- Ytterbium(II)-aromatic imine dianion complexes-catalyzed isomerization of terminal alkynes
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Ytterbium-aromatic imine dianion complexes, easily prepared from ytterbium metal and aromatic imines, can act as effective catalysts for the isomerization of terminal alkynes to afford internal alkynes in good to high yields.
- Makioka, Yoshikazu,Saiki, Akira,Takaki, Ken,Taniguchi, Yuki,Kitamura, Tsugio,Fujiwara, Yuzo
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- Migratory Hydrogenation of Terminal Alkynes by Base/Cobalt Relay Catalysis
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Migratory functionalization of alkenes has emerged as a powerful strategy to achieve functionalization at a distal position to the original reactive site on a hydrocarbon chain. However, an analogous protocol for alkyne substrates is yet to be developed. Herein, a base and cobalt relay catalytic process for the selective synthesis of (Z)-2-alkenes and conjugated E alkenes by migratory hydrogenation of terminal alkynes is disclosed. Mechanistic studies support a relay catalytic process involving a sequential base-catalyzed isomerization of terminal alkynes and cobalt-catalyzed hydrogenation of either 2-alkynes or conjugated diene intermediates. Notably, this practical non-noble metal catalytic system enables efficient control of the chemo-, regio-, and stereoselectivity of this transformation.
- Liu, Bingxue,Liu, Qiang,Liu, Xufang
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supporting information
p. 6750 - 6755
(2020/03/13)
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- Unprecedented Spectroscopic and Computational Evidence for Allenyl and Propargyl Titanocene(IV) Complexes: Electrophilic Quenching of Their Metallotropic Equilibrium
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The synthesis and structural characterization of allenyl titanocene(IV) [TiClCp2(CH=C=CH2)] 3 and propargyl titanocene(IV) [TiClCp2(CH2-C≡C-(CH2)4CH3)] 9 have been described for the first time. Advanced NMR methods including diffusion NMR methods (diffusion pulsed field gradient stimulated spin echo (PFG-STE) and DOSY) have been applied and established that these organometallics are monomers in THF solution with hydrodynamic radii (from the Stokes-Einstein equation) of 3.5 and 4.1 ? for 3 and 9, respectively. Full 1H, 13C, Δ1H, and Δ13C NMR data are given, and through the analysis of the Ramsey equation, the first electronic insights into these derivatives are provided. In solution, they are involved in their respective metallotropic allenyl-propargyl equilibria that, after quenching experiments with aromatic and aliphatic aldehydes, ketones, and protonating agents, always give the propargyl products P (when carbonyls are employed), or allenyl products A (when a proton source is added) as the major isomers. In all the cases assayed, the ratio of products suggests that the metallotropic equilibrium should be faster than the reactions of 3 and 9 with electrophiles. Indeed, DFT calculations predict lower Gibbs energy barriers for the metallotropic equilibrium, thus confirming dynamic kinetic resolution.
