Total Synthesis of (−)-Ceforalide B and (−)-Cephanolides B–D

(−)-Ceforalide B (1) and (−)-cephanolides B–D (2–4) are benzenoid cephanolide diterpenoids possessing the same pentacyclic skeleton, which contains three C13–C15 substituent patterns and different benzylic oxidation states. An olefination/6π-electrocyclization/oxidative aromatization cascade has been verified as divergent access to three C13–C15 patterns. The benzylic aerobic oxidations enabled by the Co(OAc)2·4H2O/bromide salt/O2/PPh3/N-hydroxyphthalimide system have been developed to deliver expected site-selectivity and different oxidation states. Through the divergent strategy, total synthesis of (−)-ceforalide B and (−)-cephanolides B–D is accomplished.