Synthesis of norabietane core.

A practical and efficient approach for the total synthesis of arucadiol and 1-oxomiltirone is reported. The key step which involves an intramolecular [4+2] cycloaddition catalyzed by gold(III) bromide or copper(II) triflate leads to the formation of 6-6-6-fused aromatic abietane core.

We synthesized [6,6,6]- and [6,6,7]-tricyclic compounds via intramolecular [4+2] cycloaddition by gold or copper catalysts. Substrates for cyclization were prepared by coupling reactions between eight types of diyne and four types of aromatic moieties. We have successfully synthesized eleven tricyclic compounds.