Hydrochloric Acid → Ethyl 5-chloro-1-(pyridin-2-YL)-1H-pyrazole-4-carboxylate

Beteiligte Stoffe

Reaktionsschritte

The product from Example 4, 21.6 g, was dissolved in 100 mL of concentrated hydrochloric acid at 0° C. To this resulting clear solution was added a solution of sodium nitrite, 7.3 g, in 10 mL of water at 0° C. during 15 minutes. The resulting suspension was stirred an additional 30 minutes then added portionwise during 10 minutes to a solution of cuprous chloride, 9.3 g, in 100 mL concentrated hydrochloric acid. The reaction was very exothermic and accompanied by rapid nitrogen evolution. The suspension was then heated on the steambath until a test for diazonium salts was negative. The contents of the flask were cooled and the pH of the suspension adjusted to 8 with ammonium hydroxide and finally diluted with 100 mL of water. The solid were removed from the reaction by filtration through Celite® and the aqueous filtrate was washed with 200 mL of methylene chloride. After separating and drying the organic solution with anhydrous sodium sulfate, 17.4 g of a light brown oil was isolated after removal of the solvent by evaporation. The crude oil was flash chromatographed in Kieselgel 60, 230-400 mesh, using 1-1 hexanes/ethyl acetate as the eluent. 14.2 g of the title compound was obtained melting at 52°-53° C.

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