Acetic Acid → 3-Propyl-1,4-dihydropyrazol-5-one

Methyl butyrylacetate (4 g, 27.7 mmol) was stirred in ethanol and acetic acid (10:1, 8:0.8 mL) and treated with hydrazine (1.05 mL, 33.3 mmol). After 2 hrs, the resulting solid was filtered off and washed with a minimum amount of acetonitrile to yield 3-propyl-1H-pyrazol-5(4H)-one. Then, the 3-propyl-1H-pyrazol-5(4H)-one (4.68 g, 11.8 mmol) and 4-chloroquinoline N-oxide (1.5 g, 11.8 mmol) were stirred in acetic anhydride (20 mL) at ambient temperature for 30-40 minutes. The reaction mixture was concentrated, and the resulting solid filtered off, washed with a minimum amount of methanol, and treated with hydrazine (0.84 mL, 26.7 mmol) in methanol (12 mL) to yield Example 23 as a solid. 1H NMR (400 MHz, DMSO-d6) δ ppm 0.97 (t, J=7.33 Hz, 3H) 1.66-1.76 (m, 2H) 3.02 (t, J=7.07 Hz, 2H) 7.62 (t, J=7.58 Hz, 1H) 7.80 (t, J=7.71 Hz, 1H) 7.93 (d, J=8.34 Hz, 1H) 8.10 (d, J=8.34 Hz, 2H); ESI-MS: m/z calc'd for C15H14ClN3O 287.74. found 288.2 (M+H)+.