- Nickel-Mediated Enantiospecific Silylation via Benzylic C-OMe Bond Cleavage
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Benzylic stereocenters are found in bioactive and drug molecules, as enantiopure benzylic alcohols have been used to build such a stereogenic center, but are limited to the construction of a C-C bond. Silylation of alkyl alcohols has the potential to build bioactive molecules and building blocks; however, the development of such a process is challenging and unknown. Herein, we describe an unprecedented AgF-assisted nickel catalysis in the enantiospecific silylation of benzylic ethers.
- Balakrishnan, Venkadesh,Murugesan, Vetrivelan,Chindan, Bincy,Rasappan, Ramesh
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supporting information
p. 1333 - 1338
(2021/02/20)
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- Divergent Synthesis of Vinyl-, Benzyl-, and Borylsilanes: Aryl to Alkyl 1,5-Palladium Migration/Coupling Sequences
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Organosilicon compounds have been extensively utilized both in industry and academia. Studies on the syntheses of diverse organosilanes is highly appealing. Through-space metal/hydrogen shifts allow functionalization of C?H bonds at a remote site, which are otherwise difficult to achieve. However, until now, an aryl to alkyl 1,5-palladium migration process seems to have not been presented. Reported herein is the remote olefination, arylation, and borylation of a methyl group on silicon to access diverse vinyl-, benzyl-, and borylsilanes, constituting a unique C(sp3)?H transformation based on a 1,5-palladium migration process.
- Han, Jie-Lian,Ju, Cheng-Wei,Qin, Ying,Zhao, Dongbing
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supporting information
p. 6555 - 6560
(2020/03/03)
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- Fluoroalkylselenolation of Alkyl Silanes/Trifluoroborates under Metal-Free Visible-Light Photoredox Catalysis
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Herein a metal-free fluoroalkylselenolation of alkylsilanes as well as potassium alkyltrifluoroborates under visible light photocatalysis is disclosed. The developed methodologies are performed under mild conditions, room temperature in the presence of an organic photocatalyst and blue LED irradiation. Mechanistic investigations including luminescence and EPR spectroscopy allow us to shed light on both mechanisms.
- Ghiazza, Clément,Khrouz, Lhoussain,Billard, Thierry,Monnereau, Cyrille,Tlili, Anis
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supporting information
p. 1559 - 1566
(2019/11/03)
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- Singlet vs Triplet Reactivity of Photogenerated α,n-Didehydrotoluenes
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The reactivity of α,n-didehydrotoluenes (DHTs) in protic media (organic/aqueous mixtures) was explored by means of a combined computational and experimental approach. These intermediates were generated via a photoinduced double elimination process occurring in (chlorobenzyl)trimethylsilanes and led to the formation of a varied products distribution, depending on the isomer tested. Irradiation of ortho- and para-derivatives resulted, respectively, in the formation of triplet α,2- and α,4-DHTs, whose diradical reactivity led to both radical and polar products. On the other hand, irradiation of the meta-precursor led to the singlet α,3-DHT isomer. The latter showed a marked preference for the formation of polar products and this was rationalized, as supported by computational evidence, via the involvement of a zwitterionic species arising through interaction of the nucleophilic solvent with the benzylic position of the DHT.
- Pedroli, Chiara,Ravelli, Davide,Protti, Stefano,Albini, Angelo,Fagnoni, Maurizio
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supporting information
p. 6592 - 6603
(2017/07/15)
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- Enantioselective Synthesis of Chiral 3-Substituted-3-silylpropionic Esters via Rhodium/Bisphosphine-Thiourea-Catalyzed Asymmetric Hydrogenation
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We have successfully developed the asymmetric hydrogenation of β-silyl-α,β-unsaturated esters to prepare chiral 3-substituted-3-silylpropionic ester products catalyzed by rhodium/bisphosphine-thiourea (ZhaoPhos) with excellent results (up to 97% yield, >99% ee, 1500 TON). Moreover, our hydrogenation products can be efficiently converted to other important organic molecules, such as chiral ethyl (R)-3-hydroxy-3-phenylpropanoate or (R)-3-[dimethyl(phenyl)silyl]-3-phenylpropanoic acid. (Figure presented.).
- Zhang, Zongpeng,Han, Zhengyu,Gu, Guoxian,Dong, Xiu-Qin,Zhang, Xumu
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supporting information
p. 2585 - 2589
(2017/08/16)
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- Direct oxidation of the C(sp2)-C(sp3) bond from benzyltrimethylsilanes to phenols
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A novel pathway for direct conversion of benzylsilanes to phenols by oxidation with Na2S2O8 and oxygen is efficiently developed under mild and neutral conditions. The reaction shows good functional group tolerance to afford phenols in moderate yields. The possible mechanism is proposed based on the isotopic labeling trials.
