A short synthetic route to the core structures of otteliones A and B

Conjugate addition of the cuprate derived from 2-lithio-2,3-butadiene to 1-cylopentenecarbaldehyde, reaction with vinylmagnesium bromide, ring closing metathesis, and oxidation gives the cis-ring fused core of the anticancer agent ottelione A. Epimerization of the initial conjugate addition product and application of the same reactions as used for the ottelione A core, give the trans-ring fused core of ottelione B.