A combination of green solvent and ultrasonic irradiation promotes the catalyst-free reaction of aldehydes, indoles and Meldrum's acid

A facile and practical approach for the preparation of 3-indole derivatives was performed by the Yonemitsu condensation of indoles with Meldrum's acid and aldehydes in a mixture of solvent from glycerol and water under ultrasonic irradiation at room temperature without catalyst. A series of aromatic aldehydes representative of various electronic and steric conditions were employed to examine the scope of substrates for this protocol in moderate to good yields. No catalyst, clean reaction conditions, tolerating the substrates with diverse functional groups and an environmentally acceptable medium are the best features in this process.