- Poly(methylhydrosiloxane) as a reductant in the catalytic base-free Wittig reaction
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Herein, we report a catalytic, base-free Wittig reaction forming highly functionalized alkenes with PMHS as a terminal reductant and butylacetate as a green solvent. Poly(methylhydrosiloxane) (PMHS) is a non-toxic, enviromentally friendly, inexpensive and easy to handle reductant. However, the inherent low reactivity hampers its applicability in catalytic reactions, such as P(iii)/P(v) redox cycling reactions. Most of these catalytic systems include highly active aryl silanes to facilitate phosphane oxide reduction and are not compatible with PMHS or similar more sustainable terminal reductants. The herein reported catalyst system which is based on a methyl-substituted phosphetane operates at low catalyst loadings without additional co-catalysts and allowes the use of PMHS as terminal reductant. A wide variety of functional groups was tolerated and 25 different alkenes were synthesized in yields up to 96% with excellent stereoselectivity. Mechanistic studies revealed the formation of water from silanol condensation as the main pathway of siloxane formation.
- Longwitz, Lars,T?njes, Jan,Werner, Thomas
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p. 4852 - 4857
(2021/07/12)
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- Phosphine-Catalyzed Cross-Coupling of Benzyl Halides and Fumarates
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A phosphine-catalyzed olefinic cross-coupling between benzyl halides and fumarates is described, which affords trisubstituted alkenes in good yields and excellent E-selectivity under metal-free conditions. Mechanistic studies suggest a catalytic cycle involving phosphorus ylide formation, Michael addition, water-assisted hydrogen transfer, and phosphine elimination.
- Yan, Tingting,Babu, Kaki Raveendra,Wu, Yong,Li, Yang,Tang, Yuhai,Xu, Silong
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supporting information
p. 4570 - 4574
(2021/06/28)
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- Phosphine-Catalyzed Reaction between 2-Aminobenzaldehydes and Dialkyl Acetylenedicarboxylates: Synthesis of 1,2-Dihydroquinoline Derivatives and Toward the Development of an Olefination Reaction
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A series of 1,2-dihydroquinolines were synthesized in good to excellent yields by reacting 2-aminobenzaldehyde derivatives and dialkyl acetylenedicarboxylates with catalytic amounts of phosphine. This reaction was rendered catalytic by the selective in situ phosphine oxide reduction with the use of phenylsilane. Furthermore, with the same starting materials and with an additional role of the reducing agent, a new olefination reaction was discovered. Hydrogen/deuterium (H/D) exchange experiments revealed the possible mechanism of this reaction.
- Han, Xu,Saleh, Nidal,Retailleau, Pascal,Voituriez, Arnaud
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supporting information
p. 4584 - 4588
(2018/08/09)
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- Novel Base-Free Catalytic Wittig Reaction for the Synthesis of Highly Functionalized Alkenes
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A highly efficient catalyst system for base-free catalytic Wittig reactions has been developed and optimized. Initially, several potential (pre)catalysts as well as different silanes as reducing agents were screened. A system based on a readily available
- Schirmer, Marie-Luis,Adomeit, Sven,Spannenberg, Anke,Werner, Thomas
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supporting information
p. 2458 - 2465
(2016/02/12)
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- First Base-Free Catalytic Wittig Reaction
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The first base-free catalytic Wittig reaction utilizing readily available Bu3P (5 mol %) as an organocatalyst is reported. The initial Michael addition of the phosphine to a suitable acceptor substituted alkene ultimately results in the formation of an ylide which is subsequently converted with an aldehyde. The presented 1H NMR studies actually reveal evidence for the Michael addition and proposed ylide formation. Under the optimized reaction conditions various maleates and fumarates were converted with aromatic, heteroaromatic, and aliphatic aldehydes to evaluate the scope and limitations of this unprecedented reaction. Notably, maleates and fumarates react in a stereoconvergent fashion. The corresponding products were obtained in up to 95% isolated yield and E/Z-selectivities up to 99:1.
- Schirmer, Marie-Luis,Adomeit, Sven,Werner, Thomas
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supporting information
p. 3078 - 3081
(2015/06/30)
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- Pd-catalyzed desulfitative Heck coupling with dioxygen as the terminal oxidant
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A Pd-catalyzed desulfitative Heck-type reaction of aromatic sulfinic acid sodium salts with various olefins is developed with O2 as the terminal oxidant under mild conditions. The presence of phosphane ligand DPEphos in anisole can significantly enhance the reaction selectivity.
- Zhou, Xianya,Luo, Jiaying,Liu, Jing,Peng, Shengming,Deng, Guo-Jun
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supporting information; experimental part
p. 1432 - 1435
(2011/05/04)
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- Asymmetric dihydroxylation of β,γ-unsaturated carboxylic esters with trisubstituted C=C bonds - Enantioselective syntheses of trisubstituted γ-butyrolactones
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β,γ-Unsaturated esters with stereodefined trisubstitued C=C double bonds were prepared by the Arndt-Eistert homologation of α,β-unsaturated carboxyl halides, by two-step methoxycarbonylation of allylbarium reagents, by deconjugation of α,β-unsaturated esters, and by Horner-Wadsworth-Emmons variants of the Stobbe condensation. Sharpless asymmetric dihydroxylation of the β,γ-unsaturated esters, followed by spontaneous cyclization, afforded β-hydroxy-γ-lactones in moderate to good yields and with enantiomeric excesses of up to 97 %. Similarly, tetrahydroxy-γ-lactones were obtained from diunsaturated esters; these lactones were converted into a bislactone and an unsaturated β-hydroxy γ-lactone. Wiley-VCH Verlag GmbH & Co. KGaA, 2006.
- Kapferer, Tobias,Brueckner, Reinhard
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p. 2119 - 2133
(2007/10/03)
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- Sequential Transformation of Diethyl Phosphite. A Convenient Synthesis of Substituted (E)-3-Alkoxycarbonyl-β,γ-unsaturated Esters
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The sequential reaction of diethyl phosphite with sodium alkoxide, dimethyl maleate and aldehydes affords substituted (E)-3-alkoxycarbonyl-β,γ-unsaturated esters in 63-73% yields.
- Shen, Yanchang,Zhang, Zenghong
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p. 642 - 643
(2007/10/03)
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- Annelation Reactions of N-Heterocycles to Condensed Pyridones with Bridgehead Nitrogen
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The Horner-Wittig reaction of aromatic and heteroaromatic aldehydes with phosphono succinates gives the methylenesuccinates 2a-m and 4a-k in satisfactory yields.The compounds obtained have the E-configuration, as shown by 1H-NMR-spectroscopic and by chemi
- Linke, Siegfried,Kurz, Juergen,Lipinski, Dietmar,Gau, Wolfgang
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p. 542 - 556
(2007/10/02)
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