- Diels-Alder reactions of masked o-benzoquinones with 1-vinylcyclohexenes: A short and efficient entry to highly functionalized decahydrophenanthrene skeleton
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Masked o-benzoquinones (MOBs), which were generated in situ from 2-methoxyphenols, underwent Diels-Alder reactions with 1-vinylcyclohexenes to produce the corresponding cycloaddition products, that is, decahydrophenanthrenes along with bicyclo[2.2.2]octenones. In the former case, the MOBs serve as the dienophile, and in the later case, the 1-vinylcyclohexenes act as the dienophile. The obtained bicyclo[2.2.2]octenones could be transformed into the corresponding decahydrophenanthrenes through a Cope rearrangement at 220 °C. Thus, these tandem reactions provide a short and efficient entry to the decahydrophenanthrene skeleton from easily available 2-methoxyphenols. Masked o-benzoquinones (MOBs), which were generated in situ from 2-methoxyphenols, underwent Diels-Alder reactions with 1-vinylcyclohexenes to produce the corresponding decahydrophenanthrenes and bicyclo[2.2.2]octenones. The obtained bicyclo[2.2.2]octenones could be transformed into decahydrophenanthrenes through a Cope rearrangement at 220 °C. Copyright
- Niu, Guang-Hao,Hou, Chieh-Shen,Chuang, Gary Jing,Wu, Chi-Phi,Liao, Chun-Chen
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Read Online
- Interception of nazarov reactions of allenyl vinyl ketones with dienes: (3+2)- Versus (4+3)-cycloaddition and subsequent rearrangement
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Capture of the cyclic oxyallyl cation intermediates from the BF3-mediated Nazarov reactions of three allenyl vinyl ketones with various dienes was accomplished by (3+2)- and (4+3)-cycloaddition. The relative amounts of these types of products were dependent on the substitution on the diene, and this could be linked to steric hindrance. Treatment of the (3+2)-cycloaddition products with BF3·Et2O led mainly to decomposition but also to ring-opened molecules and ring-enlarged structures. The computed Gibbs energies of the (3+2)-cycloaddition products, the products of the acid treatment and of some transition states leading to rearranged products were compared.
- Morgan, Timothy D. R.,Lefort, Fran?ois M.,Li, Zhe,Marx, Vanessa M.,Boyd, Russell J.,Burnell, D. Jean
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Read Online
- Controlling the Lewis Acidity and Polymerizing Effectively Prevent Frustrated Lewis Pairs from Deactivation in the Hydrogenation of Terminal Alkynes
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Two strategies were reported to prevent the deactivation of Frustrated Lewis pairs (FLPs) in the hydrogenation of terminal alkynes: reducing the Lewis acidity and polymerizing the Lewis acid. A polymeric Lewis acid (P-BPh3) with high stability was designed and synthesized. Excellent conversion (up to 99%) and selectivity can be achieved in the hydrogenation of terminal alkynes catalyzed by P-BPh3. This catalytic system works quite well for different substrates. In addition, the P-BPh3 can be easily recycled.
- Geng, Jiao,Hu, Xingbang,Liu, Qiang,Wu, Youting,Yang, Liu,Yao, Chenfei
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p. 3685 - 3690
(2021/05/31)
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- Introducing the Dihydro-1,3-azaboroles: Convenient Entry by a Three-Component Reaction, Synthetic and Photophysical Application
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The (Fmes)BH2·SMe2 reagent (7) reacts sequentially with an acetylene and, e.g., xylylisonitrile in a convenient three-component reaction to give a series of unprecedented dihydro-1,3-azaborole derivatives 16. The tolane-derived example 16a was deprotonated and used as a ligand in organometallic chemistry. Compounds 16 served as the starting materials for the straightforward synthesis of various dihydro-1,3-azaborinine derivatives by treatment with an isonitrile. Several diaryldihydro-1,3-azaboroles showed interesting photophysical properties such as aggregation-induced emission and high fluorescence quantum yields.
- Li, Jun,Daniliuc, Constantin G.,Kartha, Kalathil K.,Fernández, Gustavo,Kehr, Gerald,Erker, Gerhard
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supporting information
p. 2059 - 2067
(2021/02/06)
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- Highly selective semi-hydrogenation of alkynes with a Pd nanocatalyst modified with sulfide-based solid-phase ligands
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Soluble small molecular/polymeric ligands are often used in Pd-catalyzed semi-hydrogenation of alkynes as an efficient strategy to improve the selectivity of targeted alkene products. The use of soluble ligands requires their thorough removal from the reaction products, which adds significant extra costs. In the paper, commercially available, inexpensive, metallic sulfide-based solid-phase ligands (SPL8-4 and SPL8-6) are demonstrated as simple yet high-performance insoluble ligands for a heterogeneous Pd nanocatalyst (Pd@CaCO3) toward the semi-hydrogenation of alkynes. Based on the reactions with a range of terminal and internal alkyne substrates, the use of the solid-phase ligands has been shown to markedly enhance the selectivity of the desired alkene products by efficiently suppressing over-hydrogenation and isomerization side reactions, even during the long extension of the reactions following full substrate conversion. A proper increase in the dosage or a reduction in the average size of the solid-phase ligands enhances such effects. With their insoluble nature, the solid-phase ligands have the distinct advantage in their simple, convenient recycling and reuse while without contaminating the products. A ten-cycle reusability test with the SPL8-4/Pd@CaCO3 catalyst system confirms its well-maintained activity and selectivity over repeated uses. A mechanistic study with x-ray photoelectron spectroscopy indicates that the solid-phase ligands have electronic interactions with Pd in the supported catalyst, contributing to inhibit the binding and further reaction of the alkene products. This is the first demonstration of solid-phase ligands for highly selective semi-hydrogenation of alkynes, which show strong promise for commercial applications.
