3.2 Synthesis of 5-amino-4-cyano-1-phenyl-1H-pyrazole (3a)
Phenylhydrazine (2d) (0.45 mL, 4.2 mmol) was dissolved in ethanol (4 mL) with ethoxymethylene malononitrile (1b) (0.51 g, 4.2 mmol). Microwave irradiation was carried out using a CEM Discover microwave synthesizer at 120 °C for 45 min in a sealed pressure rated Pyrex tube (10 mL) with an initial power setting of 100 W. The reaction was carried out in a compressed air chamber with the microwave irradiated at 120 °C for 1 min. Upon completion of the reaction, the solvent was cooled in a stream of compressed air and subsequently removed by decompression distillation. The product was purified by silica gel column chromatography with petroleum ether/ethyl acetate (5:1 v/v) as eluent to afford 1-phenyl-4-cyano-5-aminopyrazole (0.738 g, 95% yield) as a light brown solid with a melting point of 137-139 °C (literature value: 137 °C). High-resolution mass spectrum (measured value: 185.0827, C10H9N4 [MH]+ calculated value: 185.0822); Fourier transform infrared spectra (KBr, cm?1) νmax: 3302 (NH), 3240 (NH), 2230 (CN), 1577, 1530, 1368; 1H NMR (400 MHz, CDCl3) δ: 7.58 (1H, s, H-3), 7.49-7.37 (5H, m, Ph), 4.52 (2H, br s, disappears after exchange of D2O, NH2); 13C NMR (100 MHz, CDCl3) δ: 141.9 (CH), 135.0 (C), 129.3 (CH), 125.5 (CH), 124.1 ( CH), 121.3 (CH), 115.6 (C), 86.2 (C); low resolution mass spectra (APcI) m/z (relative intensity): 226 ([M + MeCNH]+, 100), 185 ([MH]+, 64).
