Efficient and Eco-Friendly Procedure for the Synthesis of 2-Amino-4H-Chromenes Catalyzed by Diammonium Hydrogen Phosphate

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An efficient and eco-friendly protocol for the preparation of 2-amino-4H-chromenes employing a multi-component, one-pot condensation reaction between aromatic aldehydes, malononitrile and1-naphthol has been developed. The reaction of 1-naphthol with malononitrile and various aromatic aldehydes was carried out in water-ethanol (1:1) at reflux using 20 mol% of diammonium hydrogen phosphate as catalyst. The results show that aromatic aldehydes containing electron-donating groups or electron-withdrawing groups could react smoothly to give the corresponding products in good to excellent yields. It was also found that diammonium hydrogen phosphate can be recycled at least four times without loss of activity. The operational simplicity, easy work-up, short reaction time, together with the use of non-toxic, commercially available, inexpensive and recyclable catalyst are remarkable features of the procedure.