Addition to vinylsilanes

Addition to vinylsilanes is favoured over substitution by (i) the presence of bulky spectator ligands which hinder nucleophilic attack at silicon, and (ii) when the presence of electron-withdrawing groups on silicon lowers its leaving group ability. 

Intramolecular radical addition to vinylsilane moiety has been used for the synthesis of statine 148 (equation 124)216 and the pyrrolizidine skeleton217. Tandem [2+1] radical cyclization of bromides 149 with BusSnH is extremely sensitive to the nature of the substituent on the diene moiety. Bicyclo[3.1.0] skeleton 150 is obtained in the presence of the silyl substituent (equation 125). When the silyl substituent in 149 is replaced by a t-butyl group, the six-membered ring product 151 is obtained exclusively218. 

Nucleophilic addition to vinylsilanes is facilitated by the fact that it leads to the formation of an anion which is a to silicon the anion is thus relatively stable. The reaction should be compared to the Michael addition, in which the anion generated is stabilized by an adjacent carbonyl group (Figure Si5.13). 

Examples of applications of nucleophilic addition to vinylsilanes are to be found in Equation Si4.1 and Figure Si4.4. 

Addition to vinylsilanes stereochemistry Examples of both syn- and [Pg.920]

In addition to vinylsilanes, ATH- and MDH-filled ethylene vinylacetate copolymers can be effectively coupled to aminosilanes [37]. Fine and uniform ATH dispersion in the polymer leads to low H FFR compound viscosities (M FI) and high tear strength. The use of 3-aminopropyltriethoxysilane became an industrial standard for the production of reliable thermoplastic HFFR compounds. New primary/secondary aminosilane blends provide further improvements in the final HFFR compound [38]. Aminosilanes are also found in thermoplastic EVA, nonperoxide cross-linked. 

Addition of ethoxycarbonylnitrene across the double bond of a symmetric propelladlene has been reported to give a mixture of stereolsomeiic aziridines in 46% yield. Additions to vinylsilanes... 

Catalysis of Intramolecular Sakurai Reactions. Et AICI2 has been extensively used as a catalyst for intramolecular Sakurai additions. Enones (eqs 12 and 13) have been most extensively explored. Different products are often obtained with fluoride or Lewis acid catalysis. EtAlCl2 is the Lewis acid used most often although TiCLi and BF3 have also been used. EtAlCl2 also catalyzes intramolecular Sakurai reactions with ketones and other electrophiles. The cyclization of electrophilic centers onto alkylstannanes and Prins-type additions to vinylsilanes are also catalyzed by EtAlCl2. 

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