- Highly Stereoselective Synthesis of Vinylsilanes from Carbonyl Compounds
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The in situ generated (chlorolithiomethyl)trimethylsilane reacts at -60 deg C to -45 deg C with different aldehydes or ketones 1 to afford, after lithation with lithium naphthalenide at -78 deg C to 20 deg C, vinylsilanes 5a-h in a stereoselective manner.
- Barluenga, Jose,Fernandez-Simon, Jose L.,Concellon, Jose M.,Yus, Miguel
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Read Online
- A New Alkyllithium Reagent for the Direct Conversion of Aldehydes and Ketones to Vinylsilanes
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lithium (1), which is readily formed in hydrocarbon solvent from silane 2 and tert-butyllithium, reacts with carbonyl compounds to yield the corresponding alkenylsilanes 3 via a Peterson-type reaction.
- Bates, Tim F.,Thomas, Ruthanne D.
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Read Online
- Alkynylsilanes to cis-vinylsilanes via hydroboration
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New general non-oxidative procedures have been developed for the conversion of 1-trimethylsilylacetylenes to pure cis-1-trimethylsilylalkenes via hydroboration/protonolysis.
- Soderquist, John A.,Santiago, Braulio
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Read Online
- 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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- Catalytic Hydrogenation of Alkenes and Alkynes by a Cobalt Pincer Complex: Evidence of Roles for Both Co(I) and Co(II)
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The Co(I) complex, [Co(N2)(CyPNP)] (CyPNP = anion of 2,5-bis-(dicyclohexylphosphinomethyl)pyrrole), is active toward the catalytic hydrogenation of terminal alkenes and the semi-hydrogenation of internal alkynes under 2 bar of H2 (g) at room temperature. The products of alkyne semi-hydrogenation are a mixture of E- and Z-alkenes. By contrast, use of the related cobalt(I) precatalyst, [Co(PMe3)(CyPNP)], results in formation of exclusively Z-alkenes. A semi-stable Co(II) species, [CoH(CyPNP)], can also be generated by treatment of degassed solutions of [Co(N2)(CyPNP)] with H2. The CoII-hydride displays activity toward both alkene hydrogenation and isomerization, but its instability hampers implementation as a catalyst. Several species relevant to potential catalytic intermediates have been isolated and detected in solution. These compounds include alkene and alkyne adducts of Co(I) as well as a Co(III) dihydride species. Catalytic results with the compounds examined are most consistent with a process involving shuttling between Co(I) and Co(III) states. However, generation of small quantities of Co(II) during catalytic turnover appears to be responsible for the isomerization observed for alkyne semi-hydrogenation. The interplay of cobalt oxidation states within the same catalyst system is discussed in the context of mechanistic scenarios for catalytic hydrogenation.
- Alawisi, Hussah,Arman, Hadi D.,Tonzetich, Zachary J.
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p. 1062 - 1070
(2021/04/09)
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- Stereoselective Chromium-Catalyzed Semi-Hydrogenation of Alkynes
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Chromium complexes have found very little applications as hydrogenation catalysts. Here, we report a Cr-catalyzed semi-hydrogenation of internal alkynes to the corresponding Z-alkenes with good stereocontrol (up to 99/1 for dialkyl alkynes). The catalyst comprises the commercial reagents chromium(III) acetylacetonate, Cr(acac)3, and diisobutylaluminium hydride, DIBAL?H, in THF. The semi-hydrogenation operates at mild conditions (1-5 bar H2, 30 °C).
- Gregori, Bernhard J.,Nowakowski, Michal,Schoch, Anke,P?llath, Simon,Zweck, Josef,Bauer, Matthias,Jacobi von Wangelin, Axel
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p. 5359 - 5363
(2020/09/03)
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- Simpler and Cleaner Synthesis of Variously Capped Cobalt Nanocrystals Applied in the Semihydrogenation of Alkynes
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Unlike the classical organometallic approach, we report here a synthetic pathway requiring no reducing sources or heating to produce homogeneous hexagonal-close-packed cobalt nanocrystals (Co NCs). Involving a disproportionation process, this simple and fast (6 min) synthesis is performed at room temperature in the presence of ecofriendly fatty alcohols to passivate Co NCs. Through a recycling step, the yield of Co NCs is improved and the waste generation is limited, making this synthetic route cleaner. After an easy exchange of the capping ligands, we applied them as unsupported catalysts in the stereoselective semihydrogenation of alkynes.
- Moisset, A.,Petit, C.,Petit, M.,Salzemann, C.,Sodreau, A.,Vivien, A.
