Ruthenium-Catalyzed Oxidative Dearomatization of Phenols to 4-(tert-Butylperoxy)cyclohexadienones: Synthesis of 2-Substituted Quinones from p-Substituted Phenols

The ruthenium-catalyzed oxidation of phenols with tert-butyl hydroperoxide efficiently gives the corresponding 4-(tert-butylperoxy)cyclohexadienones. The oxidation proceeds selectively because of ruthenium's ability for rapid single-electron transfer. This biomimetic oxidation reaction is highly useful to obtain the metabolic compounds desired for confirming the safety of medicines and related compounds. Typically, the first metabolic compound of the female hormone estrone is readily obtained by this biomimetic oxidation reaction. The resulting 4-(tert-butylperoxy) cyclohexadienones are versatile synthetic intermediates, which can be transformed into 2-substituted 1,4-benzoquinones by treatment with acid catalysts. Acid-promoted rearrangement followed by a Diels-Alder reaction provides a new strategy for the synthesis of fused cyclic compounds, such as naphthoquinone and anthraquinone derivatives, from readily available phenols. The nonnatural 1,4-diacetoxy steroidal skeleton is obtained by the oxidation of estrone followed by zinc-mediated migration. Vitamin K-3 is synthesized selectively from p-cresol in an overall 79% yield in 4 steps, and the synthesis includes the ruthenium-catalyzed oxidation.