- Huang, Lingqi,Hu, Kecheng,Ye, Ganggang,Ye, Zhibin
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- Creation of Redox-Active PdSx Nanoparticles Inside the Defect Pores of MOF UiO-66 with Unique Semihydrogenation Catalytic Properties
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Semihydrogenation of alkynes to produce alkenes is very important in the industry; however, over-hydrogenation heavily complicates the postprocesses, which are highly energy consuming and not environmentally friendly. One of the most efficient pathways to solve this challenging issue is to develop highly selective catalysts that could only hydrogenate alkynes and are inactive in hydrogenation of alkenes. This work presents herein an efficient catalyst, consisting of in situ created PdS0.53 nanoparticles as the redox-active sites inside the defect pores of metal–organic framework UiO-66, which demonstrates very high alkene selectivity (up to 99.5%) in semihydrogenation of easily over-hydrogenated terminal alkynes. In contrast to the traditional catalysts, strict control over the reaction time becomes the nonessential condition because the catalyst system is almost inactive in hydrogenation of alkenes. Therefore, this paradigm work provides a practically applicable pathway for the development of efficient catalysts with unique catalytic properties for selective semihydrogenation reactions.
- Dong, Ming-Jie,Wang, Xuan,Wu, Chuan-De
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- Piperazine-promoted gold-catalyzed hydrogenation: The influence of capping ligands
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Gold nanoparticles (NPs) combined with Lewis bases, such as piperazine, were found to perform selective hydrogenation reactions via the heterolytic cleavage of H2. Since gold nanoparticles can be prepared by many different methodologies and using different capping ligands, in this study, we investigated the influence of capping ligands adsorbed on gold surfaces on the formation of the gold-ligand interface. Citrate (Citr), poly(vinyl alcohol) (PVA), polyvinylpyrrolidone (PVP), and oleylamine (Oley)-stabilized Au NPs were not activated by piperazine for the hydrogenation of alkynes, but the catalytic activity was greatly enhanced after removing the capping ligands from the gold surface by calcination at 400 °C and the subsequent adsorption of piperazine. Therefore, the capping ligand can limit the catalytic activity if not carefully removed, demonstrating the need of a cleaner surface for a ligand-metal cooperative effect in the activation of H2 for selective semihydrogenation of various alkynes under mild reaction conditions.
- Barbosa, Eduardo C. M.,Camargo, Pedro H. C.,Fiorio, Jhonatan L.,Hashmi, A. Stephen K.,Kikuchi, Danielle K.,Rossi, Liane M.,Rudolph, Matthias
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p. 1996 - 2003
(2020/04/22)
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- Selective Semi-Hydrogenation of Terminal Alkynes Promoted by Bimetallic Cu-Pd Nanoparticles
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The selective semi-hydrogenation of terminal alkynes was efficiently performed, under mild reaction conditions (H 2 balloon, 110 °C), promoted by a bimetallic nanocatalyst composed of copper and palladium nanoparticles (5:1 weight ratio) supported on mesostructured silica (MCM-48). The Cu-PdNPS@MCM-48 catalyst, which demonstrated to be highly chemoselective towards the alkyne functionality, is readily prepared from commercial materials and can be recovered and reused after thermal treatment followed by reduction under H 2 atmosphere.
- Buxaderas, Eduardo,Volpe, María Alicia,Radivoy, Gabriel
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p. 1466 - 1472
(2019/03/07)
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- Accessing Frustrated Lewis Pair Chemistry through Robust Gold@N-Doped Carbon for Selective Hydrogenation of Alkynes
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Pyrolysis of Au(OAc)3 in the presence of 1,10-phenanthroline over TiO2 furnishes a highly active and selective Au nanoparticle (NP) catalyst embedded in a nitrogen-doped carbon support, Au@N-doped carbon/TiO2 catalyst. Parameters such as pyrolysis temperature, type of support, and nitrogen ligands as well as Au/ligand molar ratios were systematically investigated. Highly selective hydrogenation of numerous structurally diverse alkynes proceeded in moderate to excellent yield under mild conditions. The high selectivity toward the industrially important alkene substrates, functional group tolerance, and the high recyclability makes the catalytic system unique. Both high activity and selectivity are correlated with a frustrated Lewis pairs interface formed by the combination of gold and nitrogen atoms of N-doped carbon that, according to density functional theory calculations, can serve as a basic site to promote the heterolytic activation of H2 under very mild conditions. This "fully heterogeneous" and recyclable gold catalyst makes the selective hydrogenation process environmentally and economically attractive.
- Fiorio, Jhonatan Luiz,Gon?alves, Renato Vitalino,Teixeira-Neto, Erico,Ortu?o, Manuel A.,López, Núria,Rossi, Liane Marcia
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p. 3516 - 3524
(2018/04/14)
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- Well-Defined Rhodium-Gallium Catalytic Sites in a Metal-Organic Framework: Promoter-Controlled Selectivity in Alkyne Semihydrogenation to E-Alkenes
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Promoters are ubiquitous in industrial heterogeneous catalysts. The wider roles of promoters in accelerating catalysis and/or controlling selectivity are, however, not well understood. A model system has been developed where a heterobimetallic active site comprising an active metal (Rh) and a promoter ion (Ga) is preassembled and delivered onto a metal-organic framework (MOF) support, NU-1000. The Rh-Ga sites in NU-1000 selectively catalyze the hydrogenation of acyclic alkynes to E-alkenes. The overall stereoselectivity is complementary to the well-known Lindlar's catalyst, which generates Z-alkenes. The role of the Ga in promoting this unusual selectivity is evidenced by the lack of semihydrogenation selectivity when Ga is absent and only Rh is present in the active site.
- Desai, Sai Puneet,Ye, Jingyun,Zheng, Jian,Ferrandon, Magali S.,Webber, Thomas E.,Platero-Prats, Ana E.,Duan, Jiaxin,Garcia-Holley, Paula,Camaioni, Donald M.,Chapman, Karena W.,Delferro, Massimiliano,Farha, Omar K.,Fulton, John L.,Gagliardi, Laura,Lercher, Johannes A.,Penn, R. Lee,Stein, Andreas,Lu, Connie C.
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supporting information
p. 15309 - 15318
(2018/11/30)
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- Selective Semihydrogenation of Alkynes Catalyzed by Pd Nanoparticles Immobilized on Heteroatom-Doped Hierarchical Porous Carbon Derived from Bamboo Shoots
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Highly dispersed palladium nanoparticles (Pd NPs) immobilized on heteroatom-doped hierarchical porous carbon supports (N,O-carbon) with large specific surface areas are synthesized by a wet chemical reduction method. The N,O-carbon derived from naturally abundant bamboo shoots is fabricated by a tandem hydrothermal–carbonization process without assistance of any templates, chemical activation reagents, or exogenous N or O sources in a simple and ecofriendly manner. The prepared Pd/N,O-carbon catalyst shows extremely high activity and excellent chemoselectivity for semihydrogenation of a broad range of alkynes to versatile and valuable alkenes under ambient conditions. The catalyst can be readily recovered for successive reuse with negligible loss in activity and selectivity, and is also applicable for practical gram-scale reactions.
