Synthetic Photochemistry. XLII. Total Synthesis of Cycloaraneosene, a Fundamental Hydrocarbon of 5–8–5-Membered Tricydic Diterpenoid from Sordaria araneosa

A 5–8–5-membered tricyclic diterpene, cycloaraneosene, has been totally synthesized via a stereoselective condensation of two units of optically active iridoids, a Cope rearrangement, a chemical reduction of the tetrasubstituted double bond, and the formation of an eight-membered ring. The proposed structure of natural hydroxycycloaraneosene should be revised to 8β-hydroxycycloaraneosene, judging from the NMR spectral data.