Studies on the regio- and diastereo-selective epoxidation of daphnanes and tiglianes.

Daphnanes and tiglianes are diterpenes with a shared tricyclic 5-7-6 ring system. Many members exhibit significant biological activities often associated with protein kinase C signaling. Many of these natural products (~100) have a C6-C7 α-epoxide whose influence on biological activity is little studied. Using the more readily available phorbol ester PDBu as a test substrate, we report an efficient, and potentially general, α-epoxidation method based on a vanadium-catalyzed asymmetric epoxidation with bishydroxamic acid (BHA) ligands.