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

Collective synthesis of skeletally diverse Stemona alkaloids has been achieved, featuring tailored dyotropic rearrangements of b -lactones as key elements. Specifically, three typical 5/7/5 tricyclic skeletons associated with stemoamide, tuberostemospiroline and parvistemonine were first accessed through chemoselective alkyl-, hydrogen-, and aryl-migration dyotropic rearrangements of b -lactones, respectively. With rational manipulations 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 derivatization. Along the total synthesis tour, a novel visible-light photoredox-catalyzed formal [3+2] cycloaddition was also developed, which offers a valuable tool for accessing oxaspirobutenolide and related scaffolds.