- Vinyl Carbocations Generated under Basic Conditions and Their Intramolecular C-H Insertion Reactions
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Here we report the surprising discovery that high-energy vinyl carbocations can be generated under strongly basic conditions, and that they engage in intramolecular sp3 C-H insertion reactions through the catalysis of weakly coordinating anion salts. This approach relies on the unconventional combination of lithium hexamethyldisilazide base and the commercially available catalyst, triphenylmethylium tetrakis(pentafluorophenyl)borate. These reagents form a catalytically active lithium species that enables the application of vinyl cation C-H insertion reactions to heteroatom-containing substrates.
- Wigman, Benjamin,Popov, Stasik,Bagdasarian, Alex L.,Shao, Brian,Benton, Tyler R.,Williams, Chloé G.,Fisher, Steven P.,Lavallo, Vincent,Houk,Nelson, Hosea M.
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supporting information
p. 9140 - 9144
(2019/06/08)
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- Telomerization of Z,Z-cyclooctadiene with halomethanes catalyzed by chromium, copper, and molybdenum compounds in the presence of water
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The telomerization of 1Z,5Z-cyclooctadiene with halogenated methanes (CCl4, CBrCl3, CHCl3, CH2Cl 2) mediated by chromium, copper, and molybdenum complexes has been investigated. It has been shown that the use of water as a nucleophilic additive promotes the formation of 1,4- and 1,5-epoxycyclooctanes and anti-8-(trichloromethyl)bicyclo[3.2.1]octan-exo-2-ol. Pleiades Publishing, Ltd., 2011.
- Khusnutdinov,Shchadneva,Oshnyakova,Dzhemilev
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experimental part
p. 435 - 441
(2012/04/23)
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- Cycloisomerization and [2 + 2]cyclodimerization of 1,5-cyclooctadiene catalyzed with the Ni(COD)2/BF3·OEt2 system
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The catalytic system Ni(COD)2/BF3·OEt2 has been studied in conversions of 1,5-cyclooctadiene under argon and ethylene atmosphere. It has been demonstrated that the catalytic system formed under argon exhibits a high effectiveness in cycloisomerization of 1,5-COD surpassing in this characteristic all known nickel complex catalysts (selectivity to bicyclo-[3.3.0]-octene-2 is up to 99.5% at 100% conversion). In the case of ethylene atmosphere the system produces mainly dimers (yield of cyclodimers above 70%). It has been shown that the catalytic system Ni(COD)2/BF3·OEt2 has the feature of "a living catalyst" consisting in resuming the initial activity with a new portion of 1,5-COD added when the monomer was fully exhausted. The main and side products of the 1,5-COD conversion have been identified with GC-MS and preparative liquid chromatography combined with NMR and IR spectroscopy. Based on EPR and IR spectroscopic data a mechanism for the catalytic performance of the Ni(COD)2/BF3·OEt2 system in argon or ethylene atmospheres is suggested. It has been shown that Ni(0) is oxidized by the Lewis acid to Ni(I) which is stabilized by substrate molecules in a mononuclear form without involvement of conventional organoelement entities. Three sorts of paramagnetic nickel species have been found: ionic complexes containing π-coordinated COD ligands; ionic complexes σ-bonded to COD; complexes as intimate pairs with BF4- counter ions. A mechanism for the catalytic conversion of 1,5-cyclooctadiene is proposed.
- Saraev,Kraikivskii,Matveev,Bocharova,Petrovskii,Zelinskii,Vilms,Klein, Hans-Friedrich
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scheme or table
p. 231 - 238
(2010/05/12)
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- Direct in situ synthesis of cationic N-heterocyclic carbene iridium and rhodium complexes from neat ionic liquid: Application in catalytic dehydrogenation of cyclooctadiene
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A direct synthetic route to cationic N-heterocyclic carbene (NHC) complexes of rhodium and iridium from neat dialkyl-imidazolium ionic liquids (ILs) has been found. The method uses complexes bearing basic anionic ligands, [M(COD)(PPh3)X], X = OEt, MeCO2, which react with the inactivated imidazolium cation in the absence of external bases yielding one M-NHC moiety and the free protonated base. This new one-pot synthesis leaving pure, catalytically active IL solutions is faster, cleaner and more efficient than traditional syntheses of such NHC complexes. The observed reactivity also gives insight into NHC incorporation of rhodium and iridium catalyzed reactions performed in common dialkyl-imidazolium ILs. The complexes synthesised in this manner are compared with their bis-phosphine analogues in terms of activity for catalytic dehydrogenation of 1,5-cyclooctadiene and 1,3-cyclooctadiene in neat [BMIM][NTf2] as solvent. Even at high temperature, no ligand exchange reaction is observed with [(COD)M(PPh3)2] [NTf2] catalysts. As expected, the yields of all the reactions were low, iridium was much more active in C-H activation than rhodium and the NHC ligands were more stable than triphenylphosphine. For all catalysts, the isomerisation of 1,5-cyclooctadiene is the major reaction. However, the phosphine-NHC complex of iridium seems to be more selective for dehydrogenation than its bis-phosphine counterpart, which is more active in transfer-hydrogenation and less stable under the applied conditions. Different reaction conditions were tried in order to optimise selectivity for dehydrogenation over isomerisation and transfer-hydrogenation. Surprisingly, with 1,3-cyclooctadiene as substrate selectivity for dehydrogenation is much higher than with 1,5-cyclooctadiene for all catalysts.