- Li, Wei,Gao, Guolin,Gao, Yuan,Yang, Chao,Xia, Wujiong
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supporting information
p. 5291 - 5293
(2017/07/10)
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- Selective Si?C(sp3) Bond Cleavage in (Aminomethyl)silanes by Carbanionic Nucleophiles and Its Stereochemical Course
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Selective cleavage of a silicon–carbon bond in tetraorganosilanes is still a great challenge. A new type of Si?C(sp3) bond cleavage in bench-stable (aminomethyl)silanes with common organolithium reagents as nucleophiles has now been identified. Suitable leaving groups are benzyl, allyl, and phenylthiomethyl groups. A β-donor function and polar solvents are essential for the reaction. Simple switching between α-deprotonation and substitution is possible through slight modifications of the reaction conditions. The stereochemical course of the reaction was elucidated by using a silicon-chiral benzylsilane. The new transformation proceeds stereospecifically with inversion of configuration and can be used for the targeted synthesis of enantiomerically pure tetraorganosilanes, which are otherwise difficult to access. Quantum chemical calculations provided insight into the mechanism of the new substitution.
- Koller, Stephan G.,Bauer, Jonathan O.,Strohmann, Carsten
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p. 7991 - 7994
(2017/06/27)
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- General Ambient Temperature Benzylic Metalations Using Mixed-Metal Li/K-TMP Amide
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Highly regioselective benzylic metalations in hydrocarbon solvent have been achieved at rt and 0 °C using a mixed-metal Li/K-TMP amide comprised of KOtBu, BuLi, and 2,2,6,6,-tetramethylpiperidine (TMP(H)). Mixing of KOtBu, BuLi, and TMP(H) in heptane gave a solution of the base mixture which when used in deuterium labeling experiments confirmed the requirement of the three reagent components for both reactivity and selectivity. The reaction protocol is operationally straightforward and found to be applicable to a broad range of substrates. Upon generation of the metalated products, they are reacted in heptane at ambient temperature in a variety of synthetically useful ways. Illustrated examples include generation of the benzyltrimethylsilanes and α,α-bis(trimethylsilyl)toluenes reagents, which are bench-stable surrogates of benzyl anions and α-silyl carbanions utilized for nucleophilic addition and Peterson olefination reactions. Direct C-C couplings mediated by 1,2-dibromoethane provided entries into bibenzyls and [2.2]metacyclophanes. Comparison of reaction outcomes with the same reactions carried out in THF at -78 °C showed no negative effects for conducting the reactions under these milder more user-friendly conditions.
- Manvar, Atul,Fleming, Patricia,O'Shea, Donal F.
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p. 8727 - 8738
(2015/09/15)
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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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- Benzyllithiums bearing aldehyde carbonyl groups. A flash chemistry approach
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Reductive lithiation of benzyl halides bearing aldehyde carbonyl groups followed by reaction with subsequently added electrophiles was successfully accomplished without affecting the carbonyl groups by taking advantage of short residence times in flow microreactors.
- Nagaki, Aiichiro,Tsuchihashi, Yuta,Haraki, Suguru,Yoshida, Jun-ichi
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supporting information
p. 7140 - 7145
(2015/07/01)
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- Nickel- or Cobalt-Catalyzed Cross-Coupling of Arylsulfonic Acid Salts with Grignard Reagents
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The use of arylsulfonic acid salts as electrophiles in a nickel- or cobalt-catalyzed cross-coupling with Grignard reagents is described. Bis(tricyclohexylphosphine)nickel dichloride [NiCl2(PCy3)2] was found to be the optimal catalyst, and reactions with this catalyst proceeded in most cases at room temperature. The analogous cobalt catalyst [CoCl2(PCy3)2] was also found to promote the cross-coupling reaction at higher temperature (60C).
- Malapit, Christian A.,Visco, Michael D.,Reeves, Jonathan T.,Busacca, Carl A.,Howell, Amy R.,Senanayake, Chris H.
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p. 2199 - 2204
(2015/07/27)
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- Competing pathways in the photogeneration of didehydrotoluenes from (Trimethylsilylmethyl)aryl sulfonates and phosphates
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The scope of the photochemical generation of a,n-didehydrotoluene diradicals from aryl sulfonates and phosphates and their chemistry are explored. The thermally inaccessible a,2- and a,4-intermediates are efficiently obtained by irradiation of ortho- and para-(trimethylsilylme-thyl)phenyl triflates through heterolytic splitting of the ester anion from the substrate in the triplet state. Triplet phenyl cations are formed and the loss of trimethylsilyl cation from them affords the desired diradicals (3Me3SiCH2C6H4-OZ→ 3Me3SiCH2C6H4+→CH2C6H4). Triplet sensitization is required, for which acetone is used throughout. Direct irradiation leads, on the contrary, to photo-Fries fragmentation (1Me3SiCH2C6H4O-Z→Me3SiCH2C6H4O· + Z). With mesylates, where ester cleavage is less convenient, a further competition from the triplet is direct desilylation. Didehydrotoluenes are also obtained from the corresponding phosphates, although with poor efficiency.
