Allylsilanes with alkyl halides

Trimethylsilyl-l-alkenes. The lithium reagent is prepared from the corresponding selenide by treatment with BuLi. Its reaction with alkyl halides provides the allylsilanes. 

Chatgilialoglu and Curran synthesized a variety of allyl tris(trimethylsilyl)silanes bearing substituents at the 2-position (Scheme 26) [70], These allylsilanes underwent reaction with alkyl halides when heated with a radical initiator to give very good yields of allylated products. The reactions were relatively sensitive to electronic effects electrophilic radicals reacted well only with electron-rich allyl silanes and vice versa. One potential drawback of this methodology is that the reactions reported were all carried out at 80 °C or above, suggesting that relatively high temperatures are necessary for efficient reaction. 

In certain cases, allylsilanes and trimethylsilyl enol ethers react with alkyl halides with the formation of a new carbon-carbon bond. a-Bromo imidates (eq 8) and p-chloro imines have been reported to undergo electrophilic aromatic substitution on relatively electron-rich aromatics in the presence of AgBp4. 

Allenes 185 react with arylmagnesium chlorides in the presence of trialkylsilyl chlorides and a Pd° catalyst, furnishing substituted allylsilanes 186 with high (Z)-stereoselectivity (equation 111). Alkyl halides afford in this reaction mixtures of regioisomeric trisubsti-... 

Alkylation of ketones, As expected 1 reacts readily with carbonyl compounds to form allylsilanes. The reaction can be conducted as a one pot procedure with yields of 60-85%. In the presence of Lewis acids, allylsilanes react with various electrophiles (alkyl halides, acid chlorides, ethylene oxide). A typical sequence is shown in equation (I). 

Titanium tetrachloride is a useful Lewis acid for the addition of other electrophiles to allylsilane these electrophiles include acid anhydrides (Eq. 85) [229], acyl halides (Eq. 86) [2,3,159,161,230], and SNl-active halides such as rert-alkyl halides (Eq. 87) [165] and a-halosulfides [2,3,159,161]. The allylation of the substrate shown in Eq. (88) was accompanied by stereoselective opening of the cyclobutane ring to give an open-chain triene with defined olefin geometry [231]. A benzylic selenonium... 

Treatment of the title compound with an aqueous base under phase-transfer catalysis conditions generates, by a-elimination, chloro(trifluoromethyl)carbene that can be trapped by cycloaddition to allylsilane and allylstannane derivatives, e.g. formation of 1 and 2. This method represents a fast and mild alternative to the Seyferth method that starts from the same alkyl halide and generates the carbene by thermal decomposition of l-bromo-l,2,2,2-tetra-fluoroethyl(phenyl)mercury (see Section 1.2.1.2.4.1.1). 

Chatgilialoglu and Curran have found that allyltris(triniethylsilyl)silanes react with a variety of alkyl halides to provide allylation products via an Sh2 process mediated by the tris(trimethylsilyl)silyl (TTMSS) radical (Scheme 10.199) [523]. In this system the allylsilanes work as radical-allylating agents and TTMSS radical sources. We have used the reactivity of allyltris(trimefhylsilyl)silanes for allylsilyla-tion of alkenes and alkynes via a radical chain mechanism (Scheme 10.199) [524]. 

The choice of electrophiles that reaet with allylsilanes is eonsiderable. Alkyl halides typically need to be tertiary, allylic, or benzylic and they also require a Lewis acid catalyst, as in the example below ... 

Allenes react with arylmagnesium halides and trialkylsilyl chlorides in the presence of a Pd(0)-catalyst, giving substituted allylsilanes with good (Z)-steieoselectivity (Scheme 2-55, eq. (a)). Alkyl fluorides in these reactions lead to mixtures of regioisomers of trisubstituted alkenes (Scheme 2-55, eq. (b)). ... 

Nucleophilic substitution reaction is another class of important transformations that organosilicon reagents play key roles in organic synthesis. Electrophiles such as acyl and alkyl halides activated by a Lewis acid in a stoichiometric amount readily react with silyl enol ethers, allylsilanes, and alkenylsilanes. ... 

Allylsilanes are available for Lewis acid-promoted allylation of reactive alkyl electrophiles such as allyl halides and esters. 6 Recently, much attention has been focused on catalytic allylation of alkyl esters, ethers, and alcohols with allylsilanes.217-221... 

Alkylation of ferrocene with allylsilanes catalyzed by Zr or Hf chloride was reported (Equation 29) [34]. These metal halides showed better selectivity for the monoalkylated (70) product than the other metals. 

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