Alkoxysilanes ethers

Other organic—inorganic hybrids include poly(ethyloxazoline)—siUca, poly(vinyl alcohol)—siUca, poly(arylene ether) ketone—siUca, polyimide—siUca, polyozoline—sihca, poly(ethylene oxide)—siUca, and polymers—modified alkoxysilane. 

Alkyl silyl ethers are cleaved by a variety of reagents Whether the silicon-oxygen or the carbon-oxygen bond is cleaved depends on the nature of the reagent used Treatment of alkoxysilanes with electrophilic reagents like antimony tri-fluonde, 40% hydrofluonc acid, or a boron tnfluonde-ether complex results in the cleavage of the silicon-oxygen bond to form mono-, di-, and tnfluorosiloxanes or silanes [19, 20, 21) (equations 18-20)... 

Several other papers have appeared in the literature describing hyperbranched poly(siloxysilane)s [103], poly(amine)s [104], poly(phenylene sulfidejs [105], polycarbosilanes [106], phenol-formaldehyde resins [107], poly (aryl ether sul-fone)s [108], poly(alkoxysilanes) [109], and poly(lactoside)s [110] but are not further treated in this survey. 

Homolytic substitution reactions including homolytic allylation, radical [2,3]-migrations and stereochemical reactions been reviewed. The review also highlights the possible applications of homolytic substitution reactions. ni reactions at silicon (by carbon-centred radicals in the a-position of stannylated silyl ethers) are efficient UMCT reactions producing cyclized alkoxysilanes. Bimolecular reactions can also be facilitated in good yield (Schemes 32 and 33). ... 

Transition metal complexes have been widely investigated as catalysts for the synthesis of alkoxysilanes via alcoholysis of hydrosilanes. The system provides a convenient method for the protection of hydroxy groups in organic synthesis and the synthesis of silyl ethers. The general reaction is shown in Eq. (59). 

Alkoxysilanes are frequently used as scavenger reagents for silenes. They add regiospecifically to the Si=C bond. In the case of silacyclobutadiene 296 the reaction was shown to be also stereospecific. Thus Z-404 is the sole product of the addition of trimethylsilyl methyl ether (TMSOMe) to 296 (equation 122)163. Characteristically Brook -type silenes do not react with alkoxysilanes like TMSOMe. 

Even if the SMS reaction typically involves allylsilanes, carbonyls and alcohols (or silyl ethers), some transformations can be considered as belonging to the same family. For example, in 2001, Yokozawa et al. described [43] a three-component reaction between aldehydes 6, alkoxysilanes 38 and propargylsilane 88 (instead of allylsilane). Tritylperchlorate was used as the catalyst and a-allenyl ethers 89 were... 

Yokozawa [44] also inverted the methodology and generated a-propargyl ethers 91 from carbonyls 6, alkoxysilanes 38 and allenylsilanes 90. Aromatic aldehydes remained the best substrates but aliphatic aldehydes or ketones could be induced to react, though the yields remained modest (Scheme 13.36). 

The substituted ethers of orthosilicon acid, alkyl(aryl)alkoxysilanes or al-kyl(aryl)aroxysilanes, have the common formula RnSi(OR )4. where n = 1-K3, whereas R and R are any organic radicals the radicals situated at the silicon atom and in the ether group can be the same or different. 

Catalytic alcoholysis of silanes by a variety of transition metal based catalysts is a useful method to form silyl ethers under mild conditions (Scheme 19). The process is atom-economical hydrogen gas is the only byproduct. This mild method has not been fully exploited for the preparation of unsymmetrical bis-alkoxysilanes. A catalytic synthesis using silicon alcoholysis would circumvent the need of bases (and the attendant formation of protic byproducts), and eliminate the need for excess silicon dichlorides in the first silyl ether formation. We sought catalytic methods that would ultimately allow formation of chiral tethers that are asymmetric at the silicon center (Scheme 20). Our method, once developed, should be easily transferable for use with high-value synthetic intermediates in a complex target-oriented synthesis therefore, it will be necessary to evaluate the scope and limitation of our new method. 

