Nakorone 3, durgamone 6 and abudinol A and B have been isolated from marine sponges of the Axinellidae family Ptilocaulis spiculifer. The characteristic structures of these terpenoids have led us to initiate a total synthesis program based on our stereoselective oxacyclizations of polyepoxides and on biomimetic polyene carbacyclizations. We have discovered that mixed diepoxide-alkene cyclizations proceed smoothly in the presence of catalytic Lewis acids TMSOTf or TBSOTf and one equivalent of DTBMP. The structures of cyclization products, tricyclic allene 2 and bicyclic ketone 5, have been verified by X-ray diffractometry. The success of this mixed oxa-carba polycyclization cascade will find many applications in the total synthesis of other terpenoid natural products with interesting biological activities.  The lecture will describe the total syntheses nakorone 3 and durgamone 6 as well as our work in progress towards the syntheses of abudinol A and B.