- Ji, Guijie,Duan, Yanan,Zhang, Shaochun,Fei, Benhua,Chen, Xiufang,Yang, Yong
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p. 3427 - 3434
(2017/09/15)
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- Gold-Ligand-Catalyzed Selective Hydrogenation of Alkynes into cis-Alkenes via H2 Heterolytic Activation by Frustrated Lewis Pairs
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The selective hydrogenation of alkynes to alkenes is an important synthetic process in the chemical industry. It is commonly accomplished using palladium catalysts that contain surface modifiers, such as lead and silver. Here we report that the adsorption of nitrogen-containing bases on gold nanoparticles results in a frustrated Lewis pair interface that activates H2 heterolytically, allowing an unexpectedly high hydrogenation activity. The so-formed tight-ion pair can be selectively transferred to an alkyne, leading to a cis isomer; this behavior is controlled by electrostatic interactions. Activity correlates with H2 dissociation energy, which depends on the basicity of the ligand and its reorganization on activation of hydrogen. High surface occupation and strong Au atom-ligand interactions might affect the accessibility and stability of the active site, making the activity prediction a multiparameter function. The promotional effect found for nitrogen-containing bases with two heteroatoms was mechanistically described as a strategy to boost gold activity. (Graph Presented).
- Fiorio, Jhonatan L.,López, Núria,Rossi, Liane M.
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p. 2973 - 2980
(2017/05/31)
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- High Reactivity of Strained Seven-Membered-Ring trans-Alkenes
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trans-Oxasilacycloheptenes are highly reactive strained alkenes. Competition reactions showed that these seven-membered ring trans-alkenes underwent [4+2] cycloaddition reactions faster than a trans-cyclooctene. They also reacted with quinones and dimethyl acetylenedicarboxylate to form adducts with high diastereoselectivity. Kinetic studies showed that ring strain increases nucleophilicity by approximately 109. trans-Oxasilacycloheptenes are strained seven-membered-ring trans-alkenes that underwent [4+2] cycloaddition reactions faster than a bicyclic trans-cyclooctene. They also reacted with quinones and dimethyl acetylenedicarboxylate to form adducts with high diastereoselectivity. Kinetic studies showed that ring strain increases nucleophilicity by approximately 109.
- Sanzone, Jillian R.,Woerpel
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supporting information
p. 790 - 793
(2016/02/23)
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- Cross-Linked "poisonous" Polymer: Thermochemically Stable Catalyst Support for Tuning Chemoselectivity
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Designed catalyst poisons can be deliberately added in various reactions for tuning chemoselectivity. In general, the poisons are "transient" selectivity modifiers that are readily leached out during reactions and thus should be continuously fed to maintain the selectivity. In this work, we supported Pd catalysts on a thermochemically stable cross-linked polymer containing diphenyl sulfide linkages, which can simultaneously act as a catalyst support and a "permanent" selectivity modifier. The entire surfaces of the Pd clusters were ligated (or poisoned) by sulfide groups of the polymer support. The sulfide groups capping the Pd surface behaved like a "molecular gate" that enabled exceptionally discriminative adsorption of alkynes over alkenes. H2/D2 isotope exchange revealed that the capped Pd surface alone is inactive for H2 (or D2) dissociation, but in the presence of coflowing acetylene (alkyne), it becomes active for H2 dissociation as well as acetylene hydrogenation. The results indicated that acetylene adsorbs on the Pd surface and enables cooperative adsorption of H2. In contrast, ethylene (alkene) did not facilitate H2-D2 exchange, and hydrogenation of ethylene was not observed. The results indicated that alkynes can induce decapping of the sulfide groups from the Pd surface, while alkenes with weaker adsorption strength cannot. The discriminative adsorption of alkynes over alkenes led to highly chemoselective hydrogenation of various alkynes to alkenes with minimal overhydrogenation and the conversion of side functional groups. The catalytic functions can be retained over a long reaction period due to the high thermochemical stability of the polymer.
- Yun, Seongho,Lee, Songhyun,Yook, Sunwoo,Patel, Hasmukh A.,Yavuz, Cafer T.,Choi, Minkee
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p. 2435 - 2442
(2016/04/26)
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- Fabrication of Ultrafine Palladium Phosphide Nanoparticles as Highly Active Catalyst for Chemoselective Hydrogenation of Alkynes
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Monodisperse palladium phosphide nanoparticles (Pd-P NPs) with a smallest size ever reported of 3.9nm were fabricated using cheap and stable triphenylphosphine as phosphorous source. After the deposition and calcination at 300 °C and 400 °C, the resulting Pd-P NPs increased in size to 4.0nm and 4.8nm, respectively. Notably, the latter NPs probably crystallized with a single phase of Pd3P0.95, which acted as a highly active catalyst in semi-and stereoselective hydrogenation of alkynes. X-ray photoelectron spectroscopy analysis determined a positive shift of binding energy for Pd(3d) in Pd-P NPs compared to that in Pd on carbon. It indicated the electron flow from metal to phosphorus and the larger electron deficiency of Pd in Pd-P NPs, which suppressed palladium hydride formation and subsequently increased the selectivity. Thus, this result may also indicate the applications of Pd-P and other metal-P NPs in various selective hydrogenation reactions.
- Zhao, Ming
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p. 461 - 464
(2016/03/12)
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- BISPHOSPHITE MIXTURE AND USE THEREOF AS A CATALYST MIXTURE IN HYDROFORMYLATION
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The invention relates to a mixture of bisphosphites, to a process for preparation thereof, and to the reaction thereof with metals to give mixtures comprising complexes of the constitutionally isomeric bisphosphites and the metal, and to the use thereof as a catalytically active composition in hydroformylation reactions, and also to the hydroformylation reaction itself.
