- Synthesis, Reactivity, and Coordination of Semihomologous dppf Congeners Bearing Primary Phosphine and Primary Phosphine Oxide Groups
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This contribution reports the synthesis of two phosphinoferrocene ligands desymmetrized by an inserted methylene spacer, viz., a bis-phosphine combining primary and tertiary phosphine moieties in its structure, Ph2PfcCH2PH2 (2), and a structurally unique, stable phosphine-primary phosphine oxide Ph2PfcCH2P(O)H2 (7; fc = ferrocene-1,1′-diyl). Compounds 2 and 7, together with 1,1′-bis(diphenylphosphino)ferrocene (dppf), the bis-tertiary phosphine Ph2PfcCH2PPh2, and the adduct Ph2P(BH3)fcCH2PH2 (6), were studied as ligands in Ru(II) complexes bearing auxiliary ν6-arene ligands and both free ligands and the isolated complexes were structurally authenticated, using spectroscopic methods and X-ray crystallography, and further investigated by cyclic voltammetry. The results suggest that distinct donor moieties in the unsymmetric ligands differentiate the otherwise identical coordinated metal centers and that the phosphine moiety in phosphine-phosphine oxide ligand 7 is preferably coordinated to Ru(II), before the phosphine oxide group, which must tautomerize into the hydroxyphosphine form prior to coordination.
- Horky, Filip,Císa?ová, Ivana,?těpni?ka, Petr
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p. 427 - 441
(2021/02/06)
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- Highly Z-Selective Double Bond Transposition in Simple Alkenes and Allylarenes through a Spin-Accelerated Allyl Mechanism
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Double-bond transposition in alkenes (isomerization) offers opportunities for the synthesis of bioactive molecules, but requires high selectivity to avoid mixtures of products. Generation of Z-alkenes, which are present in many natural products and pharmaceuticals, is particularly challenging because it is usually less thermodynamically favorable than generation of the E isomers. We report a β-dialdiminate-supported, high-spin cobalt(I) complex that can convert terminal alkenes, including previously recalcitrant allylbenzenes, to Z-2-alkenes with unprecedentedly high regioselectivity and stereoselectivity. Deuterium labeling studies indicate that the catalyst operates through a π-allyl mechanism, which is different from the alkyl mechanism that is followed by other Z-selective catalysts. Computations indicate that the triplet cobalt(I) alkene complex undergoes a spin state change from the resting-state triplet to a singlet in the lowest-energy C-H activation transition state, which leads to the Z product. This suggests that this change in spin state enables the catalyst to differentiate the stereodefining barriers in this system, and more generally that spin-state changes may offer a route toward novel stereocontrol methods for first-row transition metals.
- Kim, Daniel,Pillon, Guy,Diprimio, Daniel J.,Holland, Patrick L.
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supporting information
p. 3070 - 3074
(2021/03/08)
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- An Amine-Assisted Ionic Monohydride Mechanism Enables Selective Alkyne cis-Semihydrogenation with Ethanol: From Elementary Steps to Catalysis
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The selective synthesis of Z-alkenes in alkyne semihydrogenation relies on the reactivity difference of the catalysts toward the starting materials and the products. Here we report Z-selective semihydrogenation of alkynes with ethanol via a coordination-induced ionic monohydride mechanism. The EtOH-coordination-driven Cl- dissociation in a pincer Ir(III) hydridochloride complex (NCP)IrHCl (1) forms a cationic monohydride, [(NCP)IrH(EtOH)]+Cl-, that reacts selectively with alkynes over the corresponding Z-alkenes, thereby overcoming competing thermodynamically dominant alkene Z-E isomerization and overreduction. The challenge for establishing a catalytic cycle, however, lies in the alcoholysis step; the reaction of the alkyne insertion product (NCP)IrCl(vinyl) with EtOH does occur, but very slowly. Surprisingly, the alcoholysis does not proceed via direct protonolysis of the Ir-C(vinyl) bond. Instead, mechanistic data are consistent with an anion-involved alcoholysis pathway involving ionization of (NCP)IrCl(vinyl) via EtOH-for-Cl substitution and reversible protonation of Cl- ion with an Ir(III)-bound EtOH, followed by β-H elimination of the ethoxy ligand and C(vinyl)-H reductive elimination. The use of an amine is key to the monohydride mechanism by promoting the alcoholysis. The 1-amine-EtOH catalytic system exhibits an unprecedented level of substrate scope, generality, and compatibility, as demonstrated by Z-selective reduction of all alkyne classes, including challenging enynes and complex polyfunctionalized molecules. Comparison with a cationic monohydride complex bearing a noncoordinating BArF- ion elucidates the beneficial role of the Cl- ion in controlling the stereoselectivity, and comparison between 1-amine-EtOH and 1-NaOtBu-EtOH underscores the fact that this base variable, albeit in catalytic amounts, leads to different mechanisms and consequently different stereoselectivity.
- Huang, Zhidao,Wang, Yulei,Leng, Xuebing,Huang, Zheng
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supporting information
p. 4824 - 4836
(2021/04/07)
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- PET-RAFT single unit monomer insertion of β-methylstyrene derivatives: RAFT degradation and reaction selectivity
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Reversible addition-fragmentation chain transfer (RAFT) single unit monomer insertion (SUMI) of β-methylstyrene derivatives into diverse RAFT agents presented fast reaction kinetics, but significant degradation of the SUMI products occurred due to a hydrogen abstraction reaction. Fortunately, such degradation can be suppressed through appropriate design of initial RAFT agents attributed to effective chain transfer and selective photoactivation.
- Lin, Shiyang,Liu, Ruizhe,Xu, Jiangtao,Zhang, Lei
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supporting information
p. 10759 - 10762
(2021/10/20)
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- Iron Catalyzed Double Bond Isomerization: Evidence for an FeI/FeIII Catalytic Cycle
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Iron-catalyzed isomerization of alkenes is reported using an iron(II) β-diketiminate pre-catalyst. The reaction proceeds with a catalytic amount of a hydride source, such as pinacol borane (HBpin) or ammonia borane (H3N?BH3). Reactivity with both allyl arenes and aliphatic alkenes has been studied. The catalytic mechanism was investigated by a variety of means, including deuteration studies, Density Functional Theory (DFT) and Electron Paramagnetic Resonance (EPR) spectroscopy. The data obtained support a pre-catalyst activation step that gives access to an η2-coordinated alkene FeI complex, followed by oxidative addition of the alkene to give an FeIII intermediate, which then undergoes reductive elimination to allow release of the isomerization product.
- Woof, Callum R.,Durand, Derek J.,Fey, Natalie,Richards, Emma,Webster, Ruth L.
