Secondary chlorides with organometallic

Most of the early mechanistic studies that focused on the S ,j2 versus 8 2 nucleophilic substitution by an organometallic reagent were made with allylic halides. In the late 1940s, Wilson [7] showed that phenylmagnesium bromide reacted with a- and y-methylallyl chlorides 1 and 2, respectively, to afford a nearly identical mixture of primary and secondary substituted products 3 and 4, respectively, in a 75 25 ratio [Eq. (1)]. 

This is a very general reaction in that primary, secondary, and tertiary alkyl halides react with primary, secondary, or tertiary organocuprates. The halide can be a chloride, a bromide, or an iodide, but iodides are more reactive than bromides, which are more reactive than chlorides. Another example is the reaction of 49 with lithium diphenylcuprate to give 50. The reaction of alkyl halides and organocuprates is the preferred method for coupling an alkyl halide to an organometallic compound. Many different hydrocarbons can be prepared. 

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