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 alpha-, beta-, gamma-, and delta-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. (c) 2007 Elsevier Ltd. All rights reserved.