The marine sesquiterpene quinones (+)‐smenoqualone, (–)‐ilimaquinone, (+)‐smenospongine, and (+)‐isospongiaquinone were efficiently synthesized in a unified manner starting from a known trans‐decalin derivative, which is accessible from (+)‐5‐methyl Wieland–Miescher ketone. The synthetic method involved the following key steps: (i) assembly of the whole carbon skeleton by coupling the decalin segment to an aromatic moiety; (ii) p‐quinone formation by strategic salcomine oxidation of phenolic intermediates; (iii) direct conversion of (–)‐ilimaquinone into (+)‐isospongiaquinone by pTsOH‐induced isomerization of the C‐4 olefinic double bond; (iv) site‐selective amination of a dimethoxy‐p‐quinone intermediate by substitution of the C‐18 methoxy group with an amino group; and (v) one‐step construction of the requisite tetracyclic core structure by sequential BF3·Et2O‐induced rearrangement/cyclization of an olefinic decalin intermediate having an aromatic moiety. The syntheses of (+)‐smenoqualone and (+)‐smenospongine are reported here for the first time.

A pharmaceutically important natural product, β‐lapachone, was efficiently synthesized in four steps in 70 % overall yield starting from commercially available 1,4‐naphthoquinone. The key step of the synthesis was the direct conversion of 2‐prenyl‐1,4‐naphthoquinone into β‐lapachone through an advantageous cyclization/hydration/oxidation cascade process.