- Visible-Light-Mediated C-I Difluoroallylation with an α-Aminoalkyl Radical as a Mediator
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Herein, we report a protocol for direct visible-light-mediated C-I difluoroallylation reactions of α-trifluoromethyl arylalkenes with alkyl iodides at room temperature with an α-aminoalkyl radical as a mediator. The protocol permits efficient functionalization of various α-trifluoromethyl arylalkenes with cyclic and acyclic primary, secondary, and tertiary alkyl iodides and is scalable to the gram level. This mild protocol uses an inexpensive mediator and is suitable for late-stage functionalization of complex natural products and drugs.
- Yue, Fuyang,Dong, Jianyang,Liu, Yuxiu,Wang, Qingmin
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supporting information
p. 7306 - 7310
(2021/10/01)
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- Hydrocarbon-Soluble Bis(trimethylsilylmethyl)calcium and Calcium-Iodine Exchange Reactions at sp2-Hybrized Carbon Atoms
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Hydrocarbon-soluble and highly reactive [(L)xCa(CH2SiMe3)2] (L = tetrahydropyran, x = 4 (2a); L = tmeda, x = 2 (2b)) is synthesized by the metathesis reaction of Me3SiCH2CaI (1-I) with KCH2SiMe3. The durability of 2a in tetrahydropyran solution at 0 °C is sufficiently high for subsequent chemical transformations. The reaction of ICH2SiMe3 with calcium in diethyl ether yields unique cage compound [(Et2O)2Ca(I)2·(Et2O)2Ca(I)(OEt)·(Et2O)Ca(I)(CH2SiMe3)] (3). We demonstrate that alkylcalcium complexes are valuable reagents for calcium-iodine exchange reactions at Csp2-I functionalities.
- Koch, Alexander,Wirgenings, Marino,Krieck, Sven,G?rls, Helmar,Pohnert, Georg,Westerhausen, Matthias
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p. 3981 - 3986
(2017/10/31)
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- 1,3-γ-Silyl-elimination in electron-deficient cationic systems
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Placement of an electron-withdrawing trifluoromethyl group (-CF 3) at a putative cationic centre enhances γ-silyl neighbouring-group participation (NGP). In stark contrast to previously studied γ-silyl-substituted systems, the preferred reaction pathway is 1,3-γ-silyl elimination, giving ring closure over solvent substitution or alkene formation. The scope of this cyclopropanation reaction is explored for numerous cyclic and acyclic examples, proving this method to be a viable approach to preparing CF3-substituted cyclopropanes and bicyclic systems, both containing quaternary centres. Rate-constants, kinetic isotope effects, and quantum mechanical calculations provided evidence for this enhancement and further elaborated the disparity in the reaction outcome between these systems and previously studied γ-silyl systems.
- Mercadante, Michael A.,Kelly, Christopher B.,Hamlin, Trevor A.,Delle Chiaie, Kayla R.,Drago, Michael D.,Duffy, Katherine K.,Dumas, Megan T.,Fager, Diana C.,Glod, Bryanna L. C.,Hansen, Katherine E.,Hill, Cameron R.,Leising, Rebecca M.,Lynes, Catherine L.,Macinnis, Allyson E.,McGohey, Madeline R.,Murray, Stephanie A.,Piquette, Marc C.,Roy, Shaina L.,Smith, Ryan M.,Sullivan, Katherine R.,Truong, Bao H.,Vailonis, Kristina M.,Gorbatyuk, Vitaliy,Leadbeater, Nicholas E.,Tilley, Leon J.
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p. 3983 - 3994
(2014/10/15)
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- Elongated Gilman cuprates: The key to different reactivities of cyano- and iodocuprates
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In the past the long-standing and very controversial discussion about a special reactivity of cyano- versus iodocuprates concentrated on the existence of higher-order cuprate structures. Later on numerous structural investigations proved the structural equivalence of iodo and cyano Gilman cuprates and their subsequential intermediates. For dimethylcuprates similar reactivities were also shown. However, the reports about higher reactivities of cyanocuprates survived obstinately in many synthetic working groups. In this study we present an alternative structural difference between cyano- and iodocuprates, which is in agreement with the results of both sides. The key is the potential incorporation of alkyl copper in iodo but not in cyano Gilman cuprates during the reaction. In the example of cuprates with a highly soluble substituent (R = Me 3SiCH2) we show that in the case of iodocuprates during the reaction several copper-rich complexes are formed, which consume additional iodocuprate and provide lower reactivities. To confirm this, a variety of highly soluble copper-rich complexes were synthesized, and their molecular formulas, the position of the equilibriums, their monomers and their aggregation trends were investigated by NMR spectroscopic methods revealing extended iodo Gilman cuprates. In addition, the effect of these copper-rich complexes on the yields of cross-coupling reactions with an alkyl halide was tested, resulting in reduced yields for iodocuprates. Thus, this study gives an explanation for the thus far confusing results of both similar and different reactivities of cyano- and iodocuprates. In the case of small substituents the produced alkyl copper precipitates and similar reactivities are observed. However, iodocuprates with large substituents are able to incorporate alkyl copper units. The resulting copper-rich species have less polarized alkyl groups, i.e. gradually reduced reactivities.
