Cross-coupling reactions allylsilane

Tetraalkylstannanes with double bonds at allylic or more remote positions undergo cross-coupling with allylsilanes to yield dienes, as illustrated in reaction 47299. 

Silyl enol ethers undergo cross-coupling with allylsilane in the presence of a Lewis acid. For example, an oxovanadium(V) complex can induce such condensation reactions (equation 81)150. 

The direct substitution of hydroxyl groups can also be extended towards propargylic alcohols. In the presence of FeCl3, a plethora of O-, N- or S-nudeophiles are able to react with substituted propargylic alcohols [17]. Amongst the variety of nucleophiles, allylsilanes occupy an important position since this example resembles a cross-coupling reaction between an organometallic compound and an alcohol (Scheme 7.12) [17]. 

The cross-coupling of allylsilanes with alkenes [50] and styrene [58] also occurs via their preliminary isomerization followed by the reaction of 1-propenylsilane with exemplary olefin-l-decene resulting in l-(triethoxysilyl)-1-decene as a product (Eq. 31). If the cross-coupling takes place, an expected product of this reaction is l-silyl-2-undecene, which is not detected. 

The kind of a fluoride ion activator and the leaving group in electrophiles affects the stereochemistry in the cross-coupling reaction of allylsilanes as exemplified with 2-cyclohexenyl(difluoro)phenylsilane (Eq. 31) 135]. 

It is a palladium-catalyzed cross-coupling reaction between organosilanes (vinyl, ethynyl and allylsilanes) and organic halides (aryl, vinyl and allyl halides). Allylpal-ladium chloride dimmer [( ri -C3H5PdCl)2] and either tris(diethylamino)sulfonium difluorotrimethylsilicate (TASF) or tetra-n-butylammonium fluoride (TBAF) are used as catalysts. Fluoride ion acts as an activator for the coupling, forming an intermediate hypervalent anionic silicon species, which can then transmetallate with palladium as a preliminary reaction to coupling. 

Cross-Coupling Reactions. TASF(Et) activates vinyl-, alkynyl-, and allylsilanes in the Pd-mediated cross-coupling with vinyl and aryl iodides and bromides. As illustrated in eqs 8-10, the reaction is stereospecific and chemoselective. This crosscoupling protocol is remarkably tolerant towards a variety of other functional groups such as carbonyl, amino, hydroxy, and nitro. Vinylsilanes can be synthesized from hexamethyldisilane and vinyl iodides in the presence of TASF(Et) (eq 10) via cleavage of a Si-Si bond. Aryl iodides can also be synthesized by this method. TASF is superior to tetra-n-butylanunonium fluoride for these reactions. In the absence of a vinylsilane reagent, one of the methyl groups from the difluorotrimethylsilicate is substituted for the halide (eq 11). ... 

Cross-Coupling Reactions. TASF(Et) activates vinyl-, alkynyl-, and allylsilanes in the Pd-mediated cross-coupling with vinyl and aryl iodides and bromides. As illustrated in... 

Optically active (Z)-l-substituted-2-alkenylsilanes are also available by asymmetric cross coupling, and similarly react with aldehydes in the presence of titanium(IV) chloride by an SE process in which the electrophile attacks the allylsilane double bond unit with respect to the leaving silyl group to form ( )-s)vr-products. However the enantiomeric excesses of these (Z)-allylsilanes tend to be lower than those of their ( )-isomers, and their reactions with aldehydes tend to be less stereoselective with more of the (E)-anti products being obtained74. 

The asymmetric cross-coupling was successfully applied to the synthesis of optically active allylsilanes [27,28] (Scheme 8F.9). The reaction of a-(trimethylsilyl)benzylmagnesium bro-... 

The asymmetric cross-coupling was successfully applied to the synthesis of optically active allylsilanes [50,51] (Scheme 10). The reactions of a-(trimethyl-silyl)benzylmagnesium bromide (49) with vinyl bromide (4b), (E)-bromopro-pene (( )-50), and (R)-bromostyrene E)-8) in the presence of 0.5 mol % of a palladium complex coordinated with chiral ferrocenylphosphine, (R)-(S)-PPFA (10a), gave the corresponding (R)-allylsilanes (51) with 95%, 85%, and 95% ee, respectively, which were substituted with phenyl group at the chiral carbon center bonded to the siHcon atom. These allylsilanes were used for the S. ... 

Oxidative cross-coupling. a-Stannylalkanoic esters and amides undergo oxidation, and the resulting free radicals can be trapped in situ by electron-rich alkenes such as silyl enol ethers and allylsilanes. Thus y-keto esters are accessible by this reaction. Note that a-germanylalkanoic esters are less reactive toward the oxidant and the a-silylalkanoic esters do not undergo oxidation at all. 

For the first time, a simple and efficient method for the preparation of optically active allylsilanes using catalytic asymmetric Grignard cross-coupling has been reported. These allylsilanes react in a highly efficient and stereocontrolled fashion with aldehydes, in which the reaction is thought to proceed via acyclic linear diastereomeric transition states (Scheme 21). ... 

Allylsilanes can be prepared by a wide array of methods, including (1) the reaction of allyl metals with ClSiRs, (2) the reaction of silylanions (MSiRs) with allylic substrates, (3) the Kumada coupling of Me3SiCH2MgBr with vinyl halides, catalyzed by Pd or Ni species, (4) the Wittig reaction of P-silylated Wittig reagents, (5) the cross-metathesis of olefins with allylsilanes, and (6) the reductive silylation of unsaturated compounds. ... 

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