Synthesis of bicyclic tert-alcohol 1 has been accomplished by means of Hg(OTf)2-induced cyclization of tert-butyl bishomofarnesate as the key step. Bicyclic cation 2, related to the sterol biosynthesis, is generated by the reaction of 1 with BF3. The chemical destiny of the cation 2 was traced and it confirmed the structure of three kinds of cyclization products to be 3, 4, and 5. These tricyclic compounds are formed via trans-anti-trans 6/6/5 fused cation 6. The tricyclic product 3 is the stereoisomer with Corey's enzymatic cyclization product of a 2,3-oxidosqualene type epoxide. Selective formation of the trans-anti-trans 6/6/5 fused cation 6 as the intermediate that corresponds to the biosynthetic intermediate of a dammarane-type triterpenoid is noteworthy.