithiumorganic compound due to an agostic interaction rearranges by a 1,6-proton shift into a doubly bridged 1,4-dilithio compound. With α-methylbenzylidenecyclopropane (32c) this rearrangement was shown to occur intermolecularly via a trilithiumorganic compound 56. The suggested mechanism of these reductive metalation reactions via a bisected radical anion 87 where the lithium is mainly bound to the cyclopropyl carbon atom and oriented syn to the phenyl ring, was supported by MNDO (geometries) and ab initio (energies) calculations.
- Maercker, Adalbert,Daub, Volker E. E.
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p. 2439 - 2458
(2007/10/02)
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- Photochemistry of two diphenyl β,γ-enones and a series of methyl- and phenyl-substituted α-phenyl ketones
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The photochemistry of the diphenyl β,γ-enones 2 and 3 and the methyl- and phenyl-substituted α-phenyl ketones 4-9 has been studied, using mainly benzene as solvent.Irradation of 2 with λ 300 nm leads to the 1,3-acyl shift (1,3-AS) product 17, relatively small amounts of the decarbonylation products 15 and 16, and the photo-oxidation products benzophenone (18) and the α,β-unsaturated aldehyde 19.Direct irradation of the 1,3-AS product 17 yields 15, 16, 18 and 19, but no 2.Direct irradation of 3 with λ 350 nm leads mainly to the formation of 1,3-AS products (E)- and (Z)-22, the decarbonylation products (E)- and (Z)-20 and 21 and, in addition, a small amount of the cis-di-?-methane isomer 23.Direct irradation of the substituted α-phenyl ketones 4, 5, 8 and 9 with λ 300 nm leads predominantly to the formation of the radical coupling products 2,3-butanedione and 24-27, respectively, whereas 6 and 7 yield 1,2-diphenyl-1,2-ethanedione and the respective 24 and 25.The acetone-sensitized irradation of 4 leads to 4-phenyl-2-butanone (33) in addition to 2,3-butanedione and 1,2-diphenylethane (24).
- Koppes, Margareth J. C. M.,Crabbendam, Astrid M.,Cerfontain, Hans
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p. 676 - 683
(2007/10/02)
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- Reactions of Alkylmercurials with Heteroatom-Centered Acceptor Radicals
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The relative reactivities of alkylmercury halides toward PhS., PhSe., or I. decrease drastically from R = tert-butyl to R = sec-alkyl to R = n-butyl, indicative that R. is formed in the rate-determining step in the attack of these radicals upon RHgCl.The alkyl radicals thus formed will enter into chain reactions in which a heteroatom-centered radical (A.) is regenerated from substrates such as RS-SR, ArSe-SeAr, ArTe-TeAr, PhSe-SO2Ar, Cl-SO2Ph; ZCH=CHA (A = Cl, I, SPh, SO2Ph); or PhCCHA (A = I, SPh, SO2Ph). β-Styrenyl (PhCH=CHA, Ph2C=CHA) and β-phenethynyl (PhCCA) systems with A = I, Br, SO2Ph also enter into chain reactions with mercury(II) salts with the ligands PhS, PhSe, PhSO2, or (EtO)2PO.The relative reactivities of a series of reagents toward t-Bu. and of PhCH=CHA, Ph2C=CHA, and PhCCA toward c-C6H11. are reported as well as the regioselectivity of t-Bu. attack observed for 1,2-disubstituted ethylenes (ZCH=CHA) with Z and A from the group Ph, Cl, Br, I, SO2Ph, SPh, Bu3Sn.Reactions of (E)- and (Z)-PhCH=CHI or MeO2CCH=CHI with t-Bu. or c-C6H11. occurred in a regioselective and stereospecific (retention) manner.Reactions of (E)- and (Z)-ClCH=CHCl occurred in a nonstereospecific manner in which the E/Z product ratio increased with the bulk of the attacking radical.A similar effect on the E/Z product ratios was observed for (Z)-MeO2CCH=CHCl.
- Russell, Glen A.,Ngoviwatchai, Preecha,Tashtoush, Hasan I.,Pla-Dalmau, Anna,Khanna, Rajive K.
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p. 3530 - 3538
(2007/10/02)
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- Relative Reactivities of Alkyl-Substituted Alkenes and Cycloalkenes towards Diarylcarbenium Ions
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The relative reactivities of alkyl-substituted alkenes 4 towards diarylmethyl cations 2 generated in situ from diarylmethyl chlorides 1 and Lewis acids were determined by competition experiments.The relative reactivities were almost independent of the nature of the Lewis acid. Eventual differences of the solvation free enthalpies of various activated complexes are, therefore, independent of the nature of the gegen ions.The rate acceleration by methyl groups - 6-50 by CH3 at the attacked vinylic position and approximately 104 at the developing carbenium centre - indicates a scarcely bridged transition state.
- Mayr, Herbert,Pock, Rudolf
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p. 2473 - 2496
(2007/10/02)
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- Electron transfer reactions from alkali metal surfaces to (+/-) and (S)-(-)-1,3-dimethoxy-1,1-diphenylbutane. Studies on 1,3-elimination
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The 1,3-elimination of methoxide by carbanions generated from the reaction of (+/-)-1,3-dimethoxy-1,1-diphenylbutane with the alkali metals, lithium, sodium, and potassium, in various solvents was studied to determine the significance of cation-methoxyl c
- Walborsky, Harry M.,Murari, Martha Pass
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p. 2464 - 2470
(2007/10/02)
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- Reaction of Thiobenzophenone S-Oxide (Diphenylsulfine) with Carbon Nucleophiles
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The reaction of diphenylsulfine with a Grignard reagent or alkyllithium gives a variety of products depending on the structure of the Grignard reagent or alkyllithium.
- Ohno, Atsuyoshi,Uohama, Misao,Oka, Shinzaburo
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p. 3231 - 3232
(2007/10/02)
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