A novel and direct synthetic route to substituted 1,5-dihydro-4H-[1]benzopyrano[4,3-b]pyridine-4,5-diones

The condensation of 4-hydroxy-6-methyl-2H-pyran-2-one and substituted 2-hydroxybenzaldehydes with ammonium acetate gave the title heterocycles. Synthesis of 1,5-dihydro-2-methyl-4H-[1]naphtho-[1′,2′:5,6]pyrano[4,3-b]-pyridine-4,5-dione is also described. A reaction mechanism is discussed.