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supporting information
p. 13972 - 13978
(2020/10/09)
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- Geometric E→Z Isomerisation of Alkenyl Silanes by Selective Energy Transfer Catalysis: Stereodivergent Synthesis of Triarylethylenes via a Formal anti-Metallometallation
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An efficient geometrical E→Z isomerisation of alkenyl silanes is disclosed via selective energy transfer using an inexpensive organic sensitiser. Characterised by operational simplicity, short reaction times (2 h), and broad substrate tolerance, the reaction displays high selectivity for trisubstituted systems (Z/E up to 95:5). In contrast to thermal activation, directionality results from deconjugation of the π-system in the Z-isomer due to A1,3-strain thereby inhibiting re-activation. The structural importance of the β-substituent logically prompted an investigation of mixed bis-nucleophiles (Si, Sn, B). These versatile linchpins also undergo facile isomerisation, thereby enabling a formal anti-metallometallation. Mechanistic interrogation, supported by a theoretical investigation, is disclosed together with application of the products to the stereospecific synthesis of biologically relevant target structures.
- Fa?bender, Svenja I.,Molloy, John J.,Mück-Lichtenfeld, Christian,Gilmour, Ryan
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p. 18619 - 18626
(2019/11/16)
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- Stereoselective Alkyne Hydrogenation by using a Simple Iron Catalyst
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The stereoselective hydrogenation of alkynes constitutes one of the key approaches for the construction of stereodefined alkenes. The majority of conventional methods utilize noble and toxic metal catalysts. This study concerns a simple catalyst comprised of the commercial chemicals iron(II) acetylacetonate and diisobutylaluminum hydride, which enables the Z-selective semihydrogenation of alkynes under near ambient conditions (1–3 bar H2, 30 °C, 5 mol % [Fe]). Neither an elaborate catalyst preparation nor addition of ligands is required. Mechanistic studies (kinetic poisoning, X-ray absorption spectroscopy, TEM) strongly indicate the operation of small iron clusters and particle catalysts.
- Gregori, Bernhard J.,Schwarzhuber, Felix,P?llath, Simon,Zweck, Josef,Fritsch, Lorena,Schoch, Roland,Bauer, Matthias,Jacobi von Wangelin, Axel
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p. 3864 - 3870
(2019/07/31)
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- Efficient Z-Selective Semihydrogenation of Internal Alkynes Catalyzed by Cationic Iron(II) Hydride Complexes
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The bench-stable cationic bis(σ-B-H) aminoborane complex [Fe(PNPNMe-iPr)(H)(η2-H2B = NMe2)]+ (2) efficiently catalyzes the semihydrogenation of internal alkynes, 1,3-diynes and 1,3-enynes. Moreover, selective incorporation of deuterium was achieved in the case of 1,3-diynes and 1,3-enynes. The catalytic reaction takes place under mild conditions (25 °C, 4-5 bar H2 or D2) in 1 h, and alkenes were obtained with high Z-selectivity for a broad scope of substrates. Mechanistic insight into the catalytic reaction, explaining also the stereo- and chemoselectivity, is provided by means of DFT calculations. Intermediates featuring a bisdihydrogen moiety [Fe(PNPNMe-iPr)(η2-H2)2]+ are found to play a key role. Experimental support for such species was unequivocally provided by the fact that [Fe(PNPNMe-iPr)(H)(η2-H2)2]+ (3) exhibited the same catalytic activity as 2. The novel cationic bisdihydrogen complex 3 was obtained by protonolysis of [Fe(PNPNMe-iPr)(H)(η2-AlH4)]2 (1) with an excess of nonafluoro-tert-butyl alcohol.
- Gorgas, Nikolaus,Brünig, Julian,St?ger, Berthold,Vanicek, Stefan,Tilset, Mats,Veiros, Luis F.,Kirchner, Karl
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supporting information
p. 17452 - 17458
(2019/11/03)
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- Phosphine-free cobalt pincer complex catalyzed: Z -selective semi-hydrogenation of unbiased alkynes
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Herein, we report a novel, molecularly defined NNN-type cobalt pincer complex catalyzed transfer semi-hydrogenation of unbiased alkynes to Z-selective alkenes. This unified process is highly stereo- and chemo-selective and exhibits a broad scope as well as wide functional group tolerance. Ammonia-borane (AB), a bench-stable substrate with high gravimetric hydrogen capacity, was used as a safe and practical transfer hydrogenating source.
