Tailored Synthesis of Skeletally Diverse Stemona Alkaloids through Chemoselective Dyotropic Rearrangements of β‐Lactones

The collective synthesis of skeletally diverse Stemona alkaloids featuring tailored dyotropic rearrangements of β‐lactones as key elements is described. Specifically, three typical 5/7/5 tricyclic skeletons associated with stemoamide, tuberostemospiroline and parvistemonine were first accessed through chemoselective dyotropic rearrangements of β‐lactones involving alkyl, hydrogen, and aryl migration, respectively. By the rational manipulation of substrate structures and reaction conditions, these dyotropic rearrangements proceeded with excellent efficiency, good chemoselectivity and high stereospecificity. Furthermore, several polycyclic Stemona alkaloids, including saxorumamide, isosaxorumamide, stemonine and bisdehydroneostemoninine, were obtained from the aforementioned tricyclic skeletons through late‐stage derivatizations. A novel visible‐light photoredox‐catalyzed formal [3+2] cycloaddition was also developed, which offers a valuable tool for accessing oxaspirobutenolide and related scaffolds. Three types of multisubstituted chiral γ‐butyrolactones have been constructed in a predictable and controllable manner through chemoselective dyotropic rearrangements of β‐lactones involving alkyl, hydrogen, and aryl migration. These transformations enabled the tailored synthesis of a series of skeletally diverse Stemona alkaloids with high efficiency (see scheme).