Tandem [5 + 2]/[4 + 2] Cycloadditions To Construct the [6–7–6] Tricyclic Skeleton of Icetexane Diterpenes: Total Synthesis of Euolutchuol E, Przewalskine E and Brussonol

The collective total synthesis of the icetexane diterpenoids euolutchuol E, przewalskine E, and brussonol is described. An efficient synthetic strategy features two key transformations: (a) a tandem [5 + 2]/[4 + 2] cycloaddition reaction strategy to efficiently build the full-carbon skeleton of the icetexane diterpenoids; (b) an efficient aromatization of the C-ring of the icetexane diterpenoids using SeO2.