- Landge, Vinod G.,Pitchaimani, Jayaraman,Midya, Siba P.,Subaramanian, Murugan,Madhu, Vedichi,Balaraman, Ekambaram
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p. 428 - 433
(2018/02/07)
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- Z-Selective alkyne semi-hydrogenation catalysed by piano-stool N-heterocyclic carbene iron complexes
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NHC iron(ii) piano-stool complexes catalyse the selective semi-hydrogenation of alkynes to alkenes using silanes as reducing agents. Aromatic terminal alkynes are converted to styrenes without over-reduction to ethylbenzene derivatives. Furthermore, internal aryl alkynes afford cis-alkenes with excellent Z-selectivity.
- Johnson, Chloe,Albrecht, Martin
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p. 2779 - 2783
(2018/06/14)
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- COBALT COMPLEXES, PROCESS FOR PREPARATION AND USE THEREOF
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The present invention discloses a cobalt compound of formula (I), a process for the preparation and use thereof. The present invention further relates to a pharmaceutical composition and a method inhibition of Tau Aggregation in a subject in need thereof using compound of formula (I).
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Page/Page column 15; 16
(2019/01/06)
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- Palladium-catalyzed olefination of aryl/alkyl halides with trimethylsilyldiazomethane via carbene migratory insertion
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The direct olefination of aryl/alkyl halides with trimethylsilyldiazomethane (TMSD) as a C1- or C2-unit was achieved successfully via a metal carbene migratory insertion process, which offered a new access to afford (E)-vinyl silanes and (E)-silyl-substituted α,β-unsaturated amides in good yields and high chemoselectivity.
- Mu, Qiu-Chao,Wang, Xing-Ben,Ye, Fei,Sun, Yu-Li,Bai, Xing-Feng,Chen, Jing,Xia, Chun-Gu,Xu, Li-Wen
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supporting information
p. 12994 - 12997
(2018/11/23)
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- Selective partial hydrogenation of alkynes to (Z)-alkenes with ionic liquid-doped nickel nanocatalysts at near ambient conditions
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A selective hydrogenation method for forming (Z)-alkenes from alkynes has been developed using a catalyst system of cheap Ni-NPs in a nitrile functionalised imidazolium based ionic liquid (IL) operating under very mild reaction conditions of 30-50 °C and 1-4 bar H2 pressure.
- Konnerth, Hannelore,Prechtl, Martin H. G.
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supporting information
p. 9129 - 9132
(2016/07/22)
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- Enantioselective synthesis of α-aminosilanes by copper-catalyzed hydroamination of vinylsilanes
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The synthesis of α-aminosilanes by a highly enantio- and regioselective copper-catalyzed hydroamination of vinylsilanes is reported. The system employs Cu-DTBM-SEGPHOS as the catalyst, diethoxymethylsilane as the stoichiometric reductant, and O-benzoylhyd
- Niljianskul, Nootaree,Zhu, Shaolin,Buchwald, Stephen L.
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p. 1638 - 1641
(2015/02/05)
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- Stereoselective peterson olefinations from bench-stable reagents and N-phenyl imines
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The synthesis of bench-stable α,α-bis(trimethylsilyl)toluenes and tris(trimethylsilyl)methane is described and their use in stereoselective Peterson olefinations has been achieved with a wide substrate scope. Product stereoselectivity was poor with carbonyl electrophiles (E/Z ~1:1 to 4:1) though this was significantly improved by employing the corresponding substituted N-benzylideneaniline (up to 99:1) as an alternative electrophile. The olefination byproduct was identified as N,N-bis(trimethylsilyl)aniline and could be easily separated from product by aqueous acid extraction. Evidence for an autocatalytic cycle has been obtained.
- Das, Manas,Manvar, Atul,Jacolot, Ma?wenn,Blangetti, Marco,Jones, Roderick C.,O'Shea, Donal F.
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supporting information
p. 8737 - 8740
(2015/06/08)
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- Stereoselective iron-catalyzed alkyne hydrogenation in ionic liquids
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Iron(0) nanoparticles in ionic liquids (ILs) have been shown to catalyse the semi-hydrogenation of alkynes. In the presence of a nitrile-functionalised IL or acetonitrile, stereoselective formation of (Z)-alkenes was observed. The biphasic solvent system allowed facile separation and re-use of the catalyst. The Royal Society of Chemistry 2014.
