Cu(
Under the catalysis of 1 mol% of Br2 or HBr at room temperature, indoles undergo a rapid reaction with 3-hydroxy-3-(indol-3-yl)indolin-2-ones to give asymmetric 3,3-di(indol-3-yl)indolin-2-ones with high efficiency and wide substrate scope. This is a rare example of Br2 acting as a Lewis acid catalyst. Theoretical calculations suggest that both the catalytic activity of the catalysts and the stability of reaction intermediates are responsible for the high efficiency of this reaction.