Synthesis of Diterpenoid Steenkrotin A

Key words

steenkrotin A - terpenoids - O–H bond insertion - carbonyl-ene reaction - Ueno–Stork reaction - ketyl-olefin cyclization - aldol condensation

Significance

Ding and co-workers report the first total synthesis of (±)-steenkrotin A, a diterpenoid isolated from an African shrub. Structurally, this natural product is characterized by a pentacyclic skeleton, embedded with a sterically congested tetrahydrofuran moiety. The authors focused first on the construction of tricycle I, which set the stage for further elegant transformations to access the target.

 

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Comment

The tetrahydrofuran subunit was installed by a Rh-catalyzed O–H bond insertion and a carbonyl-ene reaction. A SmI₂-mediated Ueno–Stork reaction and a ketyl-olefin cyclization were used to construct spirocycle L. Interestingly, (±)-steenkrotin A could be accomplished by a cascade aldol condensation–vinylogous retro-aldol–aldol reaction, followed by elimination.

 

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