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supporting information
p. 5972 - 5977
(2021/03/17)
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- Semihydrogenation of Alkynes Catalyzed by a Pyridone Borane Complex: Frustrated Lewis Pair Reactivity and Boron–Ligand Cooperation in Concert
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The metal-free cis selective hydrogenation of alkynes catalyzed by a boroxypyridine is reported. A variety of internal alkynes are hydrogenated at 80 °C under 5 bar H2 with good yields and stereoselectivity. Furthermore, the catalyst described herein enables the first metal-free semihydrogenation of terminal alkynes. Mechanistic investigations, substantiated by DFT computations, reveal that the mode of action by which the boroxypyridine activates H2 is reminiscent of the reactivity of an intramolecular frustrated Lewis pair. However, it is the change in the coordination mode of the boroxypyridine upon H2 activation that allows the dissociation of the formed pyridone borane complex and subsequent hydroboration of an alkyne. This change in the coordination mode upon bond activation is described by the term boron-ligand cooperation.
- Wech, Felix,Hasenbeck, Max,Gellrich, Urs
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supporting information
p. 13445 - 13450
(2020/09/23)
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- Radical-Mediated Strategies for the Functionalization of Alkenes with Diazo Compounds
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One of the most common reactions of diazo compounds with alkenes is cyclopropanation, which occurs through metal carbene or free carbene intermediates. Alternative functionalization of alkenes with diazo compounds is limited, and a methodology for the addition of the elements of Z-CHR2 (with Z = H or heteroatom, and CHR2 originates from N2 CR2) across a carbon-carbon double bond has not been reported. Here we report a novel reaction of diazo compounds utilizing a radical-mediated addition strategy to achieve difunctionalization of diverse alkenes. Diazo compounds are transformed to carbon radicals with a photocatalyst or an iron catalyst through PCET processes. The carbon radical selectively adds to diverse alkenes, delivering new carbon radical species, and then forms products through hydroalkylation by thiol-assisted hydrogen atom transfer (HAT), or forms azidoalkylation products through an iron catalytic cycle. These two processes are highly complementary, proceed under mild reaction conditions, and show high functional group tolerance. Furthermore, both transformations are successfully performed on a gram-scale, and diverse γ-amino esters, γ-amino alcohols, and complex spirolactams are easily prepared with commercially available reagents. Mechanistic studies reveal the plausible pathways that link the two processes and explain the unique advantages of each.
- Su, Yong-Liang,Liu, Geng-Xin,Liu, Jun-Wen,Tram, Linh,Qiu, Huang,Doyle, Michael P.
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supporting information
p. 13846 - 13855
(2020/09/21)
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- Cobalt-Catalyzed Z to e Isomerization of Alkenes: An Approach to (E)-β-Substituted Styrenes
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An efficient cobalt-catalyzed Z to E isomerization of β-substituted styrenes using the amido-diphosphine ligand was developed, delivering the (E)-isomers with good functional tolerance and high stereoselectivity. The reaction could be scaled up to gram-scale with a catalyst loading of 0.1 mol %, using a mixture of (Z)- and (E)-alkene as the starting material. Preliminary mechanistic studies indicated that cobalt(I)-hydride and a benzylic-cobalt species were probably involved in the reaction, as supported by experiments and DFT calculations.
- Liu, Hongmei,Xu, Man,Cai, Cheng,Chen, Jianhui,Gu, Yugui,Xia, Yuanzhi
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supporting information
p. 1193 - 1198
(2020/02/04)
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- Cycloaddition Reactions of Alkene Radical Cations using Iron(III)-Phenanthroline Complex
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Single electron oxidation of electron-rich alkenes using the iron(III)-phenanthroline complex produced electrophilic alkene radical cations, which promoted efficient radical cation [2+1] cycloaddition reactions with diazo compounds. Subsequent chain propagation afforded tri- and tetra-substituted cyclopropanes. This methodology was also expanded to [3+2] cycloaddition reactions with vinyl diazoesters, validating this sustainable, first-row transition metal iron system for the single electron redox reactions. (Figure presented.).
- Cho, Yong Hyun,Kim, Jae Hyung,An, Hyeju,Ahn, Kwang-Hyun,Kang, Eun Joo
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supporting information
p. 2183 - 2188
(2020/04/29)
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- Hydrophilic (ν6-Arene)-Ruthenium(II) Complexes with P-OH ligands as catalysts for the isomerization of allylbenzenes and C-H bond arylation reactions in water
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Half-sandwich ruthenium(II) complexes containing ν6-coordinated 3-phenylpropanol and phosphinous-acid-type ligands, namely, [RuCl2(ν6-C6H5CH2CH2CH2OH){P(OH)R2}] (R = Me (2a), Ph (2b), 4-C6H4CF3 (2c), 4-C6H4OMe (2d), OMe (2e), OEt (2f), and OPh (2g), have been synthesized in 44-88% yield by reacting [RuCl2{ν6:κ1(O)-C6H5CH2CH2CH2OH}] (1) with the appropriate pentavalent phosphorus oxide R2P(═O)H. The structure of [RuCl2(ν6-C6H5CH2CH2CH2OH){P(OH)Me2}] (2a) was unequivocally confirmed by X-ray diffraction methods. Compounds 2a-g proved to be catalytically active in the isomerization of allylbenzenes into the corresponding (1-propenyl)benzene derivatives employing water as the sole reaction solvent, with [RuCl2(ν6-C6H5CH2CH2CH2OH){P(OH)(OPh)2}] (2g) showing the best performance and a broad substrate scope (73-93% isolated yields with E/Z ratios around 90:10 employing 1 mol % of 2g and 3 mol % of K2CO3, and performing the catalytic reactions at 80 °C for 4-24 h). The results herein presented show for the first time the utility of phosphinous acids as auxiliary ligands for metal-catalyzed olefin isomerization processes, reactions in which a cooperative role for the P - OH unit is proposed. On the other hand, the utility of complexes 2a-g as catalysts for ortho-arylation reactions of 2-phenylpyridine in water is also briefly discussed.
- González-Fernández, Rebeca,Crochet, Pascale,Cadierno, Victorio
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supporting information
p. 3696 - 3706
(2019/10/11)
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- Radical Cation Diels-Alder Reactions by TiO2 Photocatalysis
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Radical cation Diels-Alder reactions by titanium dioxide (TiO2) photocatalysis in lithium perchlorate/nitromethane solution are described. TiO2 photocatalysis promotes reactions between electron-rich dienes and dienophiles, which would otherwise be difficult to accomplish due to electronic mismatching. The reactions are triggered by hole oxidation of the dienophile and are completed by the excited electron reduction of the radical cation intermediate at the dispersed surface in the absence of any sacrificial substrate.
