- Diastereoselective synthesis of trisubstituted olefins using a silicon-tether ring-closing metathesis strategy
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The diastereoselective synthesis of trisubstituted olefins with concomitant C-C bond formation is still a difficult challenge, and olefin metathesis reactions for the formation of such alkenes are usually not high yielding or/and diastereoselective. Herein we report an efficient and diastereoselective synthesis of trisubstituted olefins flanked by an allylic alcohol, by a silicon-tether ring-closing metathesis strategy. Both E- and Z-trisubstituted alkenes were synthesised, depending on the method employed to cleave the silicon tether. Furthermore, this methodology features a novel Peterson olefination for the synthesis of allyldimethylsilanes. These versatile intermediates were also converted into the corresponding allylchlorodimethylsilanes, which are not easily accessible in high yields by other methods.
- Prunet, Jo?lle,Tiniakos, Alexander F.,Wittmann, Stéphane
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p. 2297 - 2306
(2020/04/03)
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- 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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- METHOD OF PREPARING ALLYLCHLOROSILANE DERIVATIVE
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Provided is a method of preparing allylchlorosilane, and more particularly, a method of preparing allylchlorosilane with high yield by Si—C coupling reaction of an allyl chloride derivativce with a hydrosilane derivative under specific reaction conditions without using a catalyst.
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Page/Page column 4
(2011/06/23)
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- Selective mono- and di-allylation and allenylation of chlorosilanes using indium
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Allyl and allenyl groups have been introduced into silicon systems by the allylation and allenylation of chlorosilanes using allyl bromide or propargyl bromide with indium. The allylation of chlorosilanes afforded a variety of aryl, aralkyl, and alkenyl substituted allylsilanes. By applying this method, the reactions of 1-bromo-3-methylbut-2-ene, 3-bromo-2-methylprop-1-ene and 3-bromobut-1-ene with chlorosilanes also proceed smoothly to give regioselectively allylic rearrangement products in good yields. Mediated by indium, dichlorosilanes (R2SiCl2) and trichlorosilanes (RSiCl3) can either afford monoallylated silanes or diallylated silanes depending on the amount of allyl bromide and indium used.
- Li, Zhifang,Yang, Chenjun,Zheng, Hongfang,Qiu, Huayu,Lai, Guoqiao
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scheme or table
p. 3771 - 3779
(2009/02/08)
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- Method for obtaining halogenated monoorganoxysilanes useful in particular as synthesis intermediates
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The invention concerns the preparation of halogenated monoorganoxysilanes, of formula (I), said compounds being useful as synthesis intermediate in organic chemistry. Said method for preparing monoorganoxysilanes consists in: using as starting product halogenoalkylsilanes of the (CH3)2SiCl2 type and in substituting the silicon with a radical bearing a divalent unit bound to an electrophilic reactive group capable of reacting with at least an appropriate nucleophilic agent to form a functionalised monoorganoxysilane of formula (II) with, for example: R=C1-C4 alkyl; R, R=C1-C6 alkyl; B═C1-C10 alkylene; m=1 or 2; Hal=halogen; W=amino, mercapto, (organosilyl)-organopolythio radical.
