A mixture of 3-aminorhodanine (148 mg, 1.00 mmol), 1-(3,4-dimethylphenyl)-5-hydroxy-3-methyl-1H-pyrazole-4-carbaldehyde (230 mg, 1.00 mmol) and ethanol (10 mL) was stirred 96 h. The solid was filtered, washed with ethanol and ether and dried. A mixture of the resulting crude imine (80 mg, 0.222 mmol), piperidine (2 mg, 0.022 mmol), 4-formylbenzoic acid (33 mg, 0.222 mmol), benzoic acid (3 mg, 0.022 mmol) and toluene (10 mL) was heated under reflux for 6 h in an apparatus fitted with a Dean and Stark separator to remove water. After cooling, the solid was filtered off, washed with toluene and ether, and purified by reverse phase HPLC (CombiPrep ODS-A, 10-90% acetonitrile/water+0.1% trifluoroacetic acid) to give the title compound (18 mg, 16%) as a solid. LCMS, m/e 493 [M+H]+.
