Oxygenations of Vitamin E (α-Tocopherol) and Its Model Compound 2,2,5,7,8-Pentamethylchroman-6-ol in the Presence of the Superoxide Radical Solubilized in Aprotic Solvents: Unique Epoxidations and Recyclizations

Article abstract of DOI:10.1021/jo00392a004

Vitamin E (1a, α-tocopherol) and its model compound 2,2,5,7,8-pentamethylchroman-6-ol (1b) were oxygenated in aprotic solvents in the presence of the solubilized superoxide radical under an oxygen atmosphere to give diepoxides 2a and 2b as main products, respectively.The reactions proceeded only slighty under anaerobic conditions.Extensive product analysis was carried out on the oxygenation of 1b, revealing that it gave rise to the products 2b, 3b, 4b, 5b, 6b and 7b.The novel compounds were determined to be 4a,5;7,8-diepoxy-4a,7,8,8a-tetrahydro-8a-hydroxy-2,5,7,8-tetramethyl-2-(4,8,12-trimethyltridecyl)chroman-6(5H)-one (2a), 4a,5;7,8- diepoxy-4a,7,8,8a-tetrahydro 8a-hydroxy-2,2,5,7,8-pentamethylchroman-6(5H)-one (2b), 1,1-dimethyl-3-(2,3-epoxy-2,3,5-trimethylbenzoquinon-6-yl)propanol (5b), 6-acetyl-7,8-epoxy-6-hydroxy-2,2,7,8-tetramethyl-1-oxaspiro<4.5>nonan-9-one (6b), and 6-acetyl-6-hydroxy-2,2,7,8-tetramethyl-1-oxaspiro<4.5>non-7-en-9-one (7b); the previously suggested structures of 6b and 7b should be revised.Compounds 6b and 7b are unique spiro compounds containing two five-membered rings..The structures 2b, 5b, and 6b were confirmed by X-ray crystallography.The reactions are suggested to be superoxide-catalyzed oxygenations, being characteristic of epoxidations and recyclizations, in which hydroperoxides 9a and 9b may be key intermediates.Possible reaction pathways for the formation of the products are discussed.