Synthesis of (plus or minus)-7,8-epoxy-4-basmen-6-one by a transannular cyclization strategy

A transannular cyclization approach was used to prepare the diterpenoid tobacco isolate 7,8-epoxy-4-basemen-6-one. The macrocycle 5 was stereoselectively produced from the cationic cyclization of the olefinic acid 4. The allene functional group was introduced in high yield, because an organocopper reagent obtained from acetoacetate, was used to transform the alcohol 2 to the enol phosphate 3 in a two-phase procedure. The stereoselective construction of the tricyclic product 9 resulted from the transannular radical cyclization of 8 by a photochemical technique.