Enantioselective synthesis of hushinone, birkenol, and birkenal

The first enantioselective synthesis of hushinone, a tricyclic norsesquiterpenoid with an unprecedented carbon framework identified from the essential oils of birch trees, was accomplished by using intramolecular halolactone alkylation as the key step. Two other bicyclic norsesquiterpenoids in the essential oils, birkenol and birkenal, which share the same carbon skeleton as hushinone, were also synthesized for the first time through eliminative lactone ring opening of hushinone. Comparison of the specific rotation data between the synthetic and natural products led to the confirmation of the absolute configuration of the natural products.