[N:1]1[CH:6]=[CH:5][C:4]([C:7]([OH:9])=[O:8])=[CH:3][N:2]=1.CO.[CH2:12](Cl)Cl>>[CH3:12][C:3]1[N:2]=[N:1][CH:6]=[CH:5][C:4]=1[C:7]([OH:9])=[O:8]To a solution of 4-pyridazinecarboxylic acid (490 mg, 3.9 mmol) in MeOH/DCM (20/10 ml) was added at 0° C. trimethylsilildiazomethane (25.5 mmol). The solution was warm at r.t. and stirred overnight. Volatiles were evaporated in vacuo, the crude dissolved in DCM, washed with NaHCO3 satured and dried over Na2SO4. After filtration and concentration to dryness in vacuo, the crude was purified by column chromatography (DCM:MeOH=98 to 2) to give 400 mg of the title compound.
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