10-Electron systems

The [5,5] sigmatropic rearrangement of 2,4-pentadienylphenyl ethers can be considered a homologous Claisen rearrangement.

Fig.1

[5,5] Sigmatropic rearrangement

The major reaction is a Claisen rearrangement ([3,3] sigmatropic). In addition, formation of the para-substituted aromatic compound by a [5,5] sigmatropic rearrangement is being observed. A [3,5] sigmatropic rearrangement does not take place because, as a reaction with 8 electrons, it is suprafacially forbidden. The benzidine rearrangement represents another example of a [5,5] sigmatropic reaction.

Fig.2

Benzidine rearrangement