- 1,1-Diethynylsilacycloalkanes and propellanes based thereon
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Previously unknown 1,1-diethylnylsilacycloalkanes (CH2)nSi(C=CH)2 (n = 3, 4) were prepared by the reaction of HC=CMgBr with 1,1-dichlorosilacycloalkanes (CH2)nSiCl2 (n = 3, 4). The reaction of (CH2)4Si(C=CMgBr)2 with (CH2)4SiCl2 in THF under conditions of high dilution gives cyclo(tetramethylene)-silethynes [(CH2)4SiC=C]4 with an admixture of cyclodi(tetramethylene)silethyne [(CH2)4SiC=C]2. The reaction of Me2Si(C=CSiMe2C=CMgBr)2 with (CH2)4SiCl2 was used to prepare 1,1,4,4,7,7-hexamelhyl-10,10-tetramethylene-1,4,4,10-tetrasilacyclododeca-2,5,8, 11-tetrayne.
- Voronkov,Zhilitskaya,Yarosh,Burnashova,Albanov,Klyba
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- (1,3-Propanediyl)silylene-bis(1-indenyl)dichlorozirconium. Synthesis and polymerization catalysis
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Reaction of indenyllithium with 1,1-dichlorosilacyclobutane gave a mixture of diastereomeric isomers of 1,1-bis(1-indenyl)-1-silacyclobutane (1), and the product was in turn converted into diastereomeric (1,3-propanediyl)silylene-bis(1-indenyl)dichlorozirconium complexes (2) in a 5:2 racemic:meso ratio.Complex 2 was activated with either methyl aluminoxane (MAO) or Ph3CB(C6F5)4 to perform ethylene and propylene polymerizations over a very broad range of temperature of polymerization (-55 deg C Tp 85 deg C).Variations of the polymerization activity (A) and molecular weight (MW) with Tp were investigated as well as the isotactic yield (IY) in the case of propylene polymerizations.Comparisons of those results with other closely related ansa-zirconocene precursors were also made. Keywords: Zirconocene; Homogeneous polymerization; α-olefin; Isospecific polymerization
- Chen, You-Xian,Rausch, Marvin D.,Chien, James C. W.
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- Rhodium-Catalyzed Intermolecular Silylation of Csp?H by Silacyclobutanes
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The signature reactivity of silacyclobutane (SCB) is their cycloaddition reactions with various π bonds. Recently, the first cases were disclosed where SCBs reacted with both Csp2?H and Csp3?H σ bonds in an intramolecular fashion. Herein, it is reported that SCB is also an efficient reagent for Csp?H bond silylation. Thus, rhodium-catalyzed intermolecular reactions between SCBs and terminal alkynes produced a series of symmetrical and unsymmetrical tetraorganosilicons bearing a Csp?Si functionality. Preliminary studies suggested that the reaction did not involve a cycloaddition pathway, but instead a direct activation of Csp?H bonds.
- He, Tao,Li, Bin,Liu, Lichuan,Ma, Wenpeng,He, Wei
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supporting information
p. 5648 - 5652
(2021/03/08)
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- Palladium-Catalyzed Enantioselective Carbene Insertion into Carbon-Silicon Bonds of Silacyclobutanes
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We report herein a highly efficient palladium-catalyzed carbene insertion into strained Si-C bonds with excellent enantioselectivity, which provides a rapid and distinct method to access silacyclopentanes with a three- or four-substituted stereocenter asymmetrically. Mechanistic studies using hybrid density functional theory suggest a catalytic cycle involving oxidative addition, carbene migratory insertion, and reductive elimination. In addition, roles of the chiral ligands in controlling the reaction enantioselectivity are also elucidated.
- Huo, Jingfeng,Lan, Yu,Liu, Zhenxing,Lyu, MyeeMay,Ping, Yifan,Wang, Jianbo,Xue, Yazhen,Zhong, Kangbao
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supporting information
p. 12968 - 12973
(2021/09/03)
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- A kind of preparation method of the midbody of entecavir, and intermediate
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The invention discloses Entecavir intermediates and a preparation method thereof. The preparation method of an Entecavir intermediate represented by a formula IV or IV' shown in descriptions comprises the following step of enabling a compound V to be subjected to amino protecting group and hydroxyl protecting group removal reaction in the presence of protonic acid in a solvent. The preparation method disclosed by the invention has the advantages that raw materials are cheap and are easily obtained, reaction conditions are mild, side reactions are few, the yield is high, the pollution to the environment is little, and the intermediates are easily purified and separated, so that the preparation method is applicable to industrial production.
