Approach to the Core Structure of Signermycin B

Abstract

Among the natural tetramic acids with a decalinoyl part, signermycin B is unique because it contains a cis‐decalin. In this paper, we demonstrate that the cis‐decalin section of signermycin B can be accessed by an anionic oxy‐Cope rearrangement. The substrate, a tricyclic dienol was prepared by an intramolecular Diels‐Alder reaction of a masked ortho‐benzoquinone, generated by oxidation of an α‐methoxyphenol in presence of cis‐2‐hexenol. After a superfluous bromine on the cycloadduct was removed, reaction of the tricyclic ketone with isopropenylmagnesium bromide led to the tricyclic trienol that underwent the oxy‐Cope rearrangement to a cis‐decalinone. While we could show, that introduction of the 4‐ethyl substituent (signermycin B numbering) is possible by enolate alkylation, the 4‐epi‐isomer was formed.