- Crespi, Stefano,Ravelli, Davide,Protti, Stefano,Albini, Angelo,Fagnoni, Maurizio
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p. 17572 - 17578
(2015/02/18)
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- Synthesis and application of benzyl-TMS derivatives as bench stable benzyl anion equivalents
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The regioselective benzylic metalation of toluenes using BuLi/KO tBu/TMP(H) (LiNK metalation conditions) and subsequent transmetalation to Si by reaction with TMSCl provides a general one-pot procedure for the synthesis of substituted benzyltrimethylsilanes. ArCH 2Si(Me)3 derivatives are bench stable reagents yet can serve as benzyl anion equivalents under mild reaction conditions. Following activation with fluoride they can successfully participate in a wide range of additions to both non-enolizable and enolizable carbonyls. In addition, their use in the synthesis of isochromanones and trifluoromethylated amines is illustrated. The broad synthetic scope and mild practical conditions of use for ArCH2Si(Me)3 reagents demonstrate their general potential as benzyl anion equivalents.
- Das, Manas,O'Shea, Donal F.
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p. 6448 - 6460
(2013/07/26)
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- α,n-didehydrotoluenes by photoactivation of (chlorobenzyl) trimethylsilanes: An alternative to enyne-allenes cyclization
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Doubly radical: A novel entry to ?,n-didehydrotoluene (DHT) diradicals is disclosed and proceeds through the photochemical activation of (chlorobenzyl)trimethylsilanes with chloride loss and elimination of the SiMe3+ group (see scheme). The products formed in solution are indicative of the intermediacy of the three isomers of the ?,n-DHT
- Protti, Stefano,Ravelli, Davide,Mannucci, Barbara,Albini, Angelo,Fagnoni, Maurizio
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supporting information; experimental part
p. 8577 - 8580
(2012/09/22)
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- Rhodium-catalyzed silylation and intramolecular arylation of nitriles via the silicon-assisted cleavage of carbon-cyano bonds
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A rhodium-catalyzed silylation reaction of carbon - cyano bonds using disilane has been developed. Under these catalytic conditions, carbon-cyano bonds in aryl, alkenyl, allyl, and benzyl cyanides bearing a variety of functional groups can be silylated. The observation of an enamine side product in the silylation of benzyl cyanides and related stoichiometric studies indicate that the carbon-cyano bond cleavage proceeds through the deinsertion of silyl isocyanide from η2-iminoacyl complex B. Knowledge gained from these studies has led to the development of a new intramolecular biaryl coupling reaction in which aryl cyanides and aryl chlorides are cross-coupled.
- Tobisu, Mamoru,Kita, Yusuke,Ano, Yusuke,Chatani, Naoto
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supporting information; experimental part
p. 15982 - 15989
(2009/05/16)
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- Polymer supported naphthalene-catalysed sodium reactions
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Arene-catalysed sodium reactions have been utilised in the generation of organosodium complexes, from a variety of organochloride complexes, in high yield. Phenyltrimethylsilane, benzene and 2-methyl-1-phenyl-1-propanol were prepared in yields >80%, using polymer supported naphthalene-catalysed sodium reactions, whereby phenylsodium, prepared from the reaction of chlorobenzene, sodium powder and polymer-supported naphthalene (5-100%), was quenched with chlorotrimethylsilane, water or PriCHO respectively. The Royal Society of Chemistry.
- Van Den Ancker, Tania R.,Love, Cameron J.
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p. 3520 - 3523
(2008/09/19)
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- Synthesis of functionalized benzylsilanes from arylzinc compounds and (iodomethyl)trimethylsilane by means of a novel Rh catalysis
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The catalytic activity of a Rh complex in cross-coupling between ArZnI and TMSCH2l was examined in which the Rh complex, generated in situ from [RhCl(1,5-cyclooctadiene)]2 and 1,1′-bis(diphenylphosphino)- ferrocene, exhibited excellent catalytic activity for the production of various functionalized benzylsilanes in good yields. From 31P NMR studies of various solutions containing several of the reaction components, confirmation of the rapid and quantitative transfer of aryl groups from ArZnI to the Rh complex to form arylrhodium species was ascertained. A catalytic cycle, commencing with the transmetalation, was thus proposed for the reaction.
- Takahashi, Hideki,Hossain, Kabir M.,Nishihara, Yasushi,Shibata, Takanori,Takagi, Kentaro
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p. 671 - 675
(2007/10/03)
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- Direct transformation of allylic and benzylic thiols, thioethers, and disulfides into organolithium compounds
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The reaction of allylic and benzylic thiols 1, disulfides 3, and thioethers 4 and 5 with an excess of lithium and a catalytic amount of 4,4′-di-tert-butylbiphenyl (DTBB, 5mol%) afforded the corresponding allylic and benzylic organolithium reagents via reductive cleavage of the carbon-sulfur bond. The generated organolithium compounds gave the expected products 2 by reaction with several electrophiles followed by hydrolysis with water. The reaction conditions and the lithiation procedure (stepwise of Barbier-type process) depended on the starting sulfur containing compound.
- Yus, Miguel,Martinez, Pedro,Guijarro, David
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p. 2365 - 2376
(2007/10/03)
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- Should anionised benzylic sulfones be considered as carbenoids?
