Benign synthesis of N-aryl-3,10-dihydroacridin-1(2H)-one derivatives via ZnO nanoparticle-catalyzed Knoevenagel condensation/intramolecular enamination reaction

An efficient construction of 2-(N-arylamino)benzaldehydes and N-aryl-3,10-dihydroacridin-1(2H)-one derivatives starting from 2- hydroxybenzaldehydes has been developed. The synthesis of N-aryl-3,10-dihydroacridin-1(2H)-ones is based on the Knoevenagel condensation of dimedone to various 2-(N-arylamino)benzaldehydes, followed by an intramolecular enamination in the presence of 20 mol% of nanocrystalline ZnO. Moderate to high yields, operation simplicity, and cheap starting materials are the key features of the present method. The structures of the products were confirmed by 1H and 13C NMR spectroscopy and mass spectrometry (EI). Probable mechanisms for the present reactions to account for the formation of 2-(N-arylamino)benzaldehydes 3a-h and N-aryl-3,10-dihydroacridin-1(2H)-one derivatives 4a-h are also reported.