E-Vinyl silanes

A1C13 can interact electrophilically with allenes to form zwitterionic intermediate 37, which would react with HSiR3 to produce the (E)-vinylic silane 39 by a hydrosily-lation [22], This hydrosilylation shows trans-diastereoselectivity. 

Instead of adding two hydrogen atoms to an alkynyl silane we could add H and SiMe3 to a simple alkyne by hydrosilylation (addition of hydrogen and silicon). This is a cis addition process catalysed by transition metals and leads to a tram (E-) vinyl silane. One of the best catalysts is chloroplatinic acid (H2PtCl6) as in this formation of the E-vinyl silane from phenylacetylene. In this case photochemical isomerization to the Z-isomer makes both available. Other than the need for catalysis, this reaction should remind you of the hydroboration reactions earlier in the chapter. The silicon atom is the electrophilic end of the Si-H bond and is transferred to the less substituted end of the alkyne. 

The commonest combination here is trichlorosilane with H2PtCl6 as catalyst. Cis addition of the silane is preferred, probably via a metal complex such as 116, giving the E-vinyl silane 117. The SiCl3 group is not easily replaced but the dianion 118 formed with KF reacts cleanly with NBS to give the E-vinyl bromide 119 with retention of configuration.24... 

Ruyter, I.E., Sjovik, I.J. Acta Odont. Scand. 1981, 22., 133. Bowen, R.L. Dental filling material comprising vinyl silane treated fused silica and a binder consisting of the reaction product of blsphenol A and glycidyl acrylate. USP 3066112 (1962) et seq. 

The vinyl silanized samples from Mr. Robert E. Schultz of J. M. Huber had been prepared as follows liquid vinylmethoxyethoxy silane (Union Carbide A172) was quantitatively added to a known volume of a mixture of 60% de-ionized water and 40% 2-propanol in a polyethylene beaker via a disposable polyethylene syringe. 100 g of ATH (aluminum trihydrate) was stirred into exactly 300 ml of the vinyl silane mixture for 10 min with a polyethylene rod. The resulting slurry was placed in a 100°C oven and allowed to dry for 24 h. 

We have shown that the determination of vinyl silane on aluminum hydroxide powders is comparable to similar analyses on kaolin clays as reported earlier [2] and suggest with confidence that this technique can be extended to other powder substrate systems with sufficiently small particle sizes, i.e. comparable or less than the wavelength of the analytical frequency radiation as well as to the various other silanes that have been deposited on other substrates. 

The authors are greatly indebted to Mr. Robert E. Schultz, from the J. M. Huber, Solem Division, Fairmount, GA, who supplied the eight vinyl silanized aluminum hydroxide powder samples used in this study, and details of their preparation. 

As early as 1997, Hiemstra and Speckamp postulated the participation of an oxonia-Cope rearrangement as a crucial step during the cyclization of vinyl silane 146 (Scheme 13.50) [75]. Both ( )- and (Z)-vinylsilanes, (E)-146 and (Z)-146 respectively, were used in this study. The cyclization proceeded in both cases in good to excellent yields, furnishing the 2,6-disubstituted dihydropyrans 147. Surprisingly, the cyclization of (E)-vinylsilanes ( )-146 gave anti-2,6-dihydropyran anti-147 as the major stereoisomer, whilst in the case of (Z)-vinylsilane (Z)-146, the syn-dihydropyran syn-147 was formed as the major product. 

Vinylsilanes 236 undergo Lewis acid-mediated stereoselective cyclizations to afford 3,6-dihydropyrans. The stereochemistry of the dihydropyran product is dictated by the geometry of the vinyl silane with (Z)-236 and (E)-236 providing syn-237 and a -3,6-dihydropyrans 238, respectively (Scheme 67) <1997JOC3426>. 

Treatment of. E-vinyl sulfonates 340 with tris(trimethylsilyl)silane and triethylborane provides a diastereoselective route to yy -2,6-tetrahydropyans 341 in high yield (Equation 145) <2000JOG4523>. 

Controlled reduction of alkynyl silanes produces the corresponding vinyl silanes and the method of reduction dictates the stereochemistry. Lindlar hydrogenation adds a molecule of hydrogen across the alkyne in a cis fashion to produce the 2-vinyl silane. Red Al reduction of a propargylic alcohol leads instead to the E-isomer. 

The intermediate cation has only a single bond and so rotation might be expected to lead to a. mixture of geometrical isomers of the product but this is not observed. The bonding interaction between the C-Si bond and the empty p orbital means that rotation is restricted. This stabilization weakens the C-Si bond and the silyl group is quickly removed before any further rotation can occur. The stabilization is effective only if the C-Si bond is correctly aligned with the vacant orbital, which means it must be in the same plane—rather like a it bond. Here is the result for both E- and Z-iso-mers of the vinyl silane. 

The product is a vinyl silane as the M Si group is retained in this reaction of the anion. The reaction is stereoselective in favour of the E-alkene as might be expected. The alkene can be epoxidized... 

A variable pressure oil pump was used in this distillation. Approximately 10 g of a volatile component, consisting mostly of hexamethyl-disiloxane, was obtained at room temperature (15 inn) before the forerun. The forerun contained the desired product and mineral oil from the n-butyl11thlurn solution. The pot residue was about 5 g. The submitters find the disilyl compound thus obtained is contaminated with a trace amount of mineral oil and 4-6% of a vinyl silane, probably 2-methyl-l-trimethylsiloxy-3-trimethylsilyl-2-propene. This impurity becomes quite significant if the reaction medium is less polar than the one described (e.g., too much hexane from n-butyllithium is allowed to remain behind). The spectral properties of the desired product determined by the checkers are as follows IR (neat) cm" - 2955, 1643, 1636, 1250, 1085, 885-830 XH NMR (chloroform-d, 90 MHz) 6 0.03 (s, 9 H, CHgSI(CH3)3), 0.14 (s, 9 H, 0S1(CH3)3), 1.50 (broad s, 2 H, CH2-Si(CH3)3), 3.93 (broad s, 2 H, CH2-0Si(CH3)3), 4.62 (m, 1 H, vinyl H), 4.92 (m, 1 H, vinyl H). 

Other vinyl esters and other monomers (e.g., acrylates and methacrylates, or ethylene and vinyl silanes) can also be copolymerized with vinyl-functional silicones. The introduction of chemical functions (e.g., carboxyl groups) and charged groups is possible in order to further improve the properties. 

An agent, e.g., a vinyl silane, used to protect fiberous glass laminates from effects of water absorption. 

Those 0-hydroxyalkylsilanes resulting in the first reaction step (e.g. 275) can be converted by means of thionyP or acetyl chloride into the corresponding chlorides which yield the desired alkenes via subsequent elimination under mild conditions (Scheme 36). The a-lithiated triphenyl-vinyl silane (281) and 135 give 3,3-di-... 

---