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Na·Hg reduction of benzyl sulfones 1c-e in aprotic solvent conditions affords stilbenes 4c-e, an olefination process best explained by assuming that the corresponding sulfone carbanion, which was formed under these conditions, is decomposed into a carbene species.
- Jolivet,Uguen
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p. 7907 - 7911
(2007/10/03)
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- Synthesis, structure, and photochemistry of 2-silyl-and 2-disilanyl-2-aryl-1,3-dithiane derivatives
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A series of 2-silyl-and 2-disilanyl-substituted 2-aryl-1,3-dithiane derivatives were prepared by the reactions of 2-aryl-2-lithio-1,3-dithianes with the corresponding chlorosilanes. Photolysis of 2-phenyl-2-(pentamethyldisilanyl)-1,3-dithiane resulted in the intermediary formation of 1,1-dimethyl-2-phenyl-2-(trimethylsilyl)-1-silaethene.
- Reddy, Anugula Mahipal,Tsutsui, Shinobu,Sakamoto, Kenkichi
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p. 476 - 477
(2007/10/03)
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- Generation of allylic and benzylic organolithium compounds by fluorine-lithium exchange: Reaction with electrophiles
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The application of the naphthalene-catalysed lithiation methodology to allylic and benzylic fluorides 1 led to the corresponding allylic and benzylic organolithium reagents, which, in the presence of different electrophiles (Barbier-type reaction conditions), afforded the expected products 2 in moderate yields. The procedure was useful for the transformation of primary, secondary and tertiary benzylic fluorides into the corresponding lithium derivatives. When a two-step lithiation process was used (treatment of fluoride 1 with lithium and a catalytic amount of naphthalene, followed by addition of the electrophilic reagent), only Wurtz-type coupling products were formed.
- Guijarro, David,Yus, Miguel
-
-
- Process for the preparation of benzyl-metal compounds and process for the preparation of 4-phenyl-1-butenes by the use of the same
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There is disclosed a method of preparing benzyl metal compounds represented by general formula (2), comprising reacting a phenyl metal compound represented by general formula (1) with toluene, in the presence of a catalytic amount of amine. According to this method, benzyl metal compounds can be prepared at a high yield, and in an industrially advantageous manner. Further, there is also disclosed a method of preparing 4-phenyl-1-butenes, comprising reacting the benzyl metal compound obtained in the method, with an allyl halide. STR1 wherein M represents an alkali metal, STR2 wherein M has the same meaning as the above.
- -
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- Alkoxides of o-silyl benzyl alcohols in cleavage reactions: Approaches to benzyl and silyl anion equivalents
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The alkoxides of o-silyl benzyl alcohols 4 undergo cleavage reactions under mild conditions allowing transfer of a benzyl or silyl group to an electrophile. Reactions 3a → 8, and 3c or 4c → 11 illustrate their potential as benzyl and silyl anion equivalents.
- Hudrlik, Paul F.,Arango, Jose O.,Hijji, Yousef M.,Okoro, Cosmas O.,Hudrlik, Anne M.
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p. 1421 - 1427
(2007/10/03)
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- Nucleophile-assisted cleavage of benzyltrialkylsilane cation radicals
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The cation radicals of benzyltrialkylsilanes have been generated using photoinduced electron transfer and characterized using transient absorption spectroscopy. Absolute rate constants for nucleophile-assisted C-Si bond cleavage have been determined, for different nucleophiles in different solvents and with different substituents on the phenyl ring. The short lifetime (-9 s) of the parent benzyltrimethylsilane cation radical in acetonitrile was unambiguously shown to be due to a rapid nucleophile-assisted bond cleavage, with the solvent acting as the nucleophile. Even in less polar solvents, such as dichloromethane, the lifetime of benzyltrimethylsilane cation radical is quite short (ca. 20 ns) unless trace amounts of water, which acts as an efficient nucleophile, are removed. Consistent with the nucleophile-assisted cleavage mechanism for the benzyltrialkylsilanes, sterically-demanding substituents on silicon decrease the rate constant for cleavage by as much as 4 orders of magnitude, depending upon the nucleophile. Similarly, increasing steric crowding on the nucleophile also decreases the rate constant, although smaller changes in the rate constants are observed. Electron-donating substituents (4-methyl and 4-methoxy) on the phenyl group also lead to a substantial decrease in the rate constant for cleavage of the cation radicals. When measurements are performed in the least nucleophilic solvent and under conditions that minimize contributions from adventitious nucleophiles, the lifetimes of the cation radicals of the benzyltrialkylsilanes can be so long that the rate of pseudofirst-order decay can not be accurately determined. If the cation radicals undergo unimolecular C-Si bond cleavage (i.e., not nucleophile-assisted) under these conditions, the rate constant for this process is estimated to be less than 104 s-1.
- Dockery, Kevin P.,Dinnocenzo, Joseph P.,Farid, Samir,Goodman, Joshua L.,Gould, Ian R.,Todd, William P.
