Silanes, generation using

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. 

Nowick and Danheiser148 have explored a-cyclopropyl acyl silane generation from a-haloacyl silanes through McCoy reactions (Scheme 57) and via sulphur ylids (Scheme 58). Ylid species such as 24 were found to be stable in aprotic solvents in the presence of lithium salts, and were used for the cyclopropanation of a,/3-unsaturated aldehydes. 

If, for example, methacrylic acid is used as a complexing agent, particles of about 2-5 mn in diameter can be generated by hydrolysis mid condensation, and if, in addition to this, methacryloxy group containing hydrolyzable silanes are used in combination with the zirconia colloids, transparent composite systems have been synthesized. 

The synthetic power of these silylcuprate and stannylcuprate reactions lies in the synthetic utility of the product silanes and stannanes for carbon-carbon bond formation and also in the utilization of the silyl [38] or stannyl substituents as agents for stereocontrol and regiocontrol. Additionally use of appropriate silylcuprates permits conversion of the produced C Si bond into a C OH bond (Tab. 3.1) [39]. This C Si to C OH conversion is a particularly difficult transformation for an allyl silane and the development of lithium diphenyl(2-methyl-2-butenyl)silylcuprate for this purpose illustrates the characteristic transformations of silylcuprates (Scheme 3.1) [14e]. Several silyl substituents convertible into hydrosy groups are not amenable to the cuprate methodologj vinyl silanes - generated by... 

Modifications in which the benzylic hydrogens are acidified also allow the use of mild conditions one example is the generation of a phosphonium ylide and then an intramolecular Wittig-like reaction, involving the amide carbonyl ° another variant uses a benzyl-silane. The use of an amino-silane permits reaction at both nitrogen and benzylic carbon to take place in one pot." ... 

Table 7.2 Coupling of an N-acyliminium ion and an allylic silane generated by using a paired electrochemical microsystem.

However, polypropylene has no functional groups present for the silane to react with. Therefore, vinyl silanes are used. In this case, the vinyl group must react with the polymer molecule via a free radical reaction mechanism. Free radicals can be generated through heat, shear, or with a catalyst, such as an organic peroxide. There are various examples of two-component silane-peroxide systems. In 1986, Union Carbide introduced a product called UCARSIL PC-1 A/ PC-IB. This system was a complex mixture of organosilane and peroxide. The... 

In order to study the strucmre-activity relationship of pharmaceutically active derivatives of baccatin HI, radical-based deoxygenations were used to generate a systematic defunctionalization of the taxole core. When tris(trimethylsilyl)silane was used as reducing agent of the xanthate functionality (equation 17 yields based on the consumption of the starting mataial), a cascade of intramolecular rearrangements took place, due to the slower hydrogen donation of silane relative to tin hydrides. ... 

The first route is based on generating sol—gel particles in an hydrophobic medium. Since the Stober process is based oti water or alcohol solvents and uses agents (ammonium hydroxide) that are not miscible with the polymerization medium of toluene, adaption was necessary. Higher alcohol (butanol, pentanol, octanol), toluene and toluene-ethanol mixtures were screened and, in addition to TEOS, TBOS (tetrabutoxy silane) was used as precursor [85]. It was found that the formation of defined and spherical particles is not easily achieved. For example, in a... 

Matrix IR spectra of various silenes are important analytical features and allow detection of these intermediates in very complex reaction mixtures. Thus, the vibrational frequencies of Me2Si=CH2 were used in the study of the pyrolysis mechanism of allyltrimethylsilane [120] (Mal tsev et al., 1983). It was found that two pathways occur simultaneously for this reaction (Scheme 6). On the one hand, thermal destruction of the silane [120] results in formation of propylene and silene [117] (retroene reaction) on the other hand, homolytic cleavage of the Si—C bond leads to the generation of free allyl and trimethylsilyl radicals. While both the silene [117] and allyl radical [115] were stabilized and detected in the argon matrix, the radical SiMc3 was unstable under the pyrolysis conditions and decomposed to form low-molecular products. 

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