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Paragraph 0239; 0240
(2015/12/20)
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- Soft propargylic deprotonation: Designed ligand enables au-catalyzed isomerization of alkynes to 1,3-Dienes
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By functionalizing the privileged biphenyl-2-ylphosphine with a basic amino group at the rarely explored 3′ position, the derived gold(I) complex possesses orthogonally positioned "push" and "pull" forces, which enable for the first time soft propargylic deprotonation and permit the bridging of a difference of >26 pKa units (in DMSO) between a propargylic hydrogen and a protonated tertiary aniline. The application of this design led to efficient isomerization of alkynes into versatile 1,3-dienes with synthetically useful scope under mild reaction conditions.
- Wang, Zhixun,Wang, Yanzhao,Zhang, Liming
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supporting information
p. 8887 - 8890
(2014/07/08)
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- Copper-catalyzed Z-selective semihydrogenation of alkynes with hydrosilane: A convenient approach to cis-alkenes
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A copper catalyst generated in situ from widely available copper salt and imidazolium salt in the presence of t-BuOK showed high efficiency for the semihydrogenation of a wide range of internal and terminal alkynes to their corresponding alkenes without obvious over-reduction. Functional groups, such as hydroxyl, nitro, halides, and amino, etc. were tolerated. The Z/E ratios of the obtained alkenes were generally >99%. Finally, semireduction of bulky alkynes also went smoothly.
- Wang, Guang-Hui,Bin, Huai-Yu,Sun, Miao,Chen, Shu-Wei,Liu, Ji-Hong,Zhong, Chong-Min
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supporting information
p. 2175 - 2179
(2014/03/21)
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- Copper-catalyzed selective semihydrogenation of terminal alkynes with hypophosphorous acid
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A novel copper-catalyzed selective semihydrogenation of terminal alkynes using hypophosphorous acid as hydrogen donor took place efficiently to afford the corresponding alkenes in high yields. A broad range of substituted terminal aromatic and aliphatic alkenes, including terminal dienes and enynes bearing internal triple bonds, can be efficiently synthesized by this reaction.
- Cao, Huanyang,Chen, Tieqiao,Zhou, Yongbo,Han, Daoqing,Yin, Shuang-Feng,Han, Li-Biao
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p. 765 - 769
(2014/04/03)
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- Synthesis, characterization, and catalytic behavior of dioxomolybdenum complexes bearing AcAc-type ligands
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A series of [MoO2(acac′)2] [acac′ = acetylacetonato-type ligand: dibenzoylmethane (3), 1-benzoylacetone (4), bis(p-methoxybenzoyl)methane (5), 2-acetylcyclopentanone (6), 2-acetylcyclohexanone (7), and 2-acetyl-1-tetralone (8)] complexes have been synthesized in yields of 44-83 % by a simple synthetic method by using sodium molybdate and the desired acac-type ligand as starting materials. All the complexes were characterized by IR, UV/Vis, NMR, and high-resolution ESI-MS, and for compounds 3, 4, and 8, solid-state structures were obtained by X-ray diffraction. All the complexes contain a cis-dioxomolybdenum moiety, as proven by the characteristic Mo=O vibrations in the IR spectra and the occurrence of four sets of signals in the NMR spectra of the complexes bearing asymmetrical ligands (4 and 6-8), and confirmed by the solid-state structures. The complexes were found to be active as catalysts in the dehydration of 1-phenylethanol to styrene using technical-grade toluene as the solvent in air at 100 °C. The highest catalytic activity was found for [MoO2{(tBuCO) 2CH}2] (2), followed by [MoO2{(C 6H5CO)2CH}2] (3). Both complexes were also found to be active in the dehydration of other alcohols, including allylic, aliphatic, and homoallylic alcohols, as well as secondary and tertiary alcohols, with 2 generally showing better activity and selectivity than 3. These catalytic results were compared with those previously obtained with the metal-based catalyst Re2O7 and the benchmark acid catalyst H2SO4. The results were dependent on the substrate: By using 2, good selectivities but lower activities were generally obtained with tertiary alcohols, whereas good activities but lower selectivities were obtained with secondary alcohols. The industrially important dehydration of 2-octanol to octenes was very efficiently catalyzed by 2. Overall, the [MoO 2(acac′)2] complexes reported herein could offer a cheaper and more abundant metal-based catalyst alternative to the previously reported rhenium-based catalytic system for the dehydration reaction. Copyright
- Korstanje, Ties J.,Folkertsma, Emma,Lutz, Martin,Jastrzebski, Johann T.B.H.,Klein Gebbink, Robertus J.M.
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p. 2195 - 2204
(2013/05/22)
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- Metal-ligand core-shell nanocomposite catalysts for the selective semihydrogenation of alkynes
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Catalysts with a sheltered upbringing: Novel core-shell nanocomposite catalysts consisting of active metal nanoparticles encapsulated by macroligands have been prepared. They have Pd nanoparticles (PdNPs) as an active core and shell ligands having sulfoxide moieties coordinated to the PdNPs. The shell protects the catalyst from coordination by alkenes and allows the lead-free selective semihydrogenation of a wide range of alkynes without any additives (see scheme). Copyright
- Mitsudome, Takato,Takahashi, Yusuke,Ichikawa, Satoshi,Mizugaki, Tomoo,Jitsukawa, Koichiro,Kaneda, Kiyotomi
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supporting information
p. 1481 - 1485
(2013/04/10)
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- Antiandrogenic, maspin induction, and antiprostate cancer activities of tanshinone IIA and its novel derivatives with modification in ring A
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Expression of metastatic suppressor maspin is lost in advanced prostate cancer. Clinically relevant mutations in androgen receptor (AR) convert antiandrogens into AR agonists, promoting prostate tumor growth. We discovered tanshinone IIA (TS-IIA) is a potent antagonist of mutated ARs and induces maspin expression through AR. TS-IIA suppressed AR expression and induced apoptosis in LNCaP cells. Syntheses of TS-IIA derivatives (1-9) revealed that the 4,4-dimethyl group at ring A is important for TS-IIA's antiandrogenic and maspin induction activities.
