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.