Alkylation of Alkenes with Organic Halides

The isomer distribution strongly depends on the catalyst used. ZnCl2 affords the best selectivity, giving exclusively 4-chloro-2,2-dimethylpentane (10). 

A mechanism with the involvement of the rt-butyl cation attacking the less substituted carbon of the double bond accounts for the formation of the main product44 [Eqs (5.19)—(5.21)]. The other two products (11, 12) are formed by the isomerization of the 13 carbocation through methyl and hydride migration to give the more stable tertiary carbocations  

The scope and limitations of the Lewis acid-catalyzed additions of alkyl chlorides to carbon-carbon double bonds were studied.51 Since Lewis acid systems are well-known initiators in carbocationic polymerizations of alkenes, the question arises as to what factors govern the two transformations. The prediction was that alkylation products are expected if the starting halides dissociate more rapidly than the addition products.55 In other words, addition is expected if the initial carbocation is better stabilized than the one formed from the dissociation of the addition product. This has been verified for the alkylation of a range of alkyl-and aryl-substituted alkenes and dienes with alkyl and aralkyl halides. Steric effects, however, must also be taken into account in certain cases, such as in the reactions of trityl chloride.51 

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