- Novel α,ω-bis(trialkylsilyl)-allyl and -1-azapentadienyl ligands; structures of [Li{η3-CH(CHSiMe2But)2} (tmen)], [Li {N(SiMe3)CBut(CH)3SiMe2Bu t} (tmen)] and [K{η4-N(SiMe2But)CBut(CH) 3SiMe2But}]
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The η3-allyl-lithium or -potassium compounds [Li{η3-CH(CHSiMe2But)(CHSiMe 2R)}(tmen)] (R = But 3a, Me 3b) and K{η3-CH(CHSiMe2But)2} (obtained from ButMe2SiCH2CH=CHSiMe2R) with ButCN afford the 1-azapentadienyl-lithium or -potassium compounds [Li{η1-N(SiMe2R)C(But)(CH) 3SiMe2But}L] (L = tmen, R = But 6a, Me 6b; L absent, R = But 8a, Me 8b) or [K{η4-N(SiMe2But)C(But)(CH) 3SiMe2But}]∞ 7.
- Hitchcock, Peter B.,Lappert, Michael F.,Wang, Zhong-Xia
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Read Online
- Catalysis and chemodivergence in the interrupted, formal homo-nazarov cyclization using allylsilanes
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A chemodivergent, Lewis acid catalyzed allylsilane interrupted formal homo-Nazarov cyclization is disclosed. With catalytic amounts of SnCl4 and in the presence of allyltrimethylsilane, a formal Hosomi-Sakurai-type allylation of the oxyallyl cation intermediate is observed. A variety of functionalized donor-acceptor cyclopropanes and allylsilanes were shown to be amenable to the reaction transformation and the allyl products were formed in up to 92% yield. Under dilute reaction conditions with stoichiometric SnCl4 and at reduced temperatures, an unusual formal [3 + 2]-cycloaddition between the allylsilane and the oxyallyl cation occurred to give hexahydrobenzofuran products in up to 69% yield.
- Shenje, Raynold,Williams, Corey W.,Francois, Katherine M.,France, Stefan
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supporting information
p. 6468 - 6471
(2015/02/05)
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- Mesoporous aluminosilicate-catalyzed allylation of carbonyl compounds and acetals
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A mesoporous aluminosilicate (Al-MCM-41) was found to be an effective heterogeneous catalyst for the reaction of both carbonyl compounds and acetals with allylsilanes to afford the corresponding homoallyl silyl ethers and homoallyl alkyl ethers, respectively. Both the mesoporous structure and the presence of aluminum moiety were indispensable for the high catalytic activity of Al-MCM-41. Moreover, Al-MCM-41 could catalyze the reaction of acetals chemoselectively in the presence of the corresponding carbonyl compounds. The solid acid catalyst Al-MCM-41 could be recovered easily by filtration and could be reused three times without a significant loss of catalytic activity.
- Ito, Suguru,Hayashi, Akira,Komai, Hirotomo,Yamaguchi, Hitoshi,Kubota, Yoshihiro,Asami, Masatoshi
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supporting information; body text
p. 2081 - 2089
(2011/04/19)
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- Zinc-catalyzed nucleophilic substitution reaction of chlorosilanes with organomagnesium reagents
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Zinc-catalyzed nucleophilic substitution reactions of chlo-rosilanes with organomagnesium reagents afford various tetraorganosilanes under mild reaction conditions. The reactions can be performed on large scale and allow efficient preparation of functionalized tetraorganosilanes.
- Murakami, Kei,Yorimitsu, Hideki,Oshima, Koichiro
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experimental part
p. 1415 - 1417
(2009/06/28)
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- Evaluation of β- and γ-Effects of Group 14 Elements Using Intramolecular Competition
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To evaluate β-effects and γ-effects of group 14 elements, we have devised a system in which the intramolecular competition between γ-elimination of tin and β-elimination of silicon, germanium, and tin can be examined. Thus, the reactions of α-acetoxy(arylmethyl)stannanes with allylmetals (metal = Si, Ge, Sn) in the presence of BF3·OEt2 were carried out. The reactions seem to proceed by the initial formation of an α-stannyl-substituted carbocation, which adds to an allylmetal to give the carbocation that is β to the metal and γ to tin. The β-elimination of the metal gives the corresponding allylated product, and the γ-elimination of tin gives the cyclopropane derivative. In the case of allylsilane, the cyclopropane derivative was formed as a major product, whereas in the case of allylgermane the allylated product was formed predominantly. In the case of the allystannane the allylated product was formed exclusively. These results indicate that the y-elimination of tin is faster than the β-elimination of silicon, but slower than the β-elimination of germanium and tin. The theoretical studies using ab initio molecular orbital calculations of the carbocation intermediates are consistent with the experimental results. The effect of substituents on silicon was also studied. The introduction of sterically demanding substituents on silicon disfavored the β-elimination of silicon probably because of the retardation of nucleophilic attack on silicon to cleave the carbon-silicon bond.
