- Surfactant-Free Palladium Nanoparticles Encapsulated in ZIF-8 Hollow Nanospheres for Size-Selective Catalysis in Liquid-Phase Solution
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Encapsulation of surfactant-free Pd nanoparticles (NPs) in the metal–organic framework material ZIF-8 hollow nanospheres was achieved. Pd@ZIF-8 hollow nanospheres showed excellent size-selective catalytic properties in the liquid-phase hydrogenation of olefins. As a result of the uniform pore size of the ZIF-8 shell (apertures of 3.4 ?), the catalyst showed high activity for the hydrogenation of 1-hexene (1.9×8.2 ?) but very low activity for larger molecules such as cis-cyclooctene (5.3×5.5 ?), trans-stilbene (4.2×11.3 ?), and triphenylethylene (9.1×9.2 ?). Other surfactant-free noble-metal nanoparticles could also be employed to produce NPs@MOFs for catalysis.
- Wang, Xiaoshi,Li, Mingyu,Cao, Changyan,Liu, Chang,Liu, Jian,Zhu, Yanan,Zhang, Sidi,Song, Weiguo
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- A facile and versatile electro-reductive system for hydrodefunctionalization under ambient conditions
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A general electrochemical system for reductive hydrodefunctionalization is described, employing the inexpensive and easily available triethylamine (Et3N) as a sacrificial reductant. This protocol is characterized by facile operation, sustainable conditions, and exceptionally wide substrate scope covering the cleavage of C-halogen, N-S, N-C, O-S, O-C, C-C and C-N bonds. Notably, the selectivity and capability of reduction can be conveniently switched by simple incorporation or removal of an alcohol as a co-solvent.
- Huang, Binbin,Guo, Lin,Xia, Wujiong
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supporting information
p. 2095 - 2103
(2021/03/26)
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- Photo-induced thiolate catalytic activation of inert Caryl-hetero bonds for radical borylation
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Substantial effort is currently being devoted to obtaining photoredox catalysts with high redox power. Yet, it remains challenging to apply the currently established methods to the activation of bonds with high bond dissociation energy and to substrates with high reduction potentials. Herein, we introduce a novel photocatalytic strategy for the activation of inert substituted arenes for aryl borylation by using thiolate as a catalyst. This catalytic system exhibits strong reducing ability and engages non-activated Caryl–F, Caryl–X, Caryl–O, Caryl–N, and Caryl–S bonds in productive radical borylation reactions, thus expanding the available aryl radical precursor scope. Despite its high reducing power, the method has a broad substrate scope and good functional-group tolerance. Spectroscopic investigations and control experiments suggest the formation of a charge-transfer complex as the key step to activate the substrates.
- K?nig, Burkhard,Wang, Hua,Wang, Shun
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supporting information
p. 1653 - 1665
(2021/06/17)
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- Metallic Barium: A Versatile and Efficient Hydrogenation Catalyst
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Ba metal was activated by evaporation and cocondensation with heptane. This black powder is a highly active hydrogenation catalyst for the reduction of a variety of unactivated (non-conjugated) mono-, di- and tri-substituted alkenes, tetraphenylethylene, benzene, a number of polycyclic aromatic hydrocarbons, aldimines, ketimines and various pyridines. The performance of metallic Ba in hydrogenation catalysis tops that of the hitherto most active molecular group 2 metal catalysts. Depending on the substrate, two different catalytic cycles are proposed. A: a classical metal hydride cycle and B: the Ba metal cycle. The latter is proposed for substrates that are easily reduced by Ba0, that is, conjugated alkenes, alkynes, annulated rings, imines and pyridines. In addition, a mechanism in which Ba0 and BaH2 are both essential is discussed. DFT calculations on benzene hydrogenation with a simple model system (Ba/BaH2) confirm that the presence of metallic Ba has an accelerating effect.
- Stegner, Philipp,F?rber, Christian,Zenneck, Ulrich,Knüpfer, Christian,Eyselein, Jonathan,Wiesinger, Michael,Harder, Sjoerd
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supporting information
p. 4252 - 4258
(2020/12/22)
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- HIGHLY SELECTIVE ELECTROCHEMICAL HYDROGENATION OF ALKYNES
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Disclosed are electrochemical methods to prepare an alkane or an alkene, such as a cis- alkene, from an alkyne, or an alkane from an alkene. The method utilizes an electrochemical cell having a cathode and an anode and a reactor.
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Page/Page column 7
(2020/10/20)
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- Nitrenium Salts in Lewis Acid Catalysis
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Molecular compounds featuring nitrogen atoms are typically regarded as Lewis bases and are extensively employed as donor ligands in coordination chemistry or as nucleophiles in organic chemistry. By contrast, electrophilic nitrogen-containing compounds are much rarer. Nitrenium cations are a new family of nitrogen-based Lewis acids, the reactivity of which remains largely unexplored. In this work, nitrenium ions are explored as catalysts in five organic transformations. These reactions are the first examples of Lewis acid catalysis employing nitrogen as the site of substrate activation. Moreover, these compounds are readily accessed from commercially available reagents and exhibit remarkable stability toward moisture, allowing for benchtop transformations without the need to pretreat solvents.
- Mehta, Meera,Goicoechea, Jose M.
