Oxidations of Vitamin E (α-Tocopherol) and Its Model Compound 2,2,5,7,8-Pentamethyl-6-hydroxychroman. A New Dimer

Article abstract of DOI:10.1021/jo00241a029

Oxidation of α-tocopherol (1a) with tert-butyl hydroperoxide in reagent-grade chloroform gave a new dimeric product which appeared to be both aromatic quinonoid.Repetition of the reaction with the tocopherol model compound 2,2,5,7,8-pentamethyl-6-hydroxychroman (1b) gave the corresponding dimer in high yield (30percent).This product was shown by two-dimensional, long-range proton-carbon correlation NMR spectra and subsequently by X-ray diffraction to be 2,3-dihydro-3,3,5,6,9,10,11a(R)-heptamethyl-7a(S)-(3-hydroxy-3-methylbutyl)-1H-pyrano<2,3-a>xanthene-8(7aH),11(11aH)-dione (16b).It appeared to be formed by Diels-Alder addition of the intermediate quinone methide 7b to 2-(3-hydroxy-3-methylbutyl)-3,5,6-trimethylbenzo-1,4-quinone (14b), a known product of oxidation.