Synthesis
4.1.1.1 Synthesis of 5-(4-methylphenyl)-1H-pyrazole-3-carboxylic acid (1): 0.4 g of 4-(4-methylphenyl)-2,4-dioxobutanoic acid and 20 mL of glacial acetic acid were added to a 50 mL round bottom flask. Under stirring conditions, 280 μL (3 equivalents) of hydrazine monohydrate (N2H4-H2O) was added slowly and dropwise. Immediately after the dropwise addition of hydrazine, the solution changed to a light yellow color. The reaction process was monitored by thin layer chromatography (TLC). After completion of the reaction, the reaction mixture was poured into 50 mL of water and stirred overnight. The white precipitate was collected by filtration, dried in air and subsequently recrystallized by hexane/ethanol (ca. 9:1) solvent mixture to give 0.34 g of product in 87% yield.4.1.2.14 Synthesis of 5-(naphthalen-2-yl)-1H-pyrazole-3-carboxylic acid (14): 0.58 g of 4-(naphthalen-2-yl)-2,4-dioxobutyric acid was used as a starting material and following the same steps as above operation, 0.49 g of product was obtained in 82% yield. The product is a white solid with a melting point of 274-276°C (decomposition). Molecular formula: C14H10N2O2, molecular weight: 238.24. ESI-MS: calculated value [M+H]+: 239.08150, measured value: 239.08065. IR (ν, cm-1): 3206 (N-H stretching vibration), 1683 (C=O stretching vibration), 1501,1274. 1H NMR (200MHz, DMSO-d6): 3206, 1683, 1501,1274. DMSO-d6) δ (ppm): 7.23 (s, 1H), 7.50 (t, J=3.93 Hz, 2H), 7.89 (d, 7.95 Hz, 1H, overlapping bimodal peaks), 7.95 (d, J=8.42 Hz, 2H), 8.04 (d, J=8.42 Hz, 1H), 8.39 (s, 1H).13C NMR ( 50MHz, DMSO-d6) δ (ppm): 104.77,123.81,124.00,126.23,126.71,127.93,128.31,128.55,130.40,132.77,133.50,141.89,149.21,163.07.
References
[1] Bioorganic and Medicinal Chemistry, 2015, vol. 23, # 15, p. 4649 - 4659