- Nakayama, Kaii,Maeta, Naoya,Horiguchi, Genki,Kamiya, Hidehiro,Okada, Yohei
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supporting information
p. 2246 - 2250
(2019/04/10)
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- Enantioselective Oxy-Heck–Matsuda Arylations: Expeditious Synthesis of Dihydrobenzofuran Systems and Total Synthesis of the Neolignan (?)-Conocarpan
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This work discloses the first examples of an effective enantioselective oxy-Heck–Matsuda reaction using a variety of styrenic olefins to generate chiral dihydrobenzofurans. The reaction proceeds in moderate to good yields, with high trans diastereoselectivity (up to 20:1) in enantioselectivities up to 90:10 using the N,N-ligand pyrimidine-bisoxazoline (PyriBox). The oxy-Heck–Matsuda reactions were carried out under mild conditions and rather low catalyst loadings. The feasibility and practicality of the process is demonstrated by a concise total synthesis of the neolignan (?)-conocarpan. X-ray diffraction of an advanced brominated intermediate in the route to (?)-conocarpan has allowed the unequivocal assignment of the absolute stereochemistry of the oxy-Heck–Matsuda aryldihydrobenzofuran products. A rationale for the mechanism operating in these enantioselective oxy-Heck–Matsuda reactions is also presented. (Figure presented.).
- Silva, Allan R.,Polo, Ellen C.,Martins, Nelson C.,Correia, Carlos Roque D.
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p. 346 - 365
(2018/01/26)
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- A Dual-Functional Catalyst for Cascade Meerwein–Pondorf–Verley Reduction and Dehydration of 4″-Methoxypropiophenone to Anethole
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Anethole is an ingredient in many flavours, fragrances and pharmaceutical formulations. To reduce the dependence of its supply on natural oils, a green route for anethole synthesis was designed on the basis of Meerwein–Pondorf–Verley (MPV) reduction and dehydration of 4′-methoxypropiophenone. The one-pot cascade reactions were heterogeneously catalysed by dual-functional Zr-MSU-3, a predominantly Lewis-acidic catalyst with a Si/Zr ratio of 10 and pores with sizes in the range of 3.2–4.2 nm. The use of 2-pentanol as solvent and hydrogen donor for the MPV reduction was advantageous, as its high boiling point enhances the rate of the reactions, especially the dehydration of the MPV product, 1-(4-methoxyphenyl)-propan-1-ol. This dispenses with the need for a strong acid catalyst that could result in by-products of acid-catalysed reactions. Anethole yields of 91 % with a trans/cis isomer ratio of about 92:8, similar to that of natural anethole, were obtained. In comparison, microporous Zr-beta (Si/Zr 12.5) gave lower activity owing to pore-size constraints. Hence, through design of the reactions and catalyst, 4′-methoxypropiophenone can be efficiently converted to anethole in a sustainable and green manner.
- Zhang, Hongwei,Lim, Candy Li-Fen,Zaki, Muhammad,Jaenicke, Stephan,Chuah, Gaik Khuan
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p. 3007 - 3017
(2018/08/03)
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- Arylsulfonylacetamides as bifunctional reagents for alkene aminoarylation
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Alkene aminoarylation with a single, bifunctional reagent is a concise synthetic strategy.We report a catalytic protocol for the addition of arylsulfonylacetamides across electron-rich alkenes with complete anti-Markovnikov regioselectivity and excellent diastereoselectivity to provide 2,2-diarylethylamines. In this process, single-electron alkene oxidation enables carbon-nitrogen bond formation to provide a key benzylic radical poised for a Smiles-Truce 1,5-aryl shift. This reaction is redox-neutral, exhibits broad functional group compatibility, and occurs at room temperature with loss of sulfur dioxide. As this process is driven by visible light, uses readily available starting materials, and demonstrates convergent synthesis, it is well suited for use in a variety of synthetic endeavors.
- Monos, Timothy M.,McAtee, Rory C.,Stephenson, Corey R.J.
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p. 1369 - 1373
(2018/10/08)
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- Redox-Neutral Photocatalytic Cyclopropanation via Radical/Polar Crossover
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A benchtop stable, bifunctional reagent for the redox-neutral cyclopropanation of olefins has been developed. Triethylammonium bis(catecholato)iodomethylsilicate can be readily prepared on multigram scale. Using this reagent in combination with an organic photocatalyst and visible light, cyclopropanation of an array of olefins, including trifluoromethyl- and pinacolatoboryl-substituted alkenes, can be accomplished in a matter of hours. The reaction is highly tolerant of traditionally reactive functional groups (carboxylic acids, basic heterocycles, alkyl halides, etc.) and permits the chemoselective cyclopropanation of polyolefinated compounds. Mechanistic interrogation revealed that the reaction proceeds via a rapid anionic 3-exo-tet ring closure, a pathway consistent with experimental and computational data.
- Phelan, James P.,Lang, Simon B.,Compton, Jordan S.,Kelly, Christopher B.,Dykstra, Ryan,Gutierrez, Osvaldo,Molander, Gary A.
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p. 8037 - 8047
(2018/07/03)
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- Production technique to prepare anethole by catalyzing dewatering of 3-(4-methoxyphenyl)-1-propanol
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The invention discloses a production technique to prepare anethole by catalyzing dewatering of 3-(4-methoxyphenyl)-1-propanol. The production technique comprises: using acid alumina and/or aluminum hydroxide weak-acidity solid material to catalyze dewatering of 3-(4-methoxyphenyl)-1-propanol at 100-150 DEG C to generate anethole. The production technique has the advantages that the reaction process is free of waste gas, the reaction rate is high, the yield is high, few polymer impurities occur to anethole, the economic value is high, the reaction requires no post-treatment or solvent, the requirement on equipment is low, and the production technique is easy to industrially popularize.
- -
-
Paragraph 0084-0099; 0169
(2018/09/13)
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- A General Strategy for Open-Flask Alkene Isomerization by Ruthenium Hydride Complexes with Non-Redox Metal Salts
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A homogenous metal hydride (M?H) catalyst for isomerization normally requires rigorous air-free techniques. Here, we demonstrate a highly efficient protocol in which simple non-redox metal ions as Lewis acids can promote olefin isomerization dramatically with a commercially available RuH2(CO)(PPh3)3 complex in an open-flask system. Isomerization can be accomplished within a short time, and a satisfactory selectivity for different types of unsaturated compounds can be obtained. Meanwhile, an excellent turnover number up to 17208 was achieved under air, and open-flask gram-scale experiments further demonstrated the efficiency of the RuH2(CO)(PPh3)3/non-redox-metals system. We used FTIR spectroscopy, GC–MS, NMR spectroscopy and kinetics studies to evidence that in the sluggish RuH2(CO)(PPh3)3 catalyst, bloated PPh3 ligands cause steric hindrance for the coordination of the free alkene. Alternatively, the addition of non-redox metal ions could induce the dissociation of the PPh3 ligand to offer unoccupied coordination sites for the alkene and to form the Mg-bridged adduct OC?Ru?H2?Mg2+ as the highly active species, which benefited the isomerization significantly through the metal hydride addition–elimination pathway. Finally, this strategy was demonstrated as an impactful approach for hydride catalysts of other transition metals such as Os.