- Gieshoff, Tim N.,Welther, Alice,Kessler, Michael T.,Prechtl, Martin H.G.,Jacobi Von Wangelin, Axel
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supporting information
p. 2261 - 2264
(2014/03/21)
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- Steric effects in reactions of decamethyltitanocene hydride with internal alkynes, conjugated diynes, and conjugated dienes
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Titanocene hydride [Cp*2TiH] (Cp* = η5-C5Me5) (1) readily inserts simple internal alkynes R1C≡CR2 into its Ti-H bond, yielding titanocene alkenyl Ti(III) compounds of two structural types. The less sterically congested products [Cp*2Ti(R1C=CHR 2)] (2a-e) contain a σ1-bonded alkenyl group, whereas the products bearing at least one trimethylsilyl substituent and other bulky substituents (R1 = SiMe3; R2 = SiMe 3, 4a; CMe3, 4b; and Ph, 4c) possess a remarkable Ti-H agostic bond of the σ1-bonded alkenyl group. This feature is consistent with solution EPR spectra of 4a-4c showing a doublet due to coupling of the hydrogen nucleus with the Ti(III) d1 electron. Compound 1 reacts with one molar equivalent of conjugated buta-1,3-diynes (RC≡C) 2 to give η3-butenyne complexes (R = SiMe3, 5a; CMe3, 5b). The Ti(III) complexes 2a-2e and 5a and 5b were oxidatively chlorinated with PbCl2 to give Ti(IV) chloro-alkenyl complexes [Cp*2TiCl(R1C=CHR2)] 3a-3e and chloro-alkenynes 6a and 6b, respectively. 1H and 13C NMR spectra of 3a-3e and 6a and 6b revealed that these compounds form equilibria of two atropisomers differing by the anti- and syn-position of the chlorine and the alkenyl hydrogen atoms. Such atropisomers are denoted by appended (a) and (b), respectively. Compound 1 reacted with 1,3-butadiene to give a thermally stable π-bonded 1-methylallyl complex (7) and with penta-1,3-diene to give a thermally labile 1,3-dimethylallyl complex (8). In toluene-d8 solutions 7 dissociated at 80 °C and 8 at room temperature to give [Cp*Ti(C5Me4CH2)] and corresponding alkenes. Other methyl-substituted dienes, isoprene, 4-methylpenta-1,3-diene, and 2,3-dimethylbuta-1,3-diene, did not yield observable π-bonded allyl products; the dienes were, however, hydrogenated to olefins with concomitant formation of [CpTi(C5Me4CH2)]. Compound 1 was shown to catalyze the hydrogenation of the alkynes and dienes to olefins and ultimately to alkanes under lower than atmospheric hydrogen pressure at room temperature. Single-crystal structures were determined for 3d(a), 3e(a), 4a-4c, 5a, 6b, and 7.
- Pinkas, Jiri,Gyepes, Robert,Cisarova, Ivana,Kubista, Jiri,Horacek, Michal,Mach, Karel
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p. 3399 - 3413
(2014/08/05)
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- A frustrated-Lewis-pair approach to catalytic reduction of alkynes to cis-alkenes
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Frustrated Lewis pairs are compounds containing both Lewis acidic and Lewis basic moieties, where the formation of an adduct is prevented by steric hindrance. They are therefore highly reactive, and have been shown to be capable of heterolysis of molecular hydrogen, a property that has led to their use in hydrogenation reactions of polarized multiple bonds. Here, we describe a general approach to the hydrogenation of alkynes to cis-alkenes under mild conditions using the unique ansa-aminohydroborane as a catalyst. Our approach combines several reactions as the elementary steps of the catalytic cycle: hydroboration (substrate binding), heterolytic hydrogen splitting (typical frustrated-Lewis-pair reactivity) and facile intramolecular protodeborylation (product release). The mechanism is verified by experimental and computational studies.
- Chernichenko, Konstantin,Madarasz, Adam,Papai, Imre,Nieger, Martin,Leskelae, Markku,Repo, Timo
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p. 718 - 723
(2013/08/23)
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- Copper-catalyzed highly selective semihydrogenation of non-polar carbon-carbon multiple bonds using a silane and an alcohol
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A copper catalyst bearing a suitable Xantphos derivative or NHC ligand was found to be highly efficient for the selective semihydrogenation of non-polar unsaturated compounds using a mixture of a silane and an alcohol as reducing agent. The catalytic system was useful for the selective semihydrogenation of internal alkynes to (Z)-alkenes with suppression of overreduction to the corresponding alkanes. Furthermore, semihydrogenations of terminal alkyne, 1,2-diene, 1,3-diene, 1,3-enyne and 1,3-diyne systems were also achieved selectively. Copyright
- Semba, Kazuhiko,Fujihara, Tetsuaki,Xu, Tinghua,Terao, Jun,Tsuji, Yasushi
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supporting information; experimental part
p. 1542 - 1550
(2012/08/08)
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- Facile regio- and stereoselective hydrometalation of alkynes with a combination of carboxylic acids and group 10 transition metal complexes: Selective hydrogenation of alkynes with formic acid
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A facile, highly stereo- and regioselective hydrometalation of alkynes generating alkenylmetal complex is disclosed for the first time from a reaction of alkyne, carboxylic acid, and a zerovalent group 10 transition metal complex M(PEt3)4 (M = Ni, Pd, Pt). A mechanistic study showed that the hydrometalation does not proceed via the reaction of alkyne with a hydridometal generated by the protonation of a carboxylic acid with Pt(PEt 3)4, but proceeds via a reaction of an alkyne coordinate metal complex with the acid. This finding clarifies the long proposed reaction mechanism that operates via the generation of an alkenylpalladium intermediate and subsequent transformation of this complex in a variety of reactions catalyzed by a combination of Bronsted acid and Pd(0) complex. This finding also leads to the disclosure of an unprecedented reduction of alkynes with formic acid that can selectively produce cis-, trans-alkenes and alkanes by slightly tuning the conditions.
