[CH3:1][O:2][C:3]1[CH:24]=[CH:23][C:6]([CH2:7][N:8]2[C:12]3[NH:13][CH:14]=[C:15]([C:18]([O:20][CH2:21][CH3:22])=[O:19])[C:16](=O)[C:11]=3[CH:10]=[N:9]2)=[CH:5][CH:4]=1.O=P(Cl)(Cl)[Cl:27]>ClCCCl>[Cl:27][C:16]1[C:15]([C:18]([O:20][CH2:21][CH3:22])=[O:19])=[CH:14][N:13]=[C:12]2[N:8]([CH2:7][C:6]3[CH:23]=[CH:24][C:3]([O:2][CH3:1])=[CH:4][CH:5]=3)[N:9]=[CH:10][C:11]=12To a solution of ethyl 1-(4-methoxybenzyl)-4-oxo-4,7-dihydro-1H-pyrazolo[3,4-b]pyridine-5-carboxylate (4.0 g, 13 mmol) in 1,2-dichloroethane (9.8 mL) was added POCl3 (2.4 mL, 26 mmol). The resulting mixture was heated at 90° C. for 3 h. After cooling, the most volatile were removed by vacuum, and the residue was diluted with EtOAc and washed with aq. Na2CO3 solution. The organic layer was washed water and brine, dried and concentrated under reduced pressure. The residue was purified by column chromatography on silica gel using CombiFlash® apparatus, eluting with 10 to 60% EtOAc in hexanes, to give the sub-title compound (3.9 g, 95%). LCMS calc. for C17H17ClN3O3 (M+H)+: m/z=346.1. Found: 346.1.
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