New Pathway for the Synthesis of Pyrimido[4,5‐b]quinolines via One‐pot Reaction of Isatins, 6‐Aminouracils and 1,3‐Dimethylbarbituric Acid

The reaction between 6‐aminouracils and isatins having no substitution on nitrogen was carried out in acetic acid at 80 °C. This was followed by the oxidative decarboxylation of the resulting intermediates in the presence of Pb(OAc) 4 , resulting in the synthesis of the corresponding 6‐aminouracil substituted pyrimido[4,5‐ b ]quinolines with good to excellent yields. Additionally, the reaction of 6‐aminouracils, isatin derivatives, and 1,3‐dimethylbarbituric acid yielded similar results, and the corresponding products were efficiently obtained with symmetric and asymmetric structures. Furthermore, N ‐substituted isatins were also subjected to the reaction conditions and the resulted spirooxindoles prepared, showing resistance against oxidation with (Pb(OAc) 4 . Notably, the condensation reaction of N ‐substituted isatins with N ‐arylaminouracils was also investigated, leading to spiro[indoline‐3,5′‐pyrimido[4,5‐ b ]quinoline] derivatives.