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20.10 Reaction of Organometallic Reagents with Aldehydes and Ketones

  • Page ID
    28386
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    Because organometallic reagents react as their corresponding carbanion, they are excellent nucleophiles. The basic reaction involves the nucleophilic attack of the carbanionic carbon in the organometallic reagent with the electrophilic carbon in the carbonyl to form alcohols.

    File:/C:\Users\Joy\AppData\Local\Temp\msohtmlclip1\01\clip_image018.png

    Both Grignard and Organolithium Reagents will perform these reactions

    Addition to formaldehyde gives 1o alcohols

    File:/C:\Users\Joy\AppData\Local\Temp\msohtmlclip1\01\clip_image020.png

    Addition to aldehydes gives 2o alcohols

    11.jpg

    Addition to ketones gives 3o alcohols

    File:/C:\Users\Joy\AppData\Local\Temp\msohtmlclip1\01\clip_image024.png

    Addition to carbon dioxide (CO2) forms a carboxylic acid

    File:/C:\Users\Joy\AppData\Local\Temp\msohtmlclip1\01\clip_image026.png

    Examples

    File:/C:\Users\Joy\AppData\Local\Temp\msohtmlclip1\01\clip_image028.png

    Going from Reactants to Products Simplified

    File:/C:\Users\Joy\AppData\Local\Temp\msohtmlclip1\01\clip_image030.png

    Mechanism for the Addition to Carbonyls

    The mechanism for a Grignard agent is shown. The mechanism for an organometallic reagent is the same.

    1) Nucleophilic attack

    File:/C:\Users\Joy\AppData\Local\Temp\msohtmlclip1\01\clip_image032.png

    2) Protonation

    File:/C:\Users\Joy\AppData\Local\Temp\msohtmlclip1\01\clip_image034.png

    Nucleophilic Addition of Acetylides to Carbonyls

    Acetylide anions will add to aldehydes and ketones to form alkoxides, which, upon protonation, give propargyl alcohols.

    clipboard_1395414402579.png

    With aldehydes and non-symmetric ketones, in the absence of chiral catalyst, the product will be a racemic mixture of the two enantiomers.

    The triple bond in the propargyl alcohol can be modified by using the reactivity of the alkyne. For example, Markovnikov and anti-Markovnikov hydration of the triple bond leads to formation of the hydroxy-substituted ketone and aldehyde, respectively, after enol-keto tautomerization.

    clipboard_1395415355931.png

    Contributors

    • Layne A. Morsch - University of Illinois Springfield

    This page titled 20.10 Reaction of Organometallic Reagents with Aldehydes and Ketones is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Layne Morsch.

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