- New functionalized vinyl monomers by ethylene-(functionalized)-norbornene hetero-trimerization catalyzed by cobalt(II)-(imino)pyridine complexes
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On activation by MAO the (imino)pyridine cobalt(II) complex CoCl 2N2Ph/i-Pr2 catalyzes the enchainment of one norbornene (NB) molecule with two ethylene molecules to give exo-2,exo-3-ethylvinylnorbornane with high activity and complete diastereoselectivity. Turnover frequencies [TOF, mol NB (mol Co×h) -1] as high as 270,000 have been obtained. The 2E-1NB hetero-trimerization reaction has been also accomplished with NBs bearing polar substituents such as norbornenemethanol and norbornenecarboxylic acid provided that the substrate is protected with triisobutylaluminum and the less sterically demanding complex CoCl2N2Ph/Me2 is used as catalyst precursor. A mechanism for the hetero-trimerization reactions is proposed on the basis of experimental evidence.
- Toti, Alessandro,Giambastiani, Giuliano,Bianchini, Claudio,Meli, Andrea,Luconi, Lapo
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- Environmentally responsible, safe, and chemoselective catalytic hydrogenation of olefins: ppm level Pd catalysis in recyclable water at room temperature
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Textbook catalytic hydrogenations are typically presented as reactions done in organic solvents and oftentimes under varying pressures of hydrogen using specialized equipment. Catalysts new and old are all used under similar conditions that no longer reflect the times. By definition, such reactions are both environmentally irresponsible and dangerous, especially at industrial scales. We now report on a general method for chemoselective and safe hydrogenation of olefins in water using ppm loadings of palladium from commercially available, inexpensive, and recyclable Pd/C, together with hydrogen gas utilized at 1 atmosphere. A variety of alkenes is amenable to reduction, including terminal, highly substituted internal, and variously conjugated arrays. In most cases, only 500 ppm of heterogeneous Pd/C is sufficient, enabled by micellar catalysis used in recyclable water at room temperature. Comparison with several newly introduced catalysts featuring base metals illustrates the superiority of chemistry in water.
- Gallou, Fabrice,Gao, Eugene S.,Lipshutz, Bruce H.,Takale, Balaram S.,Thakore, Ruchita R.
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supporting information
p. 6055 - 6061
(2020/10/14)
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- Highly stereoselective tandem cyclizations of 5-hexenyllithiums: Preparation of endo-2-substituted bicyclo[2.2.1]heptanes and 3-substituted trans-bicyclo[ 3.3.0] octanes
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Tandem cyclization of diolefinic alkyllithiums, derived from acyclic diolefinic alkyl iodides by low-temperature lithium-iodine exchange, proceeds via two highly stereoselective and totally regiospecific 5-exo-trig ring closures to deliver bicyclic alkyllithiums. Trapping of the organolithium product by addition of an electrophile cleanly affords functionalized bicyclic molecules in good yield. In this way both endo-2-substituted bicyclo[2.2.1]heptanes and 3-substituted trans-bicyclo[3.3.0]octanes have been prepared in isolated yields of 65-80% from the readily available 3-(2-iodoethyl)-1,5-hexadiene (5) and 7-iodo-4-ethenyl-1-heptene (9), respectively. Attempts to effect tandem cyclization of 5,10-undecadienyllithium (11), which would be mediated by a secondary alkyllithium species, were unsuccessful. The results suggest that tandem anionic cyclization provides a convenient route to a variety of bicyclic systems not readily available by other approaches.
- Bailey, William F.,Khanolkar, Atmaram D.,Gavaskar, Kaustubh V.
