Isolation and Bioinspired Total Synthesis of Rugosiformisin A, A Skeleton-Rearranged Abietane-Type Diterpenoid from Isodon rugosiformis

Rugosiformisin A, a skeleton-rearranged abietane-type diterpenoid with a spiro[4.5]decane motif, was isolated from Isodon rugosiformis. Its structure was unambiguously established via NMR spectroscopic analysis and single-crystal X-ray diffraction. A bioinspired asymmetric synthesis of rugosiformisin A was achieved in 15 steps with 2.7% overall yield. The synthesis features an iridium-catalyzed asymmetric polyene cyclization and a semipinacol rearrangement.