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p. 2715 - 2719
(2020/01/24)
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- Highly Active Superbulky Alkaline Earth Metal Amide Catalysts for Hydrogenation of Challenging Alkenes and Aromatic Rings
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Two series of bulky alkaline earth (Ae) metal amide complexes have been prepared: Ae[N(TRIP)2]2 (1-Ae) and Ae[N(TRIP)(DIPP)]2 (2-Ae) (Ae=Mg, Ca, Sr, Ba; TRIP=SiiPr3, DIPP=2,6-diisopropylphenyl). While monomeric 1-Ca was already known, the new complexes have been structurally characterized. Monomers 1-Ae are highly linear while the monomers 2-Ae are slightly bent. The bulkier amide complexes 1-Ae are by far the most active catalysts in alkene hydrogenation with activities increasing from Mg to Ba. Catalyst 1-Ba can reduce internal alkenes like cyclohexene or 3-hexene and highly challenging substrates like 1-Me-cyclohexene or tetraphenylethylene. It is also active in arene hydrogenation reducing anthracene and naphthalene (even when substituted with an alkyl) as well as biphenyl. Benzene could be reduced to cyclohexane but full conversion was not reached. The first step in catalytic hydrogenation is formation of an (amide)AeH species, which can form larger aggregates. Increasing the bulk of the amide ligand decreases aggregate size but it is unclear what the true catalyst(s) is (are). DFT calculations suggest that amide bulk also has a noticeable influence on the thermodynamics for formation of the (amide)AeH species. Complex 1-Ba is currently the most powerful Ae metal hydrogenation catalyst. Due to tremendously increased activities in comparison to those of previously reported catalysts, the substrate scope in hydrogenation catalysis could be extended to challenging multi-substituted unactivated alkenes and even to arenes among which benzene.
- Eyselein, Jonathan,F?rber, Christian,Grams, Samuel,Harder, Sjoerd,Knüpfer, Christian,Langer, Jens,Martin, Johannes,Thum, Katharina,Wiesinger, Michael
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supporting information
p. 9102 - 9112
(2020/03/30)
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- Birch-Type Photoreduction of Arenes and Heteroarenes by Sensitized Electron Transfer
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The direct reduction of arenes and heteroarenes by visible-light irradiation remains challenging, as the energy of a single photon is not sufficient for breaking aromatic stabilization. Shown herein is that the energy accumulation of two visible-light photons allows the dearomatization of arenes and heteroarenes. Mechanistic investigations confirm that the combination of energy-transfer and electron-transfer processes generates an arene radical anion, which is subsequently trapped by hydrogen-atom transfer and finally protonated to form the dearomatized product. The photoreduction converts planar aromatic feedstock compounds into molecular skeletons that are of use in organic synthesis.
- Chatterjee, Anamitra,K?nig, Burkhard
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supporting information
p. 14289 - 14294
(2019/08/30)
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- Cobalt-Catalyzed Hydrogenations via Olefin Cobaltate and Hydride Intermediates
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Redox noninnocent ligands are a promising tool to moderate electron transfer processes within base-metal catalysts. This report introduces bis(imino)acenaphthene (BIAN) cobaltate complexes as hydrogenation catalysts. Sterically hindered trisubstituted alkenes, imines, and quinolines underwent clean hydrogenation under mild conditions (2-10 bar, 20-80 °C) by use of the stable catalyst precursor [(DippBIAN)CoBr2] and the cocatalyst LiEt3BH. Mechanistic studies support a homogeneous catalysis pathway involving alkene and hydrido cobaltates as active catalyst species. Furthermore, considerable reaction acceleration by alkali cations and Lewis acids was observed. The dinuclear hydridocobaltate anion with bridging hydride ligands was isolated and fully characterized.
- Sandl, Sebastian,Maier, Thomas M.,Van Leest, Nicolaas P.,Kr?ncke, Susanne,Chakraborty, Uttam,Demeshko, Serhiy,Koszinowski, Konrad,De Bruin, Bas,Meyer, Franc,Bodensteiner, Michael,Herrmann, Carmen,Wolf, Robert,Von Jacobi Wangelin, Axel
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p. 7596 - 7606
(2019/08/20)
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- Electrochemical Hydrogenation with Gaseous Ammonia
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As a carbon-free and sustainable fuel, ammonia serves as high-energy-density hydrogen-storage material. It is important to develop new reactions able to utilize ammonia as a hydrogen source directly. Herein, we report an electrochemical hydrogenation of alkenes, alkynes, and ketones using ammonia as the hydrogen source and carbon electrodes. A variety of heterocycles and functional groups, including for example sulfide, benzyl, benzyl carbamate, and allyl carbamate were well tolerated. Fast stepwise electron transfer and proton transfer processes were proposed to account for the transformation.
- Li, Jin,He, Lingfeng,Liu, Xu,Cheng, Xu,Li, Guigen
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supporting information
p. 1759 - 1763
(2019/01/16)
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- Amine-Borane Dehydrogenation and Transfer Hydrogenation Catalyzed by α-Diimine Cobaltates
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Anionic α-diimine cobalt complexes, such as [K(thf)1.5{(DippBIAN)Co(η4-cod)}] (1; Dipp=2,6-diisopropylphenyl, cod=1,5-cyclooctadiene), catalyze the dehydrogenation of several amine-boranes. Based on the excellent catalytic properties, an especially effective transfer hydrogenation protocol for challenging olefins, imines, and N-heteroarenes was developed. NH3BH3 was used as a dihydrogen surrogate, which transferred up to two equivalents of H2 per NH3BH3. Detailed spectroscopic and mechanistic studies are presented, which document the rate determination by acidic protons in the amine-borane.
- Maier, Thomas M.,Sandl, Sebastian,Shenderovich, Ilya G.,Jacobi von Wangelin, Axel,Weigand, Jan J.,Wolf, Robert
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supporting information
p. 238 - 245
(2019/01/04)
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- Engineering channels of metal-organic frameworks to enhance catalytic selectivity
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This report describes a facile strategy to enhance the catalytic selectivity by tuning the pore sizes of metal-organic frameworks (MOFs) in nanoparticles (NPs)/MOF composite catalysts. A general post-synthetic modification method was used to adjust the pore sizes of MOFs by using anhydrides with different chain lengths to react with amino groups in the ligands. The modified NPs/MOF catalysts exhibited enhanced size selectivity performance in the hydrogenation of olefins, which revealed the flexibility of MOFs as supporting materials for heterogeneous catalysis.