- Hintermair, Ulrich,Gutel, Thibaut,Slawin, Alexandra M.Z.,Cole-Hamilton, David J.,Santini, Catherine C.,Chauvin, Yves
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p. 2407 - 2414
(2008/09/20)
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- Carbacyclin compounds; pharmaceutical compositions and method of use
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Compounds of formula (Ic): STR1 having valuable platelet-aggregation inhibitory activities useful for the prophylaxis and treatment of such diseases as thrombosis and pharmaceutical compositions containing said compounds.
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- Reactions of enaminones with 1-nitroolefins. Scope and limitations of a polyquinane synthesis
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The reaction of several 2-aminocyclohex-2-en-1-ones with cyclic nitroolefins has been explored as a possible synthetic approach to polyquinanes. 2-Pyrrolidino, 2-piperidino and 2-morpholinocyclohex-2-en-1-one react with 1-nitrocyclopentene to provide substituted triquinanes. Reactions involving 5,5-dimethyl-2-morpholinocyclohex-2-en-1-one were unseccessful as were those using 4,4-dimethyl-1-nitrocyclopentene. 5-Methyl-2-morpholinocyclohex-2-en-1-one and 1-nitrocyclopentene provide the corresponding triquinane, plus a by-product in which the amino substituent has been lost. The reactions of other selected nitroolefins have been carried out, and the products are described. The results of these reactions are rationalized in terms of an inverse electron demand Diels-Alder reaction to afford an intermediate oxazine N-oxide, which then undergoes further transformations to afford the observed products.
- Huffman,Cooper,Miburo,Pennington
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p. 8213 - 8228
(2007/10/02)
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- Selective Isomerization of 1,5-Cyclooctadiene to 1,4-Cyclooctadiene Catalyzed by Bis(acetylacetonato)nickel-Triethyldialuminum Trichloride-Phosphorus Ligand
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The isomerization of 1,5-cyclooctadiene (1,5-COD) with Ni(acac)2-Et3Al2Cl3-phosphorus ligand (Ni:Al2:P = 1:10:3) was first examined with varying P ligands in toluene in order to find suitable conditions for the formation of 1,4-COD.The product distribution depended largely on the P ligands.For several phosphites possessing very strong ?-acceptor properties, the main product was 1,4-COD.In particular, the less-bulky bicyclic phosphite, 4-ethyl-2,6,7-trioxa-1-phosphabicyclooctane (L-3) was very effective and gave 1,4-COD in a high selectivity of 93 percent at 66 percent conversion (1,5-COD/Ni = 500, molar ratio) by employing a low temperature of -30 deg C.However, the reaction stopped before reaching completion because the catalyst was deactivated by the accumulation of 1,4-COD product.The conversion, depending on the 1,5-COD/toluene ratio (volume) rather than the 1,5-COD/Ni ratio, increased with a decrease in the 1,5-COD/toluene ratio and was 66-69 percent at a ratio of 0.19.On the other hand, the catalyst (P: L-3) was much less active for 1,4-COD than for 1,5-COD and was deactivated quickly under the same reaction conditions.This appeared to result in a high selectivity of 1,4-COD in the isomerization of 1,5-COD.The mechanistic implications of the experimental results are discussed.
- Sakakibara, Yasumasa,Yamamoto, Isao,Sasaki, Ken,Sakai, Mutsuji,Uchino, Norito
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p. 2236 - 2241
(2007/10/02)
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- Rearrangement and Cleavage of the Grignard Reagent from 5-(Chloromethyl)norbornene
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The Grignard reagents 1-Mg and 2-Mg from endo- and exo-5-(chloromethyl)norbornene rearrange with ring cleavage on heating to yield an allylcyclopentenyl organomagnesium compound (3-Mg).This, in turn, undergoes competitively a variety of reactions, including an alternative cyclization to a bicyclooctene organomagnesium (4-Mg) and formal loss of hydrogen or propene to produce allylcyclopentadienyl- (5-Mg) and cyclopentadienylmagnesium compounds.Endo and exo isomers 1-Mg and 2-Mg rearrange at comparable rates and are partially interconverted, probably via their cleavage and recyclization.Mechanistic possibilities are discussed.
