Triethoxysilane as a Selective Reagent in Platinum-Catalyzed Hydrosilylation Reactions

Selective hydrosilylation of terminal alkenes occurs in the presence of di- and trisubstituted, electron-rich olefins using triethoxysilane and Karstedt's catalyst. <i>Anti</i>-Markovikov addition provides the primary silanes, and reactions proceed in sterically hindered examples containing a fully substituted allylic carbon. Standard reaction conditions demonstrate considerable functional group tolerance in the case of ethers, esters, ketones, alcohols, and carboxylic acids. However, hydrosilylation is slowed by the presence of heteroatom substituents, and allylic alcohols failed to react within 24 h. Similarly, alkynes are excellent substrates for hydrosilylation using triethoxysilane. Reactions under the standard conditions exhibit excellent regio- and stereoselectivity. Terminal alkynes afford the (<i>E</i>)-alkenylsilanes. Propargylic acetates are useful substrates for the expected <i>syn</i>-addition of the silane, whereas the corresponding alcohols react more slowly. The triethoxysilyl substituent is readily used in Tamao-Fleming oxidations and in cross-coupling reactions.