Tetrahydrofuran → methyl 3-chloro-1-(pyridin-3-yl)-1H-pyrazole-5-carboxylate

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Reaction Steps

In step b of Scheme 2, methyl 3-chloro-1-(pyridin-3-yl)-4,5-dihydro-1H-pyrazole-5-carboxylate (6c) is oxidized with diammonium cerium (IV) nitrate (CAN) in water and polar solvents such as tetrahydrofuran at temperatures from about 0° C. to about 30° C. to yield methyl 3-chloro-1-(pyridin-3-yl)-1H-pyrazole-5-carboxylate (6d). It was surprisingly discovered that the oxidation in step b can also proceed with potassium permanganate (KMnO4) as the oxidant in polar solvents such as acetone at temperatures from about 0° C. to about 30° C. However, many standard oxidation procedures such as, for example potassium persulfate (K2S2O8), iodine pentoxide (I2O5), copper oxide (CuO), and hydrogen peroxide were found to be inoperative.

Provenance & Evidence