[BMIm]HSO4 as a Green and Highly Efficient Catalyst for One-pot Synthesis of 3-Substituted Indoles under Ultrasound Irradiation

A practical and green synthesis of 3-substituted indoles is reported via three-component coupling reaction of indoles, aldehydes and N-methylaniline in the presence of the acidic ionic liquid 1-butyl-3-methylimidazolium hydrogen sulfate ([BMIm]HSO4) under ultrasound irradiation at room temperature. The significant features of this procedure are high yields of the products, simple work-up, operational simplicity and non-toxicity of the catalyst. Moreover, [BMIm]HSO4 is successfully reused for four cycles without significant less of activity.