[Br:1][C:2]1[C:3]([Cl:11])=[C:4]2[C:8](=[CH:9][CH:10]=1)[NH:7][N:6]=[CH:5]2.[CH2:12]1[CH2:17][O:16][CH:15]=[CH:14][CH2:13]1.CC1C=CC(S(O)(=O)=O)=CC=1.C([O-])(O)=O.[Na+]>ClCCl>[Br:1][C:2]1[C:3]([Cl:11])=[C:4]2[C:8](=[CH:9][CH:10]=1)[N:7]([CH:15]1[CH2:14][CH2:13][CH2:12][CH2:17][O:16]1)[N:6]=[CH:5]2To a mixture of 5-bromo-4-chloro-1H-indazole (8.0 g, 34.6 mmol) and DHP (8.72 g, 0.104 mol) in dry dichloromethane (200 mL) was added PTSA (0.657 g, 3.46 mmol) at room temperature. The resulting mixture was stirred at room temperature overnight. Upon completion, saturated aqueous NaHCO3 (100 mL) was added slowly to the reaction mixture. The organic layer was separated, dried over Na2SO4, and concentrated in vacuo. The residue was purified by column chromatography on silica gel (0-3% EtOAc in petroleum ether) affording the title compound (8.9 g). 1H NMR (300 MHz, DMSO-d6): δ 8.19 (s, 1H), 7.71 (m, 2H), 5.88 (dd, 1H), 3.89-3.84 (m, 1H), 3.79-3.73 (m, 1H), 2.42-2.32 (m, 1H), 2.05-1.95 (m, 2H), 1.75-1.70 (m, 1H), 1.60-1.54 (m, 2H).
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