Total synthesis of diterpenoid steenkrotin a.

A concise and diastereoselective total synthesis of the diterpenoid (+/-)-steenkrotinA is described for the first time. The strategy mainly features three key ring formations: 1)a rhodium-catalyzed OH bond insertion followed by an intramolecular carbonyl-ene reaction to build up the tetrahydrofuran subunit; 2)sequential SmI2-mediated Ueno-Stork and ketyl-olefin cyclizations to construct the [5,7] spirobicyclic skeleton; and 3)an intramolecular aldol condensation/vinylogous retro-aldol/aldol sequence to form the final six-membered ring with inversion of the relative configuration at the C7 position.