Chemical conversion of vibsanin C to vibsanin E and structure of 3-hydroxyvibsanin E from Viburnum awabuki

Vibsanin E (4), a tricyclic vibsane-type diterpene, has been prepared in 50 % yield from vibsanin C (2), a seven-membered ring vibsane-type diterpene b y reaction with BF3. OEt2 at -78 degrees C. This chemical correlation not o nly established structure, including absolute configurations, but also has demonstrated a possible biosynthetic route to 4 via 2 derived from vibsanin B (1). The structure of 3-hydroxyvibsanin E (5), another example of a tric yclic seven-membered ring vibsane, isolated from the leaves of Viburnum awa buki, has been established by extensive analyses of 2D NMR data and compari son of its spectral data with those of 4.