Bond stabilisation in tocopherols. Part I. The Claisen rearrangement of allyl tocopheryl ethers

Abstract

The Claisen rearrangement of a series of allyl tocopheryl ethers has been studied kinetically in order to examine the possibility that the pronounced Mills–Nixon effect in 6-chromanols can be attributed to a significant degree of bond fixation in these compounds. The rearrangements of allyl tocyl ether and allyl δ-tocopheryl ether were similar and gave the 5-allyltocopherol predominantly in each case. There were kinetic differences in the rearrangements of the β-tocopheryl and γ-tocopheryl ethers, and a difference of 2·6 kcal./mole in their activation energies, which suggests that a mild degree of bond fixation might exist in these compounds. The pyrolysis of allyl α-tocopheryl ether at 192° yields α-tocopherol rapidly and in good yield.