Synthesis of new steroid analogues by samarium diiodide induced cyclisations of γ-naphthyl 1,3-diones

We present the synthesis of new steroid analogues via samarium diiodide mediated intramolecular ketyl–aryl coupling reactions of γ-naphthyl-substituted 1,3-diones. From previous experiments with γ-naphthyl monoketones high stereoselectivities with the ‘unnatural’ cis/cis annulation of rings B/C/D were expected. Surprisingly, we observed the formation of two diastereomers with cis- and trans-fused rings B and C of the tetracyclic skeleton. The diastereoselectivity proved to be strongly dependent on the amount of the proton source employed in the reaction. A rationale for this unexpected behaviour is discussed. In addition, we observed a smooth aluminium chloride induced cyclisation of one of the γ-naphthyl-substituted 1,3-diones to furnish an equilenine precursor. Another cyclisation product was converted by Grob-fragmentation into a naphthannulated cyclononane derivative.

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