Allylation of Unactivated Alkynes and Alkenes

The Lewis acid-catalyzed reactions of allylsilanes with simple alkenes and alkynes introduce both allyl and silyl groups into the unsaturated bonds (Equations (53) and (54)).209 210b These allylsilylations are 7-regiospecific with respect to allylsilanes. The /raor-addition of allylsilanes occurs in the reaction with alkynes. There are two possible mechanisms for the Lewis acid-promoted allylsilylations, that is, trimethylsilyl cation- and Lewis acid-mediated pathways. 

Intramolecular allylsilylation of alkynes is a convenient route to cyclic vinylsilanes.211 Propargylsilanes are available for Lewis acid-promoted carbosilylation of alkynes.212 Unlike allylsilanes, both cr-substituted and unsubstituted propargylsilanes react at the a-position, which can be rationalized by in situ isomerization of these reagents to allenylsilanes (Equation (55)). 

In the presence of GaCl3, allylsilanes add to simple terminal alkynes and silylated alkynes to give m-allylation products.213 A stepwise mechanism including formation and ar-addition of an allylgallium species is plausible for this allylation. 

Intramolecular allylation of alkynes with allylsilanes can be catalyzed by electrophilic transition metal halides and complexes (e.g. Pt(ll), Pd(ll), Ru(ll), Au(m), and Ag(l)).214,2143 A Pd(ll)-catalyzed system using a reoxidant is effective in oxidative intramolecular allylation of 1,3-dienes (Equation (56)).215,2153 These allylations are initiated by coordination of the electrophilic metals to alkynes and 1,3-dienes. 

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