Novel tocopheryl compounds XXV: synthesis and comparison of the para-quinones of all four homologous tocopherol model compounds and their 3,4-dehydro derivatives

Four tocopherol model compounds, the chroman-6-ols (1–4) having the typical substitution pattern of α-, β-, γ-, and δ-tocopherol (vitamin E), were oxidized to the corresponding para-quinones (5–8), and dehydrogenated to the 2H-chromen-6-ols (17–20) involving initial acetyl protection of the phenolic OH and deprotection as the last step. The chromenols were also converted into the para-quinones (21–24), which existed in the bicyclic hemiketal form, in contrast to the chromanol-derived, monocyclic quinones 5–8, the ketalization behavior agreeing well with computations on the DFT level.