Vinigrol: A compact, diene-transmissive Diels-Alder strategy to the tricyclic core

A short (six steps from 17), versatile route to the tricyclic core of Vinigrol is described. A Lewis acid catalyzed and self-assembled Diels-Alder (LACASA-DA) reaction from the homoallylic cross-conjugated trienol 15 with N-methylmaleimide afforded the monoadduct 17 with diastereo-, regio-, and chemoselective control. Oxidation and installation of an acetylene (Ohira's reagent) followed by further manipulations afforded trienone 24. The second intramolecular Diels-Alder (at 45 degrees C) reaction assembled the tricyclic skeleton 25 directly. The configuration of 25 was confirmed by X-ray analysis.