Convergent Route to ent-Kaurane Diterpenoids: Total Synthesis of Lungshengenin D and 1α,6α-Diacetoxy-ent-kaura-9(11),16-dien-12,15-dione

The Hoppe’s homoaldol reaction of a cyclo-hexenyl carbamate with an aldehyde followed by an unprecedented BF 3 ·OEt 2 mediated intramolecular Mukaiyama–Michael-type reaction affords the tetracyclic core structure of ent -kaurane diterpenoids. The usage of this convergent approach for assembling these natural products is demonstrated by the first asymmetric total syntheses of two highly oxidized ent -kaurane diterpenoids: Lungshengenin D and 1α,6α-diacetoxy- ent -kaura-9(11),16-dien-12,15-dione.