Synthesis of 4-aryl-5-hydroxy- and 5-aryl-4-hydroxypyridazin-3(2H)-ones and their use in the preparation of 4,5-diarylpyridazin-3(2H)-ones and hitherto unknown isochromeno[3,4-d]pyridazinediones

Easily accessible 2-substituted 4-aryl-5-methoxy- and 2-substituted 5-aryl-4-methoxypyridazin-3(2H)-ones were transformed into the corresponding aryl-hydroxypyridazin-3(2H)-ones by alkaline hydrolysis. The use of these compounds in the synthesis of 2-substituted 4,5-diarylpyridazin-3(2H)-ones with two differently substituted aryl groups was investigated. Two aryl-hydroxypyridazin-3(2H)-ones, 2-(2-benzyl-5-hydroxy-3-oxo-2,3-dihydropyridazin-4-yl)benzaldehyde and 2-(1-benzyl-5-hydroxy-6-oxo-1,6-dihydropyridazin-4-yl)benzaldehyde, were transformed into 2-benzyl-1H-isochromeno[3,4-d]pyridazine-1,6(2H)-dione and 3-benzyl-3H-isochromeno[3,4-d]pyridazine-4,6-dione, respectively, via oxidation of the formyl group with KMnO4 followed by lactonization.