- Liu, Weiguo,Zhou, Jinming,Geng, Guoyan,Shi, Qingwen,Sauriol, Francoise,Wu, Jian Hui
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supporting information; experimental part
p. 971 - 975
(2012/03/11)
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- Copper-catalyzed highly selective semihydrogenation of non-polar carbon-carbon multiple bonds using a silane and an alcohol
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A copper catalyst bearing a suitable Xantphos derivative or NHC ligand was found to be highly efficient for the selective semihydrogenation of non-polar unsaturated compounds using a mixture of a silane and an alcohol as reducing agent. The catalytic system was useful for the selective semihydrogenation of internal alkynes to (Z)-alkenes with suppression of overreduction to the corresponding alkanes. Furthermore, semihydrogenations of terminal alkyne, 1,2-diene, 1,3-diene, 1,3-enyne and 1,3-diyne systems were also achieved selectively. Copyright
- Semba, Kazuhiko,Fujihara, Tetsuaki,Xu, Tinghua,Terao, Jun,Tsuji, Yasushi
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supporting information; experimental part
p. 1542 - 1550
(2012/08/08)
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- Selective iron-catalyzed transfer hydrogenation of terminal alkynes
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A novel iron-catalyzed transfer hydrogenation of alkynes to the corresponding alkenes applying formic acid as a hydrogen donor is reported. An in situ combination of Fe(BF4)2·6H2O and tetraphos allows for highly selective hydrogenation of a broad range of aromatic and aliphatic alkynes tolerating different functional groups.
- Wienhoefer, Gerrit,Westerhaus, Felix A.,Jagadeesh, Rajenahally V.,Junge, Kathrin,Junge, Henrik,Beller, Matthias
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supporting information; experimental part
p. 4827 - 4829
(2012/06/04)
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- Regioselective rhodium-catalyzed hydroformylation of 1,3-dienes to highly enantioenriched β,γ-unsaturated aldehyes with diazaphospholane ligands
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Regioselective and enantioselective rhodium-catalyzed hydroformylation of 1,3-dienes with chiral bisdiazaphospholane ligands yields β,γ- unsaturated aldehydes that retain a C=C functionality for further conversion. The reaction conditions are mild, featuring low catalyst loadings (0.5 mol %), pressures readily obtained in glass bottles, and convenient reaction times (1.5-12 h). Optimized reaction conditions produce high enantioselectivity (>90% ee), regioselectivity (88-99%), and conversion to β,γ- unsaturated aldehydes (99%) for ten 1,3-dienes encompassing a variety of substitution patterns.
- Watkins, Avery L.,Landis, Clark R.
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supporting information; experimental part
p. 164 - 167
(2011/04/12)
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- Highly efficient Pd/SiO2-dimethyl sulfoxide catalyst system for selective semihydrogenation of alkynes
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Silica-supported Pd nanoparticles (Pd/SiO2) with dimethyl sulfoxide (DMSO) show excellent catalytic activity and selectivity for the semihydrogenation of alkynes. Small amounts of DMSO drastically suppress the overhydrogenation and isomerization of alkenes. This catalyst system is also applicable to both internal and terminal alkynes. Furthermore, the Pd/SiO 2 catalyst was separable from the reaction mixture after the hydrogenation and reusable without loss of its high catalytic activity or selectivity.
- Takahashi, Yusuke,Hashimoto, Norifumi,Hara, Takayoshi,Shimazu, Shogo,Mitsudome, Takato,Mizugaki, Tomoo,Jitsukawa, Koichiro,Kaneda, Kiyotomi
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p. 405 - 407
(2012/10/29)
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- Low pressure vinylation of aryl and vinyl halides via Heck-Mizoroki reactions using ethylene
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Aryl bromides and iodides in the presence of catalytic amounts of a palladacycle derived from acetophenone oxime and 2 equiv of potassium acetate react with ethylene under ambient pressure (15-30 psi) to give the corresponding vinylarenes. The reactions work with both electron-deficient and electron-rich aryl compounds and tolerate wide variety of common functional groups. Vinyl bromides lead to 1,3-dienes in moderate yields.
- Smith, Craig R.,RajanBabu
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supporting information; experimental part
p. 1102 - 1110
(2010/03/25)
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- α-Selective Ni-catalyzed hydroalumination of aryl- and alkyl-substituted terminal alkynes: Practical syntheses of internal vinyl aluminums, halides, or boronates
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A method for Ni-catalyzed hydroalumination of terminal alkynes, leading to the formation of α-vinylaluminum isomers efficiently (>98% conv in 2-12 h) and with high selectivity (95% to >98% α), is described. Catalytic α-selective hydroalumination reactions proceed in the presence of a reagent (diisobutylaluminum hydride; dibal-H) and 3.0 mol % metal complex (Ni(dppp)Cl2) that are commercially available and inexpensive. Under the same conditions, but with Ni(PPh3)2Cl2, hydroalumination becomes highly β-selective, and, unlike uncatalyzed transformations with dibal-H, generates little or no alkynylaluminum byproducts. All hydrometalation reactions are reliable, operationally simple, and practical and afford an assortment of vinylaluminums that are otherwise not easily accessible. The derived α-vinyl halides and boronates can be synthesized through direct treatment with the appropriate electrophiles [e.g., Br 2 and methoxy(pinacolato)boron, respectively]. Ni-catalyzed hydroaluminations can be performed with as little as 0.1 mol % catalyst and on gram scale with equally high efficiency and selectivity.
- Gao, Fang,Hoveyda, Amir H.
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supporting information; experimental part
p. 10961 - 10963
(2010/09/17)
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- Aerobic alcohol oxidation coupled to palladium-catalyzed alkene hydroarylation with boronic esters
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(Chemical Equation Presented) An oxidation exercise: An aerobic alcohol oxidation coupled with a regioselective palladium-catalyzed reductive functionalization of styrenes and arylboronic esters has been developed (see scheme). The mechanism is thought to proceed by initial oxidation of the solvent to generate a PdII-hydride species, which subsequently reacts with the alkene and arylboronic ester to ultimately generate a new C-C bond.
- Iwai, Yasumasa,Gligorich, Keith M.,Sigman, Matthew S.
