5-nitro-3-phenylsulfanyl-1-(2-trimethylsilanylethoxymethyl)-1H-indazole → 5-amino-3-phenylsulfanyl-1-(2-trimethylsilanylethoxymethyl)-1H-indazole

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5-Amino-3-phenylsulfanyl-1-(2-trimethylsilanylethoxymethyl)-1H-indazole can be obtained in the following way: a solution of 0.4 g of 5-nitro-3-phenylsulfanyl-1-(2-trimethylsilanylethoxymethyl)-1H-indazole in 16 ml of ethyl acetate containing 40 mg of 10% palladium-on-charcoal is hydrogenated under a pressure of 200 kPa at a temperature in the region of 25° C. for 18 hours. After filtration of the catalyst through Celite® under argon and washing with ethyl acetate, the filtrate is concentrated to dryness under reduced pressure (2 kPa) at a temperature in the region of 25° C. 0.33 g of crude 5-amino-3-phenylsulfanyl-1-(2-trimethylsilanylethoxymethyl)-1H-indazole is thus obtained in the form of a burgundy-colored oil. A second attempt using 1.1 g of 5-nitro-3-phenylsulfanyl-1-(2-trimethylsilanylethoxymethyl)-1H-indazole makes it possible to obtain, in the same way, 0.99 g of crude 5-amino-3-phenylsulfanyl-1-(2-trimethylsilanylethoxymethyl)-1H-indazole in the form of a burgundy-colored oil. The two crude products are pooled and purified by chromatography under argon pressure (50 kPa), on a column of 53 g of silica (particle size 40-63 μm), eluting successively with pure cyclohexane then with cyclohexane/ethyl acetate (97/3; 95/5; 90/10; 80/20 by volume) mixtures. The fractions containing the expected product are pooled and concentrated to dryness under reduced pressure (2 kPa) at a temperature in the region of 30° C. 0.78 g of 5-amino-3-phenylsulfanyl-1-(2-trimethylsilanylethoxymethyl)-1H-indazole is thus obtained in the form of a burgundy-colored oil (El mass analysis: m/z 371 (M+) (base peak)).

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