- Enantioselective 1,2-Anionotropic Rearrangement of Acylsilane through a Bisguanidinium Silicate Ion Pair
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Highly enantioselective bisguanidinium-catalyzed tandem rearrangements of acylsilanes are reported. The acylsilanes were activated via an addition of fluoride on the silicon to form a penta-coordinate anionic silicate intermediate. The silicate then underwent alkyl or aryl group migration from the silicon atom to the neighboring carbonyl carbon atom (1,2-anionotropic rearrangement), followed by [1,2]-Brook rearrangement to provide the secondary alcohols in high yields with excellent enantioselectivities (up to 95% ee). The isolation of an α-silylcarbinol intermediate as well as DFT calculations revealed that the 1,2-anionotropic rearrangement occurred via a bisguanidinium silicate ion pair, which is the stereodetermining step. The chiral center formed is then retained without inversion through the subsequent [1,2]-Brook rearrangement. Crotyl acylsilanes were smoothly transformed into homoallylic linear crotyl alcohols with retention of E/Z geometry, and no branched alcohols were detected. This clearly suggested that the 1,2-anionotropic rearrangement occurred through a three-membered instead of a five-membered transition state.
- Cao, Weidi,Tan, Davin,Lee, Richmond,Tan, Choon-Hong
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supporting information
p. 1952 - 1955
(2018/02/17)
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- Triorganomonohalogenosilane
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A triorganomonohalogenosilane is prepared by reacting a triorganomonohydrosilane represented by the following general formula (I): with a halogenated allyl compound represented by the following general formula (II): STR1 in the presence of metal palladium, or a salt or complex of palladium to replace the hydrogen atom directly bonded to the silicon atom of the triorganomonohydrosilane with a halogen atom. In Formula ( I ), the substituents R1 's directly bonded to the silicon atom may be identical to or different from one another and each represents a monovalent organic group. In Formula (II), the substituents R2 's may likewise be identical to or different from one another and each represents a hydrogen atom or a monovalent alkyl group and X represents a chlorine atom, a bromine atom or an iodine atom.
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- Preparation of the iodides (Me3Si)2C(SiMe2C6H4Y)(SiMe2I) and some related compounds
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The preparations of: (a) the iodides (Me3Si)2C(SiMe2C6H4Y)(SiMe2I) (Y=H, p-OMe, p-Me, p-Cl, m-CF3), via the corresponding hydrides; (b) the compounds (Me3Si)2C(SiMe2Ph)(SiMe2X) with X=F, O2CCF3, OMe, N3, NCS and Cl: and (c) the iodide (p-MeC6H4)3CSiMe2I are described. Key words: Silicon; Iodide; Fluoride; Hydride; Trimethylsilyl
- Eaborn, Colin,Jones, Karen L.,Lickiss, Paul D.
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- Photochemical treatment of transition metal substituted disilanes, (η5-C5H5)Fe(CO)2Si 2Me4(C6H4X) (X = Cl, CF3, NMe2, OMe, H), including trapping
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A series of complexes (η5-C5H5)Fe(CO)2Si 2Me4Ar, FpSi2Me4Ar (Ar = C6H4X; X = H, p-Cl, m-CF3, o-Me, p-OMe p-NMe2), have been
- Jones, Karen L.,Pannell, Keith H.
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p. 11336 - 11340
(2007/10/02)
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- Synthesis and polymerization of p-pentamethyldisiloxanyl-α,β,β-trifluorostyrene and the oxygen permeability of the polymer
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A novel monomer, p-pentamethyldisiloxanyl-α,β,β-trifluorostyrene, has been synthesized and polymerized to give a white polymer.Membranes obtained from the polymer exhibited an oxygen permeability coefficient (PO2: cc(STP) cm/cm2scmHg) and an oxygen separation factor (α=PO2/PO2) of 1.8 * 10-9 amd 2.4, respectively.The PO2 value is considerably higher than values for other poly(mono-substituted tetrafluoroethylenes).The introduction of a pentamethyldisiloxanylphenyl group into poly(tetrafluoroethylene) has been found to be very effective the enhancement of PO2 values.
- Aoki, Toshiki,Watanabe, Jun,Ishimoto, Yoshiyuki,Oikawa, Eizo,Hayakawa, Yoshio,Nishida, Masakazu
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p. 285 - 288
(2007/10/02)
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- Silylative Decarbonylation: A New Route to Arylsilanes
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A new synthetic procedure for the preparation of aromatic chlorosilanes via the palladium-catalyzed reaction of methylchlorodisilanes and aromatic acid chloride is described.The silylative decarbonylation process is solventless, can utilize low metal catalyst loadings (500-1000 ppm Pd), is carried out under moderate conditions (145 deg C), and selectively gives aromatic chlorosilanes in good yield, generally 60-85percent.The procedure is tolerant of a variety of aromatic substituents, for example, alkyl, halo, nitro, cyano, imide, acid anhydride, etc., and the synthesis ofseveral new substituted aromatic chlorosilanes containing benzoyl chloride and phthalic anhydride moieties is described.Chloromethyldisilane starting reagents are available from the direct reaction of methyl chloride and silicon, making this methodology an attractive synthetic route to functionalized aromatic chlorosilanes.
- Rich, Jonathan D.
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p. 5886 - 5893
(2007/10/02)
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- Zur Synthese von Siloxanen XIV. Die Umsetzung von Chlorsilanen mit Silanolen im sauren Medium
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The reactions of aryldimethylchlorosilanes with benzyldimethylsilanol in C6D6/dioxane (2.8/1) have been investigated by 1H NMR spectroscopy.Fast substituent exchange reactions were observed in the presence of H2O or HCl.In this process both substances establish chlorosilane/silanol equilibria which are related to the concetration of H2O and HCl formed.A ρ-value of 1.3 was found for the reaction of substituted aryldimethylchlorosilanes with benzyldimethylsilanol in the presence of H2O.In time the equilibria are disturbed by condensation processes.
- Ruehlmann, K.,Grosse-Ruyken, H.,Scheller, D.,Scheim, U.
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- Synthesis of siloxanes. XII. Cleavage of siloxanes by hydrogen chloride
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1H NMR spectroscopy has been used in a kinetic study of the cleavage of siloxane bonds by hydrogen chloride in dioxane.The cleavages show an induction period which is associated with the autocatalytic effect of the water formed during the reaction.The kinetic behavior can be expressed in terms of a rate law that includes rate constants for cleavage by both dioxane*HCl (k1) and H2O*HCl (k2).The k'1 (k'1 = k1*-4) and k'2 (k'2 = k2*-3) values correlate with ?* values; thus ρ* values of -1.4 and -0.7 were obtained for k'1 and k'2, respectively.The ?* value of 0.35 that we previously derived for the Me3SiO group applies in this reaction.The reaction of 1,3-bis(p-methoxyphenyl)tetramethyldisiloxane with hydrogen chloride involves cleavage of silicon-aryl rather than Si-O bonds.
- Scheim, U.,Lehnert, R.,Porzel, A.,Ruehlmann, K.
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p. 141 - 150
(2007/10/02)
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- REACTIONS IN THE CHLOROSILANE-SILANOL-SILOXANE SYSTEM
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We obtained the first ?*-values and ES-values for siloxy groups by spectroscopic and kinetic methods.Detailed mechanistic investigations are performed on the hydrolysis of chlorosilanes, the cleavage of Si-O-Si bonds by HCl, and the substituent exchange reaction between silanols and chlorosilanes.
- Ruehlmann, K.
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p. 139 - 152
(2007/10/02)
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