- Lv, Zhanao,Chen, Zhuqi,Hu, Yue,Zheng, Wenrui,Wang, Haibin,Mo, Wanling,Yin, Guochuan
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p. 3849 - 3859
(2017/09/18)
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- Nitrogen-Doped Carbon-Encapsulated Nickel/Cobalt Nanoparticle Catalysts for Olefin Migration in Allylarenes
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Olefin migration in allylarenes is typically performed with precious-metal-based homogeneous catalysts. In contrast, very limited progress has been made with the use of cheap, Earth-abundant base metals as heterogeneous catalysts for these transformations—in spite of the obvious economic and environmental advantages. Herein, we report on the use of an easily prepared heterogeneous catalyst material for the migration of olefins, in particular, for allylarenes. The catalyst material consists of nickel/cobalt alloy nanoparticles encapsulated in nitrogen-doped carbon shells. The encapsulated nanoparticles are stable in air and are easily collected by centrifugation, filtration, or magnetic separation. Furthermore, we demonstrate that the catalysts can be reused several times and provide continuously high yields of the olefin-migration product.
- Kramer, S?ren,Mielby, Jerrik,Buss, Kasper,Kasama, Takeshi,Kegn?s, S?ren
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p. 2930 - 2934
(2017/08/14)
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- Mononuclear Ruthenium and Osmium Complexes with a Bicyclic Guanidinate Ligand: Synthesis and Catalytic Behavior in Olefin Isomerization Processes
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The preparation of the first mononuclear RuII, RuIV, and OsII complexes containing the anion of the bicyclic guanidine 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine (Hhpp) as a chelating ligand, namely [RuX{κ2-(N,N′)-hpp}(η6-arene)] [arene = p-cymene, X = Cl (2a), Br (2b), I (2c); arene = C6Me6, X = Cl (7)], [RuCl{κ2-(N,N′)-hpp}(η3:η3-C10H16)] (9; C10H16 = 2,7-dimethylocta-2,6-diene-1,8-diyl), and [OsCl{κ2-(N,N′)-hpp}(η6-p-cymene)] (11), is described. Compounds 2a–c, 7, 9, and 11 have been fully characterized by elemental analysis, HRMS, IR and NMR spectroscopy. In addition, the structure of 2a has been unequivocally confirmed by single-crystal X-ray diffraction methods. The catalytic behavior of these metal guanidinate complexes in the base-free redox isomerization of allylic alcohols is explored, with the ruthenium(IV) derivative 9 showing the best performance (TOF up to 5940 h–1). All of the synthesized complexes have also proven to be active in the isomerization of the allylbenzene estragole into the industrially relevant 1-propenylbenzene anethole, with a trans selectivity of up to 95 %.
- Gámez-Rivera, Sebastián A.,Francos, Javier,Borge, Javier,Cadierno, Victorio
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p. 4138 - 4146
(2017/09/28)
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- (E)-Selective Wittig Reactions between a Nonstabilized Phosphonium Ylide Bearing a Phosphastibatriptycene Skeleton and Benzaldehydes
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Wittig reactions between benzaldehyde derivatives and a nonstabilized phosphonium ylide bearing a phosphastibatriptycene skeleton, regarded as a tridentate aryl ligand, gave (E)-alkenes with high selectivity in the presence of both lithium and sodium salts. As previously reported, reactions between a triphenylphosphonium ylide and benzaldehyde derivatives under the same conditions afforded mainly (Z)-alkenes. Variable-temperature (VT)31P{1H} NMR spectra showed two signals, assigned to cis- and trans-1,2-oxaphosphetanes, which were observed at different temperatures (–80 °C and –40 °C, respectively) in the Wittig reaction between benzaldehyde and the nonstabilized phosphonium ylide bearing the phosphastibatriptycene skeleton, in the presence of both lithium and sodium salts, and showed the existence of equilibrium between these products at –40 °C. On the other hand, this equilibrium was not clearly observed in the reaction between the triphenylphosphonium ylide and benzaldehyde, for which only one signal was detected. The observed intermediates were confirmed to be 1,2-oxaphosphetanes by deprotonation of the isolated β-hydroxyalkylphosphonium salts bearing a phosphastibatriptycene skeleton and a triphenylphosphine moiety, respectively. Crossover reactions were conducted in the deprotonations of β-hydroxyalkylphosphonium salts with TMS2NNa in the presence of p-chlorobenzaldehyde, resulting in the observation of signals corresponding to 1,2-oxaphosphetanes containing phenyl and p-chlorophenyl groups at the 4-positions, indicating the exchange process between benzaldehyde and p-chlorobenzaldehyde at –40 °C for the phosphastibatriptycene system and at 0 °C for triphenyl derivatives. These results clearly indicated that stereochemical drift occurred at those temperatures, even in reactions using nonstabilized phosphonium ylides. The stereochemical drift in the phosphastibatriptycene system occurred at a lower temperature than in the case of the triphenyl derivative, thus explaining the (E)-selective Wittig reactions between the benzaldehyde derivatives and the nonstabilized phosphastibatriptycene-based phosphonium ylide in the presence of lithium and sodium salts.
- Uchiyama, Yosuke,Ohtsuki, Takemaru,Murakami, Rikiya,Shibata, Munenori,Sugimoto, Jun
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p. 159 - 174
(2017/01/14)
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- A Stereoconvergent Cyclopropanation Reaction of Styrenes
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The first stereoconvergent cyclopropanation reaction by means of photoredox catalysis using diiodomethane as the methylene source is described. This transformation exhibits broad functional group tolerance and it is characterized by an excellent stereocontrol en route to trans-cyclopropanes regardless of whether E- or Z-styrene substrates were utilized.
- del Hoyo, Ana M.,Herraiz, Ana G.,Suero, Marcos G.