- Sugawara, Masanobu,Yoshida, Jun-Ichi
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p. 3135 - 3142
(2007/10/03)
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- Reorientation dynamics within ion-paired allylic lithium compounds: Isolation of inversion processes
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Among the several ion-ion reorientational processes that take place within several newly studied allylic lithium compounds, the dynamics of transfer of TMEDA-coordinated lithium between the two ally1 faces has been determined independently by use of 13C NMR line shape studies of diastereotopic geminal methylsilyl groups strategically incorporated close to the chiral lithium in the organometallic species. With increasing temperature, the 13C shift between these methyls is progressively averaged due to faster rates of lithium transfer (inversion). Typical ΔH((+)) values of 5-7 kcal·mol-1 with ΔS((+)) = ca. -20 eu are encountered. A faster process, the reorientation of coordinated TMEDA on one side of the allyl plane, has been monitored from the NCH3 13C resonance of TMEDA-coordinated Li+, with ΔH((+)) = 7 kcal·mol-1 and ΔS((+)) = ca. -12 eu.
- Fraenkel,Cabral,Lanter,Wang
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p. 1302 - 1310
(2007/10/03)
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- Synthesis and structures of some silylallyl-lithium or -potassium complexes
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The η3-1,3-bis(silyl)allyllithium[Li{η3-CH(CHSiMe 2But)(CHSiMe2R)}(tmen)] (R = But or Me) and 1,3-bis(trimethylsilyl)cyclohexenyllithium [Li{C(SiMe3)CHC(SiMe3)(CH
- Hitchcock, Peter B.,Lappert, Michael F.,Leung, Wing-Por,Liu, Dian-Sheng,Mak, Thomas C. W.,Wang, Zhong-Xia
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p. 1257 - 1262
(2007/10/03)
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- A one-pot preparation of allylsilanes and (Z)-alk-2-enylsilanes
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Metalation of alk-1-enes, using the mixture of butyllithium and potassium tert-butoxide in tetrahydropyran, followed by stereohomogenization and ultimate treatment with chlorotrimethylsilane afforded a series of alk-2-enyltrimethylsilanes in good yield and with (Z/E) ratios ranging from 95:5 to 98:2. The deprotonation of propene can be rapidly and readily accomplished with a stoichiometric amount of the superbase suspended in pentane on a 1 mol scale.
- Desponds, Olivier,Franzini, Livia,Schlosser, Manfred
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p. 150 - 152
(2007/10/03)
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- Kinetics of the reactions of allylsilanes, allylgermanes, and allylstannanes with carbenium ions
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Second-order rate constants for the reactions of para-substituted diarylcarbenium ions (ArAr'CH+ = 1) with allylsilanes 2, allylgermanes 3, and allylstannanes 4 have been determined in CH2Cl2 solution at -70 to -30°C. Generally, the attack of ArAr'CH+ at the CC double bond of the allylelement compounds 2-4 is rate-determining and leads to the formation of the β-element-stabilized carbenium ions 5, which subsequently react with the negative counterions to give the substitution products 6 or the addition products 7. For compounds H2C = CHCH2MPh3, the relative reactivities are 1 (M = Si), 5,6 (M = Ge), and 1600 (M = Sn). From the relative reactivities of compounds H2C=CHCH2X (X = H, SiBu3, SnBu3), the activating effect of an allylic trialkylsilyl (5 × 105) and trialkylstannyl group (3 × 109) is derived. This effect is strongly reduced, when the alkyl groups at Si or Sn are replaced by inductively withdrawing substituents, and an allylic SiCl3 group deactivates by a factor of 300 (comparison isobutene/2k). A close analogy between the reactions of alkenes and allylelement compounds with carbenium ions is manifested, and the different reaction series are connected by well-behaved linear free energy relationships. The relative reactivities of terminal alkenes and allylelement compounds are almost independent of the electrophilicities of the reference carbenium ions (constant selectivity relationship), thus allowing the construction of a general nucleophilicity scale for these compounds.
- Hagen, Gisela,Mayr, Herbert
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p. 4954 - 4961
(2007/10/02)
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- USE OF ALLYLSILANES AS A NEW TYPE OF SILYLATING AGENT FOR ALCOHOLS AND CARBOXYLIC ACIDS
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A new convenient route to silyl ethers and esters from alcohols and carboxylic acids using allylsilanes in the presence of an acid catalyst in acetonitrile was developed.The present method is also applicable to t-butyldimethylsilylation.
- Morita, Tsuyoshi,Okamoto, Yoshiki,Sakurai, Hiroshi
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p. 835 - 838
(2007/10/02)
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