To a solution of 1,2-diphenylethanone (46 mg, 0.233 mmol), 3-(isoxazol-4-yl)benzaldehyde (Intermediate 46) (36 mg, 0.209 mmol) and urea (48 mg, 0.627 mmol) in EtOH (10 mL) was added concentrated HCl (0.4 mL). The mixture was stirred at 85° C. for 14 h. The volatiles were removed under reduced pressure and the residue was purified by silica gel column chromatography (PE:EA=1:1) to afford Compound 91 as an off-white power (18 mg, 22.2%). 1H NMR (MeOH-d4 500 MHz): δ 8.99 (s, 1H), 8.74 (s, 1H), 7.50-7.53 (m, 2H), 7.39-7.50 (m, 2H), 7.23-7.25 (m, 5H), 7.00-7.02 (m, 2H), 6.84-6.87 (m, 2H), 5.35 (s, 1H); MS (ESI): m/z 394.1 [M+1]+.
