Friedel–Crafts alkylation of indoles with β-nitroalkenes using ammonium niobium oxalate as a recyclable catalyst

Abstract

An environmentally benign method has been developed for the Friedel–Crafts alkylation of indoles with nitroalkenes using ammonium niobium oxalate (ANO) as a recyclable catalyst. The reactions were carried out under mild conditions with a low catalyst loading using a green solvent, a water–ethanol mixture. ANO was compatible with a variety of substituted indoles and β-nitroalkenes, including aromatic, heterocyclic and organometallic substrates, and the desired products were obtained in good yields. The catalyst was used for seven cycles without considerable loss in its activity. Overall, the high turnover number (TON) and mild reaction conditions make this method a sustainable and efficient one for synthesizing C3-alkylated indole derivatives.