The association of the Claisen rearrangement with a novel [1,5] sigmatropic rearrangement

Thermal rearrangement of the allyl aryl ether (5) gave, in addition to the expected Claisen rearrangement product (6), the isomer (7), and similarly thermal transformation of the allyl ether (8) gave the mixture (9) and (10); the formation of (7) and (10) is rationalised as involving a [1,5] acetyl shift.