Enantioselective Total Synthesis of Taiwaniadducts I, J, and L

The first enantioselective total synthesis of the structurally unique tetraterpenoid, (+)-taiwaniadduct J (<b>1</b>), has been accomplished via late-stage pericyclic reactions involving an intermolecular Diels-Alder reaction followed by an intramolecular [2 + 2]-cycloaddition reaction. In this reaction, <i>trans</i>-ozic acid methyl ester (<b>20</b>) serves as the diene (HOMO counterpart) and a <i>p</i>-benzoquinone of <i>abeo</i>-abietane <b>5</b> serves as the corresponding LUMO counterpart to affect the [4 + 2]-cycloaddition to set vicinal all-carbon quaternary stereogenic centers. In the process, the first total syntheses of (-)-taiwaniadducts I (<b>2</b>) and L (<b>3</b>) were also accomplished. The absolute configuration of (+)-taiwaniadduct J (<b>1</b>) was confirmed through an enantioselective total synthesis and X-ray analysis. This synthesis demonstrates the elegant application of pericyclic reactions, such as the Diels-Alder cycloaddition and [2 + 2] cycloaddition, to construct multiple quaternary centers in the synthesis of taiwaniadduct J (<b>1</b>).