Enantioselective Michael‐Type Friedel–Crafts Reactions of Indoles to Enones Catalyzed by a Chiral Camphor‐Based Brønsted Acid

Abstract Chiral Brønsted acid, D‐camphorsulfonic acid, was found to be practical and efficient in the catalysis of the enantioselective Michael‐type Friedel–Crafts reactions of indoles with aromatic enones to afford the corresponding β‐indolyl ketones in excellent yields and moderate enantioselectivities. A surprising synergistic effect was discovered between BmimBr and D‐CSA which leads to active catalytic systems for the Friedel–Crafts reaction. The efficiency of these systems might result from the catalytic Lewis acid activation of the Brønsted acids. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)