- Liu, Ye,Shen, Yu,Zhang, Weina,Weng, Jiena,Zhao, Meiting,Zhu, Tingshun,Chi, Yonggui Robin,Yang, Yanhui,Zhang, Hua,Huo, Fengwei
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supporting information
p. 11770 - 11773
(2019/10/02)
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- Biomolecule-derived supported cobalt nanoparticles for hydrogenation of industrial olefins, natural oils and more in water
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Catalytic hydrogenation of olefins using noble metal catalysts or pyrophoric RANEY nickel is of high importance in the chemical industry. From the point of view of green and sustainable chemistry, design and development of Earth-abundant, less toxic, and more environmentally friendly catalysts are highly desirable. Herein, we report the convenient preparation of active cobalt catalysts and their application in hydrogenations of a wide range of terminal and internal carbon-carbon double bonds in water under mild conditions. Catalysts are prepared on multi-gram scale by pyrolysis of cobalt acetate and uracil, guanine, adenine or l-tryptophan. The most active material Co-Ura/C-600 showed good productivity in industrially relevant hydrogenation of diisobutene to isooctane and in natural oil hardening.
- Pews-Davtyan, Anahit,Scharnagl, Florian Korbinian,Hertrich, Maximilian Franz,Kreyenschulte, Carsten,Bartling, Stephan,Lund, Henrik,Jackstell, Ralf,Beller, Matthias
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supporting information
p. 5104 - 5112
(2019/09/30)
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- Olefin-Stabilized Cobalt Nanoparticles for C=C, C=O, and C=N Hydrogenations
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The development of cobalt catalysts that combine easy accessibility and high selectivity constitutes a promising approach to the replacement of noble-metal catalysts in hydrogenation reactions. This report introduces a user-friendly protocol that avoids complex ligands, hazardous reductants, special reaction conditions, and the formation of highly unstable pre-catalysts. Reduction of CoBr2 with LiEt3BH in the presence of alkenes led to the formation of hydrogenation catalysts that effected clean conversions of alkenes, carbonyls, imines, and heteroarenes at mild conditions (3 mol % cat., 2–10 bar H2, 20–80 °C). Poisoning studies and nanoparticle characterization by TEM, EDX, and DLS supported the notion of a heterotopic catalysis mechanism.
- Sandl, Sebastian,Schwarzhuber, Felix,P?llath, Simon,Zweck, Josef,Jacobi von Wangelin, Axel
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supporting information
p. 3403 - 3407
(2018/02/13)
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- Application of Silicon-Initiated Water Splitting for the Reduction of Organic Substrates
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The use of water as a donor for hydrogen suitable for the reduction of several important classes of organic compounds is described. It is found that the reductive water splitting can be promoted by several metalloids among which silicon shows the best efficiency. The developed methodologies were applied for the reduction of nitro compounds, N-oxides, sulfoxides, alkenes, alkynes, hydrodehalogenation as well as for the gram-scale synthesis of several substrates of industrial importance.
- Gevorgyan, Ashot,Mkrtchyan, Satenik,Grigoryan, Tatevik,Iaroshenko, Viktor O.
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p. 375 - 382
(2018/06/04)
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- Catalytic Use of Low-Valent Cationic Gallium(I) Complexes as π-Acids
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Transformations of alkene and alkyne substrates relevant to π-Lewis acid catalysis have been performed using low-valent Ga(I) species for the first time. [Ga(I)(PhF)2]+[Al(ORF)4]? and gallium dichloride (i. e. [Ga(I)]+[GaCl4]?) proved to be efficient catalysts for cycloisomerizations, Friedel-Crafts reactions, transfer hydrogenations, and reductive hydroarylations. Their activity is compared to more common Ga(III) complexes. This study shows that even the readily available and yet overlooked gallium dichloride salt can be a more active π-Lewis acid catalyst than gallium trichloride or other Ga(III) species. (Figure presented.).
- Li, Zhilong,Thiery, Guillaume,Lichtenthaler, Martin R.,Guillot, Régis,Krossing, Ingo,Gandon, Vincent,Bour, Christophe
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supporting information
p. 544 - 549
(2017/11/27)
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- A Manganese Nanosheet: New Cluster Topology and Catalysis
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While the coordination chemistry of monometallic complexes and the surface characteristics of larger metal particles are well understood, preparations of molecular metallic nanoclusters remain a great challenge. Discrete planar metal clusters constitute nanoscale snapshots of cluster growth but are especially rare owing to the strong preference for three-dimensional structures and rapid aggregation or decomposition. A simple ligand-exchange procedure has led to the formation of a novel heteroleptic Mn6 nanocluster that crystallized in an unprecedented flat-chair topology and exhibited unique magnetic and catalytic properties. Magnetic susceptibility studies documented strong electronic communication between the manganese ions. Reductive activation of the molecular Mn6 cluster enabled catalytic hydrogenations of alkenes, alkynes, and imines.
- Chakraborty, Uttam,Reyes-Rodriguez, Efrain,Demeshko, Serhiy,Meyer, Franc,Jacobi von Wangelin, Axel
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supporting information
p. 4970 - 4975
(2018/03/28)
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- Recyclable cobalt(0) nanoparticle catalysts for hydrogenations
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The search for new hydrogenation catalysts that replace noble metals is largely driven by sustainability concerns and the distinct mechanistic features of 3d transition metals. Several combinations of cobalt precursors and specific ligands in the presence of reductants or under high-thermal conditions were reported to provide active hydrogenation catalysts. This study reports a new method of preparation of small, monodisperse Co(0) nanoparticles (3-4 nm) from the reduction of commercial CoCl2 in the absence of ligands or surfactants. High catalytic activity was observed in hydrogenations of alkenes, alkynes, imines, and heteroarenes (2-20 bar H2). The magnetic properties enabled catalyst separation and multiple recyclings.
- Büschelberger, Philipp,Reyes-Rodriguez, Efrain,Sch?ttle, Christian,Treptow, Jens,Feldmann, Claus,Jacobi Von Wangelin, Axel,Wolf, Robert
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p. 2648 - 2653
(2018/05/30)
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- Ni-Catalyzed Reductive Cross-Coupling of Amides with Aryl Iodide Electrophiles via C-N Bond Activation
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A Ni-catalyzed reductive cross-coupling reaction between two electrophiles, amides and aryl iodides, has been developed. This work is the first example using amide as an electrophile to couple with another electrophile, instead of using highly basic and pyrophoric nucleophiles. Furthermore, the Ni catalyst chemoselectively inserting the C-N bond of amide triggered the reductive cross-coupling reaction, which solves the problem that the Ni catalyst preferentially inserts the more reactive C-I bond to form a self-coupling product.
