Alcohols from silanes

This compound can disproportionate, generating silane (SiH4) which is liable to be pyrophoric. Presumably other alkoxy silanes can do likewise [ 1 ]. Its use as a reducing agent for the preparation of alcohols from esters is considered safer in air than under... 

The reactivity of silylene-Lewis base complexes toward a variety of silylene traps such as olefins, alcohols, and silanes is significantly reduced, as can be seen from Table VII. 

Silane reacts with methanol to give the alkoxysUanes (MeO) SiH4 (n = 2, 3, 4) and with higher alcohols in the presence ofbase to give tetraalkoxysilanes (equation 8). This type of reaction is, however, rarely carried out as the alkoxysi-lanes produced are more conveniently prepared from alcohols and SiCU (which is more readily available than SiELi and much more easily handled). Similarly, silyl esters, Si(OCOR)4, are also usually prepared from polyhalogenosUanes rather than from silane and a carboxylic acid. 

Hydrosilylation of terminal alkenes using the air-stable silane (EtO>2MeSiH in the presence of either H2PtCl6 or (Ph3P)3RhCl results in the introduction of silicon exclusively at the terminal carbon atom. When coupled with oxidative cleavage, this protocol provides a simple one-pot synthesis of anti-Mar-kovnikov alcohols from terminal alkenes (Scheme 7). 

The reaction may proceed as homo- or cross-dehydrodimerization [105] and takes place with a wide range of substituted substrates such as higher alcohols, ethers, silanes, and partially fluorinated alcohols and ethers, but also with ketones, carboxylic acids, esters, amides, and amines [106]. Besides the formation of 1,2-diols from saturated alcohols, unsaturated substrates are also dimerized under hydrogen to form l,n-diols other than the 1,2-isomers [107]. The regio-selectivity of the diols is controlled by the formation of the most stable radical, which then dimerizes. 

Homopropargyl and allenyl alcohols. Chiral silanes are formed from propargylic mesylates. Subsequent reaction with aldehydes proceeds in a manner depending on the substituent on the sp-carbon of the mesylates. Starting from nonracemic mesylates the products are obtained with excellent ee. 

Asymmetric hydrosilylation has thus become one of the most useful methods for the preparation of optically active alcohols from alkenes [9,10]. Another important application of catalytic asymmetric hydrosilylation is the 1,4-hydros-ilylation of 1,3-dienes which efficiently produces optically active allyHc silanes. 

Oxidative desilylation. From silanes bearing an electron-withdrawing substituent (e.g., Ph, OR), the method provides access to alcohols with retention of configuration. A double bond in the same molecule is retained. Vinylsilanes furnish ketones. ... 

Asymmetric hydrosilylation of alkenes, catalysed by ferrocenylphosphine-palladium complexes, can be utilized in a synthesis of optically active alcohols from alkenes (Scheme 1). The initial optically active silane adducts are converted to alkyl pentafluorosilicates (1) which are then cleaved oxidatively, with retention of configuration, using peracid (c/. 3,132). Complex (2) was the best of several hydrosilylation catalysts examined using this, alcohols with enantiomeric purities of approx. 50% were obtained from norbornene and styrene as the alkenes. 

Formation of allylic alcohols from ketones with [l,2]-transposition of the oxygen function can be achieved via ene-silanes (38) (Scheme 14) ° the dye-sensitized oxygenation in regiospecific across silicion, possibly an ene reaction. The less substituted ene-silane is obtained from unsymmetrical ketones,... 

Chlorotris(triphenylphosphine)rhodium(l) Alkoxysilanes from alcohols and silanes... 

Allylic and Propargylic Alcohols. Allyl silanes (22), formed as Diels-Alder adducts from 1-trimethylsilyl butadiene, can be converted regiospecifically into allylic alcohols (Scheme 8), either with allylic rearrangement, using peracids, or without rearrangement. The latter transformation is achieved by first reacting the allyl... 

In 1976, Akira Hosomi and Hideki Sakurai of Tohoku University in Sendai, Japan, published a letter entitled Syntheses of y,S-Unsaturated Alcohols From Allylsilanes And Carbonyl Compounds In The Presence of Titanium Tetrachloride"The letter describes the reaction depicted in equation 1, in which allyl silanes react with aldehydes or ketones to provide homoallylic alcohols. The following year, Hosomi and Sakurai extended their finding to ketals, which provide homoallylic ethers (eq. 2)," and to a,P-unsaturated ketones (eq. 3), in which case the addition occurs in a 1,4-fashion and becomes a valuable method to generate quaternary centers. 

Dianion formation from 2-methyl-2-propen-l-ol seems to be highly dependent on reaction conditions. Silylation of the dianion generated using a previously reported method was unsuccessful in our hands. The procedure described here for the metalation of the allylic alcohol is a modification of the one reported for formation of the dianion of 3-methyl-3-buten-l-ol The critical variant appears to be the polarity of the reaction medium. In solvents such as ether and hexane, substantial amounts (15-50%) of the vinyl-silane 3 are observed. Very poor yields of the desired product were obtained in dirnethoxyethane and hexamethylphosphoric triamide, presumably because of the decomposition of these solvents under these conditions. Empirically, the optimal solvent seems to be a mixture of ether and tetrahydrofuran in a ratio (v/v) varying from 1.4 to 2.2 in this case 3 becomes a very minor component. 

The length of the axial bond would be expected on all theories to be important. The barrier height does decline from ethane to methyl silane to methyl germane, but of course the bonded atoms are different. Unfortunately reliable values are not available for dimethyl mercury, dimethyl acetylene, and similar molecules with still longer bonds. An apparent exception is provided by methyl mercaptan and methyl alcohol. The latter, with the shorter axial bond, has the lower barrier. 

These poly(2-alkyl-2-oxazoline) silane coupling agents were copolycondensed with tetraethoxysilane by acid-catalyst to produce poly(2-alkyl-2-oxazoline)-modified silica gel. The composite gel from 2-ethyl-2-oxazoline was also homogeneous and transparent glass. Poly(2-alkyl-2-oxazoline)-modified silica gels, especially gels based on poly(2-ethyl-2-oxazoline) absorbed water and also organic solvents such as DMF or alcohols as shown in Table 7. This result means that the obtained composite gel shows the amphiphilic adsorption property. 

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