- Shen, Ruwei,Chen, Tieqiao,Zhao, Yalei,Qiu, Renhua,Zhou, Yongbo,Yin, Shuangfeng,Wang, Xiangbo,Goto, Midori,Han, Li-Biao
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supporting information; experimental part
p. 17037 - 17044
(2011/12/04)
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- A convenient titanium-mediated intermolecular alkyne-carbonate coupling reaction
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A direct diastereoselective titanium-mediated intermolecular coupling of internal alkynes with dialkyl carbonates under Kulinkovich-type reaction conditions is presented. The influence of the structures of the coupling partners on the yields and regioselectivities of this transformation is described.
- Wolan, Andrzej,Cadoret, Frédéric,Six, Yvan
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experimental part
p. 7429 - 7439
(2009/12/06)
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- Stereo- and regiocontrol in ene-dimerisation and trimerisation of 1-trimethylsilyl-3-phenylcyclopropene
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1-Trimethylsilyl-3-phenylcyclopropene and its 2D-analog undergo a highly stereocontrolled ene-reaction to give a single dimer. Further reaction leads to one or more trimers derived through two ene-reactions. The dimer formed easily undergoes cycloaddition
- Sheshenev, Andrey E.,Baird, Mark S.,Bolesov, Ivan G.,Shashkov, Alexandre S.
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experimental part
p. 10552 - 10564
(2010/03/01)
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- Regio- and stereoselective synthesis of multisubstituted vinylsilanes via zirconacycles
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Image Persented A series of novel multisubstituted vinylsilanes are prepared regio- and stereoselectively by carbozirconation of various alkynylsilanes through zirconacycles such as zirconacyclopropenes and zirconacyclopentenes and the subsequent transformation of the formed alkenylzirconocene complexes.
- Nishihara, Yasushi,Saito, Daisuke,Tanemura, Kenki,Noyori, Shintaro,Takagi, Kentaro
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supporting information; scheme or table
p. 3546 - 3549
(2011/02/22)
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- Platinum-catalyzed nucleophilic addition of vinylsilanes at the β-position
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In the presence of catalytic amounts of PtCl2 and metal Iodides, β-substituted vlnylsllanes reacted with aldehydes at the β-position to give allyl silyl ethers. The Pt-catalyzed addition to aromatic aldehydes proceeded efficiently in the presence of Lil. The combined use of PtCl 2 and Mnl2 was found to be effective In addition to aliphatic aldehydes.
- Miura, Katsukiyo,Inoue, Gen,Sasagawa, Hisashi,Kinoshita, Hidenori,Ichikawa, Junji,Hosomi, Akira
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supporting information; experimental part
p. 5066 - 5069
(2009/12/28)
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- Synthesis of (E)-alkenes via hydroindation of C{triple bond, long}C in InCl3-NaBH4 system
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In InCl3-NaBH4-MeCN system, terminal aryl alkynes could couple with aryl iodides and bromides to give disubstituted alkenes via hydroindation of C{triple bond, long}C. In the similar way, (E)-alkenylsilanes were synthesized via reduction of alkynylsilanes in tetrahydrofuran (THF) in high yields. The processes showed high regio- and stereoselectivity.
