A mixture of 1-(3-chlorophenyl)-2-phenylethanone (450 mg, 1.95 mmol), 3-ethoxy-4-hydroxy-5-nitrobenzaldehyde (411 mg, 1.95 mmol), and urea (350 mg, 5.83 mmol) in anhydrous EtOH (15 mL) was added concentrated HCl solution (0.5 mL), the reaction mixture was refluxed overnight. TLC (EtOAc:MeOH=10:1) showed that about 30% of starting materials were consumed, and the reaction mixture was concentrated. The residue was purified by column chromatography (EtOAc:MeOH=40:1) and preparative HPLC to afford Compound 37 as a yellow solid (78.1 mg, yield: 8.6%). 1H NMR (DMSO-d6 400 MHz): δ 10.30 (s, 1H), 8.81 (s, 1H), 7.56 (s, 1H), 7.42 (d, J=1.2 Hz, 1H), 7.30 (d, J=8.0 Hz, 1H), 7.20-7.25 (m, 2H), 7.02-7.7.13 (m, 5H), 6.85 (d, J=6.8 Hz, 2H), 5.25 (d, J=2.8 Hz, 1H), 4.00-4.10 (m, 2H), 1.33 (t, J=6.8 Hz, 3H); MS (ESI): m/z 466.0 [M+1]+.
