Silanes vinyl substitution

However, most asymmetric 1,3-dipolar cycloaddition reactions of nitrile oxides with alkenes are carried out without Lewis acids as catalysts using either chiral alkenes or chiral auxiliary compounds (with achiral alkenes). Diverse chiral alkenes are in use, such as camphor-derived chiral N-acryloylhydrazide (195), C2-symmetric l,3-diacryloyl-2,2-dimethyl-4,5-diphenylimidazolidine, chiral 3-acryloyl-2,2-dimethyl-4-phenyloxazolidine (196, 197), sugar-based ethenyl ethers (198), acrylic esters (199, 200), C-bonded vinyl-substituted sugar (201), chirally modified vinylboronic ester derived from D-( + )-mannitol (202), (l/ )-menthyl vinyl ether (203), chiral derivatives of vinylacetic acid (204), ( )-l-ethoxy-3-fluoroalkyl-3-hydroxy-4-(4-methylphenylsulfinyl)but-1 -enes (205), enantiopure Y-oxygenated-a,P-unsaturated phenyl sulfones (206), chiral (a-oxyallyl)silanes (207), and (S )-but-3-ene-1,2-diol derivatives (208). As a chiral auxiliary, diisopropyl (i ,i )-tartrate (209, 210) has been very popular. 

One organic group is readily transferred from tetraorganosilanes (and some other silanes) to palladium ). Tetramethylsilane, lithium tetrachloropalladate(II) and styrene at 120 C in acetonitrile solution form 1 -phenyl- 1-propene in 65% yield along with ca. 1.5% 2-phenyl-1-propene.33 Trimethylphenylsil-ane transfers phenyl and with styrene under the above conditions gives fra/w-stilbene in 94% yield.33 Similar vinyl substitution reactions have been achieved with potassium ( )-alkenyl pentafluorosili-cates.34... 

Previous reports on the reaction of vinyl-substituted silanes [9] and silsesquioxane [15] with vinyl allQrl ethers catalyzed by ruthenium complexes containing or generating Ru-H and/or Ru-Si bonds show that the process proceeds according to the nonmetallacarbene mechanism as in SC and yields (usually in 5-fold excess of alkene) l-silyl-2-alkoxy-ethenes with a high preference for the E-isomer (Eq. 1). 

The reactions of vinyl-substituted silanes and silsesquioxane with vinyl-substituted hetero(N,S,B)organic compounds proceed according to the equations presented in Scheme 2. 

The reaction of vinyl-substituted silanes and octavinylsilsesquioxane with vinyl-substituted amides, amines (carbazole) as welt as boronates catalyzed by I proceeds effectively to yield under optimum conditions stereo- and/or regio-selectively l-silyl-2-/V- and 1,1-silylboryl-substituted ethenes. 1-silylvinyl carbazole can also be obtained via cross-metathesis of vinylsilane with vinylcarbazole, but only in the presence of the 2nd generation Grubbs catalyst (IV). 

There are two recent studies of vinyl-substituted silanes but they are neither self-consistent nor convincing. For example, Voronkov and coworkers13 have obtained — 81.6 + 6.8 kJ mol 1 for AHf ((C2H3)4Si) whilst Gadzhiev and Gubareva29 report... 

Vinyl-substituted silanes always show a strong CH in-plane bending absorption at 7.1—7.2 p, as well as a distinctive doublet at 9.8-10 and 10.2-10.5 p264,259,265,260. These latter bands arise from out-of-plane CH bending vibrations266. A weak but distinctive overtone at 5.2 p is also characteristic. 

U.v.-induced addition of secondary phosphines to chlorovinylsilanes and allyl(chloro)silanes leads to the silylphosphines (36). A similar addition to vinyl-substituted heterocyclic silanes has given compounds such as (37). ... 

Reactions of Vinyl-Substituted Silanes with Vinyl-Snbstitnted Hetero(N,S3)organic Derivatives... 

On the other hand, although well-defined or in-situ initiated metallacarbenes are inactive for selfmetathesis of vinyl-substituted silanes and siloxanes, we revealed recently a high catalytic activity of Grubbs catalyst in cross-metathesis of vinyltrialkoxysilanes and vinyltrisiloxanes with styrene, 1-alkenes and selected allyl ethers and other derivatives [10-12]. 

The silica gel-bound macrocycles were prepared as shown in Scheme I. The allyloxymethyl-substituted macrocycle, a catalytic amount of chloroplatinic acid and an excess of diethoxymethysilane were refluxed in benzene for 8 to 24 hours. The benzene and excess diethoxymethysilane were removed under reduced pressure to give the crude silane product. The IR and NMR spectra of these materials were examined to determine the extent of the hydrosilylation reaction. An absence of an IR band at about 2170 cmand an NMR peak at about 4.6 S indicated that there were no free Si—H functions in the mixture. Also loss of the peaks at 4.5-6.0 S in the NMR indicated a complete reaction of the vinyl-substituted macrocycle due to the absence of peaks indicative of the vinyl group. 

The effect of substituents at silicon on the reaction is outlined. We discuss advantages and drawbacks of cross-metathesis of vinylsilanes with olefins as a general method for the synthesis of vinyl-trisubstituted silanes and finally present a general mechanistic scheme that explains the processes taking place in the studied systems. Moreover, recent results on the cross-metathesis of a variety of (di)vinyl-substituted silanes, disiloxanes, and monovinyl-substituted siloxanes with olefins are reported [5]. 

A more stable matrix can be created using high temperature -vulcanisation. The polymer used for this process contains a proportion of -vinyl substituted silane units of the type shown in Figure 7.19. 

Such model networks may be prepared by very specific chemical reactions in which the network cross-links are introduced in a carefully controlled manner. For example, polydimethylsiloxane (PDMS) networks of this type have been synthesized by end-linking hydroxyl-terminated chains by means of silicates, and vinyl-terminated or vinyl-substituted chains with silanes containing active hydrogen atoms ... 

With the use of trimethylsilyl-substituted starting materials after Denmark et al., the disadvantageous formation of a mixture of isomers can be avoided. The vinyl silane derivatives react by loss of the TMS group in the last step ... 

Alkenyl silanes and stannanes have the potential for nucleophilic delivery of vinyl groups to a variety of electrophiles. Demetallation also occurs in these reactions, so the net effect is substitution for the silyl or the stannyl group. 

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