Trimethylsiloxy group

Danshefsky s diene [19] is the 1,3-butadiene with amethoxy group at the 1-position and a trimethylsiloxy group at the 3-position (Scheme 18). This diene and Lewis acids extended the scope of hetereo-Diels-Alder reactions with aldehydes [20], This diene reacts with virtually any aldehyde in the presence of Lewis acids whereas dienes usually react with only selected aldehydes bearing strongly electron accepting a-substituents. There are two (Diels-Alder and Mukaiyama aldol) reaction pathways (Scheme 18) identified for the Lewis acids catalyzed reactions of Danishefsky diene with aldehydes [21, 22]. The two pathways suggest that these reactions occur on the boundary between the delocahzation band (the pericyclic... 

The potential for coordination depends on the oxy substituents.82 Alkoxy substituents are usually chelated, whereas highly hindered silyloxy groups usually do not chelate. Trimethylsiloxy groups are intermediate in chelating ability. The extent of chelation also depends on the Lewis acid. Studies with a-alkoxy and (3-alkoxy aldehydes with lithium enolates found only modest diastereoselectivity.83... 

The chemical shifts of jp3-hybridized silicon atoms, such as a trimethyl-silyl group attached to the jp2-hybridized silicon in silenes, are normally found from -10 to -18 ppm, as compared to the position at -9.8 ppm for the trimethylsilyl groups of (Me3Si)4Si (the central silicon atom of this compound resonates at -135.5 ppm). On the other hand, a trimethylsiloxy group attached to carbon, either sp2- or sp3-hybridized, normally absorbs in the range from +5 to +20 ppm. 

The thermal decomposition of azoalkanes bearing geminal a-cyano and a-trimethylsiloxy groups has been the subject of a report. The symmetrical compound (107) decomposes near room temperature to afford entirely C—C dimers, whereas the unsymmetrical azoalkane (108) requires heating to 75 °C. A NMR product study of photolysed (107) in the presence of TEMPO showed that the fate of caged t-butyl-l-trimethylsiloxy-l-cyanoethyl radical pairs is disproportionation (17%), cage recombination (20%), and cage escape (63%). 

The facile photochemical sigmatropic 1,3-trimethylsilyl shift in polysilylacylsilanes from silicon to oxygen (equation 33) was utilized historically to prepare the first relatively stable silenes3 86 87. Silenes prepared by isomerization of acylpolysilanes bear, due to the synthetic approach, a trimethylsiloxy group at the sp2-hybridized carbon and relatively stable silenes of this type have in addition also at least one trimethylsilyl group at the silicon. These substituents strongly influence the physical properties and the chemical behaviour of these silenes. This is noticeable in many reactions in which these Brook -type silenes behave differently from simple silenes or silenes of the Wiberg type. 

Preparation of branched oligo(eo-alkoxyalkyleneoxypropyl-organosiloxy)dimethylsiloxanes with end trimethylsiloxy groups... 

Branched oligoorganosiloxanes with alkoxyalkyleneoxypropylorganosi-loxane elements in their branches and with end trimethylsiloxy groups are liquids consisting of oligomer homologues with the following common composition ... 

Oligo(co-methoxyethyleneoxypropylmethylsiloxy)dimethylsiloxane with end trimethylsiloxy groups (oligomer II) is synthesised... 

If the greenish-yellow mixture of excess Z- and little -isomeric [2,2-dimethyl-l-(trimethylsiloxy)propylidene]trimethylsilylphosphane obtained fi-om the tris(trimethylsilyl) compoimd and 2,2-dimethylpropionyl chloride in a molar ratio of 1 1 (Eq. 3) is stored in a refrigerator before further use, it usually remains liquid even at -20 °C. However, several months ago colourless squares crystallized from that mixture by chance. Due to their low melting point of about -5 °C they had to be handled very carefully at -50 °C and transferred in sealed capillaries to the diffractometer. An X-ray structure determination showed the Z-isomer which has the trimethylsilyl and the trimethylsiloxy group on the same side of the P=C unit, to be present in the solid state (Fig. 1). Most of the molecular parameters such as a P=C distance of 169.4 pm and angles at the p -hybridized carbon, which sum up to 359.9 ° are as... 

Reaction Mechanism The mechanism of the sodium hydroxide-catalyzed elimination of hexamethyldisiloxane may easily be understood when the reaction is compared to the well-known Peterson olefination in organic chemistry [24], Provided that an enolate anion is formed as an intermediate, either directly or via a proceeding hydrolysis of the 0-Si bond with traces of water which are always present on the hot surface of the crude catalyst, trimethylsilanolate splits off readily and thus the PsC triple bond is introduced into the molecule (Eq. 5). Subsequent attack of trimethylsilanolate at the trimethylsiloxy group of the starting compound results in a formation of hexamethyldisiloxane and the initial enolate anion so that the reaction circle is closed. 

Spherical siloxanes (RSiOi 5), with polyhedral frameworks, also called silsesquioxanes, can be used as defined oligomeric models for surface-modified silica gels or polysiloxanes. Whereas silsesquioxanes with alkyl-, aryl-, hydrido-, and trimethylsiloxy groups are known for a long time [1], functionalized octa-[propyl-silsesquioxanes], [X-(CH2)3]g(SiOi.5)g, were synthesized for the first time in 1990 by Weidner, Zeller, Deubzer, and Frey [2]. Octa[(3-chloropropyl)-silsesquioxane], [Cl-(CH2)3]g(SiO, 5)g, could be obtained by hydrolysis of (3-chloropropyl)-trichlorosilane. 

Comparing PDMS/HMDS- and HMDS-modified silica particles, a lower phase shift of up to 70° has been observed for the PDMS/HMDS silicas, and for the HMDS silicas a higher phase shift of up to 90° has been found. Differences in phase shift values indicate the impact of surface modification on the local hardness of the silica particles. PDMS modification leads to a softer, polymer-like grafting, whereas pure HMDS modification oidy increases the hydrophobicity by a hard monolayer formation of trimethylsiloxy groups. HMDS-treated silicas seemed to show a weaker interaction with the toner resin surfaces. In contrast, PDMS/HMDS-treated silicas show stronger adhesion to the toner resin surfeces, so they can easily be imaged at high resolution. 

Aminocyclopropanecarbonitriles represent important intermediate products en route to aminocyclopropanecarboxylic acid derivatives. Introduction of the cyano group by nucleophilic substitution into a suitable aminocyclopropane precursor, therefore, is of interest. Thus, the hydroxy- or trimethylsiloxy group of monocyclic A,0-acetals or hemiaminals is readily displaced by the cyanide anion as nucleophile to give products 1. Weak acids catalyze these displacements. ... 

The trimethylsiloxy group can also act as a donor function and gives rise to the formation of similar cleavage products with a methoxy substituent. When alkyl 2-(trimethylsiloxy)cyclo-propanecarboxylates 21 were treated with acid, products arising from an aldehyde intermediate were obtained. ... 

The chloromethylcarbene addition step produces a mixture of two stereoisomeric bicyclo-[n. 1. OJalkanes. The -isomers, i.e. those having the chlorine atom and the trimethylsiloxy group traits to each other, rearranged more rapidly, but in each case satisfactory results were obtained by using the erude mixture of isomers. ... 

---