Alkoxysilanes cyclic

Scheme 6.16 Sni reaction at silicon preparation of cyclic alkoxysilanes...

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... 

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... 

Diphenyl silaketals 196 can be readily converted to the ( -symmetrical 1,4-diol 293 by reduction with Raney-Ni, followed by desilylation with TBAF in 65% yield. Another potentially powerful application of cyclic alkoxysilanes 196 consists in dihydroxylation with catalytic amount of osmium tetraoxide in the presence of A-methylmorpholine A-oxide (NMO), followed by treatment with TBAF which gives D-altriol 294 (Scheme 51) <1998JOC6768>. 

Precrosslinked poly(organosiloxane) particles are synthesized (Scheme 2) by emulsion polycondensation/polymerization of (functionalized) alkoxysilanes and (optionally) cyclic siloxanes [6, 7]. 

In a thorough study on the homolytic substitution reaction at silicon, Studer and Steen reported a mild method for the formation of cyclic five-membered alkoxysilanes based on tandem intermolecular add-ition/intramolecular homolytic substitution [137], whereby the reaction of homoallylic stannylated silylether 149 with ethyl iodoacetate in the presence of (Me3Sn)2 led to the desired Sni product 150 in high yield as the sole trans diastereoisomer (Scheme 49). While the 1,2 induction proved to be very high, leading in some cases to a unique diastereoisomer, 1,3 stereoselectivities were... 

Summary A synthetic route to highly fluorescent organic semiconductors with rigid connections to curable alkoxysilanes is described. The title compounds are prepared via Heck reactions of monodisperse bromo-OPVs with allyl-alkoxysilanes. A combined extension of the Jt-system and coimection with alkoxysilanes is possible when an alkoxysilyl-styrene is used as a substrate. Hydrolysis and condensation of alkoxysilanes yields linear and cyclic oligo-OPV-siloxanes or three-dimensional networks, thus allowing the transformation of small molecules into luminescent materials with well-defined chromophores. 

The physical properties of commercial alkoxysilanes are provided in Table 1. Two classes of silane esters have very distinct properties and are generally considered apart from alkoxysilanes. Silatranes are compounds derived from trialkanol amines and have silicon—nitrogen coordination. These are generally hydrolytically stable and have unique physiological properties (3). A second special class of monomeric esters are cyclic diesters of polyethyleneoxide glycols designated sila-crowns, which have application as catalysts (4). Neither silatranes nor sila-crowns are considered herein. 

The hydrolysis of (EtO)4Si (and the subsequent polycondensation of Si-OH containing molecules) has been the subject of considerable investigation because of its importance in the fabrication of glasses and colloidal silica via the sol-gel process see Sol-Gel Synthesis of Solids). Hydrolysis of the Si-0 bond in alkoxysilanes is also very widely used to attach silicon compounds to surfaces and in coupling reactions. The fundamental reaction types involved in the formation of polymeric silica materials (via, for example, cyclic oligomers similar to those shown in Figures 4 and 5) from monomeric (RO)4Si compounds are shown in Scheme 43. 

The alcohol used as a reagent in alkoxysilane direct synthesis has a space network of hydrogen bonds just like water, and therefore it forms cyclic and linear associates whose composition is determined by the nature of solvent. 

Without additional reagents Halogenosilylalcohols from cyclic alkoxysilanes s. 18, 563... 

While the five-membered cyclic alkoxysilane moiety has been found to tolerate a wide range of chemical transformations (OSO4 oxidation, Swern oxidation, Horner-Emmons alkenation, protection conditions such as Tr/py+ BF4 and Mel/NaH, and catalytic hydrogenation), the carbon-silicon bond can be cleaved efficiently by tetra- -butylammonium fluoride in DMF (eq 7). ... 

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