Über die Chemie des Vitamins E. 1. Mitteilung. Die Umkehrung der Konfiguration am Kohlenstoffatom 2 von natürlichem (2<i>R</i>, 4′<i>R</i>, 8′<i>R</i>)-α-Tocopherol
(2 S, 4′R, 8′R)-α-Tocopherol with unnatural configuration at C-2 is prepared by oxidation of natural, so called d-α-tocopherol (I), which has the (2R, 4′R, 8′R)-configuration, to α-tocopherylquinone (II), followed by recyclization of the corresponding α-tocopherylhydroquinone (III). Experiments showed that the configuration of carbon atom 2 of natural α-tocopherol is retained during the ferric chloride
Upon oxidation in aprotic media, β-tocopherol (2) forms a spiro-dimer (10) as the main product. The reaction mechanism is a hetero-Diels–Alder process with inverse electron demand of two intermediate ortho-quinone methide molecules. The spiro-dimer can be reduced to the corresponding symmetric ethano-dimer (11). In contrast to the well-studied α-tocopherol case, spiro-dimer and ethano-dimer do not