Exploring TiO₂ NPs as efficient catalyst for 1,6 Michael addition of 3-methyl-5-pyrazolone on 3-methyl-4-nitro-5-alkenyl isoxazoles and rapid synthesis of 3,3‐bis(indolyl)oxindoles in water

Abstract

We here present a report on development of a column chromatography free, heterogenous titanium dioxide nanoparticles (TiO2 NPs) catalyzed 1, 6 Michael addition of 3-methyl-5-pyrazolone on 3-methyl-4-nitro-5-alkenyl isoxazoles and rapid synthesis of 3,3-di(indolyl)indolin-2-ones by reaction of indole on isatin at room temperature in water for the first time. Moderate to good yield was obtained in case of 1, 6 Michael addition reaction and quantitative yield in case of a 3,3‐bis(indolyl)oxindole products. A scale up experiment on gram scale was performed successfully for both the reactions. Recyclability experiment was carried out for 4 cycles and turn over frequency (TOF) calculation for each cycle are presented for both reactions, which clearly indicate the sustainability of the protocol. In addition, green chemistry matrices (atom economy, reaction mass efficiency (RME), E-factor, process mass intensity (PMI)) values suggest that the presented methodology is green and eco-friendly.