The first total synthesis and structural determination of epi-cochlioquinone A

Abstract

The first total synthesis of epi-cochlioquinone A has been achieved in a highly convergent manner via [3+3] cycloaddition of catechol 2 and oxadecalin 3 as the key reaction. The synthesis of the catechol segment, possessing the side chain with multi stereogenic centers, features the asymmetric vinylogous Mukaiyama aldol reaction, the stereoselective conjugate addition to the nitroalkene, the stereospecific nitro-Dieckmann condensation, and the transformation of 6-nitrocyclohex-2-enone into catechol 2, using two new methodologies, such as (i) the hydrogen-transfer reaction to o-aminophenol and the subsequent auto-redox-catalysis to catechol and (ii) the direct oxidation of 6-nitrocyclohex-2-enone to o-quinone and the subsequent reduction. The oxadecalin segment was synthesized from a glycosyl cyanide by the [3+3] annulation with a ketone and an acetoacetate. These segments were connected by the [3+3] cyclization, and the resulting tetracyclic compound was subjected to a specific oxidation of the protected hydroquinone to provide epi-cochlioquinone A.