- Ni, Shengyang,Zhang, Wenzhong,Mei, Haibo,Han, Jianlin,Pan, Yi
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supporting information
p. 2536 - 2539
(2017/05/24)
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- Synthesis and Catalysis of Redox-Active Bis(imino)acenaphthene (BIAN) Iron Complexes
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Reactions of various substituted bis(imino)acenaphthenes (R-BIANs) with FeCl2(thf)1.5 afforded the tetrahedral complexes (R-BIAN)FeCl2 (2) from bulky α-diimines and the octahedral complexes [Fe(R-BIAN)3][FeCl4]2 (3) from less bulky ligands. The driving force for the formation of complexes 3 is the high ligand-field stabilization of the low-spin FeII center. The two sets of complexes exhibit distinct charge-transfer band intensities and redox activities. (R-BIAN)FeCl2 complexes showed reversible ligand-centered reductions at ?0.9 V (vs. FcH/FcH+; FcH: ferrocene); further reduction led to decomposition. Irreversible oxidations were observed at 0.2 and 0.4 V, associated with a reduction at ?0.4 V, as well as a ligand-centered redox event at 1.0 V. First applications of the Fe(BIAN) complexes to hydrogenations of alkenes indicated good catalytic activity under mild conditions.
- Villa, Matteo,Miesel, Dominique,Hildebrandt, Alexander,Ragaini, Fabio,Schaarschmidt, Dieter,Jacobi von Wangelin, Axel
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p. 3203 - 3209
(2017/08/29)
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- Alkene Hydrogenations by Soluble Iron Nanocluster Catalysts
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The replacement of noble metal technologies and the realization of new reactivities with earth-abundant metals is at the heart of sustainable synthesis. Alkene hydrogenations have so far been most effectively performed by noble metal catalysts. This study reports an iron-catalyzed hydrogenation protocol for tri- and tetra-substituted alkenes of unprecedented activity and scope under mild conditions (1–4 bar H2, 20 °C). Instructive snapshots at the interface of homogeneous and heterogeneous iron catalysis were recorded by the isolation of novel Fe nanocluster architectures that act as catalyst reservoirs and soluble seeds of particle growth.
- Gieshoff, Tim N.,Chakraborty, Uttam,Villa, Matteo,Jacobi von Wangelin, Axel
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supporting information
p. 3585 - 3589
(2017/03/21)
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- Reductive cross-coupling of conjugated arylalkenes and aryl bromides with hydrosilanes by cooperative palladium/copper catalysis
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A method for the reductive cross-coupling of conjugated arylalkenes and aryl bromides with hydrosilanes by cooperative palladium/copper catalysis was developed, thus resulting in the highly regioselective formation of various 1,1-diarylalkanes, including a biologically active molecule. Under the applied reaction conditions, high levels of functional-group tolerance were observed, and the reductive cross-coupling of internal alkynes with aryl bromides afforded trisubstituted alkenes. Forming a Co-op: A method for the reductive cross-coupling of conjugated arylalkenes or internal alkynes and aryl bromides with hydrosilanes using cooperative palladium/copper catalysis was developed. The resulting 1,1-diarylalkanes and trisubstituted alkenes were isolated with high regio- and stereoselectivity. Under the applied reaction conditions, high levels of functional-group tolerance were observed.
- Semba, Kazuhiko,Ariyama, Kenta,Zheng, Hong,Kameyama, Ryohei,Sakaki, Shigeyoshi,Nakao, Yoshiaki
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supporting information
p. 6275 - 6279
(2016/05/24)
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- Sterically congested phosphonium borate acids as effective Br?nsted acid catalysts
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Phosphonium borate acids [HPPh2(C6F5)][B(C6F5)4] (2), [HPMes2(C6F5)][B(C6F5)4] (3) and [HPMes(C6F5)2][B(C6F5)4] (4) were synthesized via heterolytic dihydrogen cleavage in the presence of triisopropylsilylium and characterized by spectroscopic and crystallographic methods. Br?nsted acid catalysis using compounds 2–4 proved to be efficient for a number of challenging reactions (namely ionic hydrogenation, hydroamination and hydroarylation), owing to the restrained nucleophilicity of the sterically hindered conjugate bases. Reactivity of compounds 2–4 suggests that their pKavalues are similar to that of diethyl oxonium acid.
- Sinha, Arup,Jaiswal, Amit K.,Young, Rowan D.
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- Decomposition of lignin model compounds by Lewis acid catalysts in water and ethanol
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The conversion of benzyl phenyl ether, diphenyl ether, diphenyl methane and biphenyl as representative model compounds for α-O4, 5-O4, α 1 (methylene bridges) and 5-5′ lignin linkages was investigated. We compared the use of metal chlorides and acetates. The reactions were studied in sub- and supercritical water and supercritical ethanol between 300 and 400 °C. At low temperature in water, Lewis acids mainly catalyzed condensation of hydrolysis products of the dimeric model compounds. At higher temperature, mono-aromatic products were formed. The yield of monomeric products was higher in ethanol than in water. The preference for ethanol is due to extensive alkylation of the mono-aromatic products, which inhibits their condensation into larger products. The highest yields of deoxygenated mono-aromatics were obtained using Lewis acid catalysts at 400 °C in supercritical ethanol. The preferred Lewis acid catalysts were Fe, Cu, Ni and Al chlorides.
- Güvenatam, Burcu,Heeres, Erik H.J.,Pidko, Evgeny A.,Hensen, Emiel J.M.
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- Electron transfer-induced coupling of haloarenes to styrenes and 1,1-diphenylethenes triggered by diketopiperazines and potassium tert-butoxide
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The coupling of haloarenes to styrenes and 1,1-diarylethenes has been achieved with potassium tert-butoxide in the presence of N,N'-dialkyldiketopiperazines. In contrast to previously reported reactions where phenanthroline has been used to mediate the reactions, the use of diketopiperazines can lead to either 1,1,2-triarylethenes or 1,1,2-triarylethanes, depending on the conditions used.