- Wang, Chunyan,Yan, Lei,Zheng, Zhiguo,Yang, Deyu,Pan, Yuanjiang
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p. 7712 - 7717
(2007/10/03)
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- Transformation of aldehydes into (E)-1-alkenylsilanes and (E)-1-alkenylboronic esters with a catalytic amount of a chromium salt
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(Diiodomethyl)trimethylsilane (Me3SiCHI2, 1) is produced by treatment of iodoform with manganese in the presence of Me 3SiCl. Aldehydes are converted to (E)-1-trimethylsilyl-1-alkenes in a stereoselective manner with a geminal dichromium reagent generated from 1, manganese, Me3SiCl, and a catalytic amount of CrCl 3[thf]3 in THF. Similarly, (E)-1-alkenylboronic esters are prepared stereoselectively in good to excellent yields by treatment of aldehydes with a geminal dichromium reagent derived from Cl2CHB(OR) 2 [(OR)2 = OCMe2CMe2O] and LiI instead of 1.
- Takai, Kazuhiko,Kunisada, Yuji,Tachibana, Yukiko,Yamaji, Nana,Nakatani, Emi
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p. 1581 - 1586
(2007/10/03)
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- Transmetalation as a Route to Novel Styryllithium Reagents
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(Equation presented) Transmetalation of β-tributyl(styryl)stannanes with n-BuLi gives the functional equivalents of the corresponding styryllithium intermediates. Reaction of the intermediates with chlorotrimethylsilane, iodomethane, or dimethyl sulfate gives the substituted styryl products in moderate to good yields. In all cases, the configuration about the double bond was retained in the products.
- Rim, Chinwon,Son, David Y.
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p. 3443 - 3445
(2007/10/03)
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- Cross-coupling reaction of thermally stable titanium(II)-alkyne complexes with aryl halides catalysed by a nickel complex
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The first cross-coupling reaction of thermally stable titanium(II)-alkyne complexes with aryl iodides in the presence of a catalytic amount of Ni(cod)2 is presented.
- Obora, Yasushi,Moriya, Hiroyuki,Tokunaga, Makoto,Tsuji, Yasushi
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p. 2820 - 2821
(2007/10/03)
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- Titanium-mediated carboxylation of alkynes with carbon dioxide
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The regioselective carboxylation of nonactivated internal alkynes can be performed with carbon dioxide under atmospheric pressure using a simple procedure based on the chemistry of Sato-type diisopropyloxytitanacyclopropenes. Various polysubstituted vinylcarboxylic acids and butenolides can be prepared in this way. In addition, this paper describes an experimental protocol for the preparation of solutions of (η2-cyclopentene)diisopropyloxytitanium. This complex also reacts with carbon dioxide, and mediates pinacol coupling of acetophenone. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.
- Six, Yvan
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p. 1157 - 1171
(2007/10/03)
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- Synthesis of the racemic forms of carbon-carbon double bond locked analogues of strobilurins which are characterized by a 2-arylcyclopropane ring cis-substituted at C-1 by the methyl (E)-3-methoxypropenoate unit
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The racemic forms of three new carbon-carbon double bond locked analogues of strobilurins, which are characterized by a 2-arylcyclopropane ring cis-substituted at C-1 by the methyl (E)-3-methoxypropenoate unit, have been synthesized according to a strateg
- Carpita, Adriano,Ribecai, Arianna,Rossi, Renzo,Stabile, Paolo
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p. 3673 - 3680
(2007/10/03)
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- Synthesis of (Z)-vinylsilanes with high diastereoselectivity by using samarium diiodide
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matrix presented β-Elimination of O-acetyl 1-chloro-1-trimethylsilylalkan-2-ols 1 was achieved by using samarium diiodide as a metaling reagent and afforded the corresponding (Z)-vinylsilanes with high stereoselectivity. The starting compounds 1 were easi
- Concelloen, Jose M.,Bernad, Pablo L.,Bardales, Eva
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p. 937 - 939
(2007/10/03)
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- α-Lithioalkoxysilanes: Applications to alkene synthesis
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α-Lithioalkoxysilanes [RO(Me2)Si]CH(Li)(X), where R=Me or Et and X=H or SiMe3, react with carbonyl compounds in hydrocarbon solution to produce alkenes in moderate to high yield via Peterson-type reactions. For X=SiMe3, the corresponding vinylsilanes are isolated directly following work-up. The reaction is regiospecific and shows fair stereoselectivity. When the carbonyl substrates are cyclic ketones in six- or seven-membered rings, the products are exocyclic alkenes. For X=H, the initial product is a β-hydroxysilane, which is then efficiently converted to the corresponding terminal alkene by heating with sodium acetate in acetic acid. Both types of α-lithioalkoxysilane reagents are amenable to reaction with enolizable carbonyl compounds.
- Bates, Tim F.,Dandekar, Sushama A.,Longlet, Jon J.,Thomas, Ruthanne D.
