Total Synthesis of (−)-Steganone Utilizing a Samarium(II) Iodide Promoted 8-Endo Ketyl−Olefin Cyclization

Abstract

A six-step synthesis of (±)-steganone from commercially available 3,4,5-trimethoxybenzyl alcohol features a samarium(II) iodide promoted 8-endo ketyl−olefin coupling to install, in a single transformation, the 8,5 ring system common to the lignan lactones. The racemic synthesis provided the basis for the construction of (−)-steganone, which exploited a chromium tricarbonyl moiety both to establish and protect the desired absolute stereochemistry through key transformations, including a SmI2-promoted 8-endo radical cyclization and two palladium-catalyzed couplings.