The [4 + 3]-cycloaddition/quasi-Favorskii process. Synthesis of the carbocyclic core of tricycloclavulone.

[reaction: see text] The [4 + 3]-cycloadduct derived from the reaction of 2,5-dibromocyclopentanone with cyclopentadiene was converted via a quasi-Favorskii rearrangement and ring-opening, ring-closing metathesis sequence to the carbocyclic core of the prostanoid tricycloclavulone.