- ACTION DE SILANES PROPARGYLIQUES SUR DES DERIVES CARBONYLES α-ETHYLENIQUES
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Propargylsilanes RCCCH2Si(CH3)3 easily react with dialkyl alkylidenemalonates, in the presence of TiCl4, to lead to the only product corresponding to an 1,4-addition; the reaction takes place with propargylic rearrangement.
- Pornet, Jaques,Kolani, N'Baneyape,Mesnard, Danielle,Miginiac, Leone,Jaworski, Krzysztof
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- Stereoselectivity in N-Iminium Ion Cyclization: Development of an Efficient Synthesis of (±)-Cephalotaxine
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A stereoselective N-iminium ion cyclization with allylsilane to construct vicinal quaternary-tertiary carbon centers was developed for the concise synthesis of (±)-cephalotaxine. The current strategy features a TiCl4-promoted cyclization and ring-closure metathesis to furnish the spiro-ring system. The stereochemical outcome in the N-acyliminium ion cyclization was rationalized by the stereoelectronic effect of the Z- or E-allylsilane. Two diastereomers arising from the cyclization were merged into the formal synthesis of (±)-cephalotaxine.
- Liu, Hao,Yu, Jing,Li, Xinyu,Yan, Rui,Xiao, Ji-Chang,Hong, Ran
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- Indium Catalyzed Hydrofunctionalization of Styrene Derivatives Bearing a Hydroxy Group with Organosilicon Nucleophiles
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Hydrofunctionalization is one of the most important transformation reactions of alkenes. Herein, we describe the development of an indium-triiodide-catalyzed hydrofunctionalization of alkenes bearing a hydroxy group using various types of organosilicon nucleophiles. Indium triiodide was the most effective catalyst, whereas typical Lewis acids such as TiCl4, AlCl3, and BF3·OEt2 were ineffective. Many functional groups were successfully introduced, and these resulted in yields of 31-86%. Various styrene derivatives were also applicable to this reaction. Mechanistic investigation revealed that the present hydrofunctionalization proceeded through Br?nsted acid-catalyzed intramolecular hydroalkoxylation of alkenes followed by InI3-catalyzed substitution reaction of cyclic ether intermediates.
- Kita, Yuji,Yata, Tetsuji,Nishimoto, Yoshihiro,Yasuda, Makoto
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p. 740 - 753
(2018/01/28)
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- Temporary silicon connection strategies in intramolecular allylation of aldehydes with allylsilanes
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(Chemical Equation Presented) Three γ-(amino)silyl-substituted allylsilanes 14a-c have been prepared in three steps from the corresponding dialkyldichlorosilane. The aminosilyl group has been used to link this allylsilane nucleophile to a series of β-hydroxy aldehydes through a silyl ether temporary connection. The size of the alkyl substituents at the silyl ether tether governs the outcome of the reaction on exposure to acid. Thus, treatment of aldehyde (E)-9aa, which contains a dimethylsilyl ether connection between the aldehyde and allylsilane, with a range of Lewis and Bronsted acid activators provides an (E)-diene product. The mechanism of formation of this undesired product is discussed. Systems containing a sterically more bulky diethylsilyl ether connection react differently: thus in the presence of TMSOTf and a Bronsted acid scavenger, intramolecular allylation proceeds smoothly to provide two out of the possible four diastereoisomeric oxasilacycles, 23 (major) and 21 (minor). A diene product again accounts for the remaining mass balance in the reaction. This side product can be completely suppressed by using a sterically even more bulky diisopropylsilyl ether connection in the cyclization precursor, although this is now at the expense of a slight erosion in the 1,3-stereoinduction in the allylation products. The sense of 1,3-stereoinduction observed in these intramolecular allylations has been rationalized by using an electrostatic argument, which can also explain the stereochemical outcome of a number of related reactions. Levels of 1,4-stereoinduction in the intramolecular allylation are more modest but can be significantly improved in some cases by using a tethered (Z)-allylsilane in place of its (E)-stereoisomer. Oxidation of the major diastereoisomeric allylation product 23 under Tamao-Kumada conditions provides an entry into stereodefined 1,2-anti-2,4-syn triols 28.
- Beignet, Julien,Jervis, Peter J.,Cox, Liam R.
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p. 5462 - 5475
(2008/12/21)
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- Stereoselective synthesis of 2,4,5-trisubstituted tetrahydropyrans using an intramolecular allylation strategy
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A highly stereoselective route to 2,4,5-trisubstituted tetrahydropyrans is reported. The key step employs an intramolecular allylation of a (Z)-allylsilane onto an aldehyde under Bronsted acid activation. Complete 1,4-stereoinduction accounts for the form
- Jervis, Peter J.,Kariuki, Benson M.,Cox, Liam R.