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supporting information
p. 1610 - 1613
(2017/02/05)
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- Tandem catalysis: Versus one-pot catalysis: Ensuring process orthogonality in the transformation of essential-oil phenylpropenoids into high-value products via olefin isomerization-metathesis
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Conversion of essential-oil allylbenzenes (phenylpropenoids) to high-value fine chemicals via isomerization-metathesis is reported. The target reaction sequence involves isomerization of ArCH2CH=CH21 into the corresponding conjugated olefins 2, and ensuing cross-metathesis with acrylates to generate ArCH=CHCO2R 3. The second-generation Hoveyda catalyst HII was chosen for the metathesis step. A range of lead candidates was assessed for the isomerization step, of which most active was the Grotjahn catalyst [CpRu(PN)(MeCN)]PF6([4]PF6; PN = 2-PiPr2-4-tBu-1-Me-imidazole). The following order of isomerization activity was determined, using the isomerization of estragole 1a to anethole 2a (Ar = p-MeOC6H4) as a probe reaction: [CpRu(PN)(MeCN)]PF6> RuHCl(CO)(PPh3)3> Ru(Me-allyl)2(COD) > Pd2Br2(PtBu3)2> RuHCl(PPh3)3> RuCl3(μ2-C)(μ2,κ1-C,η6-Mes-H2IMes)Ru(H)(H2IMes) (the "Grubbs hydride") > RuHCl(CO)(H2IMes)(PCy3) > RuHCl(CO)(IMes)(PCy3) > RuHCl(CO)(PCy3)2. To maximize process efficiency, a systematic comparison of orthogonal tandem catalysis versus sequential catalyst addition was undertaken, using catalysts [4]PF6and HII. The impact of each process type on product selectivity and catalyst compatibility was assessed. Selectivity was undermined in tandem isomerization-metathesis by competing metathesis of 1. Sequential catalyst addition eliminated this problem. The isomerization catalyst [4]PF6adversely affected metathesis yields when equimolar with HII, an effect traced to the imidazole functionality in [4]PF6. However, at the low catalyst loadings required for efficient isomerization (0.1 mol% [4]PF6), negligible impact on metathesis yields was evident. The target cinnamates and ferrulates were obtained in quantitative yields by coupling these steps in a one-pot isomerization-metathesis protocol.
- Higman, Carolyn S.,De Araujo,Fogg, Deryn E.
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p. 2077 - 2084
(2016/04/26)
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- Nonredox Metal-Ion-Accelerated Olefin Isomerization by Palladium(II) Catalysts: Density Functional Theory (DFT) Calculations Supporting the Experimental Data
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Redox metal-ion-catalyzed olefin isomerization represents one of the important chemical processes. This work illustrates that nonredox metal ions can sharply accelerate Pd(II)-catalyzed olefin isomerization, while Pd(II) alone is very sluggish. Nuclear magnetic resonance (NMR) and ultraviolet-visible light (UV-vis) characterizations disclosed that the acceleration effect originates from the formation of heterobimetallic Pd(II) species with added nonredox metal ions, which improves the C-H activation capability of the Pd(II) moiety. Density functional theory (DFT) calculations further confirmed the sharp decrease of the energy barrier in C-H activation by the heterobimetallic Pd(II)/Al(III) species.
- Senan, Ahmed M.,Qin, Shuhao,Zhang, Sicheng,Lou, Chenling,Chen, Zhuqi,Liao, Rong-Zhen,Yin, Guochuan
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p. 4144 - 4148
(2016/07/12)
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- Copper-catalyzed semihydrogenation of internal alkynes with molecular hydrogen
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A copper-catalyzed system using a commercially available simple N-heterocyclic carbene ligand under atmospheric pressure of H2 (1 atm, balloon) enables the semihydrogenation of internal alkynes, which proceeds with high Z selectivity. Thus, this copper catalysis provides a useful method for the preparation of (Z)-alkenes from internal alkynes.
- Wakamatsu, Takamichi,Nagao, Kazunori,Ohmiya, Hirohisa,Sawamura, Masaya
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supporting information
p. 1354 - 1357
(2016/06/09)
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- Engineering P450 Peroxygenase to Catalyze Highly Enantioselective Epoxidation of cis-β-Methylstyrenes
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P450 119 peroxygenase and its site-directed mutants are discovered to catalyze the enantioselective epoxidation of methyl-substituted styrenes. Two new site-directed P450 119 mutants, namely T213Y and T213M, which were designed to improve the enantioselectivity and activity for the epoxidation of styrene and its methyl substituted derivatives, were studied. The T213M mutant is found to be the first engineered P450 peroxygenase that shows highly enantioselective epoxidation of cis-β-methylstyrenes, with up to 91 % ee. Molecular modeling studies provide insights into the different catalytic activity of the T213M mutant and the T213Y mutant in the epoxidation of cis-β-methylstyrene. The results of the calculations also contribute to a better understanding of the substrate specificity and configuration control for the regio- and stereoselective peroxygenation catalyzed by the T213M mutant.
- Zhang, Chun,Liu, Ping-Xian,Huang, Lu-Yi,Wei, Si-Ping,Wang, Li,Yang, Sheng-Yong,Yu, Xiao-Qi,Pu, Lin,Wang, Qin
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supporting information
p. 10969 - 10975
(2016/07/27)
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- Preparation of Vinyl Arenes by Nickel-Catalyzed Reductive Coupling of Aryl Halides with Vinyl Bromides
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This work emphasizes the synthesis of substituted vinyl arenes by reductive coupling of aryl halides with vinyl bromides under mild and easy-to-operate nickel-catalyzed reaction conditions. A broad range of aryl halides, including heteroaromatics, and vinyl bromides were employed to yielding products in moderate to excellent yields with high functional-group tolerance. The nickel-catalytic system displays good chemoselectivity between the two C(sp2)-halide coupling partners, thus demonstrating a mechanistic pathway distinct from other stepwise protocols.
- Liu, Jiandong,Ren, Qinghua,Zhang, Xinghua,Gong, Hegui
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supporting information
p. 15544 - 15548
(2016/12/09)
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- Direct Olefination of Alcohols with Sulfones by Using Heterogeneous Platinum Catalysts
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Carbon-supported Pt nanoparticles (Pt/C) were found to be effective heterogeneous catalysts for the direct Julia olefination of alcohols in the presence of sulfones and KOtBu under oxidant-free conditions. Primary alcohols, including aryl, aliphatic, allyl, and heterocyclic alcohols, underwent olefination with dimethyl sulfone and aryl alkyl sulfones to give terminal and internal olefins, respectively. Secondary alcohols underwent methylenation with dimethyl sulfone. Under 2.5 bar H2, the same reaction system was effective for the transformation of alcohol OH groups to alkyl groups. Structural and mechanistic studies of the terminal olefination system suggested that Pt0 sites on the Pt metal particles are responsible for the rate-limiting dehydrogenation of alcohols and that KOtBu may deprotonate the sulfone reagent. The Pt/C catalyst was reusable after the olefination, and this method showed a higher turnover number (TON) and a wider substrate scope than previously reported methods, which demonstrates the high catalytic efficiency of the present method. Olefination of alcohols: The first heterogeneous catalytic terminal and internal olefination of primary alcohols and methylenation of secondary alcohols with sulfones, a reusable carbon-supported Pt catalyst, and KOtBu is reported (see scheme).
