Enantioselective Total Synthesis of Taiwaniadducts I, J, and L.

The first enantioselective total synthesis of the structurally unique tetraterpenoid, (+)-taiwaniadduct J (1), 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, trans-ozic acid methyl ester (20) serves as the diene (HOMO counterpart) and a p-benzoquinone of abeo-abietane 5 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 (2) and L (3) were also accomplished. The absolute configuration of (+)-taiwaniadduct J (1) 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 (1).