Exploring the synthetic utility of vinyldichlorosilanes and vinylarylsilanes

Abstract

<p>The addition of electrophiles to styrylsilanes when electronegative chloride ligands replaced electron-donating ligands on silicon has been investigated. These addition reactions were shown to be advantageous over the normal electrophilic substitution reactions found in the literature, in that the retained silicon may subsequently direct the regiocbemistry and stereochemistry of further synthetic reactions. In addition, the retained silicon offers the advantage of being replaced by other useful functional groups, in a controllable manner, as we have demonstrated by an oxidative cleavage reaction. Our results showed that allylsilanes, unlike vinyl silanes, perhaps due to their inherently higher reactivity (relative to vinylsilanes), are not prone to electrophilic addition when electron-withdrawing ligands are placed on silicon. Our experimental results also suggest that the success of these addition reactions depends on the stability of the intermediate adduct cations formed; addition products are typically obtained for the more stable cations.</p> <p>Carbocationic organosilicon chemistry has been dominated by the ability of silicon to electronically stabilize positive charges in the β-position, thereby influencing the reactivity of species that pass through such stabilized intermediates. However, steric influences on reactivity are not so well documented. Therefore, the reactivity of arylsilylstyrenes when the silylaryl group is sterically crowded with methyl substituents was investigated. The ability of silicon to effect electrophiIic substitution on the silylaryl substituent of (E)-β-dimethylmesitylsilyl)styrene rather than on the silylstyryl substituent, even though substitution on the arene required destroying aromaticity, is reported. This anomaly has been rationalized as being primarily due to steric factors.</p>