13.05 Gilman Reagent | OrganicChemGuide

Gilman Reagent

Home

Grignard reagents with alkyl halides

Although Grignard reagents are excellent nucleophiles when attacking carbonyls and epoxides, we find that they are lousy nucleophiles when it comes to attacking alkyl halides in an SN2 reaction. Grignard reagents are a little too hard to react with the alkyl halide. The electron pair on the Grignard reagent is not polarizable enough to do the reaction well. This is too bad, because you would think this would be a great way to make carbon-carbon bonds and larger molecules.

If you think about it, it is actually a good thing that Grignard reagents do not attack alkyl halides. This is because Grignard reagents are made from alkyl halides. If Grignard reagents reacted with alkyl halides, when the first Grignard reagent was made, it would immediately begin reacting with the alkyl halide starting material, and we would never be able to make a flask of Grignard reagent to react with carbonyls or epoxides!

Gilman Reagents with alkyl halides

The good news is there is another way to do a similar reaction. Instead of using a Grignard reagent, another reagent called the Gilman reagent will attack an alkyl halide in an SN2 reaction. The Gilman reagent is a lithium dialkyl cuprate. Gilman reagents are made from alkyl lithium reagents reacting with cuprous iodide (CuI). Alkyl lithium reagents can be made from the reaction of alkyl halides with lithium.

Then alkyl groups of the Gilman reagent are softer and can react with alkyl halides substituting an alkyl group for a halide.

The Gilman reagent also reacts with vinyl and phenyl halides. This is not an SN2 reaction, because SN2 reactions do not work on sp2 carbon atoms, but this works!