Oxidation of -tocopherol (1) conventionally leads to its
spiro-dimer (3) via ortho-quinone methide 2 (path A). The zwitterionic oQM precursor 2a is stabilized by NMMO in complex 4,
which upon rapid heating produces small amounts of the new dioxocine dimer 5 (path B). Acid treatment of 5 causes quantitative conversion into
spiro-dimer 3, via oQM 2 (path C).
