[NH:1]1[C:5]2=[N:6][N:7]=[CH:8][CH:9]=[C:4]2[CH:3]=[N:2]1.[I:10]I.[OH-].[K+].Br[CH2:15][C:16]([O:18][CH3:19])=[O:17]>CN(C=O)C.CCOC(C)=O>[I:10][C:3]1[C:4]2[C:5](=[N:6][N:7]=[CH:8][CH:9]=2)[N:1]([CH2:15][C:16]([O:18][CH3:19])=[O:17])[N:2]=1To a solution of 1H-pyrazolo[3,4-c]pyridazine [271-75-0] (450 mg, 3.75 mmol) in DMF (10 mL) was added iodine (951 mg, 3.75 mmol) and KOH (525 mg, 9.37 mmol). The mixture was stirred at RT for 16 h until completion of the reaction. Methyl 2-bromoacetate (0.380 mL, 4.12 mmol) was then added to the reaction mixture and stirring was continued at RT for 2 h. The mixture was diluted with EtOAc and washed with water (10 mL), the organic phase was dried (Na2SO4) and evaporated under vacuum. The crude mixture was purified by flash column chromatography on silica gel (c-Hex/EtOAc 66:33) to afford the title compound as a brown solid. TLC, Rf (c-Hex/EtOAc 1:1)=0.40; MS (LC/MS): 318.9 [M+H]+; tR (HPLC conditions c): 3.35 min.
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