Efforts have been made to establish a method of synthesizing the picrotoxane sesquiterpenoids such as picrotoxinin (1) and tutin. Starting from the acid (6), the intermediate (11) possessing the isotwistane skeleton was prepared in a stereo-controlled manner. The tricyclic compound (11) was transformed into the bicyclic compound (27) by the following sequence: (11)→(12)→(13)→(14)→(15)→(16)→(18)→(26)→(27). The bicyclic intermediate (27) was further converted to the compound (30).
