Trifluoroacetic acid → 6-Chloro-2-(4-fluorophenyl)pyrazolo[1,5-a]pyridine

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Reaction Steps

Solid t-butoxycarbonyl-O-mesitylenesulfonylhydroxylamine (8.45 g 26.8 mmol) was added portionwise with stirring to TFA (100 ml) over 10 min then stirred for a further 30 minutes. The solution was poured onto ice (˜250 ml) and left until the ice melted. The resulting white solid was filtered off, washed with water, and dissolved in chloroform (200 ml). The solution was dried over 4 Å mol. sieves for 1.5 hours, filtered and 2-(5-chloropyridin-2-yl)-1-(4-fluorophenyl)ethanone oxime (3.56 g 13.4 mmol) in chloroform (100 ml) was added. The reaction was stirred at room temperature for 18 hours, washed with water (2×50 ml) and dried. Removal of solvent gave a brown solid which was purified by Biotage chromatography. Elution with cyclohexanelethyl acetate (35/1) gave the title compound as a yellow solid (2.476 g 75%). NMR (CDCl3) δ 6.76 (1H, s, H-3); 7.08 (1H, dd, J 9 & 2 Hz, H-5); 7.13 (2H, t, J 9 Hz, H-3′); 7.45 (1H, d, J 9 Hz, H-4); 7.9 (2H, dd, J 9 & 5 Hz, H-2′); 8.5 (1H, d, J 2 Hz, H-7);

Provenance & Evidence