FIRST SYNTHESIS OF CYTOTOXIC 8,9-SECOKAURENE DITERPENOIDS - AN ENANTIOSELECTIVE ROUTE TO (-)-O-METHYLSHIKOCCIN AND (-O-METHYLEPOXYSHIKOCCIN())

A practical route for the total synthesis of 8,9-secokaurene diterpene s is described. The central step is the [3.3]sigmatropic rearrangement of spirocyclic intermediates such as 35, 40, and 41. All three compou nds must necessarily respond identically to properly install the absol ute configuration of the bridgehead methine carbon. The total synthesi s of (-)-O-methylshikoccin (2b) was realized in 8% overall yield from the Wieland-Miescher ketone 9. Its naturally occurring epoxide 47 was prepared with comparable efficiency. The preparative route developed h erein should provide a general entry into this important class of dite rpenoids.