Symmetry‐Driven Strategy for the Assembly of the Core Tetracycle of (+)‐Ryanodine: Synthetic Utility of a Cobalt‐Catalyzed Olefin Oxidation and α‐Alkoxy Bridgehead Radical Reaction

Ryanodine ( 1 ) is a potent modulator of intracellular calcium release channels, designated as ryanodine receptors. The exceptionally complex molecular architecture of 1 comprises a highly oxygenated pentacyclic system with eleven contiguous stereogenic centers, which makes it a formidable target for organic synthesis. We identified the embedded C 2 ‐symmetric tricyclic substructure within 1 . This specific recognition permitted us to design a concise synthetic route to enantiopure tricycle 9 by utilizing a series of pairwise functionalizations. The four tetrasubstituted carbon centers of 9 were effectively constructed by three key reactions, a dearomatizing Diels–Alder reaction, the kinetic resolution of the obtained racemic 14 through asymmetric methanolysis, and the transannular aldol reaction of the eight‐membered diketone 10 . A new combination of cobalt‐catalyzed hydroperoxidation and NfF‐promoted elimination enabled conversion of the hindered olefin of 9 into the corresponding ketone, thus realizing the desymmetrization. Finally, the tetrasubstituted carbon was stereospecifically installed by utilizing the α‐alkoxy bridgehead radical to deliver the core tetracycle 7 with the six contiguous tetrasubstituted carbon centers. Consequently, the present work not only accomplishes efficient assembly of four out of the five fused rings of 1 , but also develops two new powerful methodologies: two‐step ketone formation and bridgehead radical reaction.