Camphor Sulfonic Acid-Catalyzed Michael Reaction of Indoles with Enones

Background: Michael addition reaction is one of the most important and widely used reactions for making carbon-carbon or carbon-hetero bonds in organic synthesis. The reaction involves a facile attack of nucleophile to enone in a conjugated manner across a carbon-carbon double bond. We herein report an expeditious camphor sulfonic acid-catalyzed Michael reaction for the synthesis of different 3-substituted indole derivatives at room temperature. This method is convenient, environmentally friendly and produces products in high yields. Method: Commercially available camphor sulfonic acid is used as organo-catalyst to activate the reaction. The newly synthesized compounds are characterized by using (HNMR)-H-1, C-13 NMR and IR spectroscopy. Result: A highly substituted 3-indoyle carbonyl compounds has been synthesized in excellent yield under very mild reaction conditions. Conclusion: We developed an environmentally benign synthetic method to access novel synthesis of substituted indoles under remarkably simple and high yielding reaction.