Revisiting the three component synthesis of isoxazolo[5,4-b]pyridines, 4-aryl-3,7,7-trimethyl-isoxazolo[5,4-b]quinolin-5(6H)-ones and related heterocycles

The one-step three-component microwave assisted synthesis between aromatic aldehydes with tetronic acid or 1,3-indandione readily produced Knoevenagel adducts that underwent addition of 3-methylisoxazol-5-amine (1) to form the isoxazolopyridine products (8). With dimedone, the Knoevenagel adduct was generated using 2-hydroxyammonium formate and then reacted with 1 to give pure products.