POTASSIUM TERT-BUTOXIDE-CATALYZED OXYGENATIONS OF VITAMIN-E AND ITS MODEL-COMPOUND 2,2,5,7,8-PENTAMETHYLCHROMAN-6-OL

Oxygenation of vitamin E[1a, (RRR)-alpha-tocopherol] in tetrahydrofura n in the presence of potassium tert-butoxide under oxygen gave product s 2a, 3a, 4a, 5a and 6a arising from oxidation of the aromatic moiety. Under similar conditions, a vitamin E model compound, 2,2,5,7,8-penta methylchroman-6-ol 1b, gave the analogous products 2b, 3b, 4b, 5b and 6b. Initial attack at the 5 position leads to the acyloin 6b, which is converted into the isomer 5b. The hydroperoxide 7b is derived from th e acyloin 5b and transformed into the 7-methylene compound 3b. The 8-m ethylene compound 2b is converted into the carbolactone 4b. The molecu lar structures of compounds 2b, 3b, 4b and 7b were confirmed by X-ray crystallographic analysis. Possible reaction pathways for the product formation and relationships between the product distribution and the b asicity of reaction media are discussed.