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p. 1876 - 1883
(2007/10/03)
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- Arene-catalysed lithiation of triflates and triflamides under Barbier-type conditions: An indirect transformation of alcohols and amines into organolithium compounds
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The reaction of alkyl triflates 1 or benzyl triflamides 3 with an excess of lithium powder and a catalytic amount of naphthalene (4 mol%) in the presence of different electrophiles [Me3SiCl, Pr(i)CHO, Bu(t)CHO, PhCHO, 4-MeOC6H4-CHO, CH3(CH2)6CHO, Et2CO, (CH2)5CO, (c-C3H5)2CO, PhCOMe, 4-MeC6H4COPh, PhCh=NPh, n-C8H7CON(CH2)4] in THF at temperature ranging between -78 and 0°C leads, after hydrolysis with water, to the corresponding condensation products 2. When α,β-unsaturated carbonyl compounds are used as electrophilic compounds 1,2- (3-cyclohexenone) or 1,4-addition (cinnamaldehyde or benzylideneacetone) takes place depending on the electrophile used.
- Alonso, Emma,Ramon, Diego J.,Yus, Miguel
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p. 14341 - 14348
(2007/10/03)
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- Benzylic lithium compounds: The missing link in carbon-lithium covalency. Dynamics of ion reorientation, rotation around the ring-benzyl bond, and bimolecular C-Li exchange
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Benzyllithium compounds, hitherto assumed from NMR data to consist of ion pairs, have been found to exhibit spin coupling between 13C and directly bound 6Li under conditions wherein bimolecular carbon - lithium bond exchange is too slow to average the coupling constants. These conditions involved the use of species in which lithium is internally solvated or of dilute solutions (0.005 M) of benzyllithium-13C-6Li (enriched at Cα) at low temperature. The low values of 1J(13C-6Li), 3-4 Hz, imply a small detectable degree of C-Li covalence with the arrangement around Cα distorted from coplanarity. The C-Li bonds in benzyllithium are concluded to lie in a continuum of C-Li covalency between the many monomeric species in which 1J(13C-6Li) is 16 ± 1 Hz and separated ion pairs. NMR line shape analysis of data for internally solvated benzyllithium 2b provides quantitative insight into the dynamics of intramolecular reorientation of coordinated lithium with respect to the benzyl plane, rotation around the ring-Cα bond, and bimolecular carbon-lithium bond exchange, listed in order of widely different increasing rates, the activation parameters being ΔH? (kcal/mol) and ΔS? (eu) in the same order: 14 and 6.6; 6.4 and -14; 10.8 and -21.
- Fraenkel, Gideon,Martin, Kevin V.
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p. 10336 - 10344
(2007/10/02)
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- Direct Transformation of Allylic and Benzylic Alcohols or Their Silylated Derivatives into Orgnolithium Compounds
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The reaction of allylic or benzylic alcohols 1 with n-butyllithium followed by treatment with lithium powder and a catalytic amount of DTBB (5 mol percent) in THF at room temperature gives a solution of the corresponding alkyllithium reagent, which reacts in situ with different electrophiles to yield the expected products 2.Alternatively, the O-silylated derivatives of the same alcohols are lithiated under Barbier-type reaction conditions to afford the same reaction products with better yields.
- Alonso, Emma,Guijarro, David,Yus, Miguel
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p. 11457 - 11464
(2007/10/02)
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- Arene-catalysed reductive desulfonylation and desulfinylation reactions: New routes for alkyllithiums
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The reactions of alkyl phenyl sulfones (1) with an excess of lithium powder and a catalytic amount of naphthalene (8 mol %) in the presence of a carbonyl compound or chlorotrimethylsilane (Barbier-type conditions) in THF at temperatures ranging between -78 and 20°C leads, after hydrolysis, to the expected products (2) arising from the corresponding alkyllithium generated in situ. When the same methodology is applied to sulfolene (3) or different alkyl phenyl sulfoxides (6), cyclic sulfinates 5 or products 2 are, respectively, obtained, the yields being, in general modest.
- Alonso, Emma,Guijarro, David,Yus, Miguel
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p. 2699 - 2708
(2007/10/02)
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- Direct Transformation of Trialkyl Phosphates into Organolithium Compounds by a DTBB-Catalysed Lithiation
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The reaction of different alkylic or phenylic phosphates 1 with an excess of lithium powder and a catalytic amount of DTBB (5 mol percent) in the presence of an electrophile -Barbier-type reaction conditions- in THF at -30 deg C leads to the formation of the expected products 2, resulting from the reaction of the in situ generated organolithium compound with the corresponding electrophile.
- Guijarro, David,Mancheno, Balbino,Yus, Miguel
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p. 8551 - 8558
(2007/10/02)
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- Naphthalene-Catalysed Reductive Desulfonylation with Lithium: Alkyllithiums from Alkyl Phenyl Sulfones
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The reaction of alkyl aryl sulfones 1 with an excess of lithium powder and a catalytic amount of naphthalene (8 mol percent) in the presence of a carbonyl compound iCHO, PhCHO, Et2CO, (CH2)5CO> or trimethylchlorosilane (Barbier-type conditions) in THF at temperatures ranging between -78 and 20 deg C leads, after hydrolysis with water, to the expected coupling products, arising from the corresponding alkyllithium in situ generated, in 30-61percent yields.