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Page/Page column 8
(2008/06/13)
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- On the question of cyclopropylidene intermediates in cyclopropene-to-allene rearrangements - Tetrakis(trimethylsilyl)cyclopropene, 3-alkenyl-1,2,3-tris(trimethylsilyl)cyclopropenes, and related model compounds
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Several tetrasubstituted cyclopropenes have been prepared and their pyrolyses and photolyses have been investigated. Tetrakis(trimethylsilyl)cyclopropene (10), which was obtained in 25% yield from tris(trimethylsilyl)cyclopropenylium hexachloroantimonate (9), gave tetrakis(trimethylsilyl)allene (12) as the sole product both thermally and photochemically. Kinetic studies in [D8]toluene indicated first-order behavior with Arrhenius parameters log(A/s-1) = 11.75±1.20 and Ea = (37.5±2.5) kcal mol-1. All three new 3-alkenyl-1,2,3-tris(trimethylsilyl)cyclopropenes (17a-c, with C1-, C2-, and C3-alkenyl groups as tethers, respectively) gave allenes upon irradiation, but thermally only two (17a, 17c) gave allenes, whilst 17b yielded a bicyclo[4.1.0]hept-3-ene derivative 22 as a result of an intramolecular ene reaction. Photolyses of two further cyclopropenes (33a,b) bearing 1,2-bis(alkenyldimethylsilyl) substituents also gave the corresponding allenes as the sole products. For none of these tethered cyclopropenes was a product found that could have originated from intramolecular trapping of a cyclopropylidene intermediate. Quantum mechanical (ab initio) calculations have been carried out on the silyl-substituted cyclopropene model compounds 3,3-dimethyl-1-silyl- (36a), 3,3-dimethyl-1,2-disilyl- (37), and tetrasilylcyclopropene (38) at the QCISD(T)/6-311G*//B3LYP/6-311G* + ZPVE level of theory, and on 3,3-dimethyl-1-(trimethylsilyl)cyclopropene (36b) at the B3LYP/6-311G*//B3LYP/ 6-311G* + ZPVE level. These calculations provided us with detailed energy surfaces for the potential pyrolysis pathways. Although the potential cyclopropylidene species in these rearrangements are significantly stabilized, for none of the systems was this sufficient to permit isomerization via these intermediates. 36b is calculated to rearrange via a vinylidene intermediate to give 3-methyl-1-trimethylsilyl-1-butyne (47), in agreement with experiment. Comparison of the calculations for 36a and 36b shows that H3Si- is a poor model for an Me3Si- substituent in these rearrangements. When an appropriate correction is applied, the calculations on disilyl-(37) and tetrasilylcyclopropenes (38) are consistent with the experimental findings that the trimethylsilyl-substituted cyclopropenes 48 and 10 form allenes 49 and 12, respectively, via vinylcarbene-type intermediates. These findings considerably extend our understanding of silyl group substituent effects on the various intermediates involved in cyclopropene rearrangements. Wiley-VCH Verlag GmbH, 2001.
- De Meijere, Armin,Faber, Dietmar,Heinecke, Ute,Walsh, Robin,Mueller, Thomas,Apeloig, Yitzhak
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p. 663 - 680
(2007/10/03)
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- Method for preparing monohalogenosilanes
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This invention relates to a method for preparing a monohalogenosilane, R1R2R3SiX which comprises the step of subjecting, to a rearrangement reaction, an organodisiloxane, (R1R2R3Si)2O and a polyhalogenosilane, R4nSiX4-nin the presence of active carbon or an ammonium salt, R5R6R7R8NY as a catalyst (wherein R1, R2, R3 and R8 each represents a hydrogen atoms or a monovalent hydrocarbon group; R4, R5, R6 and R7 each represents a monovalent hydrocarbon group, a part or whole of the hydrogen atoms in each hydrocarbon group may be substituted with other atoms or groups; X represents a halogen atom; Y represents a monovalent anion; n is 0, 1 or 2). The method permits the easy preparation of monohalogenosilanes, in a high yield, which are useful as starting materials for use in making silylating agents as well as a variety of organosilicon compounds without using any harmful hexaalkylphosphoric acid triamide type catalyst.
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- METATHESIS OF FUNCTIONAL DERIVATIVES OF OLEFINS BY THE ACTION OF THE WCl6-1,1,3,3-TETRAMETHYL-1,3-DISILACYCLOBUTANE CATALYTIC SYSTEM
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A study was carried out on the metathesis of esters of unsaturated carboxylic acids and nitriles by the action of the WCl6-1,1,3,3-tetramethyl-1,3-disilacyclobutane catalytic system.The possibility of efficient homometathesis and cometathesis with α-olefins and allyltrimethylsilane was demonstrated for ethyl 4-pentenoate and allyl cyanide.
- Bespalova, N. B.,Bovina, M. A.
