Electrochemical bromocyclization enables 3,5-diversification of heterocyclic indolines

Electrophilic bromocyclization reactions are widely used as key steps in the synthesis of diverse functionalized tetrahydrofuroindolines and hexahydropyrroloindolines. However, the direct dibromination variants of these reactions for the synthesis of 3,5-dibromoindolines remain undeveloped. Here, we report a protonic-acid-promoted electrooxidative protocol for the dearomative C3,C5-dibromocyclizations of tryptophol and tryptamine derivatives. This electrosynthetic approach, which enables direct selective construction of heterocyclic 3a,5a-dibromoindolines with inexpensive, non-hazardous NaBr as both the electrolyte and Br source, provides a convenient, practical method for the late-stage 3,5-diversification of heterocyclic indolines.