- Doni, Eswararao,Zhou, Shengze,Murphy, John A.
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p. 1755 - 1774
(2015/02/05)
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- Electrophilic Fluorophosphonium Cations in Frustrated Lewis Pair Hydrogen Activation and Catalytic Hydrogenation of Olefins
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The combination of phosphorus(V)-based Lewis acids with diaryl amines and diaryl silylamines promotes reversible activation of dihydrogen and can be further exploited in metal-free catalytic olefin hydrogenation. Combined experimental and density functional theory (DFT) studies suggest a frustrated Lewis pair type activation mechanism. FLP hydrogenation: The combination of a phosphorus(V)-based Lewis acid with diaryl amines or diaryl silylamines promotes reversible activation of dihydrogen and can be further exploited in metal-free catalytic olefin hydrogenation. Combined experimental and density functional theory (DFT) studies suggest a frustrated Lewis pair (FLP)-type activation mechanism.
- Vom Stein, Thorsten,Perz, Manuel,Dobrovetsky, Roman,Winkelhaus, Daniel,Caputo, Christopher B.,Stephan, Douglas W.
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supporting information
p. 10178 - 10182
(2015/09/01)
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- A clean and selective radical homocoupling employing carboxylic acids with titania photoredox catalysis
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A titania photoredox catalysis protocol was developed for the homocoupling of C-centered radicals derived from carboxylic acids. Intermolecular reactions were generally efficient and selective, furnishing the desired dimers in good yields under mild neutral conditions. Selective cross-coupling with two acids proved unsuccessful. An intra-molecular adaptation enabled macrocycles to be prepared, albeit in modest yields. (Chemical Equation Presented).
- Manley, David W.,Walton, John C.
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supporting information
p. 5394 - 5397
(2015/02/19)
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- Metal-free transfer hydrogenation of olefins via dehydrocoupling catalysis
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A major advance in main-group chemistry in recent years has been the emergence of the reactivity of main-group species that mimics that of transition metal complexes. In this report, the Lewis acidic phosphonium salt [(C 6F5)3PF][B(C6F5) 4] 1 is shown to catalyze the dehydrocoupling of silanes with amines, thiols, phenols, and carboxylic acids to form the Si-E bond (E = N, S, O) with the liberation of H2 (21 examples). This catalysis, when performed in the presence of a series of olefins, yields the concurrent formation of the products of dehydrocoupling and transfer hydrogenation of the olefin (30 examples). This reactivity provides a strategy for metal-free catalysis of olefin hydrogenations. The mechanisms for both catalytic reactions are proposed and supported by experiment and density functional theory calculations.
- Pérez, Manuel,Caputo, Christopher B.,Dobrovetsky, Roman,Stephan, Douglas W.
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p. 10917 - 10921
(2014/08/18)
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- Identification of dihydrostilbenes in Pholidota chinensis as a new scaffold for GABAA receptor modulators
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A dichloromethane extract of stems and roots of Pholidota chinensis (Orchidaceae) enhanced GABA-induced chloride currents (IGABA) by 132.75 ± 36.69% when tested at 100 μg/mL in a two-microelectrode voltage clamp assay, on Xenopus laevis oocytes
- Rueda, Diana C.,Sch?ffmann, Angela,De Mieri, Maria,Raith, Melanie,J?hne, Evelyn A.,Hering, Steffen,Hamburger, Matthias
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p. 1276 - 1284
(2014/03/21)
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- Determination of the effective redox potentials of SmI2, SmBr2, SmCl2, and their complexes with water by reduction of aromatic hydrocarbons. Reduction of anthracene and stilbene by samarium(II) iodide-water complex
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Samarium(II) iodide-water complexes are ideally suited to mediate challenging electron transfer reactions, yet the effective redox potential of these powerful reductants has not been determined. Herein, we report an examination of the reactivity of SmI2(H2O)n with a series of unsaturated hydrocarbons and alkyl halides with reduction potentials ranging from -1.6 to -3.4 V vs SCE. We found that SmI 2(H2O)n reacts with substrates that have reduction potentials more positive than -2.21 V vs SCE, which is much higher than the thermodynamic redox potential of SmI2(H2O) n determined by electrochemical methods (up to -1.3 V vs SCE). Determination of the effective redox potential demonstrates that coordination of water to SmI2 increases the effective reducing power of Sm(II) by more than 0.4 V. We demonstrate that complexes of SmI2(H 2O)n arising from the addition of large amounts of H 2O (500 equiv) are much less reactive toward reduction of aromatic hydrocarbons than complexes of SmI2(H2O)n prepared using 50 equiv of H2O. We also report that SmI 2(H2O)n cleanly mediates Birch reductions of substrates bearing at least two aromatic rings in excellent yields, at room temperature, under very mild reaction conditions, and with selectivity that is not attainable by other single electron transfer reductants.
- Szostak, Michal,Spain, Malcolm,Procter, David J.