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p. 4649 - 4652
(2007/10/03)
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- Using a temporary silicon connection in a highly stereoselective synthesis of a new class of cyclic allenylsilanes
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Aldehyde 4 reacts in the presence of TMSOTf and an acid scavenger to provide the corresponding oxasilacycle 5 in very good yield and as a single diastereoisomer. The sense of 1,3-stereoinduction serves to introduce a 1,3-syn-diol relationship into the cyc
- Ramalho, Rui,Beignet, Julien,Humphries, Alexander C.,Cox, Liam R.
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p. 3389 - 3397
(2007/10/03)
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- SYNTHESIS AND ELECTROPHILIC SUBSTITUTION REACTIONS OF 1,3-DISUBSTITUTED PROPYNES CONTAINING GROUP-IVB ELEMENTS
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The reaction of trialkylstannyldialkylamines and trialkylstannylpropadienes produces 1,3-bis(trialkylstannyl)propynes in high yield. 1,3-Bistrialkylsilyl(germyl)propynes and also certain 1,3-bis(trialkylstannyl)propynes can be obtained by the organomagnesium method.During the bromination of 1,3-bis(trialkylsilyl)(trialkylgermyl)propynes, the E-CH2Csp bond is preferentially split.In contrast to these, 1,3-bis(trialkylstannyl)propynes may undergo a bromodestannylation reaction at the Sn-Csp bond with the formation of 1-bromo-3-trialkylstannyl-1-propynes. 1,3-Bis(trialkylstannyl)propynes react with halosilanes with the formation of acetylene compounds only, whereby the variation of the nature of the silane and the structure of stannylpropyne enables selective splitting of the Sn-Csp or Sn-CH2Csp bond.
- Bogoradovskii, E. T.,Zavgorodnii, V. S.,Liepin'sh, E. E.,Birgele, I. S.,Petrov, A. A.
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p. 1295 - 1306
(2007/10/02)
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- STANNYLDIENES, NEW TOOLS FOR ORGANIC SYNTHESIS. PREPARATION AND REACTIVITY.
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Tributylstannyl-1,3-dienes could be considered synthetic equivalents of conjugated dienic anions.The preparation of differently substituted 2- and 3-trialkylstannyl-1,3-dienes is reported starting from propargyltrimethylsilane.The position of the stannyl moiety on the dienic skeleton can be controlled by hydrostannylation of (trimethylsilyl)propargyl alcohols or stannyl cupration of (trimetylsilyl)propargyl ketones.The so obtained stannyldienes are submitted to Diels Alder reaction and the corresponding cycloadducts functionalized through the C-Sn bond.Stannyldienes are also suitable for a regiocontrolled transfer of the dienic structure by : a) tin-lithium exchange and further reaction with aldehydes to give conjugated dienic alcohols; b)coupling with acyl chlorides in the presence of palladium catalysts to give conjugated dienic ketones; c) AlCl3 promoted reaction with acyl chlorides to give allenic ketones.
- Nativi, Cristina,Taddei, Maurizio,Mann, Andre
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p. 1131 - 1144
(2007/10/02)
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- STEREOSELECTIVE SYNTHESIS OF FUNCTIONALIZED ERYTHRO/1,3-DIOLS
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V(5+)-Catalyzed t-butylhydroperoxide epoxidation of (Z)-5-hydroxy-2-alkenylsilanes 4 exhibit good to excellent erythro selectivity.The resulting epoxides undergo fragmentation to afford 1,3-diols 8, albeit in low chemical yield.
- Mohr, Peter,Tamm, Christoph
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p. 391 - 394
(2007/10/02)
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- SYNTHESE ET REACTIVITE DE SILANES PROPARGYLIQUES ω-FONCTIONNELS : PREPARATION DE VINYLIDENE-3 OXOLANNES, OXANNES, OXEPANNES ET OXOCANNES
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The ω-silyloxypropargyltrimethylsilanes regiospecifically react with aliphatic and aromatic aldehydes to lead to vinylidene oxigen-containing heterocycles, such as 3-vinylidene oxolanes, oxanes, oxepanes and oxocanes.
- Pornet, J.,Damour, D.,Miginiac, L.
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p. 2017 - 2024
(2007/10/02)
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- Gas-Phase Reactions of Anions with Substituted Silanes
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The gas-phase reactions of fluoride, amide, hydroxide, and methoxide ions with a variety of substituted silanes have been studied by the flowing afterglow technique.Fluoride reacts readily with trimethylsilyl derivatives to displace benzyl, alkenyl, and alkynyl anions.These reactions have also been used to generate specific structural isomers (CH3CC- and CH2C=C=CH-).Anions more basic than phenide ion cannot be produced in this manner, and their parent trimethylsilanes interact with fluoride by more complex mechanisms.Amide, hydroxide, and methoxide ions react with substituted trimethylsilanes by both displacement and proton abstraction whenever an acidic hydrogen is present; in the absence of displaceable groups and acidic hydrogen, the reactions of amide, hydroxide, and methoxide parallel those of fluoride ion.
- DePuy, C. H.,Bierbaum, Veronica M.,Flippin, L. A.,Grabowski, Josef J.,King, Gary K.,et al.
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p. 5012 - 5015
(2007/10/02)
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