Tautomeric variety and methylation of 3,6-dihydroxy-4-methylpyridazine

The method of exhaustive methylation has been applied for investigating tautomeric stability and its temperature variation of 6-hydroxy-5- methyl-3-pyridazinone (1) and its N-phenyl derivative (2)—two model compounds chosen for studying tautomeric transformations of pyridazine medicinal drugs, either in the process of their production, or then their activity in the living tissue. The resulting N-methylated and O-methylated products were separated, and characterized by 1H NMR and X-ray diffraction. The methylation of 1 and 2 in the dimethyl sulfate as well as in its aqueous solution leads predominantly to the O-methylated forms, but the rising temperature favours the Nmethylation. q 2004 Elsevier B.V. All rights reserved.