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Paragraph 0386; 0395; 0401
(2017/08/02)
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- Entecavir intermediate and its preparation method
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The invention discloses an entecavir intermediate and a preparation method thereof. A provided preparation method for an entecavir intermediate compound 3 comprises the following steps: performing reducing reaction on a compound 4 in a solvent, so as to obtain the compound 3. A provided preparation method for an entecavir intermediate compound 4 comprises the following steps: performing transacetalation reaction on a compound 5 and a compound 18 in an organic solvent under an acid condition, so as to obtain the compound 4. The preparation methods are cheap and easily available in raw materials, mild in reaction conditions, relatively high in product yield, good in atom economy, friendly to environment, and suitable for industrialized production.
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Paragraph 0373; 0381; 0388-0390
(2017/10/28)
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- Entecavir intermediate and its preparation method
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The invention discloses an entecavir intermediate and a preparation method thereof. A provided preparation method for an entecavir intermediate compound 10 comprises the following steps: performing reducing reaction on an ester compound 11 in an organic solvent under the effect of a reducing agent, so as to obtain the compound 10. A provided preparation method for an entecavir intermediate compound 11 comprises the following steps: reacting a compound 12 with a hydroxyl protection reagent in an organic solvent in the presence of an acid to add a hydroxyl protection group, so as to obtain the compound 11. The preparation methods are cheap and easily available in raw materials, mild in reaction conditions, relatively high in product yield, good in atom economy, friendly to environment, and suitable for industrialized production.
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Paragraph 0380; 0385-0387; 394
(2017/12/28)
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- Hexacoordinate silacyclobutane dichelate complexes: Structure, properties, and ligand crossover
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Hexacoordinate dichelate silacyclobutane complexes have been synthesized from dichlorosilacyclobutane and O-trimethylsilylated hydrazides by transsilylation. Like previously reported hexacoordinate silicon complexes, they readily and quantitatively undergo ligand exchange with other silicon compounds (XSiCl3 and differently substituted O-trimethylsilylated hydrazides), evidence that ionic dissociation does not play a significant role in the exchange mechanism. Germanium tetrachloride causes central-element exchange and formation of analogous hexacoordinate germanium complexes. Likewise, silicon tetrachloride replaces germanium from its hexacoordinate complexes, obeying certain selectivity constraints. When silicon complexes have strongly electron-withdrawing chelate-ring substituents (CF3 or CH2CN), GeCl4 causes, in addition to central-element exchange, also oxidative opening of the four-membered ring and addition of two chlorine atoms. Both chelate exchange and central-element exchange are shown to be dominated by monodentate ligand priorities.
- Yakubovich, Shiri,Gostevskii, Boris,Kalikhman, Inna,Botoshansky, Mark,Gusel'Nikov, Leonid E.,Pestunovich, Vadim A.,Kost, Daniel
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scheme or table
p. 405 - 413
(2011/03/21)
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- Method of preparing silacycloalkanes
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According to the present invention, a method of preparing a silacycloalkane, comprising the steps of (A) adding a substituted silacycloalkane having the formula: wherein X1is —F, —Cl, —Br, or —OR1and X2is X1or H, wherein R1is C1-C8hydrocarbyl, and n is 1, 2, or 3, to a suspension of lithium aluminum hydride in a glycol diether at a temperature not greater than 50° C. to form a mixture, wherein the glycol diether consists essentially of a linear arrangement of oxyalkylene units having formulae independently selected from —OCH2CH2—, —OCH2CH(CH3)—, and —OCH2CH(CH2CH3)—, and end-groups having the formulae —R2and —OR2, wherein each R2is independently selected from C1-C8alkyl, phenyl, and C1-C8alkyl-substituted phenyl, provided the glycol diether has a normal boiling point of at least 85° C. and a viscosity not greater than 3000 mm2/s at 25° C.; and (B) distilling the mixture under reduced pressure at a temperature not greater than 50° C. to remove the silacycloalkane.
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- Chemistry of enoxysilacyclobutanes: Highly selective uncatalyzed aldol additions
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O-(Silacyclobutyl) ketene acetals derived from esters, thiol esters, and amides underwent facile aldol addition with a variety of aldehydes at room temperature without the need for catalysts. The uncatalyzed aldol addition reaction of O-(silacyclobutyl) ketene acetals displayed the following characteristics: (1) the rate of reaction was highly dependent on the spectator substituent on silicon and the geometry of the ketene acetal, (2) the O,O-ketene acetal of E configuration afforded the syn aldol products with high diastereoselectivity (93/7 to 99/1), (3) conjugated aldehydes reacted more rapidly than aliphatic aldehydes, and (4) the reaction was mildly sensitive to solvent. In addition, the aldol reaction was found to be efficiently catalyzed by metal alkoxides. Labeling experiments revealed that the thermal aldol reaction proceeds by direct intramolecular silicon group transfer, while the alkoxide-catalyzed version probably proceeds via in situ generated metal enolates. Computational modeling of the transition states suggests that the boat transition structures are preferred, supporting the observed syn selectivity of the thermal aldol reaction. Both thermal and alkoxide-catalyzed Michael additions were investigated, revealing a competition between 1,2- and 1,4-addition favoring the former.
