I'm confused about the mechanism for the isomerization of the external alkene eugenol to the internal alkene isoeugenol. I've added an image below of their structures.

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The reaction is usually carried out using a strong base (sodium or potassium hydroxide) in a polyol solvent (typically glycerol or ethylene glycol).

I have no idea why this might happen, especially given that there's no carbonyls with acidic alpha carbons in the molecule. Maybe eugenol phenoxide is responsible?

  • $\begingroup$ Looks like a sigmatropic rearrangement. $\endgroup$
    – Mithoron
    Feb 13, 2022 at 18:55
  • $\begingroup$ [1,3] sigmatropic shift? $\endgroup$
    – user102173
    Feb 13, 2022 at 19:18
  • $\begingroup$ It is thought to be a two-step reaction with cis-iso-eugenol as an intermediate as described here. The direct 1,3 sigmatropic reararrangement to the trans product has a symmetry problem. $\endgroup$
    – Karsten
    Feb 13, 2022 at 19:52


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