- Ruiz-Muelle, Ana Belén,O?a-Burgos, Pascual,Ortu?o, Manuel A.,Oltra, J. Enrique,Rodríguez-García, Ignacio,Fernández, Ignacio
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p. 2427 - 2439
(2016/02/14)
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- Highly selective barbier-type propargylations and allenylations catalyzed by titanocene(III)
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The alkyne functional group is found in many bioactive natural products and is the key to many important chemical transformations developed over recent years. Moreover, allenes have recently gained relevance as versatile reagents in organic synthesis. Mild, catalytic methods to enable the selective introduction of either alkyne or allene motifs into organic molecules are very valuable but, as yet, quite scarce. We describe an extremely mild and selective method for either the propargylation or allenylation of carbonyl compounds catalyzed by the abundant, safe, and inexpensive metal titanium. These reactions can selectively provide homopropargylic alcohols from aldehydes and ketones or α-hydroxy-allenes from aldehydes. The mechanisms involved were also investigated. Copyright
- Munoz-Bascon, Juan,Sancho-Sanz, Iris,Alvarez-Manzaneda, Enrique,Rosales, Antonio,Oltra, J. Enrique
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supporting information
p. 14479 - 14486,8
(2020/08/24)
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- Isomerization of terminal alkynes catalyzed by itterbium(II)-aromatic imine complexes
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Ytterbium-aromatic imine dianion complexes 2, which can easily be prepared from metallic ytterbium and aromatic imines 1, can act as effective catalysts for the isomerization of terminal alkynes 3 under mild conditions to afford internal alk-2-ynes 4 in good yields.In the reaction of 1-hexene 3a, 2-hexyne 3a, 2-hexyne 4a can be simply obtained by trap-to-trap distillation and the catalytic system can be reused for the isomerization of 3a without other treatments. - Keywords: lanthanoid-imine complex; terminal alkyne; isomerization; alk-2-yne
- Makioka, Yoshikazu,Taniguchi, Yuki,Kitamura, Tsugio,Fujiwara, Yuzo,Saiki, Akira,Takaki, Ken
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p. 349 - 356
(2007/10/03)
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- Carbocycle Formation via Intramolecular Insertion of Alkynes into Titanium-Carbon Bonds
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Treatment of alkyl titanocene chloride complexes with the Lewis acids EtAlCl2 or Me2AlCl resulted in intramolecular insertion of a tethered alkyne into the Ti-C bond.Regioselective alkyne insertion produced exocyclic trisubstituted alkene products resulting from four-, five-, and six-membered ring formation.In the case of cyclohexane formation, the alkyne was found to insert with syn stereoselectivity.
- Harms, Arthur E.,Stille, John R.
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p. 6565 - 6568
(2007/10/02)
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- Activation of Alkynes by the Dinitrogen Complex Towards Catalytic Oligomerization and Cyclization Reactions
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The complex catalyses oligomerization and cyclization reactions of alkynes under mild conditions.Hence, alkyne cocyclotrimerization to benzene derivatives was mainly observed for ethyl propiolate, affording the three possible isomers of tricarbethoxybenzene; phenylacetylene undergoes mainly linear dimerization to trans-PhCCCH=CHPh and trimerization; linear dimers are also the predominant products from 3-hexyne, but 1-octyne (with a long chain) undergoes mainly isomerization to 2-octyne; higher oligomers are also usually formed.Except for ethyl propiolate, hydrogenated dimers are detected in low yields (e.g. trans,trans-PhCH=CHCH=CHPh from phenylacetylene), whereas 3-hexene is formed in considerable yield from 3-hexyne.A novel type of cocyclization reaction with a nitrile (NCMe) appears to occur with phenylacetylene to give (although in low yield) 4,6-dimethyl-5-phenyl-pyrimidine.Alkynols are unreactive under the chosen conditions. - Keywords: Alkynes; Catalysis; Dinitrogen complex; Nitriles; Pyrimidine
- Herrmann, Rudolf,Pombeiro, Armando J. L.
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p. 583 - 590
(2007/10/02)
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- Selective Synthesis of Alkynes by Catalytic Dehydrogenation of Alkenes over Polymer-supported Palladium Acetate in the Liquid Phase
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A heterogenized palladium acetate catalyst, in the presence of oxygen and perchloric acid in ethanol-water caused the direct conversion of terminal and internal monoalkenes into the corresponding alkynes, under mild conditions and in high yields; Wacker-type ketonization occurs with the same reagents in dioxane-water.
- Cum, Giampietro,Gallo, Raffaele,Ipsale, Salvatore,Spadaro, Agatino
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p. 1571 - 1573
(2007/10/02)
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- Application of Phase Transfer Catalysis, 14.- Preparation of Alkynes from Halides with Solid Potassium tert-Butoxide and Crown Ether
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Preparatively very simple and mild HX eliminations with solid potassium tert-butoxide in petroleum ether in the presence of catalytic amounts of crown-6 are described. 1,2-Dihalides (from alkenes) and 1,1-dihalides (from aldehydes) yield 1-alkynes; internal geminal dihalides (from symmetric ketones) give internal alkynes in excellent yields. 2,2-Dihalides (from methyl ketones) yield homogeneous 1-alkynes only if the 3-position is blocked. (E)-Haloalkenes lead also to alkynes in a syn-elimination process.
- Dehmlow, Eckehard V.,Lissel, Manfred
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