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p. 3219 - 3222
(2008/12/23)
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- Hydrovinylation of 1,3-dienes: A new protocol, an asymmetric variation, and a potential solution to the exocyclic side chain stereochemistry problem
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Cyclic and acyclic 1,3-dienes undergo efficient (substrate/catalyst = 72) heterodimerization with ethylene in the presence of a Ni catalyst prepared from [o-(PhCH2O)]C6H4PPh2, [(allyl)2NiBr]2, and Na+ BAr4- (Ar = 3,5-bis-trifluromethylphenyl), giving 1,2-addition products. Yields up to 99% can be realized for several 1-vinylcycloalkenes and 1-substituted 1,3-butadienes. Phospholanes with suitably placed hemilabile ligating groups and phosphoramidites derived from binaphthol are excellent ligands for an asymmetric variation of this reaction, the latter giving 99% yield and >95% ee's for selected substrates. An example of how an exocyclic chiral center can be used to install other stereo-centers in the ring (e. g., the carbon to which the side chain is attached) is also provided. These discoveries open an expeditious entry into several biologically relevant classes of compounds, especially those carrying tetrahydronaphthalene and related heterocyclic moieties. Copyright
- Zhang, Aibin,RajanBabu
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- METHOD FOR THE TELOMERISATION OF NON-CYCLIC OLEFINS
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The invention relates to a method for the telomorisation of non-cyclic olefins, comprising at least two conjugated double bonds (I) or mixtures which contain said olefins, with nucleophiles (II). A metal-carbene complex is used as a catalyst.
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Page/Page column 19-20
(2008/06/13)
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- Selective liquid-phase semihydrogenation of functionalized acetylenes and propargylic alcohols with silica-supported bimetallic palladium-copper catalysts
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Silica-supported, bimetallic palladium-copper catalysts were prepared in solution under mild conditions by reacting lithium di(4-tolyl)cuprate with palladium acetate in the presence of silica particles. Small bimetallic palladium-copper particles were deposited on the silica surface as confirmed with TEM-EDAX and EXAFS. The new material has been applied as catalyst in the liquid-phase semihydrogenation of mono- and disubstituted alkynes and showed high selectivity toward the cis-alkenes. The influence of addition of quinoline or potassium hydroxide to the semihydrogenation reaction mixture and the effects of exposure of the catalyst to air before use have been investigated. Silica-supported, bimetallic palladium-copper catalysts were prepared in solution under mild conditions by reacting lithium di(4-tolyl)cuprate with palladium acetate in the presence of silica particles. Small bimetallic palladium-copper particles were deposited on the silica surface as confirmed with TEM-EDAX and EXAFS. The new material has been applied as catalyst in the liquid-phase semihydrogenation of mono- and disubstituted alkynes and showed high selectivity toward the cis-alkenes. The influence of addition of quinoline or potassium hydroxide to the semihydrogenation reaction mixture and the effects of exposure of the catalyst to air before use have been investigated.
- Spee,Boersma,Meijer,Slagt,Van Koten,Geus
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p. 1647 - 1656
(2007/10/03)
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- A general one-pot synthesis of vinyl-thiiranes and conjugated dienes
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The first general synthesis of vinyl-thiiranes 5 and an efficient preparation of conjugated dienes 6 and 7 based on thio, and selenophosphates is described.
- Maciagiewicz,Dybowski,Skowronska
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p. 3791 - 3794
(2007/10/03)
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- Synthetic Applications of the Carbanion with a Fluoroalkyl Group Generated by Palladium(0) Catalyst under Neutral Conditions
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The generation and synthetic application of stable carbanions situated in the β position from fluorine atom(s) are described. Palladium(0)-catalyzed allylation reactions under neutral conditions proceeded smoothly in the system where a methylene group is activated by fluoroalkyl and carbonyl groups. In the above systems, the 2,2,2-trifluoroethyl moiety has been introduced onto the allylic position without the release of fluoride. Further, palladium(0)-catalyzed heterocyclization was achieved from the reaction of vinyl epoxide with 2-(trifluoromethyl)acrylate and/or 2,3,3,3-tetrafluoropropionate.
- Komatsu, Yuzo,Sakamoto, Toru,Kitazume, Tomoya
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p. 8369 - 8374
(2007/10/03)
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- Selective homogeneous palladium(0)-catalyzed hydrogenation of alkynes to (Z)-alkenes
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Zero-valent palladium precatalysts containing rigid bidentate bis(arylimino)acenaphthene ligands (shown schematically) facilitate the highly stereoselective homogeneous catalytic hydrogenation of alkynes to (Z)- alkenes. Internal, terminal, aryl-substituted, and cyclic alkynes are suitable substrates, as are some enynes, which are chemoselectively hydrogenated to dienes. E=CO2Me; R1, R2 = 4-OCH3, 4-CH3, 2,6-(CH3)2.
- Van Laren, Martijn W.,Elsevier, Cornelis J.
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p. 3715 - 3717
(2007/10/03)
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- Perturbation of the degenerate, concerted cope rearrangement by two phenyl groups in "active" positions of (E)-1,4-diphenylhexa-1,5-diene. Acceleration by high pressure as criterion of cyclic transition states
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Previous examinations of radical-stabilizing substituents in the two distinct types of position in the hypothetical "aromatic" transition state of the thermal Cope rearrangement, designated "a" or active and "n" or nodal after the allyl radical have concentrated on their effect in the "n" positions. In order to provide a quantitatively reliable reference for the "a" position, the activation parameters of the degenerate rearrangement of (6-13C)-1,4-diphenylhexa-1,5-diene have been evaluated: Ea = 30.8 ± 0.4 kcal/mol; log A = 10.14 ± 0.2. The soundly energetically-based proposition that these observations relate to a concerted mechanism is strongly supported by the observation of a 3.0-fold increase in rate of approach to equilibrium on increasing the pressure from 1 bar to 6000 bar (162°C; benzene-d6). This rearrangement like that of cis-1,2-divinylcyclobutane and rac- and meso-3,4-diphenylhexa-1,5-diene, has a negative volume of activation. In contrast, trans-1,2-divinylcyclobutane, which does not rearrange by a cyclic transition state and gives cycloocta-1,5-diene, 4-vinylcyclohexene, and butadiene as products, has a positive volume of activation. To place the possibility of reaction by the homolytic/colligative (dissociative/recombinative) mechanism on a "quantitative" base, a further sighting on the heat of formation of the cinnamyl radical is provided by activation parameters for thermal syn-anti equilibration between (E)- and (Z)-1,1′-bi-3-phenylcyclohex-2-enylidene: Ea = 35.8 ± 0.2 kcal/mol; log A = 12.7 ± 0.1. After correction for conjugative interaction between phenyl and the double bond in the educts and without regard for any proposed structure for the transition state, the two phenyl groups in "a" positions appear to have lowered the enthalpy of activation by 7.7 kcal/mol relative to the paradigm, hexa-1,5-diene, whereas the two phenyl groups in the "n" positions of 3,5-diphenylhexa-1,5-diene have lowered the enthalpy of activation by 17.0 kcal/mol.
