Pyridine → 3-nitro-N-(3-phenyl-1H-indazol-5-yl)benzenesulfonamide

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3-Nitro-N-(3-phenyl-1H-indazol-5-yl)benzenesulfonamide can be obtained in the following way: 0.89 g of 3-nitrobenzenesulfonyl chloride is added to a solution, at a temperature in the region of 0° C. and under argon, of 0.7 g of 5-amino-3-phenyl-1H-indazole in 15 ml of THF. The reaction mixture is cooled to a temperature in the region of 0° C., and then a solution of 0.33 ml of pyridine in 4 ml of THF is added over 10 minutes. The reaction mixture is stirred at a temperature in the region of 0° C. for 0.5 hours then at a temperature in the region of 20° C. for 3 hours. It is then diluted with 70 ml of water and 30 ml of ethyl acetate. After settling out, the organic phase is washed with 3 times 50 ml of water, dried over magnesium sulfate, filtered and then concentrated to dryness under reduced pressure (2 kPa) at a temperature in the region of 40° C. The residue thus obtained is purified by chromatography on a silica column (particle size 63-200 μm), eluting with pure dichloromethane then with a dichloromethane/methanol (98/2 by volume) mixture. The fractions containing the expected product are pooled and concentrated to dryness under reduced pressure (2 kPa) at a temperature in the region of 40° C. The residue is taken up in 20 ml isopropanol and filtered through sintered glass. The solid is washed with 10 ml of diisopropyl ether, partially dried and then dried. 0.41 g of 3-nitro-N-(3-phenyl-1H-indazol-5-yl)benzenesulfonamide is thus obtained in the form of a white powder melting at 228° C. (analysis: C19H14N4O4S (0.44 CH2Cl2): % calculated C, 57.85; H, 3.58; N, 14.21; O, 16.23; S, 8.13. % found C, 57.84; H, 3.19; N, 14.22; S, 7.81).

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