Pyridine → 1-Acetyl-1,2-dihydro-3H-pyrazol-3-one

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A mixture of 1,2-dihydro-3H-pyrazol-3-one (4.50 g, 26.8 mmol), in pyridine (20.4 mL, 252 mmol) was heated to 95° C. then charged with a solution of acetic anhydride (5.10 mL, 54.0 mmol) in pyridine (9.64 mL, 119 mmol) over a 15 min period. The reaction was heated for an additional 1 h at 95° C. The reaction mixture was concentrated in vacuo resulting in a dark red oil which was triturated with MeOH and filtered resulting in the title compound as a light yellow solid. A 2nd crop of product was isolated from the mother liquors. 1H NMR (400 MHz, DMSO-d6): δ=2.48 (s, 3H) 6.00 (d, J=3.0 Hz, 1H), 8.12 (d, J=3.0 Hz, 1H), 10.95 (br. s., 1H). MS (ES+): m/z 127.23 (100) [MH+]. HPLC: tR=0.82 min (polar—5 min, ZQ3).

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