- Doering,Birladeanu, Ludmila,Sarma, Keshab,Teles, Joaquim Henrique,Kl?rner,Gehrke, Jan-Stephan
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p. 4289 - 4297
(2007/10/02)
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- Pyrolysis Kinetics of Octalins
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The gas phase pyrolysis of three octalins has been studied in a conventional flow system in the temperature range between 500 and 725 deg C and at pressures up to 70 Torr (educt) and 1 atm (reaction system), respectively.The reactions follow a first-order rate law.The overall rate coefficients are given by the following Arrhenius parameters. 9(10)-octalin (1): log k1 (s-1) = (14.71 +/- 1.6) - (260.0 +/- 6.2) kJ mol-1/2.303 RT; 1(9)-octalin (2): log k2 (s-1) = (13.62 +/- 0.9) - (239.1 +/- 3.7) kJ mol-1/2.303 RT; trans-1-octalin (3): log k3 (s-1) = (14.76 +/- 0.5) - (272.6 +/- 1.8) kJ mol-1/2.303 RT.The mechanism of the thermal degradation of 1 to 3 is related to Retro-Diels-Alder fragmentation.
- Ondruschka, Bernd,Zimmermann, Gerhard
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p. 547 - 550
(2007/10/02)
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- Kinetics and Stereochemistry of LiNR2-Induced 1,2-Elimination of Homoallylic Ethers
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The cis and trans isomers of 2-ethenyl-1-methoxycyclohexane were prepared and treated with LiNR2 in the solvents ether, tetrahydrofuran, and hexane.The diene 1-ethenylcyclohexene was formed in high yield from both substrates.In the ethereal solvents, syn elimination is favored over anti, although both pathways are viable and the ksyn/Kanti ratio is only 3-5.In contrast, anti elimination is favored when lithium diisopropylamide is employed in hexane solvent.This inversion in selectivity is associated with depression of ksyn rather than enhancement of kanti, relative to reactions in ether and THF.Syn elimination is favored in all three solvents for reactions of lithium tetramethylpiperidide, again by modest factors (3-5).Rates were measured under excess base conditions and, with few exceptions, first-order losses of the homoallylic ether substrates were observed.The LiNR2 concentration was varied to examine the effect on rate.The calculated second-order rate constants drifted downward with increasing concentration in ethereal solvents, suggesting a net kinetic order in base between 1/2 and 1.The ksyn/kanti ratios were only moderately sensitive to base concentration.A novel method for the preparation of cis-enriched homoallylic ether is described.Treatment of cyclohexene in methanol with N-bromosuccinimide gives trans-1-bromo-2-methoxycyclohexane, which, when subjected to vinylmagnesium bromide/CuI catalyst, affords 2-ethenyl-1-methoxycyclohexane in good yield, as a mixture of stereoisomers containing ca. 85percent of the cis product.
- Tobia, David,Rickborn, Bruce
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p. 777 - 782
(2007/10/02)
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- Isomerisation de dienes-1,5 fonctionnalises par le fer pentacarbonyle
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A series of various, functionnalized 4-vinylcyclohexene derivatives, substituted with electron-withdrawing or -donating groups on the exocyclic double bond, have been isomerized by pentacarbonyliron, under thermodynamic control with heating, into a mixture of conjugated cyclohexadiene tricarbonyliron complexes, of which the 2-substituted derivative is the predominant.When ferrous chloride is used as the co-catalyst, the isomerisation proceeds under kinetic control to give the 1-substituted cyclohexadienetricarbonyliron complex as the major derivative.Reaction mechanisms, have been proposed for these isomerisation processes, which provide a new selective route to such derivatives.The formation of η4-1,4-cyclohexadienetricarbonyl complexes as intermediates has been excluded, and it is shown that the thermal isomerisation proceeds via η2-complexes that are formed by successive 1,3-hydrogen shifts.
- Rodriguez, J.,Brun, P.,Waegell, B.
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p. 343 - 370
(2007/10/02)
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- Photosensitized Cis/Trans Izomerization of 1-(1-Propenyl)cycloalkenes
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The photosensitized cis/trans isomerization of a series of 1-(1-propenyl)cycloalkenes is reported.A plot of the photostationary state trans/cis ratio vs the sensitizer triplet energy for 1-(1-propenyl)cyclopentene shows a constant trans/cis ratio of ca. 1.0 with high-energy sensitizers (ET>61 kcal/mol).The plot shows one maxima at ET ca. 55 kcal/mol with low-energy sensitizers (ET61 kcal/mol).This type of plot is very similar to those obtained with acyclic dienes such as piperylene.The 1-(1-propenyl)cyclohexene system shows a similar plot with high-energy sensit izers, but with low-energy sensitizers this system shows two maxima occurring at 56 and 47 kcal/mol, respectively.This double-maxima plot is rationalized by an unsually low trans/cis decay ratio for the s-cis relaxed triplet state of the 1-(1-propenyl)cyclohexene system.This double maxima is not observed in other diene systems due to a high trans/cis decay ratio for their s-cis relaxed triplet states.The photosensitized cis/trans isomerization of 2-ethylidene-10-methyl-1(9)-octalin was also studied as a model for a conformationally locked s-trans system.The 1-(1-propenyl)cycloheptene system undergoes photosensitized cis/trans isomerization, but photostationary cis/trans isomerization data could not be obtained due to a very efficient photosensitized dimerization of this diene system.
- Inman, Wayne D.,Sanchez, Kenneth A. J.,Chaidez, Manuel A.,Paulson, Donald R.
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p. 4872 - 4881
(2007/10/02)
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- Cross-Coupling of Organosilanes with Organic Halides Mediated by Palladium Catalyst and Tris(diethylamino)sulfonium Difluorotrimethylsilicate
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In the presence of tris(diethylamino)sulfonium difluorotrimethylsilicate (TASF) and allylpalladium chloride dimer as a catalyst, organosilicon compounds like vinyl-, ethynyl-, and allylsilanes react with such organic halides as aryl, vinyl, and allyl halides to give the corresponding coupled products in synthetically useful yields in a stereospecific and chemoselective manner.
