Total Synthesis of Crotophorbolone.

The complex ABC-tricyclic structure of crotophorbolone, a derivative of the tigliane diterpenoids, was assembled by coupling of simple fragments. The six-membered C-ring fragment, having five contiguous stereocenters, was stereoselectively constructed from (R)-carvone. After attachment of the five-membered A-ring through the π-allyl Stille coupling reaction, the α-alkoxy bridgehead radical reaction effected the endo-cyclization of the seven-membered B-ring by forming the sterically congested bond at C9 and C10 stereospecifically and stereoselectively, respectively.