Biomimetic Cationic Cyclization toward ent ‐Kaurene‐type Diterpenoids

Terpenoids comprise the largest family of natural products and include various structurally different genus which play important roles in living organisms. Biosynthetically, diterpenoids are derived from ( E , E , E )‐geranylgeranyl diphosphate (GGPP). From GGPP, diterpene cyclase catalyzes a sequence of carbocation‐mediated cyclizations, rearrangements, and further oxidations, leading to a class of structurally unique ent ‐kaurenes, such as cafestol, gibberellin A3 and oridonin. According to the biosynthesis pathway of ent ‐kaurene, we designed a chiral acetal‐enabled and SnCl 4 ‐promoted biomimetic polyene cationic cyclization. With a following Birch reduction/alkylation cascade, a core skeleton of representative ent ‐kaurenes diterpenoids was completed.