An underrated cheap Lewis acid: Molecular bromine as a robust catalyst for bis(indolyl)methanes synthesis

• A rare example of Br2 acting as a Lewis acid catalyst
• Extraordinarily high catalytic activity
• Wide substrate scope
• Could be conducted in either organic solvents or water

A discovery that inexpensive elemental bromine can act as a potent Lewis acid catalyst is disclosed. Under the catalysis of only 2 mol% of Br2, indoles reacted rapidly with carbonyl compounds to give bis(indolyl)methanes with extremely high efficiency and wide substrate scope. Moreover, a Br2-catalyzed aqueous-phase reaction is also presented to further demonstrate the power of this novel catalyst.

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