Synthesis of a Functionalized Bicyclo[3.2.1]Octane: A Common Subunit to Kauranes, Grayananes, and Gibberellanes

Kauranes, grayananes, and gibberellanes are three important diterpenoid families. These natural products all share a bicyclo[3.2.1]octane skeleton, with oxidation at very specific positions. In this manuscript, we describe the synthesis of a bicyclo[3.2.1]octane building block, which could serve as a potential intermediate for the synthesis of natural products from these three families. A first approach relying on a 1,4-sila-Prins cyclization was first explored, which required the selective functionalization of dihydrocarvone (via C─H activation and selective oxidation). This strategy resulted in a dead end when a 1,2-cyclization product was obtained. An alternative strategy relying on ring-closing metathesis (RCM) allowed to successfully achieve the synthesis of the desired scaffold in 8 steps from cyclohexenone.