Electrochemical Total Synthesis of Pyrrolophenanthridone Alkaloids: Controlling the Anodically Initiated Electron Transfer Process

Abstract

Electrochemical intramolecular C(sp2)–H cross-coupling and dehydrogenative indole synthesis were developed. Both reactions were initiated by anodic oxidation of the same electron-rich indoline moiety, but the product selectivity was controlled by different electron-transfer processes. Intramolecular cross-coupling was achieved by the generation of a strong electrophilic radical cation intermediate in the MeNO2–HFIP–LiClO4 system. Indole formation was accomplished through benzylic oxidation and continuous deprotonation. We applied these reactions to the total synthesis of natural pyrrolophenanthridone alkaloids.