- Hatanaka, Yasuo,Hiyama, Tamejiro
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p. 918 - 920
(2007/10/02)
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- DIELS-ALDER REACTIONS OF 4,4-DIMETHYL-2-CYCLOHEXENONES. A DIRECT ROUTE TO THE 4,4-DIMETHYL-1-DECALONES
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Diels-Alder additions to enones 1 and 2, synthetic equivalents of the synthon 3, were studied using a variety of hydrocarbon dienes.The two enones have been shown to be effective and synthetically useful dienophiles.Spectroscopic (especially 1H and 13C magnetic resonance) and chemical techniques were used to define unambiguously the full structures of the adducts.The structures of the various reaction products were used to draw qualitative conclusions about the nature of the transition states involved and the various electronic and steric effects that play a role in the mechanistic course of the Diels-Alder reaction.
- Liu, Hsing-Jang,Browne, Eric N. C.
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p. 1262 - 1278
(2007/10/02)
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- Photooxygenation of 1-Vinylcycloalkenes. The Competition between "Ene" Reaction and Cycloaddition of Singlet Oxygen
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The competition between the "ene" reaction and 1,4-cycloaddition reaction of 1O2 in a series of 1-vinylcycloalkenes (n = 5-10, 12) and 1-isopropenylcycloalkenes (n = 6-8) was studied.Ring size had a profound effect.When n = 5 or 7, products of the "ene" reaction predominated, but as ring size increased cycloaddition competed closely with the "ene" process, the crossover being at ring size 10. 1-Vinylhexenes constituted an exception with 1,4-cycloaddition greatly predominant. "Ene" products were almost exclusively conjugated diene hydroperoxides or secondary products derived from them; small amounts of unconjugated diene hydroperoxides were formed only when n = 9, 10, or 12.The influence of ring size of the "ene" to cycloaddition product ratio is compared with the rates of photooxygenation and the degree of syn-regiospecificity exhibited by (Z)-1-methylcycloalkenes and attributed to the same mainly conformational factors, as is the geometry of the "ene" products.The 1,4-cycloaddition products were converted to furans by means of ferrous sulfate.
- Herz, Werner,Juo, Rouh-Rong
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p. 618 - 627
(2007/10/02)
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- THE DEHYDRATION OF ALLYLIC AND BENZYLIC CYCLOALKANOLS BY MOLECULAR SIEVES
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A mild procedure for the quantitative dehydration of 1-vinyl- and 1-phenylcycloalkanols has been developed.
- Markgraf, J. Hodge,Burns, Drew B.,Greeno, Edward W.,Leonard, Kathryn J.,Miller, Michael
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p. 647 - 654
(2007/10/02)
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- Regio- and Stereo-specific Reduction of Conjugated and Non-conjugated Triple Bonds by Activated Zinc Powder
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Regio- as well as stereo-specific reductions of a wide variety of acetylenic derivatives have been carried out in absolute ethanol with zinc powder activated with 1,2-dibromoethane, and with zinc powder activated successively with dibromoethane and copper(I) bromide, the first reagent being less powerful and more selective than the second one.
- Aerssens, Marc H. P. J.,Brandsma, Lambert
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p. 735 - 736
(2007/10/02)
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- THE DIELS-ALDER REACTION OF METHYL PROPIOLATE WITH 1-VINYLCYCLOALKENES
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The Diels-Alder reaction of methyl propiolate with 1-vinylcycloalkenes was used to assess the influence of ring strain on the regioselectivity of such cycloadditions: the ratio of 1,2,3- to 1,2,4-adducts increased with increasing size of the cycloalkene.
- Markgraf, J. Hodge,Greeno, Edward W.,Miller, Michael D.,Zaks, William J.,Lee, George A.
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p. 241 - 244
(2007/10/02)
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- Regio- and Stereoselective Hydrosulfonylation of Conjugated Dienes via a (?-Allyl)palladium Complex
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The combination of a sulfonylpalladation of acyclic dienes 1 (with 2 equiv of NaSO2R and 1 equiv of PdCl2 in acetic acid or acetic acid-H2O at 50-80 deg C under air) and a protiodepalladation of the thus obtained palladium complexes 3 with dimethylglyoxime (in a protic solvent at room temperature) provides di- and trisubstituted (Z)-Δ3-sulfones 12 selectively, irrespective of the stereochemistry of the starting dienes.Similar treatment of 1-vinylcycloalkenes 5 (n (1,3) strain between Pd and the substituent on the allylic position.
- Tamaru, Yoshinao,Yamada, Yoshimi,Kagotani, Masahiro,Ochiai, Hirofumi,Nakajo, Eiji,et al.
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p. 4669 - 4681
(2007/10/02)
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- Metal Catalysis in Organic Reactions. Part 13. The Reaction of 3-En-1-ynes with Trialkylalanes: Influence of Transition-metal Complexes
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The reaction between trialkylalanes and 3-alkyl-, or 4-alkyl-, or 3,4-dialkyl-but-3-en-1-ynes (1) lead to products which correspond to metallation, reduction, and carbalumination processes.The extent of such reactions, and the regio- and stereo-selectivity of the carbalumination, are dependent on the enyne used.A mechanism is proposed involving tautomeric equilibria among several α-unsaturated organoaluminium intermediates to explain the formation of the carbalumination products. In the presence of catalytic amounts of nickel and manganese complexes, 3-en-1-ynes (1), by reacting with tri-isobutylaluminium, are dimerized selectively in a 'head-to-tail' fashion to conjugated tetraenes having different structures in relation to the different nature of the transition-metal complex.The preparative aspect of these induced reactions is discussed, and, in the light of previous reports, some mechanistic considerations are presented.
- Caporusso, Anna Maria,Giacomelly, Giampaolo,Lardicci, Luciano
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p. 1900 - 1908
(2007/10/02)
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- METAL-ASSISTED REACTIONS-PART 10. RAPID, STEREOSELECTIVE AND SPECIFIC CATALYTIC TRANSFER REDUCTION OF ALKYNES TO CIS-ALKENES
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The rapid, stereoselective, and specific transfer reduction of alkynes to alkenes using specially-modified, but easily prepared, palladium catalysts is described.Additional use of a phase transfer catalyst in these systems affords a simple method for phase transfer catalysed catalytic transfer reduction which can be carried out in the presence of other potentially reducible functional groups.
- Johnstone, Robert A. W.,Wilby, Anna H.
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p. 3667 - 3670
(2007/10/02)
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