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Enamine Reactions

  • Page ID
    5133
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    As previously seen, aldehydes and ketones react with 2o amines to reversibly form enamines.

    Example

    1.jpg

    Reversible

    2.jpg

    Enamines act as nucleophiles in a fashion similar to enolates. Because of this enamines can be used as synthetic equivalents as enolates in many reactions. This process requires a three steps:

    1. Formation of the enamine,
    2. Reaction with an eletrophile to form an iminium salt,
    3. Hydrolysis of the iminium salt to reform the aldehyde or ketone.

    Some of the advantages of using an enamine over and enolate are enamines are neutral, easier to prepare, and usually prevent the overreaction problems plagued by enolates. These reactions are generally known as the Stork enamine reaction after Gilbert Stork of Columbia University who originated the work.

    3.jpg

    Typically we use the following 2o amines for enamine reactions

    4.jpg

    Alkylation of an Enamine

    Enamined undergo an SN2 reaction with reactive alkyl halides to give the iminium salt. The iminium salt can be hydrolyzed back into the carbonyl.

    Step 1: Formation of an enamine

    5.jpg

    Step 2: SN2 Alkylation

    6.jpg

    Step 3: Reform the carbonyl by hydrolysis

    7.jpg

    All three steps together:

    8.jpg

    Acylation of Enamines

    Enamine can react with acid halides to form β-dicarbonyls

    1) Formation of the enamine

    9.jpg

    2) Nucleophilic attack

    10.jpg

    3) Leaving group removal

    11.jpg

    4) Reform the carbonyl by hydrolysis

    12.jpg

    All three steps together:

    13.jpg

    Michael Addition using Enamines

    Enamines, like other weak bases, add 1,4 to enones. The end product is a 1,5 dicarbonyl compound.

    14.jpg

    Contributors


    Enamine Reactions is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by LibreTexts.

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