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p. 156 - 159
(2007/10/02)
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- 1H-CIDNP During the Reaction of Heavy Carbene Analogues R2M (M = Si, Ge, Sn; R = Me, n-Bu) with Halides
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During the reaction of photochemically generated silylenes Me2Si: with PhCH2Cl, PhCH2Br, and Ph2CHCl, 1H-CIDNP is observed in the products of insertion reactions into the C-X bonds (X = Cl, Br) and in the abstraction products Ms2SiX2 indicating the occurrence of a radical abstraction-recombination reaction.The silylenes react from singlet states.Me2Si: reacts with CH2=CHCH2Cl without CIDNP phenomena in a concerted way. (n-Bu2Sn)6 reacts with EtBr via a radical chain mechanism without the appearance of free stannylenes n-Bu2Sn: as intermediates.
- Lehnig, Manfred,Klaukien, Heino,Reininghaus, F.
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p. 1411 - 1414
(2007/10/02)
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- Lewis Acid Promoted Condensation of Allylalkoxysilanes with Carbonyl Co+pounds. Synthesis of Tetrahydropyrans
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Allylalkoxysilanes 1 condense with aldehydes under Lewis acid conditions to give cis-2,4,6-trisubstituted tetrahydropyrans 3 or the homoallylic alcohols 2.Factors affecting the reaction have been examined.The enantioselective synthesis of 2 using optically active 1 has also been studied.The reaction is applied to the enantioselective synthesis of (6'-methyl-2'-tetrahydropyranyl)acetic acid (11), a natural compound that has been isolated from the glandular secretion of the civet cat.
- Wei, Z. Y.,Wang, D.,Li, J. S.
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p. 5768 - 5774
(2007/10/02)
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- REACTIONS OF (Me3Si)3CSiMe2R COMPOUNDS (R = CH=CH2, CH2CH=CH2, CCPh, Ph, AND CH2Ph) WITH ELECTROPHILES
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No products of addition to the multiple bond are formed in reactions of TsiSiMe2R species (Tsi=(Me3Si)3C; R=CH=CH2, CH2CH=CH2, or (CCPh) with halogens or hydrogen halides.TsiSiMe2CH=CH2 gave (a) TsiSiMe2Cl on treatment with ICl in CCl4; (b) TsiSiMe2Br on treatment with Br2 in CCl4;.(c) TsiSiMe2I (slowly) on treatment with I2 in CCl4; and (d) TsiSiMe2OCOCF3 on treatment with neat CF3CO2H.TsiSiMe2CH2CH=CH2 gave: (a) TsiSiMe2Cl and TsiSiMe2I on treatment with ICl in CCl4; (b) TsiSiMe2Br on treatment with Br2 in CCl4; (c) TsiSiMe2I on treatment with I2 in CCl4; and (d) TsiSiMe2OCOCF3 rapidly on treatment with neat CF3CO2H.TsiSiMe2Ph gave TsiSiMe2Br on treatment with Br2 in CCl4 or CH3CO2H, and (b) TsiSiMe2Cl on treatment with HCl in Et2O.Reaction of TsiSiMe2Ph with nitric acid in (CH3CO)2O gave two mono-nitration products, probably the m- and p-isomers.Reaction of TsiSiMe2CH2Ph with Br2 gave exclusively TsiSiMe2Br, whereas reaction with nitric acid in (CH3CO)2O gave o- and p-nitro derivatives in 65/35 ratio.This last result casts serious doubt on previously proposed explanations of the predominance of ortho-nitration in the case of Me3SiCH2Ph.
- Damja, Ramadan I.,Eaborn, Colin,Sham, Wing-Cheong
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- ISOMERISATIONS THERMIQUES ORIGINALES DE COMPOSES β-CHLORES DU SILICIUM INDUITES PAR UN GROUPE β'-ETHYLENIQUE
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The thermolysis of linear and cyclic β-chloro-β'-ethylenesilicon compounds gives rise to two competitive reactions.Besides the classical β-elimination reaction, a new rearrangement reaction was observed, which depends on the Si-bonded R groups; it has not been noticed for the corresponding germanium compounds.To explain the results, we propose a mechanism involving a transient pentavalent silicon anion.
- Manuel, Georges,Bertrand, Guy,Mazerolles, Pierre,Ancelle, Jacques
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p. 311 - 323
(2007/10/02)
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