General procedure for synthesis 3,5-dimethyl-1-aryl-1H-pyrazole
derivatives (3a-b)
To a solution of acetylacetone (98 mmol) in ethanol (150 mL), aryl
hydrazine (97.37 mmol) was slowly added. After cooling the reaction
mixture to 0oC, 5 mL of concentrated hydrochloric acid
was added. The reaction mixture was refluxed for 2 hours. After the
reaction was complete, ethanol was evaporated, then the crude product
was dissolved in DCM. The reaction mixture was treated with 10 % NaOH
solution to slightly basic (pH around 9). After this mixture was
extracted with dichloromethane (2x100 mL), the combined dichloromethane
solution was washed with brine and dried over anhydrous sodium sulfate.
The product was purified using column (EtOAc:hexane; 2:8)
3,5-dimethyl-1-phenyl-1H-pyrazole (3a): Yield 94%; red liquid;1H NMR (400 MHz, CDCl3) δ 7.38-7.23
(m, 5H), 5.94 (s, 1H), 2.25 (s, 3H), 2.24 (s, 3H). 13C
NMR (101 MHz, CDCl3) δ 148.92, 139.96, 139.34, 128.97,
127.20, 124.72, 106.93, 13.51, 12.36.
1-(2,4-dinitrophenyl)-3,5-dimethyl-1H-pyrazole (3b): Yield
90%; yellow solid; 1H NMR (400 MHz,
CDCl3) δ: 8.80 (d, J = 4.0 Hz, 1H), 8.55 (dd,J = 8.0 Hz, 4.0 Hz,1H), 7.72 (d, J = 8.0 Hz, 1H), 6.12 (s,
1H), 2.29 (s, 3H), 2.27 (s, 3H). 13C NMR (101 MHz,
CDCl3) δ 152.36, 146.22, 145.64, 140.90, 137.95, 129.33,
127.34, 120.99, 108.90, 77.38, 77.06, 76.74, 13.48, 11.61.