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p. 2522 - 2537
(2014/04/17)
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- Visible-light photocatalytic reduction of sulfonium salts as a source of aryl radicals
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Triarylsulfonium salts are prompted to undergo efficient homolytic reduction by single electron transfer under mild photocatalytic conditions. The liberated aryl radical can then participate in carbon-carbon bond formation processes with allyl sulfones and activated olefins. Triarylsulfonium salts emerge as a valuable and alternative source of aryl radicals for synthesis. Copyright
- Donck, Simon,Baroudi, Abdulkader,Fensterbank, Louis,Goddard, Jean-Philippe,Ollivier, Cyril
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supporting information
p. 1477 - 1482
(2013/06/27)
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- Direct functionalization of tetrahydrofuran and 1,4-dioxane: Nickel-catalyzed oxidative C(sp3)-H arylation
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CHoose nickel: The nickel-catalyzed oxidative arylation of C(sp 3)-H bonds has been achieved. Several substituted arylboronic acids and various C(sp3)-H bonds were found to be suitable substrates for this novel transformation, which is likely to proceed through a radical pathway. This method allows the introduction of simple ether derivatives to construct α-arylated ethers. FG=functional group. Copyright
- Liu, Dong,Liu, Chao,Li, Heng,Lei, Aiwen
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supporting information
p. 4453 - 4456
(2013/05/21)
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- Additive effects on palladium-catalyzed deprotonative-cross-coupling processes (DCCP) of sp3 C-H bonds in diarylmethanes
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Palladium-catalyzed cross-coupling reactions have become one of the most useful tools in modern organic chemistry. Current methods to achieve direct functionalization of sp3 C-H bonds of arenes and heteroarenes often employ substrates with appropriately placed directing groups to enable reactivity. Examples of intermolecular arylation methods of weakly acidic sp3 C-H bonds in the absence of directing groups, however, are still limited. We describe herein a study on the use of additives in Pd-catalyzed deprotonative-cross-coupling processes (DCCP) of sp3 C-H bonds of diarylmethanes with aryl bromides at room temperature. These studies resulted in development of four new efficient Pd-catalyzed DCCP using additives that enabled the generation of a range of sterically and electronically diverse aryl- and heteroaryl containing triarylmethanes in good to excellent yields. Additive identification and optimization of all reaction conditions (additive loading, solvent and temperature) were performed using high-throughput experimentation (HTE). The approach outlined herein is expected to be generalizable to other C-H functionalization reactions involving the deprotonation of weakly acidic C-H bonds. The Royal Society of Chemistry 2013.
- Bellomo, Ana,Zhang, Jiadi,Trongsiriwat, Nisalak,Walsh, Patrick J.
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p. 849 - 857
(2013/03/28)
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- Palladium-catalyzed C(sp3)-H arylation of diarylmethanes at room temperature: Synthesis of triarylmethanes via deprotonative-cross-coupling processes
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Although metal-catalyzed direct arylation reactions of non- or weakly acidic C-H bonds have recently received much attention, chemists have relied heavily on substrates with appropriately placed directing groups to steer reactivity. To date, examples of intermolecular arylation of unactivated C(sp3)-H bonds in the absence of a directing group remain scarce. We report herein the first general, high-yielding, and scalable method for palladium-catalyzed C(sp3)-H arylation of simple diarylmethane derivatives with aryl bromides at room temperature. This method facilitates access to a variety of sterically and electronically diverse hetero- and nonheteroaryl-containing triarylmethanes, a class of compounds with various applications and interesting biological activity. Key to the success of this approach is an in situ metalation of the substrate via C-H deprotonation under catalytic cross-coupling conditions, which is referred to as a deprotonative-cross-coupling process (DCCP). Base and catalyst identification were performed by high-throughput experimentation (HTE) and led to a unique base/catalyst combination [KN(SiMe3)2/Pd-NiXantphos] that proved to efficiently promote the room-temperature DCCP of diarylmethanes. Additionally, the DCCP exhibits remarkable chemoselectivity in the presence of substrates that are known to undergo O-, N-, enolate-, and C(sp2)-H arylation.
- Zhang, Jiadi,Bellomo, Ana,Creamer, Andrea D.,Dreher, Spencer D.,Walsh, Patrick J.
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supporting information; experimental part
p. 13765 - 13772
(2012/10/08)
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- Triflic acid-mediated phenylation of N-acylaminoalkyl diethylacetals and N-acyl-2-phenyl cyclic amides
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The reaction of N-acylaminoalkyl diethylacetals with triflic acid in benzene gave N-acylamino-diphenylalkyls. The proposed intermediates are the N-acyl-2-phenyl cyclic amides, which themselves are similarly converted to N-acylamino-diphenylalkyls.
- King, Frank D.,Caddick, Stephen
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p. 4361 - 4366
(2011/07/29)
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- Pd-catalyzed cleavage of benzylic nitro bonds: New opportunities for asymmetric synthesis
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Without a trace: Benzylic nitroalkanes are reduced to the corresponding parent alkanes in good yields by using a simple procedure involving heterolytic C-N bond cleavage (see scheme). Traceless removal of the nitro group leaves behind a stereogenic center that may otherwise be difficult to install. This reaction significantly expands the scope of building blocks that can be accessed. (Chemical Equation Presented)
- Fessard, Thomas C.,Motoyoshi, Hajime,Carreira, Erick M.
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p. 2078 - 2081
(2008/02/13)
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- Formation of 8-Membered Ring Compounds by the Reaction of Styrene Oxide with MoCl5
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Styrene oxide reacted with group 5 and 6 metal halides in 1,2-dichloroethane to afford an 8-membered ring compound, 2,3,6,7-dibenzo-9- oxabicyclo[3,3,1]nona-2,6-diene. When the reaction was carried out in benzene instead of 1,2-dichloroethane as a solvent, unexpected new 8-membered ring product, tribenzobicyclo[3.3.2]decatriene, and 1,1,2-triphenylethane were obtained. The structures of the 8-membered ring compounds were confirmed by X-ray analysis.
- Guo, Qiaoxia,Nakajima, Kiyohiko,Takahashi, Tamotsu
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p. 1044 - 1045
(2007/10/03)
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- Reduction of diaryl alkenes by hypophosphorous acid-iodine in acetic acid
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A mixture of 50% aqueous H3PO2 and I2 (in catalytic amount) in HOAc efficiently reduces aryl alkenes to the corresponding alkanes in high yield. Addition of acetic anhydride to the medium results in ring-acetylation (or N-acetylation in the case of amines). H3PO2 costs only one-fifth as much as hydriodic acid on a mole basis and one mole of H3PO2 produces four moles of HI, resulting in a 20-fold cost advantage for H3PO2/I2 over aqueous HI as a source of HI.
- Fry, Albert J.,Allukian, Myron,Williams, Allison D.
