MgBr2-Mediated Electrochemical Dearomative Dihydroxylations, Hydroxycyclizations and Bromocyclizations of Indoles

We report an efficient and environmentally friendly electrochemical approach to perform dearomatization reactions of indoles at a constant potential in an undivided cell at room temperature. MgBr₂ is used as a redox mediator to indirectly oxidize the indole nucleus into a bromonium ion which is involved in dihydroxylation, hydroxycyclization and bromocyclization of indoles. Notably, we synthesized bromopyrroloindolines which are intermediates for the total synthesis of natural products. No organic byproducts are generated with this protocol which avoids the use of an additional electrolyte.