There have been a few reports on the controlled catalytic alcoholysis of dialkylsilanes to produce the mono-hydrido silyl ether. 9a,c,15 16 One such report is by Corriu and Moreau who have illustrated the use of either (PPh3)3RJiCl, (PPh3)3RuCl or Raney Ni to execute the controlled alcoholysis of diphenylsilane to give the mono-functional alkoxysilane as the only product.93 Doyle attempted to use the Rh2(pfb)4 catalyst with diphenylsilane and trans- 1,2-cyclohexanediol to prepare the cyclic silyl ketal,16 but this was not successful, perhaps because the trans-fused... 

Our idea that intramolecular pentacoordination may accelerate the reaction was tested by using an alcohol with a neighboring ether group to act as a Lewis base (Figure 9B). Ethers are known to be more basic then the carbonyl of an ester.31 The mono-alkoxysilane from... 

L. S. Whatley, and K. J. Lake Hydrogen Bonding Studies. V. The Relative Basicities of Ethers, Alkoxysilanes and Siloxanes and the Nature of the Silicon-Oxygen Bond. J. Amer. chem. Soc. 83, 761—764 (1961). 

A radical approach to cyclization is offered by the intramolecular homolytic substitution (ShO reaction at a silicon center. Reaction of phenyl bromoacetate with a stannylated silyl homoallyl ether under atom transfer conditions provides cyclic alkoxysilanes (Equation (119)).2... 

Acetalization and allyUuion of carbonyl compounds. lodotrimethyisilane is an effective catalyst for acetalization with an alkoxysilane. Addition of allyltrimcthylsilanc to this reaction results in allylation of the acetal to form a homoallyl ether. 

In our studies, the nano-sized sihca was synthesized using cheap sodium orthosilicate and sodiirm metasihcate rather than expensive alkoxysilanes. An inverse microemulsion containing NP-5/NP-9 as surfactant and cylcohexane or petroleum ether as the oil was used to carry out the hydrolysis and condensation of sodium orthosilicate or metasilicate using an acidic medium [152, 153]. The spherical silica particles of size 10-20 nm were obtained in a system using cyclohexane as the oil and with sodium orthosihcate of 0.01-0.1 M [152]. The particle size increased as the concentration of sodium orthosihcate and the pH were increased. Sihca particles prepared in basic conditions were more uniform in size than those prepared in an acidic medium. But calcined sihca powders with larger specific areas (350-400 mVg) were obtained for those prepared in an acidic medium. 

Other oiganic—inoiganic hybrids include poly(eth5ioxazoline)—silica, poly(vinyl alcohol)—silica, poly(arylene ether) ketone—silica, polyimide—silica, polyozoline—silica, poly(eth5iene oxide)—silica, and polymers—modified alkoxysilane. 

Tetrahydroaluminate reduction of siloxanes or alkoxysilanes is an effective route to SiH or alkyl or arylsilanes in ethers (Table 1) ... 

High-yield anodic oxidation of a-alkoxysilanes (XCV) to )5-hydroxy aldehyde acetals was used as the key step in an iterative preparation of optically active polyols [Eq. (59)]. The reaction apparently involves formation of the ether radical cation, followed by rapid C-Si bond scission and nucleophilic trapping by solvent [142]. 

All cationically polymerizable monomers can be potentially used in this process however, the main study has been focused so far on the most reactive oxirane and vinyl ethers [4], Alkoxysilane derivatives - the most common acid-sensitive monomers for the synthesis of siloxane materials through the use of sol-gel methods - were not used extensively. Only a few examples of their application in photo-activated cross-linking can be noted, mainly in co-reaction with oxirane sites [5]. Typically, alkoxysilanes are subjected to an acid- or base-catalyzed process involving hydrolysis of an =SiOR group and then condensation of the formed silanol with another molecule bearing an =SiOH or =SiOR function to give a siloxane linkage [6]. It was of interest to combine the properties of cross-linked silicone materials with the ones provided by sterically overloaded... 

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