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- Stereoselective synthesis of enamides by a Peterson reaction manifold
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equation presented Vinylsilanes are converted into enamides by a sequence comprising epoxidation, nucleophilic ring opening of the resulting epoxysilanes with NaN3, and reduction of the azide, followed by a "one-pot" N-acylation/Peterson elimin
- Fuerstner, Alois,Brehm, Christof,Cancho-Grande, Yolanda
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p. 3955 - 3957
(2007/10/03)
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- Preparation of methylenedifluorocyclopropanes via cyclopropyl anion promoted β-elimination
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Preparation of methylenedifluorocyclopropanes 2 through the β- elimination reaction promoted by difluorocyclopropyl anion formed by cleavage of C-Si bond with TBAF is described. Base-catalyzed isomerization of 2 to difluorocyclopropene 11 shows the latter structure thermodynamically more stable in contrast to non-fluorinated cases. Application of this method to the synthesis of methylenedifluorocyclopropylglycine (F2MCPG) derivative 17 is also presented.
- Shibuya, Akira,Okada, Midori,Nakamura, Yuko,Kibashi, Mie,Horikawa, Hiroaki,Taguchi, Takeo
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p. 10325 - 10340
(2007/10/03)
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- Reductive Pauson-Khand reaction using the (RC≡CR′) Co2(CO) 6/CF3COOH system
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Cyclopentanones are formed in the Pauson-Khand reaction of cobalt alkyne complexes in the presence of TFA. The in situ precursor complexes were formed on the reduction of CoBr2 by zinc metal in the presence of the alkynes under carbon monoxide
- Rao, M. Lakshmi Narayana,Periasamy, Mariappan
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p. 143 - 146
(2007/10/03)
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- A mild preparation of vinyliodides from vinylsilanes
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A new method for the synthesis of vinyliodides from vinylsilanes is presented. Using N-iodiosuccinimide in acetonitrile or acetonitrile/monochloroacetonitrile, this transformation is cleanly effected at room temperature under virtually neutral conditions.
- Stamos, Dean P.,Taylor, Andrew G.,Kishi, Yoshito
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p. 8647 - 8650
(2007/10/03)
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- Thermally-induced 1,2-shifts to convert olefins to carbenes: Does silicon do it? if so, why not carbon?
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Thermal isomerization of olefins to carbenes via a 1,2-silyl shift was examined by both experiment and theory. No evidence of this rearrangement was found for acyclic vinylsilanes, nor could electronic assistance by silicon be identified in cis, trans isomerizations. Serendipitous synthesis of a 2,4-dimethylene-1,3-disilacyclobutane allowed a kinetic examination of its gas-phase, thermal ring expansion to a 2-methylene-1,3-disilacyclopentene. The Arrhenius parameters (log A = 12.48, Eact = 54.09 kcal/mol) are the first to be reported for an olefin-to-carbene rearrangement. The analogous all-carbon system failed to ring expand. Ab initio calculations revealed that this was opposite to any predictions which would be made from ring strain considerations. Calculations showed that for silyl migration the transition state was late and was actually the carbene, while for carbon migration the TS was early and considerably higher in energy than the resulting carbene. The 2-methylene-1-silacyclobutane rearrangement (ref 5) was reexamined to find that reversible ring opening to a 1,4-diradical occurred at temperatures below those required to ring expand via a carbene TS.
- Barton, Thomas J.,Lin, Jibing,Ijadi-Maghsoodi, Sina,Power, Martin D.,Zhang, Xianping,Ma, Zhongxin,Shimizu, Hideaki,Gordon, Mark S.
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p. 11695 - 11703
(2007/10/03)
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- Selective reduction of alkynes by the reagent Sml2 - Transition metal catalysts - proton donors
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Alkynes were selectively reduced to cis-olefins under mild conditions by SmI2 in admixture with first-row transition metal catalysts and appropriate proton donors, in which the corresponding transition metal hydrides are presumed as the reactive species. The conditions also effected the conversion of 1,6-diynes to the corresponding five-membered carbocycles.
- Inanaga, Junji,Yokoyama, Yasuo,Baba, Yoshiyasu,Yamaguchi, Masaru
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p. 5559 - 5562
(2007/10/02)
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- Heck-type Reaction of Iodotrimethylsilane with Olefins Affording Alkenyltrimethylsilane
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Iodotrimethylsilane reacted with styrene derivatives in the presence of triethylamine and a palladium catalyst to give β-styrylsilanes.
