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Directed Aldol Reaction

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    Directed aldol reaction is a variation of crossed aldol reaction.

    crossed aldol reaction:

    directedaldolreaction1.png

    If a mixture of two enolizable aldehydes, two enolizable ketones, or an enolizable aldehyde and an enolizable ketone were subjected to the conditions of crossed aldol reaction, two enolate ions would form.

    eg:

    directedaldolreaction2.png

    Each enolate ion would react with unreacted 1 and 2, giving, after protonation by water, an aldol.

    directedaldolreaction3.png

    Since the overall reaction results in four aldols, it would not be an effective approach to synthesizing any of the aldols; the yield of each aldol would be poor and purification would be difficult. Aldols 3 and 6 can be prepared readily using aldol reaction. Directed aldol reaction provides a method to synthesize aldols 4 and 5 in high yield.

    desired aldol = 4:

    directedaldolreaction4.png

    mechanism:

    directedaldolreaction5.png

    desired aldol = 5:

    directedaldolreaction6.png

    mechanism:

    directedaldolreaction7.png

    see also diisopropylamide ion

    This page titled Directed Aldol Reaction is shared under a All Rights Reserved (used with permission) license and was authored, remixed, and/or curated by Gamini Gunawardena via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.

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