1,4-addition of organocuprates (Gilman reagents) to enones

by James

Description: Organocuprates (aka “Gilman reagents”) will add to alpha beta unsaturated ketones to give 1,4-addition products (aka “Michael addition” products). Acid is added at the end to neutralize the compound.
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Notes: Organocuprates add preferentially to the carbon (“1,4 addition”) instead of the carbonyl carbon (“1,2 addition”). The intermediate product is an enolate, which is then protonated by addition of acid. The reaction also works with alpha beta unsaturated aldehydes and esters.

Examples:

Notes: Note how each of these reaction results in C–C bond formation at the end of the alkene and the ketone is untouched. These are all examples of “1,4 addition”.

Mechanism: Carbon from the organocuprate breaks from the Cu to form the new C–C bond in a 1,4-addition (Step 1, arrows A and B). This forms an enolate. Protonation of the enolate with acid then results in the ketone (Step 2, arrows C and D).

Notes: Note that the byproducts here are the organocopper (R–Cu) and a lithium salt. There’s nothing special about Cl here, it’s just a spectator ion to balance out H3O(+).

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{ 2 comments… read them below or add one }

Karhtik Devaraj

In this above reaction why the copper add to 1,4 carbon not to the carbonyl?

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Brian Butler

The copper doesn’t add – the alkane attached to the Gilman reagent adds.

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