Synthesis of the core ring system of the sclerophytin diterpenes utilizing a Lewis acid-promoted [4+3] annulation strategy

The synthesis of the core ring system of the sclerophytin diterpenes is described. The key tetrahydrofuran-containing intermediate is assembled via a Lewis acid-promoted [4+3] annulation reaction between a mixed dimethyl acetal and a bis-TES dienol ether. The resulting β-keto ester was homologated, cyclized, and ring expanded to afford the sclerophytin ring system.