Intramolecular [4+2] cycloaddition reactions of pyridazino-[4,5-d]pyridazines with acetylenic side-chain dienophiles: Synthesis of f-annelated phthalazines

Article abstract of DOI:10.1002/jhet.5570310217

Starting from the thione 1, a series of 1-(alkynyl-X)-4-phenylpyridazino[4,5-d]pyridazines 4-8 (X = O, NH, S) was prepared. Thermally induced intramolecular [4+2] cycloaddition reactions of the ethers 4, 5 and the thioether 8 afforded f-annelated phthalaz