Halogen Bond-Catalyzed Friedel-Crafts Alkylation of Indole with Ketones and Aldehydes for the Synthesis of Symmetrical 3,3’-diindolylmethanes Using Simple Halogen Donor Catalyst

The Friedel-Crafts alkylation of indole with ketones and aldehydes had been developed to prepare 3,3’-diindolylmethanes using iodine or NCS as catalysts. Two mild and efficient catalysis systems were provided for the activation of carbonyl compounds and indoles. The reaction proceeded smoothly in ethanol to produce the corresponding products with good to excellent yields. Furtherly, the mechanism was speculated.