Vitamin E (α-tocopherol: 1a) and its model compound 2,2,5,7,8-pentamethylchroman-6-ol (1b) were oxygenated in aprotic solvents in the presence of the suspended or solubilized superoxide radial (O2ˉ) under oxygen atmosphere. The reactions proceeded only slightly under anaerobic conditions. In tetrahydrofuran having potassium superoxide (KO2) suspended, 1a gave rise to 2a and 3a, and 1b to 2b and 3b. A striking characteristic of the reactions is that in the presence of an excess amount of KO2, 1 and 3 are quantitatively converted to 2. Labeling experiments show that 3a and 3b are precursors of 2a and 2b, respectively, and that the conversion of 3 to 2 is an acyloin rearrangement. In acetonitrile having KO2 solubilized with dicyclohexano-18-crown-6, 1a gave rise to 7a, and lb to 4b, 5b, 6b, 7b, 8b, and 9b. A hydroperoxide 10b is a precursor of 4b~9b, and 5b is a precursor of 9b. The reactions are characteristic of epoxidations and recyclizations, in which the hydroperoxide 10 may be a key intermediate. The molecular structures of 2b, 3b, 6b, 7b, 8b, and 9b were confirmed by X-ray crystallographic analysis. These reactions are found to be O2ˉ-induced oxygenations. Possible reaction pathways for the formation of the products are discussed.
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