- Neumeier, Maria,Gschwind, Ruth M.
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p. 5765 - 5772
(2014/05/06)
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- Synthesis and characterization of alkylsilane ethers with oligo(ethylene oxide) substituents for safe electrolytes in lithium-ion batteries
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Alkylsilane ethers, containing one or three carbon spacer groups between the silicon atom and oligo(ethylene oxide) moiety, were designed and synthesized. These compounds are non-hydrolyzable and less flammable than their alkoxysilane counterparts. A full cell test using them as electrolyte solvents showed good cycling performance in lithium-ion batteries.
- Zhang, Lingzhi,Lyons, Leslie,Newhouse, Jocelyn,Zhang, Zhengcheng,Straughan, Megan,Chen, Zonghai,Amine, Khalil,Hamers, Robert J.,West, Robert
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supporting information; body text
p. 8224 - 8226
(2011/06/21)
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- Cationic carbohydroxylation of alkenes and alkynes using the cation pool method
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The reactions of an N-acyliminium ion pool with alkenes and alkynes gave γ-amino alcohols and β-amino carbonyl compounds, respectively, after treatment with H2O/Et3N. The present reaction serves as an efficient method for cationic carbohydroxylation of alkenes and alkynes. When vinyltrimethylsilane was used as an alkene, the reaction was highly diastereoselective and served as an access to an enantiomerically pure α-silyl-γ-amino alcohol.
- Suga, Seiji,Kageyama, Yasuhisa,Babu, Govindarajulu,Itami, Kenichiro,Yoshida, Jun-Ichi
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p. 2709 - 2711
(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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- γ-Silyl-stabilized tertiary ions? Solvolysis of 4-(trimethylsilyl)-2-chloro-2-methylbutane
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Rate constant, isotope-effect, and product studies of the solvolysis of 4-(trimethylsilyl)-2-chloro-2-methylbutane, 11, and its carbon analog, 2-chloro-2,5,5-trimethylhexane, 10, in aqueous ethanol and aqueous 2,2,2-trifluoroethanol (TFE) indicate very little participation of the γ-silyl substituent. These results are in sharp contrast to earlier reports on secondary γ-silyl substituted systems, in which the back lobe of the silicon-carbon bond has been shown to overlap with the carbocation p-orbital to form a so-called 'percaudally' stabilized intermediate. While the solvolytic behaviors of 11 and 10 are nearly identical in ethanol, differences in the TFE lead to the conclusion that there is a minor amount of participation by the silyl substituent in that solvent. Interestingly, this observation lends credence to an earlier suggestion that TFE is better than ethanol at stabilizing more highly delocalized ions. Copyright
- Tilley, Leon J.,Shiner Jr.
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p. 564 - 576
(2007/10/03)
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- The γ-silicon effect. I. Solvent effects on the solvolyses of 2,2- dimethyl-3-(trimethylsilyl)propyl and 3-(aryldimethylsilyl)-2,2- dimethylpropyl p-toluenesulfonates
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The solvolysis rates of 2,2-dimethyl-3-(trimethylsilyl)propyl and 3- (aryldimethylsilyl)-2,2-dimethylpropyl p-toluenesulfonates were measured in a wide variety of solvents at 45 °C. The solvent effects were analyzed by using the Winstein-Grunwald equation. The solvent effects observed did not give simple linear correlations with the 2-adamantyl Y(OTs) parameter, but showed dispersion behavior in a series of binary solvents. The m values of 0.59-.67 were remarkably lower than unity for the limiting k(c) solvolysis of 2-adamantyl p-toluenesulfonate. The deviation patterns could not be interpreted in terms of nucleophilic assistance by the solvent. The dispersion behavior with reduced m values was found to be more significant for the 3-(aryldimethylsilyl) than for the 3-(trimethylsilyl) derivatives and was compatible with the delocalization of the incipient cationic charge by participation of the Si-Cγ bond in the rate-determining step. An extended dual-parameter treatment, log (k/k(80E)) = m(c)Y(OTs) + m(Δ)Y(Δ), successfully correlated such γ-silyl assisted solvolyses. The M(Δ) values of 0.24-0.49 so obtained, where M(Δ) = 0.51 m(Δ)/(m(c) +0.51 m(Δ)), are a measure of the extent of charge delocalization, suggesting that the γ-silyl group in the percaudal interaction is more effective in delocalizing the cationic charge than the alkyl group in C-C σ-participation, but less so than σ-assisted interaction by the β-aryl group.
