Photochemistry. VI. Photo-induced Methylation of Pyridazines

Irradiation of Pyridazine (Ia) in methanol containing 5% HC1, afforded 4-methylated and 4, 5-dimethylated compounds. 3-Methylpyridazine (Ib) gave 4-methylated compound, along with 5-methylated and 4, 5-dimethylated compounds. 3-Methoxypyridazine (Ic) afforded 4-methylated and 4, 6-dimethylated compounds. 3, 6-Dimethylpyridazine (Ie) gave 4-methylated and 4, 5-dimethylated compounds. 3-Methoxy-6-methylpyridazine (If) gave 4-methylated compound as a sole product. 3-Methyl-6-chloropyridazine (Ig), 3, 6-dichloropyridazine (Ih), and 3-phenyl-6-chloropyridazine (Ii) afforded 5-methylated and 4, 5-dimethylated compounds, respectively. 3-Chloropyridazine (Id) did not give monomethylated, but 4, 5-dimethylated compound in a low yield. of 1-2%, presumably due to the unstability and the decomposition of the starting material.