Convergent total syntheses of the pentacyclic lamellarins K, T, U and W via the addition of azomethine ylides to tethered tolans

The title compounds, 1-4 respectively, have been prepared in a concise and fully regiocontrolled manner via the addition of an azomethine ylide to an ester-linked tolan. The resulting annulated dihydropyrrole was oxidized to the corresponding fully aromatic system and the associated isopropyl ethers then selectively cleaved with aluminium trichloride to reveal the free phenolic hydroxyl groups associated with the target compounds.