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Related Experiment Videos

Acylation through Ketene Intermediates.

Rimma Shelkov1, Moshe Nahmany, Artem Melman

  • 1Department of Organic Chemistry, The Hebrew University of Jerusalem, Israel.

The Journal of Organic Chemistry
|December 7, 2002
PubMed
Summary
This summary is machine-generated.

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Alpha-substituted carboxylic acids react with carbodiimides to form ketenes, yielding esters with alcohols. This reaction shows low steric sensitivity, suggesting a pseudopericyclic pathway for ester formation.

Area of Science:

  • Organic Chemistry
  • Synthetic Chemistry

Background:

  • Carboxylic acids with alpha-electron-withdrawing groups can be dehydrated using carbodiimides.
  • This dehydration forms reactive ketene intermediates.

Purpose of the Study:

  • To investigate the in situ formation and reactivity of ketenes derived from alpha-substituted carboxylic acids.
  • To explore the chemoselectivity and steric effects in the acylation of alcohols using these ketenes.
  • To elucidate the reaction mechanism, particularly the pathway for alcohol addition to ketenes.

Main Methods:

  • Dehydration of alpha-substituted carboxylic acids using carbodiimides (e.g., DCC).
  • In situ trapping of ketene intermediates with alcohols to form esters.
  • Investigation of reaction outcomes with varying steric bulk of alcohols.

Related Experiment Videos

  • Comparison with conventional acylation methods.

    • Main Results:

    • Facile formation of substituted ketenes from alpha-substituted carboxylic acids and carbodiimides.
    • High yields of esters obtained through in situ trapping with alcohols.
    • Ketene intermediates exhibited low sensitivity to the steric bulk of alcohols during acylation.
    • A specific instance of ketene trapping via [4+2] cycloaddition with a second DCC molecule was observed.

    Conclusions:

    • Carbodiimide-mediated dehydration offers an efficient route to ketenes for ester synthesis.
    • The acylation mechanism involving these ketenes displays unique chemoselectivity, differing from traditional reagents.
    • Evidence supports a pseudopericyclic pathway for the nucleophilic addition of alcohols to these ketenes.