Propose a mechanism for the following transformation.

enter image description here

I gather that this mechanism might be similar to decarboxylation of keto acids: enter image description here

However, I am unsure of how to begin.

  • 1
    $\begingroup$ first, addition of water will occur at the ester to form a carboxylic acid which will then be removed after heating. $\endgroup$
    – Ayushmaan
    Commented Oct 13, 2017 at 6:22

1 Answer 1


In acidic media, the ester carbonyl will be protonated and the carbonyl carbon attacked by a water molecule. The intermediate will have a proton abstracted by a water molecule and the ethoxy group will be protonated (it can happen either by intermolecular reaction with an H3O+ or by an intramolecular reaction with a proton migration from the protonated intermediate after the water attack). The carbonyl is restored and an ethanol molecule leaves the structure. A subsequent proton abstraction by water forms the carboxylic acid, which will then suffer decarboxylation following the mechanism you presented above. (I'm sorry about my ChemDraw, I suck at drawing even on a computer).



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