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p. 4411 - 4415
(2007/10/03)
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- Polyethylene glycol mediated reductive decyanation of diphenylacetonitrile moderately enhanced by microwave heating
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An efficient and clean procedure for the preparation of alkyldiphenylmethanes and 4,4-diphenylbutylamines from their corresponding nitriles by using sodium hydroxide-polyethylene glycol reagent system in a domestic microwave oven is described. The products are isolated by simple aqueous work up in excellent yields.
- Bendale,Chowdhury,Khadilkar
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p. 433 - 435
(2007/10/03)
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- Supramolecular Steric Effects as the Means of Making Reactive Carbon Radicals Persistent. Quantitative Characterization of the External Surface of MFI Zeolites through a Persistent Radical Probe and a Langmuir Adsorption Isothez
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The photochemistry of tetraphenylacetone (1) adsorbed on the external surface of a MFI zeolite (the sodium form of LZ-105) has been investigated in combination with computational chemistry, surface area measurements, EPR analysis, and classical adsorption isotherms. All of the methods are consistent with a supramolecular structural model in which 1 is first adsorbed strongly through intercalation of a single benzene ring into a hole on the LZ-105 external surface (site I) followed by a weaker binding to the external framework between the holes (site II) until a monolayer of 1 is formed. From both computational and surface area measurements, it is estimated that the site I holes on the external surface will be filled at ca. 0.3-0.5 wt %/wt loading of 1/LZ-105, which corresponds to 6.5 × 1018 (ca. 10-5 mol) of holes or molecules of 1 adsorbed in holes per gram of zeolite. The supramolecular composition of ca. 0.3-0.5% of 1 on LZ-105 characterizes a "break point" for the photochemistry and the EPR measurements, since it represents the value for saturation of the site I holes with 1. These conclusions are supported quantitatively by experimental isotherms of the adsorption of 1 on LZ-105. Photolysis of 1 intercalated in the site I holes causes fragmentation into two isomeric supramolecular diphenylmethyl (DPM) radicals, one (DMP)in which is adsorbed into the internal surface and becomes strongly persistent (half-life of many weeks) and the other (DMP)ex which diffuses on the external surface and rapidly dimerizes (less than a few minutes) to produce the radical-radical combination product tetraphenylethane (2). Photolysis of 1 adsorbed on the solid external surface produces two supramolecularly equivalent DPM radicals (DMP)ex that diffuse on the external surface and rapidly dimerize to produce 2, and do not produce persistent DPM radicals. * To whom correspondence should be addressed.
- Hirano, Takashi,Li, Wei,Abrams, Lloyd,Krusic, Paul J.,Ottaviani, M. Francesca,Turro, Nicholas J.
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p. 1319 - 1330
(2007/10/03)
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- Transformations of N-Substituted Benzotriazoles into the Corresponding Carbanions by C-Benzotriazole Bond Scission
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Various TV-substituted benzotriazoles are transformed, by scission of the C-benzotriazole bond, into the corresponding carbanions by treatment with lithium. Thus, N-(diphenylmethyl)benzotriazole (1), N-benzylbenzotriazole (6), and N-allylbenzotriazole (10) all gave carbanions that reacted with diverse electrophiles to afford the corresponding products in good yields. This new methodology was successfully utilized to convert N-benzylbenzotriazole (6) and N-allylbenzotriazole (10) into dianion synthons by a sequential lithiation and reductive coupling and bis(benzotriazolyl)toluene (18) by double reductive couplings, demonstrating the synthetic potential of the present methodology.
- Katritzky, Alan R.,Qi, Ming
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p. 4116 - 4120
(2007/10/03)
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- Synthesis of 5-Methoxy- and 5-(Dialkylamino)bicyclohept-2-en-6-one Derivatives by cine Substitution with Methoxide Anions and Dialkylamines
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exo-7-Chloro-endo-7-phenylbicyclohept-2-en-6-one (5) undergoes cine substitution reactions with methoxide anions and with dialkylamines to give 5-methoxy or 5-dialkylamino derivatives 13, 14, 16-19 in high yield.While attempts directed to an acetalization have failed, the addition of Grignard reagents to the methoxy derivatives proceeds stereoselectively in high yield.Hydrochlorides 20/21 lose amine at 110 deg C to form 2-phenyltropone (22).Thermolysis of diethylamino derivative 24 at 170 deg C (temperature determined by DSC) results in the formation of the dienoaminone 25. - Key Words: Bicyclohept-2-en-6-one, cine substitution / DSC
- Butenschoen, Holger
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p. 137 - 144
(2007/10/02)
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- Reactions with Aziridines. 48. Friedel-Crafts Reactions with N-Sulfonated Aziridines and with Open-Chain Sulfonamides. Sulfonamides as Leaving Groups in Open-Chain Structures
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AlCl3-catalyzed reactions of N-sulfonylaziridines (C substituents given) 1a (no substituent), 4b (2-phenyl), 8b (2,3-diphenyl), and 11a-c (2,2-dimethyl) with neat benzene, toluene, or anisole proceeded rapidly without heating.The expected N-sulfonyl(aryle
- Stamm, Helmut,Onistschenko, Andreas,Buchholz, Berthold,Mall, Thomas
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p. 193 - 199
(2007/10/02)
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- Photosensitized (electron transfer) carbon-carbon bond cleavage of radical cations: the 2-phenylethyl ether and acetal systems
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The scope of the photosensitized (electron transfer) carbon-carbon bond cleavage involving radical cations has been defined for 2-phenylethyl ethers and acetals.The thresholds for reactivity of the monophenylethyl and gem-diphenylethyl derivatives are compared.While the radical cation of methyl 2,2-diphenylethyl ether (7) cleaves to give ultimately diphenylmethane (2) and dimethoxymethane (8), the radical cation of methyl 2-phenylethyl ether (9) was stable under these conditions.In contrast to the lack of reactivity of the radical cation of 9, the radical cations of methyl 2-phenyl-2-propyl ether (11), methyl 2-phenylcyclopentyl ether (13), and 2-phenylmethyl-1,3-dioxolane (16) cleave.Cleavage in the monophenylethyl series is limited to formation of a carbocation at least as stable as the secondary α-oxyalkyl or di-α-oxyalkyl.The basis for predicting this type of reactivity of radical cations is defined.The rate of carbon-carbon bond cleavage is increased the oxidation potential of the molecule, by decreasing the carbon-carbon bond strength, and (or) by decreasing the oxidation potential of that fragment that will become the carbocation.The results obtained from the reactions of 2-diphenylmethyl-1,3-dioxolane (14) and 2-phenylmethyl-1,3-dioxolane (16) cast doubt on the published oxidation potential for the 1,3-dioxolan-2-yl radical.Key words: photochemistry, radical cation, electron transfer, bond cleavage, radical.
