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Coupling reactions of alkenylsilanes

To facilitate the coupling reaction of alkenylsilanes, benzenediazonium salts could be employed in place of aryl halides [4], However, the coupling reaction is sometimes accompanied by the formation of regioisomers [Eq.(4)J. This fact is ascribed to a mechanism that involves carbopalladation of an arylpalladium complex to alkenylsilanes followed by elimination of the silyl group and the palladium metal, as is the case in Heck-type reactions. [Pg.223]

Scheme 10-1 Mechanism of palladium-catalyzed coupling reaction of alkenylsilanes. Scheme 10-1 Mechanism of palladium-catalyzed coupling reaction of alkenylsilanes.
The coupling reactions of alkenylsilanes generally require activation of the silicon due to the low reactivity of the C-Si bond. Introduction of heteroatoms on the... [Pg.21]

Scheme 530 Intramolecular cross-coupling reaction of alkenylsilanes leading to medium-sized rings. Scheme 530 Intramolecular cross-coupling reaction of alkenylsilanes leading to medium-sized rings.
The cross-coupling reaction of alkenyl(fluoro)silanes with aryl halides sometimes produces, in addition to the desired ipso-cowpled products, small amounts of cmc-coupled products [14]. The czne-coupling is often striking in the reaction with organotin compounds. The isomer ratio of products produced by the reaction of l-fluoro(dimethyl)silyl-l-phenylethene with aryl iodides is found to depend on the electronic nature of a substituent on aryl iodides (Eq. 11) an electron-withdrawing group like trifluoromethyl and acetyl favors the formation of the ipso-coupled product. To explain the substituent effect, the mechanism depicted in Scheme 3 is proposed for the transmetalation of alkenylsilanes with palladium(ll) complexes. It is considered that an electron-donating substituent on Ar enhances... [Pg.68]

Allyl carbonates (Schemes 17 and 18) and diene monoxides (Scheme 19) were also employed in the Pd-catalyzed coupling reaction of aryl- and alkenylsilanes.t t The reaction does not require activation by a fluoride ion or an additional base like a hydroxide ion. [Pg.293]

Whereas the vinyl groups of Da are accessible for functionalization by hydroboration or hydrosilylation, they are inert to functionalization by cross-metathesis. Alternatively, formal metathesis products can be obtained by the ruthenium-catalyzed silylative coupling reaction. This method involves the combination of a vinyl silane and an olefin in the presence of a ruthenium catalyst, to provide an alkenylsilane (see eq 7). The application of this reaction to Da provides substitution at each of the four vinyl groups, resulting in a cyclic tetraalkenyltetramethylcyclote-trasiloxane. The silylative coupling reaction of both Da and has been demonstrated with styrenes and enol ethers. ... [Pg.485]

Alkenylsilanes generally do not participate in traditional crossmetathesis reactions. Alternatively, the ruthenium-catalyzed silylative coupling reaction of vinylsilanes and olefins provides formal metathesis products (eq 7). Although the products are the same, the reactions proceed through a distinct mechanism, converting vinylsilanes into substituted alkenylsilanes. [Pg.486]

Alkenylfluorosilanes readily couple with alkenyl iodides in the presence of a palladium ) catalyst and TASF to form dienes of high stereospecificity (equation 160)274. Since the alkenylsilane preparation and coupling reaction are conducted under neutral conditions, without the involvement of strong reducing agents, this coupling reaction has wide applicability. [Pg.453]

There are scattering examples that neutral organosilanes R-SiMe3 undergo a desilylative coupling reaction with aryl halides in the presence of a palladium catalyst. Hallberg and his co-workers disclosed that trimethyl(vinyl)silane reacts with an arylpalladium(II) complex to afford coupled products accompanied by aryl-substituted alkenylsilanes formed through the Heck type reaction... [Pg.62]

Eq. 1) [5]. On the other hand, Kikukawa and his co-workers found that the reaction of trimethyl(a- or -styryl)silane with arenediazonium tetrafluoroborates gave regioisomeric mixtures of coupling products [6-8]. The catalytic cycle of the reaction is considered to involve carbopalladation toward the C-C double bond of an alkenylsilane by an arylpalladium intermediate followed by tetraflu-oroborate-assisted elimination of the silyl group and regeneration of a palladi-um(0) species (Scheme 1). [Pg.63]

The following mechanism is suggested for the cross-coupling of alkenylsilanes. Nucleophilic attack of a fluoride ion to the silicon atom of alkenylsilanes is first assumed to afford a pentacoordinate silicate and enhance both nucleophilicity of the silicon-substituted carbon and Lewis acidity of silicon to assist transmetalation effectively through a four-centered transition state (Scheme 2). Lewis acidity on silicon is critical as evidenced by the fact that hexacoordinate pentafluorosilicates that are fully coordinated and thus should have sufficient nucleophilicity are much less effective for the cross-coupling reaction (Eq. 2, vide supra). [Pg.64]

Under an atmospheric pressure of carbon monoxide, aryl- and alkenylsilanes undergo a carbonylative coupling reaction with aryl and alkenyl halides [44,45]. The optimized conditions for arylsilanes involve the use of N,M-dimethyl-2-imidazolidinone (DMI) as a solvent and KF as a fluoride ion source (Eq. 38), whereas alkenylsilanes prefer THF and TBAF (Eq. 39). [Pg.82]

Coupling reactions involving aryl and alkenylsilanes in which the silicon atom bears an electron-withdrawing group are also valuable. Thus, 1,4-dienes arise from ally lie carbonates and alkenylfluorosilanes. Functionalized biaryls are prepared, and promotion of such reactions by NaOH has been noted. ... [Pg.287]

Although alkenylsilanes undergo palladium-catalyzed coupling reactions with aryl iodides (eq (19)) [16], the similar reactions of 5-coordinated silicates proceeds under milder conditions to give better yields (eq (20)) [17]. [Pg.396]

Although mechanistically different, functionalized alkenylsilanes are prepared stereoselectively by the reaction of 1-alkynes with iodotrimethylsilane (123) and diethylzinc. At hrst oxidative addition of 123 to Pd(0) generates 125. Then insertion of 1-octyne to 125 affords the alkenylpalladium 126. Transmetallation with Et2Zn gives 127 and reductive elimination provides the alkenylsilane 124. The reaction can be regarded as a Heck-type reaction of alkyne with MesSi-I, followed by Negishi coupling [37]. [Pg.577]


See other pages where Coupling reactions of alkenylsilanes is mentioned: [Pg.279]    [Pg.280]    [Pg.482]    [Pg.190]    [Pg.279]    [Pg.280]    [Pg.482]    [Pg.190]    [Pg.64]    [Pg.68]    [Pg.288]    [Pg.289]    [Pg.355]    [Pg.288]    [Pg.289]    [Pg.355]    [Pg.86]    [Pg.418]    [Pg.668]    [Pg.50]    [Pg.641]    [Pg.300]    [Pg.933]    [Pg.28]    [Pg.364]    [Pg.117]    [Pg.63]    [Pg.285]    [Pg.286]   


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