Fluoroazoles. III. Synthesis and ¹H and ¹–⁹F nmr spectra of 3‐, 4‐, and 5‐fluoro‐1‐methylpyrazole

The three monofluoro derivatives of N ‐methylpyrazole have been synthesized. 3‐Fluoro‐1‐methylpyrazole and 4‐fIuoro‐1‐methylpyrazole were prepared from the appropriate amines by diazotization and photochemical irradiation of the diazonium salts in tetrafluoroboric acid. 5‐Fluoro‐1‐methylpyrazole was obtained from 1‐acetyl‐3‐fluoropyrazole and methyl fluorosulfonate, and also by direct methylation of 3(5) fluoropyrazole with dimethyl sulfate. The 1–9 F chemical shifts of these N ‐methylated fluoroazoles cover a great range ( ca . 50 ppm) and show a good correlation with the chemical shifts of H 3 , H 4 , and H 5 protons of 1‐methylpyrazole. An unexpected long‐range coupling 5 J (F‐CH 3 ) is observed in 3‐fluoro‐1‐methylpyrazole.