Electrochemical Total Synthesis of Pratosine By Controlling for the Anodically Initiated One-/Two-Electron Transfer Process

Abstract

Pratosine is a type of a pyrrolophenanthridone alkaloid that includes indole ring and electron donating group-substituted N-benzoyl moiety. Many researchers demonstrated various synthetic reactions to access a simple poly-heterocyclic structure of pyrrolophenanthridone. For instance, intramolecular cyclization between indoline and N-benzoyl moiety was accomplished by stoichiometric Pd-mediated C-H activation1, hypervalent iodine mediated oxidative cross-coupling2 and inverse electron-demand Diels-Alder reaction3. Continuously DDQ oxidation to convert indoline to indole is necessary in all case. We established electrochemical intramolecular radical cation cross-coupling and indole synthesis reaction. These reaction was initiated by same anodic oxidation for electron-rich benzoyl group, but acid or base additive-dependent different electron-transfer pathway was occurred in both cyclization and indole ring forming reaction.Reference(1) DC. Black, PA. Keller, N. Kumar, Tetrahedron Lett. 1989, 30, 5807-5808.(2) MD. Ganton, MA. Kerr, Org. Lett. 2005, 7, 4777-4779.(3) DL. Boger, SE. Wolkenberg, J. Org. Chem. 2000, 65, 9120-9124. Figure 1