Collective Syntheses of Eight Phorbaketals via Total Synthesis of Phorbaketal A

A practical total synthesis of phorbaketal A, a representative natural product among spiroketal containing natural products from marine sponge Phorbas sp. that has been a productive source of structurally diverse terpene natural products with various biological activities was achieved through gold-catalyzed spiroketalization of the alkynediol precursor accompanied by the epoxide rearrangement to the corresponding allylic alcohol followed by an olefin isomerization. With the solid pathway to produce phorbaketal A in hand, we achieved collective synthesis of eight phorbaketals as they appeared to be derived from phorbaketal A in nature.