Fengjie Yao, Yufei Wu, Yidian Sheng, Kuan Yu, Peirong Rao, Jun Xuan, Hanfeng Ding
-diterpenoid alkaloids, namely, spirasines V and VI, spiradine D, and the proposed structures of spirafines II and III. Crucial transformations include an Enders asymmetric addition, an oxidative dearomatization induced Diels-Alder cycloaddition, and a MHAT-initiated transannular radical cyclization. The heterocyclic rings were assembled by an efficient reductive cyclization sequence at a late stage. Our approach has enabled the total syntheses of these natural products in 17-20 steps from commercially available starting materials with high enantio- and diastereocontrol.