- Denmark, Scott E.,Griedel, Brian D.,Coe, Diane M.,Schnute, Mark E.
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p. 7026 - 7043
(2007/10/02)
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- Silaethenes, XV. Pyrolysis of 1-Methyl-1-vinyl-1-silacyclobutane and 1,1-Divinyl-1-silacyclobutane - Follow-up Reactions of the Silaethenes Me(Vi)Si=CH2 and Vi2Si=CH2
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The pyrolysis of the silacyclobutanes Vi(Me)Si(CH2)3 (VMS) and Vi2Si(CH2)3 (V2S) at 700-800 deg C and 1E-1 - 1E-2 mbar leads to the intermediates Vi(Me)Si=CH2 and Vi2Si=CH2, which undergo isomerisation to siliranes followed by cleavage to give allene and the corresponding silylenes Me(H)Si: and Vi(H)Si: respectively.Copyrolyes of these silacyclobutanes with dienes (2,3-dimethyl-1,3-butadiene or isoprene) yield silacyclopentene derivatives (4, 14 and 20).The formation of these products supports the proposed mechanism.The simultaneous existence of silaethenes and silylenes in the gas phase is proven by the presence of the disilacyclobutanes 13 and 17, respectively, in the reaction mixtures.Using isoprene as the quenching reagent for Vi(Me)Si=CH2 the two isomeric silacyclohexenes 15 and 16 are formed in low yield, in addition to almost equal amounts of 13 and 14 (eq. (6)).
- Grobe, Joseph,Ziemer, Harald
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p. 1193 - 1202
(2007/10/02)
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- Silaheterocyclen II. Erzeugung und Cycloadditionsreaktionen der Neopentylsilaethene (R = H, Me)
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The monosilacyclobutanes (3) and (4) react with LiBut in pentane to yield the neopentylsilaethenes (1) and (2), respectively.Without suitable reactants, 1 and 2 undergo cyclodimerization to 2,4-dineopentyl-1,3-disilacyclobutanes; in the presence of organic dienes they form cycloaddition compounds: with cyclopentadiene only products are obtained, with cyclohexa-1,3-diene - and -cycloaddition reactions occur at comparable rates; in the reaction with norbornadiene the - is favoured over the -cycloaddition, whereas with 2,3-dimethyl-1,3-butadiene the -process together with the ene-reaction predominate.The -cycloadducts indicate a multistep-pathway, probably with participation of lithiated species, whereas the - and -cycloaddition reactions confirm that the silaethenes 1 and 2 are formed as reactive intermediates.
- Auner, N.
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- Conformational Study of Molecules with Asymmetric Isotopic Substitution. Ring Puckering of 1-Silacyclobutane-1-d1
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1-Silacyclobutane-1-d1, , has been prepared and its infrared spectra have been analyzed.Several ring-puckering transitions have been observed in the far-infrared region and sum and difference bands have been observed in the Si-H stretching region.A ring-puckering potential function which simultaneously fits the data for the d0, d1, and d2 isotopic forms has been determined.Calculation of the wave functions for the d1 molecule shows that each of the lowest two very nearly degenerate energy states (ν = 0 and ν = 1) corresponds to only one distinct molecular conformation.Similarly, the nearly degenerate ν = 2 and ν = 3 states are primarily restricted to specific conformations.Doublets observed for the Si-H and Si-D stretching bands, corresponding to stretches from equitorial or axial positions, confirm these calculations.Model calculations on related systems demonstrate that both a sufficiently large barrier height and an asymmetry of the kinetic energy expansions are necessary for the conformational separation according to vibrational states.Although the reduced masses of the conformers of 1-silacyclobultane-1-d1 differ by only 0.20 percent, this is enough to produce the observed conformational discrimination.
- Harthcock, M. A.,Cooke, J. M.,Laane, J.
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p. 4335 - 4342
(2007/10/02)
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- SILAETHENE I. DARSTELLUNG UND CHARAKTERISIERUNG VON MONOSILACYCLOBUTANEN
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Monosilacyclobutanes of the type RR' are prepared by ring closure reactions of 3-halopropylhalosilanes and by substitution of SiCl containing silacyclobutane rings with organometallic reagents (RMgX, LiR, NaCp).Under optimal experimental conditions yields between 50 and 95percent can be obtained by both procedures.Characterization of the compounds is accomplished by analytical (C, H, N) and NMR, IR and mass spectroscopic investigations.
- Auner, N.,Grobe, J.
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