- Guijaro, David,Yus, Miguel
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p. 2965 - 2968
(2007/10/02)
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- Sila-Reichstoffe und Riechstoffisostere XII. Geruchsvergleiche homologer Organoelementverbindungen der vierten Hauptgruppe (C, Si, Ge, Sn)
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Homologous compounds of the linalool type R(CH3)2El-OH (with R=C6H5CH2 and C6H5CH2CH2) as well as their derivatives R(CH3)2El-OCH3 and 2O show, in dependence of El=C, Si, Ge and Sn partly similar, but sometimes very different characteristics of odor.Unexpected are high qualities of fragrance with El=Ge, whereas derivatives with El=Sn remain scentless, obviously owing to polymerization.Noteworthy are the strong differences of odor in the system C6H5CH2El(CH3)3 from C via Si and Ge up to Sn, standing fully contrary to the postulation of Amoore whereupon smell qualities are only controlled by size and shape of molecules.C6H5CH2Sn(CH3)2OH(A1Sn) crystallizes as poly-μ-hydroxo-benzyldimethyltin with an one dimensional Sn-O-Sn-O chain (Sn-O 2.17(9) and 2.29(9) Angstroem) in the monoclinic space group C2 (a=12.696(4), b=4.181(2), c=10.626(3) Angstroem and β=106.8(3) deg).
- Wannagat, Ulrich,Damrath, Volker,Huch, Volker,Veith, Michael,Harder, Ulrich
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p. 153 - 165
(2007/10/02)
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- Ion Pair Carbon Acidities of Some Silanes in Tetrahydrofuran
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The relative solvent-separated ion pair (SSIP) lithium acidity (pKLi/THF) and contact ion pair (CIP) cesium acidity (pKCs/THF) were obtained for 9-fluorenyltrimethylsilane (1) (21.3, 21.6, respectively) and 9-fluorenyl-tert-butyldimethylsilane (2) (20.3, 20.6, respectively) in THF.Values for pKCs/THF were determined at 25 deg C for (p-biphenylylmethyl)-tert-butyldimethylsilane (3), 35.4, benzyltrimethylsilane (4), 37.5, α,α-bis(trimethylsilyl)toluene (5), 34.1, 2-(trimethylsilyl)-1,3-dithiane (6), 33.5, (trimethylsilyl)acetonitrile (7), 28.8, and tris(trimethylsilyl)methane (8), 36.8.Some thermodynamic parameters were determined by measurements at other temperatures, and some ionic acidities (pK(FI)) were determined by conductivity studies.Carbanion stabilization by these silyl substituents varies from about 1 to over 3 pK units in different systems. 9,9-Bis(trimethylsilyl)fluorene (9) was found to undergo silyl transfer on treatment with various carbanions, but this reaction is slower than proton transfer.
- Streitwieser, Andrew,Xie, Linfeng,Wang, Peng,Bachrach, Steven M.
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p. 1778 - 1784
(2007/10/02)
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- Rearrangements of Organosilicon Compounds Using Organoaluminum Reagents. Conversion of Phenyl- and Alkenyl(chloromethyl)silanes to Benzyl- and Allylsilanes
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Various (chloromethyl)silanes undergo Wagner-Meerwein-type rearrangements using a catalytic amount of EtAlCl2 in dichloromethane.The resulting chlorosilanes have been converted to alkyl(or aryl)silanes with RMgX and/or to fluorosilanes with NH4HF2.In this way phenyl-, alkenyl-, and allyl(chloromethyl)silanes were converted to benzyl-, allyl-, and homoallylsilanes, respectively.Attempted rearrangements of methyl-, alkynyl-, and furyl(chloromethyl)silanes under these conditions were not successful.
- Hudrlik, Paul F.,Abdallah, Yousef M.,Kulkarni, Ashok K.,Hudrlik, Anne M.
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p. 6552 - 6556
(2007/10/02)
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- The preparation of allylsilanes from vinyl cuprates
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Gilman reagents derived from vinylic nucleophiles react with iodomethyltrimethylsilane or trimethylsilylmethyltrifluoromethane sulfonate to afford allylsilanes not readily accessible by other procedures.
- Majetich,Leigh
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p. 609 - 610
(2007/10/02)
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- Dienes, enynes and styrenes from Markovnikov vinylboranes via the Suzuki reaction
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The clean, efficient Pd-catalyzed cross coupling of vinyl, alkynyl and aryl bromides with Markovnikov vinylboranes gives 56-96% yields of the corresponding 1,3-dienes, 1-en-3-ynes and styrenes, with complete retention of configuration observed for the 1,3-dienes.
- Rivera, Isaac,Soderquist, John A.
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p. 2311 - 2314
(2007/10/02)
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- Cross-coupling versus homo-coupling reactions with benzyl bromide, magnesium and chlorotrimethylsilane
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The selective synthesis of benzyltrimethylsilane from PhCH2Br, Mg and Me3SiCl requires a low reaction temperature.
