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11.5: Wolff Rearrangement

  • Page ID
    190077
  • The Wolff rearrangement is the conversion of a diazoketone to a ketene, usually under photolytic conditions.

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    The loss of dinitrogen from the diazonium compound would result in an electron-deficient carbene. Like a carbocation, the carbene would be susceptible to a 1,2-shift. If accompanied by π-donation from the carbene to the carbonyl, a ketene would result.

    ERWolffmech.png

    As with other rearrangements, the 1,2-shift could occur at the same time as the loss of the dinitrogen.

    ERWolffmechConc.png

    Ketenes are not terribly stable. In the presence of nucleophilic solvents such as water or alcohol, the ketene easily undergoes nucleophilic addition. Addition of water would result in a carboxylic acid.

    ERWolffketene.png

    The mechanism of that addition involves keto-enol tautomerism.

    ERWolffketenemech.png
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    ERWolffChloride.png
    ERWolffdiaz2.png
    ERWolffdiaz.png
    ERWolff3.png
    ERWolff2.png

    Exercise \(\PageIndex{1}\)

    Predict the products of the following Wolff rearrangements.

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    Answer

    ERWolffsolns.png