Alkyl substitution can be achieved when alkyl halides are used in conjunction with a Lewis acid; however, only activated (allylic, benzylic) or highly substituted (tert-butyl) halides are useful in this context. Nucleophilic catalysis of alkylation is rare, because protodesilylation tends to occur. Lewis acid activation is more commonly employed.
Allylsilane additions to carbonyl groups are common and synthetically useful. Vinylsilane additions are less common, as a variety of methods to access allylic alcohols are available (including epoxidation of allylsilanes; see below). If the γ position of the allylsilane is substituted, two diastereomeric products may result. In the presence of Lewis acids such as titanium tetrachloride, (E)-allylsilanes are highly selective for the syn diastereomer. (Z)-allylsilanes are much less selective (~60:40), but also favor the syn isomer.
Conjugate addition reactions of allylsilanes are possible, although unsaturated aldehydes undergo only 1,2 addition. The combination of an allylsilane with an α,β-unsaturated ketone in the presence of a Lewis acid is known as the Sakurai reaction. The enolate intermediate that results from addition can be functionalized with a separate electrophile or simply protonated. Intramolecular Sakurai reactions provide ene-6-ones
Acetals and ketals are excellent substrates for additions of allyl- and vinylsilanes. In some cases, these compounds react more cleanly than the corresponding carbonyl compounds.
Iminium ions generated in situ in the presence of protic acid react with allylsilanes to give homoallylic amines.