Orange Juice: A Remarkable Green Catalyst for the Michael Addition Reaction of Indoles

Abstract

Michael addition reaction is widely accepted as the most important reaction for making carbon-carbon bonds in the synthesis of organic compounds. In this reaction, an enone is attacked by a nucleophile in a conjugated manner across a carbon-carbon double bond. The present work reported the Michael reaction of indole with α,β-unsaturated ketones via alkylation to yield 3-(3-oxoalkyl) indole or β-indolyl ketones. Naturally available orange juice has been demonstrated to be an efficient green catalyst for the Michael addition reaction of indoles with various cyclic and acyclic unsaturated ketones. The products were characterised by 1H NMR spectroscopy and compared with literature. This one-step, simple process has afforded the 3-indolyl carbonyl compounds in short reaction times and excellent yields at room temperature. The present method developed an inexpensive synthetic process to prepare substituted indoles in a simple and eco-friendly way.