Novel tocopheryl compounds XXIV. Studies into the nitrosation chemistry of γ-tocopherol: preparation of 5-nitroso-γ-tocopherol via an organomercury derivative of vitamin E

5-Nitroso-γ-tocopherol (5) was not accessible by direct nitrosation of γ-tocopherol (3), but was synthesized for the first time by nitrosation of an organomercurial intermediate (11) under aprotic conditions. Under protic conditions 5 exists in equilibrium with its ortho-quinone monoxime tautomer 6, the latter being the major component with >99%. NMR and analytical data of the tautomeric couple are reported for the first time. The chemistry of the nitrosation of γ-tocopherol was studied in detail. In the presence of oxygen, 5 is readily oxidized to 5-nitro-γ-tocopherol (7), whereas at elevated temperatures an additional process, the conversion of monoxime 6 into 5,6-tocopheryldione (8) under loss of hydroxylamine sets in. The experimental results agreed with the outcome of DFT computations.