- Hakim Siddiki,Touchy, Abeda Sultana,Kon, Kenichi,Shimizu, Ken-Ichi
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p. 6111 - 6119
(2016/04/26)
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- Photocatalytic synthesis of dihydrobenzofurans by oxidative [3+2] cycloaddition of phenols
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We report a protocol for oxidative [3+2] cycloadditions of phenols and alkenes applicable to the modular synthesis of a large family of dihydrobenzofuran natural products. Visible-light-activated transition metal photocatalysis enables the use of ammonium persulfate as an easily handled benign terminal oxidant. The broad range of organic substrates that are readily oxidized by photoredox catalysis suggests that this strategy may be applicable to a variety of useful oxidative transformations.
- Blum, Travis R.,Zhu, Ye,Nordeen, Sarah A.,Yoon, Tehshik P.
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supporting information
p. 11056 - 11059
(2015/03/30)
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- Tailoring flavins for visible light photocatalysis: organocatalytic [2+2] cycloadditions mediated by a flavin derivative and visible light
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A new application of flavin derivatives in visible light photocatalysis was found. 1-Butyl-7,8-dimethoxy-3-methylalloxazine, when irradiated by visible light, was shown to allow an efficient cyclobutane ring formation via an intramolecular [2+2] cycloaddition of both styrene dienes, considered as electron-rich substrates, and electron-poor bis(arylenones), presumably proceeding via an energy transfer mechanism.
- Mojr, Viktor,Svobodová, Eva,Straková, Karolína,Nevesely, Tomá?,Chudoba, Josef,Dvo?áková, Hana,Cibulka, Radek
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supporting information
p. 12036 - 12039
(2015/07/28)
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- Rhodium catalyzed aqueous biphasic hydroformylation of naturally occurring allylbenzenes in the presence of water-soluble phosphorus ligands
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The rhodium-catalyzed hydroformylation of eugenol was performed in aqueous biphasic systems using various water soluble phosphines: TPPTS (triphenylphosphinetrisulphonated); BDPPETS (bisdiphenylphosphinoethanetetrasulphonated), BDPPPTS (bisdiphenylphosphi
- Baricelli, Pablo J.,Rodriguez, Mariandry,Melean, Luis G.,Alonso, Maria Modro?o,Borusiak, Margarita,Rosales, Merlin,Gonzalez, Beatriz,De Oliveira, Kelley C. B.,Gusevskaya, Elena V.,Dos Santos, Eduardo N.
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p. 163 - 169
(2015/05/05)
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- Direct catalytic cross-coupling of alkenyllithium compounds
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A catalytic method for the direct cross-coupling of alkenyllithium reagents with aryl and alkenyl halides is described. The use of a catalyst comprising Pd2(dba)3/XPhos allows for the stereoselective preparation of a wide variety of substituted alkenes in high yields under mild conditions. In addition (1-ethoxyvinyl)lithium can be efficiently converted into substituted vinyl ethers which, after hydrolysis, give readily access to the corresponding methyl ketones in a one pot procedure.
- Hornillos, Valentn,Giannerini, Massimo,Vila, Carlos,Faans-Mastral, Martn,Feringa, Ben L.
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p. 1394 - 1398
(2015/02/19)
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- Z -selective alkene isomerization by high-spin cobalt(II) complexes
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The isomerization of simple terminal alkenes to internal isomers with Z-stereochemistry is rare, because the more stable E-isomers are typically formed. We show here that cobalt(II) catalysts supported by bulky β-diketiminate ligands have the appropriate kinetic selectivity to catalyze the isomerization of some simple 1-alkenes specifically to the 2-alkene as the less stable Z-isomer. The catalysis proceeds via an "alkyl" mechanism, with a three-coordinate cobalt(II) alkyl complex as the resting state. β-Hydride elimination and [1,2]-insertion steps are both rapid, as shown by isotopic labeling experiments. A steric model explains the selectivity through a square-planar geometry at cobalt(II) in the transition state for β-hydride elimination. The catalyst works not only with simple alkenes, but also with homoallyl silanes, ketals, and silyl ethers. Isolation of cobalt(I) or cobalt(II) products from reactions with poor substrates suggests that the key catalyst decomposition pathways are bimolecular, and lowering the catalyst concentration often improves the selectivity. In addition to a potentially useful, selective transformation, these studies provide a mechanistic understanding for catalytic alkene isomerization by high-spin cobalt complexes, and demonstrate the effectiveness of steric bulk in controlling the stereoselectivity of alkene formation.
- Chen, Chi,Dugan, Thomas R.,Brennessel, William W.,Weix, Daniel J.,Holland, Patrick L.
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supporting information
p. 945 - 955
(2014/02/14)
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- Alkene isomerisation catalysed by a ruthenium PNN pincer complex
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The [Ru(CO)H(PNN)] pincer complex based on a dearomatised PNN ligand (PNN: 2-di-tert-butylphosphinomethyl-6-diethylaminomethylpyridine) was examined for its ability to isomerise alkenes. The isomerisation reaction proceeded under mild conditions after activation of the complex with alcohols. Variable-temperature (VT) NMR experiments to investigate the role of the alcohol in the mechanism lend credence to the hypothesis that the first step involves the formation of a rearomatised alkoxide complex. In this complex, the hemilabile diethylamino side-arm can dissociate, allowing alkene binding cis to the hydride, enabling insertion of the alkene into the metal-hydride bond, whereas in the parent complex only trans binding is possible. During this study, a new uncommon Ru0 coordination complex was also characterised. The scope of the alkene isomerisation reaction was examined. The catalyst tested positive! A dearomatised ruthenium PNN (2-di-tert-butylphosphinomethyl-6-diethylaminomethylpyridine) pincer complex, [Ru(CO)H(PNN)], was evaluated as an alkene isomerisation catalyst. The isomerisation reaction was greatly accelerated by the addition of alcohols, in particular isopropanol. Isomerisation of terminal to internal alkenes took place at room temperature. A mechanism was proposed based on variable-temperature NMR spectroscopy.
- Perdriau, Sébastien,Chang, Mu-Chieh,Otten, Edwin,Heeres, Hero J.,De Vries, Johannes G.
