An intramolecular cycloaddition-sigmatropic rearrangement approach to (±) gascardic acid

Abstract

A general intramolecular Diels-Alder:anionic oxy-Cope strategy for the synthesis of tricyclic skeletons and its application to the preparation of the gascardic acid precursor 12 is described. In situ generation of the appropriate cyclopentadiene 5 by isomerization (Et 3N) afforded the [4+2] adduct directly or with EtAlCl 2 as catalyst. The requisite potassium salt of the 1,5 diene 10 rearranged at 67°C to the fused ring ketone 11. Selective allylic oxidation and reduction provided 12.