The novel 4,10-dihydro-3H-pyridazino[1,6-b]isoquinolin-10-one heterocyclic system was synthesized by acid-catalyzed recyclization of 2-(difurylmethyl)benzohydrazides as well as by recyclization of (2-carboxyaryl)difurylmethanes to isocoumarins followed by the reaction with hydrazine hydrate.