Pentacyclic compounds by samarium diiodide-induced cascade cyclizations of naphthyl-substituted 1,3-diones

Treatment of naphthyl-substituted cyclopentane-1,3-diones with the samarium diiodidehexamethylphosphoramide (HMPA) complex in the presence of tert-butyl alcohol provided the expected tetracyclic diols with steroid-like structures. Surprisingly, reactions without the proton source led to the efficient formation of a new pentacyclic diol. In this case the toxic additive HMPA could be substituted by a combination of lithium bromide (in situ generation of samarium dibromide) and N,N-dimethylimidazolidone. The styrene-like alkene moiety of this product was used to prepare an ensemble of highly substituted pentacyclic steroid-like compounds.