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p. 8053 - 8060
(2007/10/02)
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- Substituent Effects on 1H Chemical Shifts I-Complete 1H Chemical Shift Assignments of Methyl-Substituted Cyclic Systems
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1H chemical shift assignments are presented for 2-methyladamantane, 2-methylnorbornane (endo and exo) and 2-methylnorbornene (endo and exo).Resonance assignment was achieved using a variety of 1D and 2D homo- and heteronuclear (1H-13C)experiments.The methyl group-induced substituent chemical shift (SCS) is derived and the SCS of protons vicinal to this group is discussed.KEY WORDS Norbornanes Norbornenes Adamantanes 1H NMR Substituent chemical shifts
- Fisher, Julie,Gradwell, Michael J.
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p. 338 - 346
(2007/10/02)
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- Carbon-13 NMR and IR Spectroscopic Studies on Some 7-Oxabicycloheptanes and -heptenes. n-? Interaction and Hydrogen Bonding
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The 13C NMR spectra of diastereomeric pairs of the title compounds together with some tetrahydrofurans were examined and the chemical shifts were compared with those for the corresponding bicycloheptanes and -heptenes.The intramolecular interaction between the n-orbital of an oxygen atom and the ?-orbital of an olefinic bond was found in 2-methylene-7-oxabicycloheptane.Intramolecular hydrogen bonding between the 7-oxygen and the hydroxyl group occurs in exo-7-oxabicycloheptane-2-methanol.
- Senda, Yasuhisa,Ohno, Akihiko,Ishiyama, Jun-ichi,Imaizumi, Shin,Kamiyama, Shin-ichi
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p. 613 - 616
(2007/10/02)
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- Optical and Neutron Inelastic Scattering Study of 2-Methylnorbornanes
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We have measured the infrared, Raman, and neutron vibrational spectra of the 2-methylnorbornanes with a CH3 or CD3 methyl group in the exo or endo position.A normal coordinate analysis has been carried out.The torsional modes of the methyl group are assigned at 240 and 235 cm-1 for the hydrogenated exo and endo isomers, respectively.The corresponding barrier is 15.2 +/- 0.2 kJ mol-1.The calculated neutron intensities are in good agreement with the experimental data.The frequencies are used for the determination of the thermodynamic contribution to the standard free energy difference.
- Brunel, Yvon,Coulombeau, Christian,Coulombeau, Christiane,Jobic, Herve
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p. 937 - 943
(2007/10/02)
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- Stereoselectivity of Ring Closure of Substituted Hex-5-enyl Radicals
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1,5-Ring closure of 1- or 3-substituted hex-5-enyl radicals affords mainly cis-disubstituted cyclic products, whereas 2- or 4-substituted species give mainly trans-products; the significance of this stereoselectivity is demonstrated in the formation of the norbornane system from acyclic precursors.
- Beckwith, Athelstan L. J.,Lawrence, Tony,Serelis, Algirdas K.
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p. 484 - 485
(2007/10/02)
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- Synthetic applications of α-hydroxydiazenes. III. Uncatalyzed and phenol catalyzed hydroalkylation of alkenes and of azobenzene with alkylazodiphenylmethanols
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Alkylazodiphenylmethanols (C6H5)2C(OH)N=NR, (R = CH(CH3)2, CH2CH3, CH3), when decomposed in the presence of olefinic substrates or in the presence of azobenzene, hydroalkylate those substrates.Addition of R and H across the double bond of an unsymmetric alkene occurs with the regiochemistry expected for a radical mechanism, in which the grooup R adds first.Radical intermediates from decomposition of alkylazodiphenylmethanols have been demonstrated earlier with spin trapping experiments.The fact that addition of phenol can enhance the yield of hydroalkylation product suggests that the process is a radical chain reaction, with chain carrying steps consisting of the reactions: (i) R. + CH2=CHY -> RCH2C.HY (ii) RCH2C.HY + (C6H5)2C(OH)N2R -> RCH2CH2Y + (C6H5)2CO + N2 + R..One deuterioalkylation and some yield-optimizing experiments are also reported.
- Yeung, Dominic W. K.,Warkentin, John
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p. 2386 - 2394
(2007/10/02)
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