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.