Hydrochloric Acid → 5-Amino-3-(phenylethynyl)-1-{[2-(trimethylsilyl)ethoxy]methyl}indazole

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Reaction Conditions

Reaction Steps

5-Amino-3-phenylethynyl-1-(2-trimethylsilanylethoxymethyl)-1H-indazole can be obtained in the following way: 18 ml of water, 0.2 ml of an aqueous 12N hydrochloric acid solution and 0.36 g of powdered iron are added to a solution of 0.84 g of 5-nitro-3-phenylethynyl-1-(2-trimethylsilanylethoxymethyl)-1H-indazole in 15 ml of absolute ethanol, at the reflux temperature of the solvent. The reaction mixture is then stirred at the reflux of the solvent for 4 hours, and is then cooled to a temperature in the region of 20° C. After filtration through Celite® and washing with absolute ethanol, the filtrate is concentrated to dryness under reduced pressure (2 kPa) at a temperature in the region of 35° C. The residue thus obtained is purified by chromatography under argon pressure (50 kPa), on a column of 60 g of silica (particle size 40-63 μm), eluting successively with cyclohexane/ethyl acetate (95/5; 90/10; 80/20; 70/30; 60/40; 50/50; 30/70 by volume) mixtures, and then with pure ethyl acetate and, finally, with pure ethanol. The fractions containing the expected product are pooled and concentrated to dryness under reduced pressure (2 kPa) at a temperature in the region of 35° C. 0.11 g of 5-amino-3-phenylethynyl-1-(2-trimethylsilanylethoxymethyl)-1H-indazole is thus obtained in the form of a brown oil (Rf=0.47, silica gel thin layer chromatography, eluent: cyclohexane/ethyl acetate (60/40 by volume)). 0.2 g of 5-amino-3-phenylethynyl-1H-indazole is also obtained in the form of a brown oil (Rf=0.17, silica gel thin layer chromatography, eluent: cyclohexane/ethyl acetate (60/40 by volume)).

Provenance & Evidence