- Yamashita, Hiroshi,Kobayashi, Toshi-aki,Hayashi, Teruyuki,Tanaka, Masato
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p. 761 - 762
(2007/10/02)
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- Simple preparation of α-bromo acyl silanes α-ketoacyl silanes and α-ketoesters from silyl acetylenes
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α-Bromo- and α-keto-acyl silanes may simply and efficiently be prepared in short reaction schemes from silyl acetylenes; α-ketoacyl silanes are also implicated in a one-pot synthesis of α-ketoesters from silyl acetylenes.
- Bulman Page, Philip C.,Rosenthal, Stephen
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p. 2573 - 2586
(2007/10/02)
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- A New Version of the Peterson Olefination Using Bis(trimethylsilyl)methyl Derivatives and Fluoride Ion as Catalyst
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Reaction between a variety of bis(trimethylsilyl)methyl derivatives and carbonyl compounds under fluoride ion as catalyst is described.The reaction works especially well with nonenolizable carbonyl compounds to give the expected alkenes in high yields and, in some cases, with high stereoselectivity.Application of this methodology to an intramolecular alkenation providing a tricyclic benzocarbacephem ring system is also described.
- Palomo, Claudio,Aizpurua, Jesus M.,Garcia, Jesus M.,Ganboa, Inaki,Cossio, F. P.,et al.
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p. 2498 - 2503
(2007/10/02)
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- TRIMETHYLSILYLDIAZOMETHANE: A USEFUL REAGENT FOR THE PREPARATION OF (Z)-1-TRIMETHYLSILYL-1-ALKENES
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The rhodium(II) pivalate-catalysed decomposition of α-trimethylsilyldiazoalkenes stereoselectivity affords (Z)-1-trimethylsilyl-1-alkenes in good yields.Keywords trimethylsilyldiazomethane; α-trimethylsilyldiazoalkane; (Z)-1-trimethylsilyl-1-alkene; rhodium(II) pivalate; catalytic decomposition
- Aoyama, Toyohiko,Shioiri, Takayuki
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p. 2261 - 2262
(2007/10/02)
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- The Stereochemistry of Organometallic Compounds. XXXIV. Regioselection in the Hydroformylation of Silylalkenes
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The regiochemistry of hydroformylation of alkenes can be controlled by use of bulky silyl groups attached to the alkene.Use of the t-butyldiphenylsilyl group leads to almost total regiocontrol and the method has been applied to the synthesis of aldols.
- Doyle, M. Michael,Jackson, W. Roy,Perlmutter, Patrick
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p. 1907 - 1918
(2007/10/02)
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- Formation and Reactions of Olefins with Vicinal Silyl and Stannyl Substituents
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The silicon-tin bond in Me3SiSnR3 (R=Me, n-Bu) adds regio- and stereospecifically to 1-alkynes and also to a limited number of nonterminal alkynes when Pd(PPh3)4 is added as a catalyst.The use of the (Z)-silylstannylalkenes thus formed in synthesis either
- Mitchell, T. N.,Wickenkamp, R.,Amamria, A.,Dicke, R.,Schneider, U.
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p. 4868 - 4874
(2007/10/02)
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- Palladium-mediated silylation of organic halides with disilane/F- reagent
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Under catalytic influence of tetrakis(triphenylphosphine)palladium, tris(diethylamino)sulfonium trimethyldiflourosilicate promoted the reaction of vynil halides with hexamethyldisilane to give corresponding vinyl silanes in good yields chemoselectivity and stereospecifically.
- Hatanaka, Yasou,Hiyama, Tamajiro
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p. 4715 - 4718
(2007/10/02)
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- Reaction of Diazonium Salts with Transition Metals. Part 11. Palladium-catalyzed Aryldesilylation of Alkenylsilanes by Arenediazonium Salts
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Under palladium(0) catalysis, both (E)- and (Z)-RCH=CHSiMe3(R=Rh, 4-MeC6H4, 4-NO2C6H4, n-C6H13, and MeOCH2) were easily aryldesilylated by ArN2X(Ar=Ph, 4-MeC6H4, 4-BrC6H4 and 4-NO2C6H4; X=BF4, PF6, and Cl) to give (E)-RCH=CHAr and RC(Ar)=CH2 as the main products at 25 deg C in acetonitrile. anti- and syn-1,2-Elimination of Pd(0) and Me3Si from the adducts, threo- and erythro-RCH(PdX)CHSiMe3, generated from ArPdX and (E) and (Z)-RCH=CHSiMe3, respectively, are proposed for the formation of (E)-RCH=CHAr from either isomer of RCH=CHSiMe3.
- Ikenaga, Kazutoshi,Kikukawa, Kiyoshi,Matsuda, Tsutomu
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p. 1959 - 1964
(2007/10/02)
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