The First Total Synthesis of (±)-Ingenol

The first total synthesis of (+/-)-ingenol has been achieved. The key features of the synthesis include the use of a highly diastereoselective Michael reaction to fix the C-11 methyl stereochemistry and the incorporation of the dimethylcyclopropane via diastereoselective carbene addition to the Delta13,14 olefin. The intramolecular dioxenone photoaddition-fragmentation sequence leads to the establishment of the critical C-8/C-10 trans intrabridgehead stereochemistry, a central challenge in the synthesis of ingenanes. The completion of the synthesis proceeds using the C-6alpha hydroxymethyl group as the sole handle for oxidation of seven contiguous carbon centers.