A (Z)-Ethylidenecyclopentane Annulation Method. Total Syntheses of (+/-)-Anhydrooplopanone, (+/-)-Oplopanone, and (+/-)-8-epi-Oplopanone

Article abstract of DOI:10.1021/jo00295a028

Transmetalation of (Z)-5-chloro-3-trimethylstannyl-2-pentene (8) with MeLi in tetrahydrofuran (THF) at -78 deg C provides the novel bifunctional reagent (E)-5-chloro-3-lithio-2-pentene (11), which can be transformed readily into the Grignard reagent (12).Copper(I)-catalyzed conjugate addition of (12) to cyclic α,β-unsatured ketones (e.g., 23-29), followed by intramolecular alkylation of the resultant chloro ketones (e.g., 30-36), affords the corresponding (Z)-ethylidenecyclopentane annulation products (e.g., 37-43).This new annulation method played a key role intotal syntheses of the sesquiterpenoids (+/-)-anhydrooplopanone (51), (+/-)-oplopanone (50), and (+/-)-8-epi-oplopanone (70).