Bond stabilisation in tocopherols. Part II. Claisen rearrangement of but-2-enyl tocopheryl ethers

Abstract

The Claisen rearrangement of but-2-enyl tocopheryl ethers gives, in addition to the normal 1-methylallyltocopherols, varied amounts of abnormal but-2-enyltocopherols. The abnormal products, formed in substantial amounts during the rearrangement of the β- and γ-tocopheryl ethers, are believed to arise from the ortho–ortho rearrangement of the original normal 1-methylallyl dienones. Cleavage of the ethers to the original tocopherols also occurs substantially and appears to be associated with breakdown of the transition state involved in the ortho–ortho shift. Study of a number of suitably substituted ethers of phenols and p-alkoxyphenols indicates that, at present, the abnormal reactions are virtually restricted to the ethers of chroman-6-ols.