- Hill, E. Alexander,Hsieh, King,Condroski, Kevin,Sonnentag, Heidi,Skalitzky, Donald,Gagas, Donald
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p. 5286 - 5292
(2007/10/02)
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- Evidence for Single Electron Transfer in the Reactions of Lithium Dimethylcuprate with Alkyl Halides
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A variety of methods have been utilized to explore the occurence of radical intermediates and free-radical chain processes initiated by electron transfer in the reactions of lithium dimethylcuprate with alkyl halides.The effect of leaving group, nature of the cuprate species, and ratio of cuprate to substrate, solvent, hydrogen atom donor, and other additives on the rate of and product distribution were investigated by using a cyclooctenyl radical probe.The presence of significant amounts of radicals strongly supports single electron transfer (SET) as a major pathway for the reaction of secondary iodides with LiCuMe2.There is some evidence of single electron transfer also accurring with secondary bromides, but tosylates appear to be reacting entirely by a SN2-like pathway.The role of dicyclohexylphosphine (DCPH) as an additive in the reaction was investigated with the result that it was shown to be capable of behaving in a unique manner depending on wheter the substrate is an alkyl iodide or bromide.The product distribution, rate, and effect of p-dinitrobenzene on the reaction of 5-iodo-1-cyclooctene were compared with three other probes and the results demonstrate that at least three reaction pathways are involved to varying degrees.These pathways could involve the initiation of free radicals or radical anion (SRN1) chain processes. these studies also demonstrate how changes in the substrate can alter the predominant reaction pathways that are followed.
- Ashby, E. C.,Coleman, David
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p. 4554 - 4565
(2007/10/02)
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- Direct Photolysis at 185-254 nm of Cyclo-octa-1,3-diene and Cyclohepta-1,3-diene. Wavelength-independent Photobehaviour
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In sharp contrast to the wavelength-dependent photobehaviour of simple mono-alkenes, the photochemistry of conjugated dienes was found to be independent of excitation wavelength in the region 185-254 nm.
- Inoue, Yoshihisa,Daino, Yoshihiko,Hagiwara, Shoji,Nakamura, Hiroyuki,Hakushi, Tadao
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p. 804 - 805
(2007/10/02)
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- A new nickel complex for the oligomerization of ethylene
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We report the synthesis of (η3-C8H13)((C6H 5)2PCH2COO)Ni (1), which proved to be an excellent one-component model catalyst for the oligomerization of ethylene as practiced in Shell's higher olefin process (SHOP). In toluene solution this complex exists in two isomeric forms, the C8H13 ligand being 60% 4-enyl and 40% η3-allyl. Under reaction conditions (75°C, 10-80 bar, ethylene in toluene) 1 catalyzed the highly selective oligomerization of ethylene to linear (99+%), α olefins (93-99%) at activities of 0.6 mol of ethylene/mol of Ni/s. The chain growth factor K ranges from 0.67 to 0.77 depending on reaction conditions. Kinetic activation parameters and reaction constants could be determined (Ea = 71 kJ mol-1; S? = -49 J mol-1 K-1; kinsert/348K = 0.81 s-1).
- Peuckert, Marcell,Keim, Wilhelm
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p. 594 - 597
(2008/10/08)
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- Investigation of Rearrangement Reactions of Cyclic Allyl and Pentadienyl Anions
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Bicyclohexenyl anion (1) and bicycloheptenyl anion (2) rearrange in THF to monocyclic pentadienyl anions, whereas bicyclooctenyl anion 3 is stable under the reaction conditions. 3 in contrary is formed by the known electrocyclic ring closure of cyclooctadienyl anion 7.Rearrangements of cyclopentenyl anion and pentadienyl anion are not detected.Cyclic allyl anions are alkylated by ethene, formed by cleavage of THF with base or independently added. 6,6-Dimethylcyclohexadienyl anion undergoes slow fragmentation to toluene at room temperature.
- Sustmann, Reiner,Dern, Heinz-Juergen
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p. 2958 - 2971
(2007/10/02)
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- Singlet photosensitization of simple alkenes. Part 2. Photochemical transformation of cyclo-octa-1,5-dienes sensitized by aromatic ester
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Irradiation of an oxygen-free pentane solution of cis,cis- or cis,trans-cyclo-octa-1,5-diene, (1cc) or (1ct), in the presence of methyl benzoate as sensitizer gave the cis,trans-isomer and tricyclo[3.3.0.0 2,6]octane. However, the tricyclo-octane was not an immediate product from (1cc), but was formed via (1ct). Kinetic evidence and energetic considerations indicate a non-vertical singlet sensitization mechanism involving a singlet exciplex, which in turn falls apart leaving a twisted, excited singlet of the cyclo-octadiene. Two exciplexes, Ex1 and Ex 2, and therefore two twisted singlet cyclo-octadienes, C, 1p and t,1p, are postulated in order to rationalize the different reactivity of (1cc) and (1ct). No evidence for transannular interaction between the two double bonds was found from the quenching rate constants. Correlations between the quenching rate constants and the oxidation potentials of the cyclo-octadienes and cyclo-octenes suggest charge-transfer character for the exciplex. Asymmetric cis-trans photoisomerization sensitized by a chiral aromatic ester also supports the involvement of exciplex with a fairly rigid structure.
- Goto, Seizi,Takamuku, Setsuo,Sakurai, Hiroshi,Inoue, Yoshihisa,Hakushi, Tadao
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p. 1678 - 1682
(2007/10/02)
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