- Muzart,Riahi
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p. 1247 - 1250
(2007/10/02)
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- Two new strongly basic systems prepared by activation of n-butyllithium with organopotassium compounds
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Treatment of n-butyllithium with potassium cyclopentadienide or potassium naphthalenide yields a strongly basic system.The activation of n-butyllithium with potassium cyclopentadienide also enhances its reactivity in nucleophilic substitution reactions.
- Scott, Frederick,Hamese, Augustine M.,Raubenheimer, Helgard G.
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p. C40 - C42
(2007/10/02)
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- Allyl, benzyl and propargyl silanes via the Suzuki reaction
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The clean, efficient Pd-catalyzed cross-coupling of vinyl, alkynyl and aryl bromides with the air-stable organoborane, 10-trimethylsilylmethyl-9-oxa-10-borabicyclo[3.3.2]decane (2) gives excellent yields of the corresponding silylmethylated products, proceeding with complete retention of configuration in the first case.
- Soderquist,Santiago,Rivera
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p. 4981 - 4984
(2007/10/02)
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- Electrochemical Synthesis of (α-Halobenzyl)silanes and Benzyl Disilanes
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Electrochemical reduction of a series of substituted benzal chlorides (4) in dimethylformamide containing excess chlorotrimetylsilane affords (α-chlorobenzyl)trimetylsilanes (5) or benzal (geminal) disilanes (6), depending upon experimental conditions.Benzal bromide (13) is reducted to (α-bromobenzyl)trimetylsilane (14) cleanly and in high yield without subsequent conversion to the geminal disilane 6a, apparently because of electrode passivation by bromide ion.The reaction are conveniently carried out at constant current in an undivided cell containing a stainless steel cathode and sacrificial magnesium anode.
- Fry, Albert J.,Touster, Jonathan
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p. 4829 - 4832
(2007/10/02)
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- Thermally induced rearrangement of α-zirconocenyl thioethers: Carbon-carbon bond formation via a transition-metal hydroxymethyl or metalloxirane analogue
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The thermal rearrangement of α-zirconocenyl thioethers (η5-C5H5)2Zr(Ar)[CH(SC 6H5)(Si(CH3)3)] (Ar = C6H5, p-C6H4CH3, p-C6H4OCH3, p-C6H4Cl) and (η5-C5H5)2ZrC6H 5[CH(SCH3)(Si(CH3)3)] in toluene solution follows clean first-order kinetics to produce (η5-C5H5)2Zr(SC 6H5)[CH(Ar)(Si(CH3)3)] and (η5-C5H5)2Zr-(SCH 3)[CH(C6H5)(Si(CH3)3)]. Labeling studies using (η5-C5H5)2Zr(p-C 6H4CH3)[CH(SC6H 5)(Si(CH3)3)] and (η5-C5H5)2ZrC6H 5[CD(SC6H5)(Si(CH3)3)] show this rearrangement to be intramolecular. Activation parameters for the rearrangement of (η5-C5H5)2ZrC6H 5[CH(SC6H5)(Si(CH3)3)] were found to be ΔH? = 20.30 (43) kcal/mol and ΔS? = -19.0 (2) eu. It is proposed that this rearrangement proceeds by intramolecular nucleophilic attack (migration) of the aryl group to the methylene carbon with commensurate breaking of the C-S bond. A Hammett plot of log (kobsd) for the rearrangement of (η5-C5H5)2Zr(Ar)[CH-(SC 6H5)(Si(CH3)3)] versus σp produces a straight line (p = -2.22 (9)), supporting this mechanism.
- Ward, A. Steven,Mintz, Eric A.,Kramer, Michael P.
-
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- Main Group Conjugated Organic Anion Chemistry. 3. Application of Magnesium-Anthracene Compounds in the Synthesis of Grignard Reagents
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Reaction of magnesium-arene compounds, , 1, and some silylanthracene, and/or tertiary amine analogues, with benzylic and allylic chlorides or bromides, and (Me3Si)3CCl, afford Grignard reagents, RMgX, in modest to high yield for chlorides and negligible to high yield for the bromides, in THF, toluene, and hexane at -10 to 20 deg C.Novel benzylic-type Grignard reagents prepared in high yield include those of 9-(chloromethyl)anthracene, 2-(chloromethyl)pyridine and 8-(chloro(or bromo)methyl)quinoline, and poly-Grignard reagents derived from 1,8-bis(chloromethyl)naphthalene, 2,2'-bis(chloromethyl)-1,1'-binaphthyl, and 1,3,5,-tris(chloro(or bromo)methyl)benzene.Grignard reagent formation occurs via electron-transfer reactions.Aryl and alkyl halides yield mainly products derived from addition of the halide across the 9,10-positions of the anthracenes, via nucleophilic substitution or collapse of a diradical cage 2+, (anthracene)-anion radical, RX-anion radical.>
- Harvey, Stephen,Junk, Peter C.,Raston, Colin L.,Salem, Geoffrey
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p. 3134 - 3140
(2007/10/02)
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- Catalytic C-H Activation. Silylation of Arenes with Hydrosilane or Disilane by RhCl(CO)(PMe3)2 under Irradiation
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Direct silylation of arenes with triethylsilane or hexamethyldisilane were catalyzed by RhCl(CO)(PMe3)2 under irradiation.
