A formal synthesis of antimalarial diterpenoid 7,20-diisocyanoadociane, isolated from marine sponge Adocia sp., was achieved. The authors synthesized Corey's synthetic intermediate 2 for 7,20-diisocyanoadociane. This synthesis involves the synthesis of a perhydropyrene derivative using a sequential isomerization-intramolecular Diels-Alder reaction as the key step.