- Arnold, Donald R.,Lamont, Laurie J.
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p. 2119 - 2127
(2007/10/02)
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- NADH Model Studies. Part 2. Cationic Hydrogenations using Acridan Derivatives as Hindered NADH Models.
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Various aryl alcohols (5), arylethylenes (6), and trityl ethers (7) are found to undergo smooth reduction in dichloromethane at room temperature when treated with an equimolar amount of the acridans (3) and trifluoroacetic acid.The limiting acidity value (H0) for the medium in which the compounds (3) are completely protonated and hence not suitable as NADH models was also determined spectrophotometrically.Kinetic studies of reduction of (5) with (3) in dilute sulphuric acid, or Hantzsch ester (2) in glacial acetic acid, indicated that during reduction steric hindrance is important in less acidic media whereas the reduction of cations performed with trifluoroacetic acid is not affected by steric factors.
- Singh, Serjinder,Gill, Sarbjeet,Sharma, Vijay K.,Nagrath, Sarita
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p. 1273 - 1276
(2007/10/02)
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- Flow ESR and Static Studies of the Decomposition of Phenyl-Substituted Ethanes
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The thermal decomposition of 1,1,2,2-tetraphenylethane (DD) was studied in high-temperature fluids by using both sealed tube and flow ESR techniques.In the sealed tube experiments its central C-C bond homolysis rate constant in tetralin solvent was 1015.92+/-0.13 exps-1 (473-550 K).Concentrations of diphenylmethyl radicals in equilibrium with DD were measured by ESR between 648 and 683 K.The equilibrium constant for the dissociation reaction was 106.69+/-0.66 expM.Combining this expression with the dissociation rate constant for diphenylmethyl radicals of 1.5 x 109M-1s-1 at 648 K.Bond homolysis of 1,1,2-triphenylethane (BD) was also studied in tetralin.Its rate constant was 1016.18+/-0.11 exps-1 (593-653 K).An analysis of the above data shows that the rate of BD dissociation is not strongly affected by release of steric energy.In contrast, the DD homolysis rate was increased by more than an order of magnitude through release of strain.
- Manka, M. J.,Brown, R. L.,Stein, S. E.
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p. 5421 - 5427
(2007/10/02)
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- Synthesis and Reactions of Sulfenic Trifluoromethanesulfonic Anhydrides
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Sulfenyl halogenides 1 and 4 react with silver trifluoromethanesulfonate (2) to give aryl 3 and alkylsulfenic trifluoromethanesulfonic anhydrides 5, resp., in good yields; 3 and 5 could not be isolated because of their instability. 1H NMR spectroscopic data of 5a, b, each in dichloromethane and nitromethane, resp., are indicative of a dissoziation to adducts of alkylsulfenylium ions and the solvent.Whereas 3 do not react with aromatic compounds, addition products with diphenylacetylene, arylsulfenylvinyl trifluoromethanesulfonates 11, are formed smoothly, which under the reaction conditions immediately cyclize to give benzothiophenes 10 in excellent yields.
- Effenberger, Franz,Russ, Werner
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p. 3719 - 3736
(2007/10/02)
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- The reinvestigation of the kinetics of the reactions of fluorodi(4-nitrophenyl)ethanes with sodium methoxide in methanol
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The procedure previously described for the preparation of 1-fluoro-2,2-di(4-nitrophenyl)ethane actually yields 1,1,2-tri(4-nitrophenyl)ethane.Fluoro-2,2-di(4-nitrophenyl)ethane has been prepared and rate constants, isotope effects, and activation parameters for the β-elimination reaction with methoxide ion in methanol are reported.These parameters indicate a concerted E2 mechanism, with a fairly symmetrical transition state.The subsequent dimerization reaction of the olefin product to yield 1,1,3,3-tetra(4-nitrophenyl)butene-1 is described.The reaction of 1,1,1-trifluoro-2,2-di(4-nitrophenyl)ethane with methoxide ion in methanol has been reinvestigated and the reaction on the first product 1,1-difluoro-2,2-di(4-nitrophenyl)ethylene with excess methoxide, to give di(4-nitrophenyl)ketene dimethylacetal in a multistep reaction, is reported.
- Leffek, Kenneth T.,Schroeder, Grzegorz
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p. 1696 - 1701
(2007/10/02)
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- Sterospoific formation of five-membered metaliacydes. Zfrconaindans from thermally generated (772-dehydrobenzene)daeyelperataclienyihre0nium( II) and cis- and frans-stilbene
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cis- and frsns-2,3-diphenylzirconaindans 7 and 8 are formed stereospecificly from thermally generated {r?2-dehydrobenzene)dicycloperrtadienyizirconium(l i) and cis- and frans -stiibene, respectively. This supports a concerted pathway suuggested for the cyciization reaction of bis(olefin) transition-metal complexes to form five-membered metallacycles.
- Kropp, Kurt,Erker, Gerhard
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p. 1246 - 1247
(2008/10/08)
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- 1,n-TRIORGANOSILYL MIGRATIONS IN THE REARRANGEMENTS OF SILYL-SUBSTITUTED ORGANOLITHIUM COMPOUNDS
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Under the agency of the potent lithiating agent, n-butyllithium in TMEDA, an array of organosilanes was found to undergo 1,n-silyl rearangements via carbanionic intermediates.Unambiguous 1,2-, 1,3- and 1,4-silyl shifts were unconvered in 1-trimethylsilyl-
- Eisch, John J.,Tsai, Miin-Rong
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