- Sakakura, Toshiyasu,Tokunaga, Yuko,Sodeyama, Touru,Tanaka, Masato
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p. 2375 - 2378
(2007/10/02)
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- Electrosynthese en Chimie Organosilicique: Preparation de Phenyl- et Benzyl-trimethylsilanes
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In a single compartment cell fitted with a sacrificial magnesium anode, electrochemical reduction of phenyl and benzyl halides in the presence of trimethylchlorosilane gave the corresponding phenyl- and benzyl-silanes in satisfactory yields.Under well chosen conditions, the synthesis of phenyltrimethylsilane from phenyl bromide or chloride was also found possible.
- Pons, P.,Biran, C.,Bordeau, M.,Dunogues, J.,Sibille, S.,Perichon, J.
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p. C27 - C29
(2007/10/02)
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- Carbanion Rearrangements of ω-Phenyl-ω-(trimethylsilyl)alkyllithium Compounds: Intramolecular Reactions of Benzyltrimethylsilanes with a Carbon-Lithium Bond
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ω-Phenyl-ω-(trimethylsilyl)alkyllithium compounds show four out of five theoretically conceivable possibilities for intramolecular stabilization depending on the solvent and on the chain length n.While transmetalation of a methyl group at the silicon atom by a 1,(n+2) proton transfer is observed in any case, the intramolecular 1,n shift of the benzylic proton does only take place with n >/= 4.The main reaction, however for n = 3 and 4 only, is represented by the 1,n trimethylsilyl shift via a cyclic ate complex as an intermediate which partly splits off methyllithium yielding the corresponding silacycloalkane derivatives.In going from diethyl ether to THF as the solvent, the silyl shifts are more accelerated than the proton shifts.In no case, however, a Grovenstein-Zimmermann rearrangement involving phenyl migration took place.Degenerate silyl shifts starting from α-deuterated ω-(trimethylsilyl)alkyllithium compounds could not be detected either.Only by introduction of a second trimethylsilyl group into the 3 position a 1,3-(C -> C)-trimethylsilyl shift is initiated again.
- Maercker, Adalbert,Stoetzel, Reinhard
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p. 1695 - 1706
(2007/10/02)
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- Les triorganosilylpotasium: nouvelle voie d'acces et quelques aspects de leur reactivite
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We report here a new procedure for the convenient and easy preparation of silylanions and especially of Me3Si-.These undergo coupling reaction with halides and α-enone in good yields.Reactions with 5-bromo-1 hexene, benzophenone and carbon dioxide provide evidence for the ability of the silylpotassium to act as monoelectron transfer reagents.The course of these reactions varies substantially with the nature of the solvent.
- Corriu, R. J. P .,Guerin, C.,Kolani, B.
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p. 973 - 979
(2007/10/02)
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- AN ELECTROREDUCTIVE SYNTHESIS OF ALLYLSILANES AND BENZYLSILANES
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The electrochemical reduction of benzyl and allyl halides carried out in the presence of chlorotrimethylsilane afforded the corresponding benzylsilanes and allylsilanes in satisfactory yields.
- Shono, Tatsuya,Matsumura, Yoshihiro,Katoh, Susumu,Kise, Naoki
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p. 463 - 466
(2007/10/02)
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- The sp3-Carbon-Attached Trimethylsilyl Group as Removable Asymmetry-Inducing Auxiliary. 1. Aromatic Resin Acid Ring Systems
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The use of the trimethylsilyl (Me3Si) unit as detachable diastereoselectivity-inducing auxiliary during cationic polycyclization reactions has been examined.Model studies show 2a,b to be easily cyclized to 3a-c in CF3COOH-containing CH2Cl2.Polycyclization of 5a, on treatment with SnCl4 in CH2Cl2, gives a 85:15 ratio of 6a/7a.The same conditions transform 5b into 5percent of 100percent diastereoselectively ortho-cyclized 6b and 46percent of para-cyclized 6c/7c, occurring as a 77:23 epimeric mixture.Desilylation of the cyclized materials, using KO-t-Bu/Me2SO, provides 4a-c and 8a,c.
- Janssen, Cornelus G. M.,Godefroi, Erik F.
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p. 3600 - 3603
(2007/10/02)
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- A New Synthesis of Allyl Nitrates from Allylmetal (Group IVb) Compounds and Thallium(III) Nitrate
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A new general method for the synthesis of allyl nitrates is described.Allylmetal (group IVb) compounds, on treatment with thallium(III) nitrate in dioxane, gave the corresponding allyl nitrates in good yields.Keywords - allyl nitrate; thallium(III) nitrate; allylsilane; allylgermane; allylstannane; umpolung.
- Ochiai, Masahito,Fujita, Eiichi,Arimoto, Masao,Yamaguchi, Hideo
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p. 887 - 890
(2007/10/02)
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