Synthesis of 6‐amino‐2‐aryl‐1,2‐dihydro‐3 H ‐pyrido[2,3‐ d ]pyrimidin‐4‐one derivatives

This paper reports the synthesis of new pyrido[2,3‐ d ]pyrimidin‐4‐one derivatives as diuretic agents. Starting with 1,2‐dihydro‐5‐nitro‐2‐oxo‐3‐pyridinecarboxylic acid 1 , ethyl 2‐ethoxy‐5‐nitro‐3‐pyridincarboxylate 4 was obtained. Compound 4 reacts with ammonia, methylamine or S ‐methylpseudothiourea to give the respective 2‐amino‐5‐nitro‐3‐pyridinecarboxamide derivatives 5 and 6 or 2‐methylthio‐6‐nitro‐3 H ‐pyrido[2,3‐ d ]pyrimidin‐4‐one 8. Treating carboxamide 5 with arylaldehydes and zinc dichloride, new 2‐aryl‐1,2‐dihydro‐6‐nitro‐3 H ‐pyrido[2,3‐ d ]pyrimidin‐4‐ones 9 were synthetised. These compounds reduced with iron(II) hydroxide gave 6‐amino‐2‐aryl‐1,2‐dihydro‐3 H ‐pyrido[2,3‐ d ]pyrimidin‐4‐ones 10 as expected.