- The Trityl-Cation Mediated Phosphine Oxides Reduction
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Reduction of phosphine oxides into the corresponding phosphines using PhSiH3 as a reducing agent and Ph3C+[B(C6F5)4]? as an initiator is described. The process is highly efficient, reducing a broad range of secondary and tertiary alkyl and arylphosphines, bearing various functional groups in generally good yields. The reaction is believed to proceed through the generation of a silyl cation, which reaction with the phosphine oxide provides a phosphonium salt, further reduced by the silane to afford the desired phosphine along with siloxanes. (Figure presented.).
- Landais, Yannick,Laye, Claire,Lusseau, Jonathan,Robert, Frédéric
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supporting information
p. 3035 - 3043
(2021/05/10)
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- Increasing the structural span of alkyne metathesis
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A new generation of alkyne metathesis catalysts, which are distinguished by high activity and an exquisite functional group tolerance, allows the scope of this transformation to be extended beyond its traditional range. They accept substrates that were previously found problematic or unreactive, such as propargyl alcohol derivatives, electron-deficient and electron-rich acetylenes of various types, and even terminal alkynes. Moreover, post-metathetic transformations other than semi-reduction increase the structural portfolio, as witnessed by the synthesis of a annulated phenol derivative via ring-closing alkyne metathesis (RCAM) followed by a transannular gold-catalyzed Conia-ene reaction. Further examples encompass a post-metathetic transannular ketone-alkyne cyclization with formation of a trisubstituted furan, a ruthenium-catalyzed redox isomerization, and a Meyer-Schuster rearrangement/oxa-Michael cascade. These reaction modes fueled model studies toward salicylate macrolides, furanocembranolides, and the cytotoxic macrolides acutiphycin and enigmazole A; moreover, they served as the key design elements of concise total syntheses of dehydrocurvularin (27) and the antibiotic agent A26771B (36). Ask for more! Many possibilities exist to take advantage of alkyne metathesis. In addition to the approved semi-reduction to stereodefined olefins, it is shown how to convert the products primarily formed into aromatic or heteroaromatic rings, enones, Michael adducts, or β-ketolactones. At the same time, new types of substrates were engaged, including electron-rich, electron-poor, and terminal alkynes, as well as propargyl alcohol derivatives. Copyright
- Persich, Peter,Llaveria, Josep,Lhermet, Rudy,Deharo, Teresa,Stade, Robert,Kondoh, Azusa,Fuerstner, Alois
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supporting information
p. 13047 - 13058
(2013/10/01)
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- Lithiation of 1,2-dichloroethene in flow microreactors: Versatile synthesis of alkenes and alkynes by precise residence-time control
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It′s all about the timing: Precise control of the residence time (tRx; see picture) of reactive intermediates in flow microreactors enables the reaction pathway of lithiated 1,2-dichloroethene to be switched to produce either alkenes or alkynes. This method also allows versatile syntheses of asymmetric disubstituted dichloroalkenes and alkynes. Copyright
- Nagaki, Aiichiro,Matsuo, Chika,Kim, Songhee,Saito, Kodai,Miyazaki, Atsuo,Yoshida, Jun-Ichi
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supporting information; experimental part
p. 3245 - 3248
(2012/05/31)
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- P-C bond activation chemistry: Evidence for 1,1-carboboration reactions proceeding with phosphorus-carbon bond cleavage
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A series of diarylphosphinyl-substituted acetylenes of the type (aryl) 2P-C≡C-R (aryl = phenyl or mesityl, R = Ph or n-propyl) react with the strongly Lewis acid reagent B(C6F5)3 in toluene at elevated temperatures (70-105 °C) to give the 1,1-carboboration products 4. Treatment of bis(diphenylphosphinyl)acetylene with B(C6F5)3 under analogous conditions proceeded with phosphinyl migration to yield the 1,1-carboboration product 4d, bearing a geminal pair of Ph2P substituents at one former acetylene carbon atom and a C6F5 substituent and the remaining -B(C 6F5)2 group at the other. Prolonged thermolysis of 4d resulted in an intramolecular aromatic substitution reaction by means of Ph2P attack on the adjacent C6F5 ring to yield the zwitterionic phospha-indene derivative 7. The compounds 4a, 4c, 4d, and 7 were characterized by X-ray diffraction.
- Ekkert, Olga,Kehr, Gerald,Froehlich, Roland,Erker, Gerhard
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supporting information; experimental part
p. 4610 - 4616
(2011/05/17)
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- X-H (X = C, N, O, P, S) Bond Activations Induced by β-Heterosubstituted Zirconaindenes
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The azazirconacyclopentene-substituted phosphines 3 and 4 have been found to activate the C-H bonds of acetylenic systems, such as methylpropiolate, diphenylphosphinoacetylene and phenylacetylene, or of methylene compounds, such as malonitrile and diethyl
- Cadierno, Victorio,Zablocka, Maria,Donnadieu, Bruno,Igau, Alain,Majoral, Jean-Pierre,Skowronska, Aleksandra
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p. 221 - 229
(2007/10/03)
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- Radical Cations of Bis(diphenylphosphino) Derivatives (Ph2P-R-PPh2): The Formation of Localized, Cyclic, and Dimeric Configurations. An ESR and Quantum Chemical Study
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A matrix ESR study on radiogenic radical cations of Ph2P-R-PPh2 derivatives with various linkers (R) is presented.The experiments show that in a frozen dichloromethane solution the radical cations can adopt localized (Ph2PR*+), cyclic , and dimeric (Ph2RP*-PRPh2+) configurations, depending on the nature of the linker.The cyclic and dimeric products are formed in the reaction of a localized cation with a second free-electron pair, resulting in an intra- or intermolecular three-electron P-P ?* bond, respectively.The formation of the cyclic structure, with a strongly bent P-P ?* bond, requires a specific proximate position of the two phosphine moieties in the precursor molecule.The mutual orientation of the two free-electron pairs of the precursors is assessed by NMR via the nJPP spin-spin coupling constant.Ab initio UHF quantum chemical calculations at the 3-21G*/SCF level support the assignments.
- Janssen, Rene A. J.,Aagaard, Olav M.,Cabbolet, Marcoen J. T. F.,Waal, Bas F. M. de
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p. 9256 - 9263
(2007/10/02)
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- Chemistry of the Podocarpaceae LXX. Synthesis and Cyclopentaannulation of a Diterpenoid Chromium Carbene Complex
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A pentacarbonylcarbene chromium complex of the diterpenoid methyl O-methylpodocarpate has been prepared and its reactions with some alkynes have been studied with the aim of synthesising ring-C aromatic steroids.The use of diphenylacetylene resulted in cyclisation to give steroidal derivatives in moderate yield.
- Cambie, Richard C.,Rutledge, Peter S.,Tercel, Moana,Woodgate, Paul D.
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p. 171 - 186
(2007/10/02)
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