We report the syntheses of 5-alkyl or 5-aryl-3, 5-dihydro [4, 5-d] imidazo-4-pyridazinones (or the 1, 5-dihydro derivatives) from the corresponding diaminopyridazinones. The methylation of 5-alkyl or 5-aryl-2-mercapto-3, 5 (or 1, 5)-dihydro [4, 5-d] imidazo-4-pyridazinones leads to mixtures of 5-alkyl or 5-aryl-1 methyl-2-methylthio-3, 5 (1, 5)-dihydro [4, 5-d] imidazo-4- pyridazinones and 5-alkyl or 5-aryl-3-methyl-2-methylthio-3, 5 (or 1, 5)-dihydro [4, 5-d] ...