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supporting information
p. 15434 - 15442
(2016/02/18)
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- Co2(CO)8-mediated Selective Reductions of Propargyl Alcohol Derivatives to Alkenes
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In the presence of Co2(CO)8 and additives, propargyl alcohol derivatives could be reduced to alkenes in moderate to good yield. The selectivity of this reaction could be controlled by adding different additives: with H2O as the additive, the major configuration of product is Z-alkene; with CF3COOH as the additive, the major configuration of product is E-alkene.
- Dou, Ying,Xing, Ping,Huang, Zuogang,Jiang, Biao
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p. 999 - 1002
(2016/02/18)
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- METHODS FOR PHOSPHINE OXIDE REDUCTION IN CATALYTIC WITTIG REACTIONS
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A method for increasing the rate of phosphine oxide reduction, preferably during a Wittig reaction comprising use of an acid additive is provided. A room temperature catalytic Wittig reaction (CWR) the rate of reduction of the phosphine oxide is increased due to the addition of the acid additive is described. Furthermore, the extension of the CWR to semi-stabilized and non-stabilized ylides has been accomplished by utilization of a masked base and/or ylide-tuning.
- -
-
Page/Page column 59; 68
(2014/09/29)
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- Catalytic wittig reactions of semi- and nonstabilized ylides enabled by ylide tuning
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The first examples of catalytic Wittig reactions with semistabilized and nonstabilized ylides are reported. These reactions were enabled by utilization of a masked base, sodium tert-butyl carbonate, and/or ylide tuning. The acidity of the ylide-forming proton was tuned by varying the electron density at the phosphorus center in the precatalyst, thus facilitating the use of relatively mild bases. Steric modification of the precatalyst structure resulted in significant enhancement of E selectivity up to >95:5, E/Z. Time for a tune up: Catalytic Wittig reactions with semi- and nonstabilized ylides were enabled by use of a masked base (NaOCO2tBu) and/or ylide tuning. The acidity of the ylide-forming proton was tuned by varying the electron density at the P center in the precatalyst, thus facilitating the use of relatively mild bases. Steric modification of the precatalyst structure resulted in significant enhancement of E selectivity.
- Coyle, Emma E.,Doonan, Bryan J.,Holohan, Andrew J.,Walsh, Killian A.,Lavigne, Florie,Krenske, Elizabeth H.,O'Brien, Christopher J.
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supporting information
p. 12907 - 12911
(2016/02/18)
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- Use of silver carbonate in the Wittig reaction
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An efficient synthesis of olefins by the coupling of stabilized, semistabilized, and nonstabilized phosphorus ylides with various carbonyl compounds in the presence of silver carbonate is reported. Wittig olefination of aromatic, heteroaromatic, and aliphatic aldehydes (yields >63%) and a ketone (yield 42%) are demonstrated. These reactions proceed overnight at room temperature, under weakly basic conditions, and as such extend the applicability of the Wittig reaction to base-sensitive reactants.
- Jedinak, Lukas,Rush, Latoya,Lee, Mijoon,Hesek, Dusan,Fisher, Jed F.,Boggess, Bill,Noll, Bruce C.,Mobashery, Shahriar
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p. 12224 - 12228
(2014/01/06)
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- Benign catalysis with iron: Unique selectivity in catalytic isomerization reactions of olefins
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The use of noble metal catalysts in homogeneous catalysis has been well established. Due to their price and limited availability, there is growing interest in the substitution of such precious metal complexes with readily available and bio-relevant catalysts. In particular, iron is a "rising star" in catalysis. Herein, we present a general and selective iron-catalyzed monoisomerization of olefins, which allows for the selective generation of 2-olefins. Typically, common metal complexes give mixtures of various internal olefins. Both bulk-scale terminal olefins and functionalized terminal olefins give the corresponding products under mild conditions in good to excellent yields. The proposed reaction mechanism was elucidated by in situ NMR studies and supported by DFT calculations and extended X-ray absorption fine structure (EXAFS) measurements.
- Jennerjahn, Reiko,Jackstell, Ralf,Piras, Irene,Franke, Robert,Jiao, Haijun,Bauer, Matthias,Beller, Matthias
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experimental part
p. 734 - 739
(2012/06/04)
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- Catalytic isomerization of hydrophobic allylarenes in aqueous microemulsions
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In the course of our attempts to replace the traditional but environmentally disfavored organic solvents in organic processes by water, we studied the double bond isomerization of hydrophobic allylarenes, in aqueous microemulsions. The catalyst for these reactions was the rhodium-trichloride- Aliquat 336 ion pair encaged within hydrophobic silica sol-gel. During the entrapment of the rhodium compound, it was converted into supported catalytically active Rh(0) nanoparticles characterized by TEM and XPS studies. The transformations of the allylarenes to (E)- and (Z)-1-phenyl-1-propenes follows the first order rate law, and proved to be significantly affected by the electronic nature of the substrates and by the hydrophobicity of the sol-gel support. Upon completion of the isomerization the catalyst could be recovered and recycled at least six times without a decrease in the catalytic activity after the first catalytic run.
- Meltzer, Diana,Avnir, David,Fanun, Monzer,Gutkin, Vitaly,Popov, Inna,Schom?cker, Reinhard,Schwarze, Michael,Blum, Jochanan
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experimental part
p. 8 - 13
(2011/04/15)
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- Ruthenium(iv) catalysts for the selective estragole to trans-anethole isomerization in environmentally friendly media
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Several ruthenium(iv) complexes have been tested as potential catalysts for the isomerization of estragole into anethole using water and glycerol as alternative green reaction media. Best results in terms of activity and E-selectivity were obtained with the dimeric species [{RuCl(μ-Cl) (η3:η3-C10H16)} 2] (C10H16 = 2,7-dimethylocta-2,6-diene-1,8- diyl) and the mononuclear derivative [RuCl2(η3: η3-C10H16){P(OMe)3}]. In particular, using a ruthenium loading of 1 mol%, almost quantitative and stereoselective formation of trans-anethole (trans/cis ratios = 99:1) could be reached at 80°C in short times (5-30 min) employing water-MeOH (EtOH) or glycerol-MeOH (EtOH) mixtures (1:1 v/v) as solvent. Recyclability issues have also been addressed.
- Lastra-Barreira, Beatriz,Francos, Javier,Crochet, Pascale,Cadierno, Victorio
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experimental part
p. 307 - 313
(2011/04/17)
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- Nickel-catalyzed cross-coupling of organogold reagents
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Organogold compounds undergo nickel-catalyzed cross-coupling reactions with aryl and vinyl bromides in high yield under mild conditions. The reaction tolerates both electron-rich and electron-poor organogold complexes, and olefinic bromides undergo cross-coupling with high stereoselectivity. This novel transformation links well-established nickel catalysis with more recent developments in organogold transformations.
