Versatile Oxabicyclic Synthons: Studies on C8-Oxygenated Eunicellin Diterpenes

Abstract

In this letter, we describe the first approach to the synthesis of C8-oxygenated eunicellin diterpenes starting with a highly functionalized 8-oxabicyclo[3.2.1]octadiene system. The route features two sequential annulations to append a six- and five-membered ring onto the core structure followed by oxidative cleavage to reveal the eunicellin skeleton. Key to this strategy is a diastereo-selective intramolecular Nozaki-Hiyama-Kishi (NHK) closure to establish the correct relative stereochemical relationship at C6 and C8 of the natural product.