General procedure for the synthesis of ethyl 5-isopropylpyrazole-3-carboxylate from ethyl 2,4-dioxo-5-methyl-hexanoate: a mixture of ethyl 2,4-dioxo-5-methyl-hexanoate (1 g, 5.37 mmol) and hydrazine hydrate (10.7 mmol, 9.64 mol/L) in ethanol (20 mL) was stirred for 1 hr at 75 °C under nitrogen atmosphere. After completion of the reaction, the mixture was concentrated under vacuum. The residue was purified by silica gel column chromatography using petroleum ether: ethyl acetate (2:1, v/v) as eluent to afford ethyl 5-isopropylpyrazole-3-carboxylate (0.55 g, 56% yield) as a light yellow solid. Mass spectrum (ESI, positive ion mode) m/z: 183.1 [M + H]+. 1H NMR (600 MHz, CDCl3) δ: 11.37 (br s, 1H), 6.63 (s, 1H), 4.40-4.37 (m, 2H), 3.07-3.05 (m, 1H), 1.43-1.40 (m, 3H), 1.39- 1.30 (m, 6H).
