Pyridazine derivatives and related compounds, Part 21: Synthesis of different heterocycles from 2-methyl-4H-pyridazino{[}4 `,3 `: 4,5]thieno{[}3,2-d]-1,3-oxazin-4-one

Starting with ethyl 5-amino-3,4-diphenylthieno{[}2,3-c] pyridazine-6-carboxyl-ate, the syntheses of 2-methyl-8,9-diphenyl-4H-pyridazino{[}4', 3': 4,5] thieno{[}3,2-d]1,3-oxazin-4-one (1), 7-amino-6-methyl-8-oxo-3,4-diphenyl-7,8-dihydropyrimido{[}4',5': 4,5] thieno{[}2,3-c] pyridazine (3), and some related compounds are described.