- Hirner, Joshua J.,Blum, Suzanne A.
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scheme or table
p. 1299 - 1302
(2011/04/22)
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- Efficient double bond migration of allylbenzenes catalyzed by Pd(OAc) 2-HFIP system with unique substituent effect
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A novel catalyst system of Pd(OAc)2-HFIP induces double-bond migration of allylbenzenes under mild conditions with low catalytic loading to afford 1-propenylbenzenes. The reaction shows a unique substituent effect that is highly dependent on the distance of substituents from the allylic moiety. Thus, the reactivity of substrates bearing a methyl group is ordered in para > meta > ortho, whereas it is entirely reversed as ortho > meta > para for methoxy and chloro substituents.
- Nishiwaki, Nagatoshi,Kamimura, Ryuichiro,Shono, Kimihiro,Kawakami, Toshihiko,Nakayama, Katsuhisa,Nishino, Kohei,Nakayama, Takayuki,Takahashi, Keisuke,Nakamura, Aki,Hosokawa, Takahiro
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supporting information; experimental part
p. 3590 - 3592
(2010/08/19)
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- Ruthenium containing hydrotalcite as a solid base catalyst for >C{double bond, long}C< double bond isomerization in perfumery chemicals
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Ruthenium containing hydrotalcite (Ru-Mg-Al) is used as a solid base catalyst for >C{double bond, long}C2 and Ru-alumina for isomerization of methyl chavicol to trans-anethole. Ru-Mg-Al catalyst was reused four times without loss in its activity, however, significant loss in the conversion of methyl chavicol and selectivity of trans-anethole was observed on reusability of other ruthenium impregnated catalysts. The conversion of methyl chavicol and selectivity of trans-anethole was found to increase on increasing the reaction temperature as well as amount of catalyst. At 0.005 g catalyst amount, 55% conversion of methyl chavicol with 68% selectivity of trans-anethole was observed that increased to 93% with 82% selectivity of trans-anethole at 0.05 g catalyst amount. On further increase in the amount of catalyst to 1 g, conversion increased to 98% with 88% selectivity of trans-anethole.
- Sharma, Sumeet K.,Parikh, Parimal A.,Jasra, Raksh V.
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experimental part
p. 27 - 33
(2010/04/28)
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- Ruthenium-catalyzed estragole isomerization: High trans-selective formation of anethole
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Complexes [RuCl2(η6-C6H 5OCH2CH2OH)(L)] (L = P(OMe)3 (1a), P(OEt)3 (1b), P(OiPr)3 (1c), P(OPh)3 (1d), PPh3 (1e)) have shown to be efficient catalysts for the isomerization of estragole into anethole, the best activities being obtained in polar solvents (water, methanol, ethanol). Interestingly, a complete selectivity toward trans-anethole could be reached under smooth conditions (80 °C) and in very short times (5-15 min). The catalytic experiments have been performed both under conventional and microwave heating, reaction rates being significantly enhanced under the latter conditions. The Royal Society of Chemistry 2010.
- Lastra-Barreira, Beatriz,Crochet, Pascale
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experimental part
p. 1311 - 1314
(2010/11/04)
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- Anethole isomerization and dimerization induced by acid sites or UV irradiation
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The formation of cis-anethole and various dimers as a result of the exposure of trans-anethole to microporous solid acids (dealuminated HY zeolites), or UV-Vis irradiation was established by means of high resolution gas chromatography coupled to mass spectrometry. 3,4-bis-(4-Methoxyphenyl)-(E)-hex- 2-ene was the most abundant compound among eight different methoxyphenyl- disubstituted hexenes produced by electrophilic addition and elimination reactions induced by HY zeolites. (1a,2a,3b,4b)-1,2-bis(4-Methoxyphenyl)-3,4- dimethylcyclobutane was the principal component in the mixture of 5 methoxyphenyl-disubstituted cyclobutanes found, together with cis-anethole, after UV-Vis irradiation of a trans-anethole solution in toluene.
- Castro, Hans T.,Martinez, Jairo Rene,Stashenko, Elena
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experimental part
p. 5012 - 5030
(2010/10/21)
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- Role of the methoxy group in product formation via TiCl 4 promoted 4-phenyldioxolane isomerizations
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The product distribution obtained from the TiCl 4 initiated intramolecular isomerizations of 4-methoxyphenyl-and trimethoxyphenyldioxolanes at -78 °C, -30 °C and 0 °C provided insights into the important regiochemical role played by these groups in such Mukaiyama-type rearrangements through their resonance effects on the aryl ring of the dioxolanes. ARKAT USA, Inc.
- Green, Ivan R.,October, Natasha
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experimental part
p. 71 - 96
(2010/07/20)
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- Fast and green microwave-Assisted conversion of essential oil allylbenzenes into the corresponding aldehydes via alkene isomerization and subsequent potassium permanganate promoted oxidative alkene group cleavage
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Essential oil allylbenzenes from have been converted quickly and efficiently into the corresponding benzaldehydes in good yields by a two-step "green" reaction pathway based on a solventless alkene group isomerization by KF/Al2O3 to form the corresponding l-arylpropene and a subsequent solventless oxidation of the latter to the corresponding benzaldehyde by KMnO4/CuSO4-5H2O. The assistance by microwave irradiation results in very short reaction times (2O3 under solvent-free conditions, respectively.
- Luu, Thi Xuan Thi,Lam, Trinh To,Le, Thach Ngoc,Duus, Fritz
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experimental part
p. 3411 - 3424
(2010/01/16)
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- Stereoselective synthesis of 3-alkyl-2-aryltetrahydrofuran-4-ols: Total synthesis of (±)-paulownin
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(Chemical Equation Presented) A formal [3 + 2]-cycloaddition involving the Lewis acid mediated reaction of α-silyloxy aldehydes and styrenes to afford 3-alkyl-2-aryltetrahydrofuran-4-ols has been developed. This methodology was applied to the total synthesis of the naturally occurring furofuran lignan (±)-paulownin.
- Angle, Steven R.,Choi, Inchang,Tham, Fook S.
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p. 6268 - 6278
(2008/12/22)
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- Stereoselective Wittig olefination reactions employing a novel ortho-P-aryl alkoxide effect
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Non-stabilized ortho-P-alkoxy-substituted ylides react with aromatic and aliphatic aldehydes providing (E)-olefins with high stereocontrol, also allowing easy phosphine oxide removal in certain cases.
- McNulty, James,Keskar, Kunal
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experimental part
p. 7054 - 7057
(2009/04/07)
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