- Nakashima, Tohru,Fujiyama, Ryoji,Fujio, Mizue,Tsuno, Yuho
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p. 741 - 750
(2007/10/03)
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- Carbonium Ion Rearrangements Controlled by the Presence of a Silyl Group
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γ-Silyl tertiary alcohols rearrange in protic acid with 1,2-shift of hydride, phenyl, or alkyl groups, and loss of the silyl group to give alkenes.The placing of the silyl group thus controls the carbonium ion rearrangement in a preparatively useful way.Methoxycarbonyl groups do not migrate; instead, cyclopropanes are formed, except when the conformation suitable for cyclopropane formation is unattainable.When the alkene product is 2,2-disubstituted, it can be reprotonated under the reaction conditions and does not therefore always survive.This can be avoided by carrying out the reaction using a Lewis acid on the silyl ether.The starting γ-silyl alcohols are prepared by a variety of versatile methods.
- Fleming, Ian,Patel, Shailesh K.,Urch, Christopher J.
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p. 115 - 124
(2007/10/02)
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- γ-Silicon Stabilization of Carbonium Ions in Solvolysis. 3. Solvolysis of 4-(Trimethylsilyl)-3-methyl-2-butyl p-Bromobenzenesulfonates
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It has been found that the rates of limiting solvolysis of 4-(trimethylsilyl)-3-methyl-2-butyl brosylate are accelerated relative to those of the corresponding 3,3-dimethyl-2-butyl and 4-(trimethylsilyl)-2-butyl esters.The relatively low α- and β-deuterium effects on the rates suggest a mechanism involving silicon-promoted γ-carbon participation.In order to determine the preferred stereochemical course of solvolytic substitution and of cyclopropane formation the threo and erythro alcohols were prepared separately, and the structure of the p-nitrobenzoate ester ofthe threo alcohol was established by X-ray crystallographic examination.Solvolysis of the brosylate esters of each diastereoisomeric alcohol produced mainly substitution products having exclusively retained configuration; the minor yields of 1,2-dimethylcyclopropane formed from the threo ester were predominantly of the cis configuration, and those from the erythro isomer were predominantly of the trans configuration.It is concluded that the mechanism involves the formation of an intermediate carbocation stabilized by the γ-silicon substituent through a "percaudal" interaction.The transition states for the formation and destruction of the intermediate ion are predominantly of the "W" conformation, but the "endo-sickle" also contributes and in each case nucleophilic attack apparently occurs from the front side of the bridged ion.
- Shiner, V. J.,Ensinger, Mark W.,Huffman, John C.
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p. 7199 - 7205
(2007/10/02)
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- Preparation of (Trimethylsilyl)methyl Halides and Trifluoromethanesulfonate by Methylene Insertion Using Diazomethane
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(Trimethylsilyl)methyl halides (1,3) and trifluoromethanesulfonate (triflate) (2) were prepared by inserting a methylene group into the silicon-heteroatom bond of trimethylsilyl halides and triflate using diazomethane.
- Lee, Jong Gun,Ha, Dong Soo
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p. 318 - 319
(2007/10/02)
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- Electrophilic cleavages in (CH3)3SnCH2M(CH3)3 (M = Sn, Ge, Si, C). 1. Product distribution
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The extent to which Sn-CH2 and/or Sn-CH3 cleavage occurs in (CH3)3SnCH2M(CH3)3 (M = Sn, Ge, Si) in reactions with several electrophiles has been determined. With iodine and with
- Hawker, Darryl W.,Wells, Peter R.
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p. 821 - 825
(2008/10/08)
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- STABILIZATION IN THE ORDER I>Br>Cl AMONG TRIMETHYLSILYLMETHYL HALIDES, COMPARED TO CARBON ANALOGS. POSSIBLE ROLE OF ELECTRONEGATIVITY IN ORGANOSILICON CHEMISTRY
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Electronegativities may be used to rationalize the observation that the equilibrium, CH3(CH2)3I + (CH3)3SiCH2Cl CH3(CH2)3Cl + (CH3)3SiCH2I, lies to the right.
- Peterson, Paul E.
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p. 1295 - 1298
(2007/10/02)
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- β-Silylcarbonyl Compounds as Masked Enones
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β-Trimethylsilylketones and lactones can be brominated (3)->(4) and desilylbrominated (4)->(5) specifically to place a double bond between the carbonyl group and the β-carbon atom to which the silicon had originally been bound.The silyl group therefore is a base- and acid stable group masking the α,β-unsaturation of enones.Several α-methylene-ketones and -lactones have been prepared in this way.With ketones, the bromination step seems always to introduce bromine mainly or exclusively at the α-position on that side of the ketone on which the β-silyl group is placed, regardless of whether it is more or the less substituted α-position.
- Fleming, Ian,Goldhill, Jon
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p. 1493 - 1498
(2007/10/02)
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