Electrochemical Synthesis of 3a-Bromofuranoindolines and 3a-Bromopyrroloindolines Mediated by MgBr2

We report an efficient and environmentally friendly electrochemical approach to perform the bromo cyclization of tryptophol, tryptamine and tryptophan derivatives. The 3a-bromofuranoindolines and 3a-bromopyrroloindolines obtained are of interest in the total synthesis of natural products. This dearomative procedure relies on the generation of an electrophilic bromine reagent by the electrochemical oxidation of MgBr₂. No organic byproducts are generated with this protocol which avoids the use of an additional electrolyte.