To a solution of sodium amide (215 mg, 5.5 mmol) in THF (5 mL) was added pinacolone (1.0 M THF solution, 5 mL, 5.0 mmol). The reaction mixture was refluxed at 80° C. for 30 min and then ethyl 5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxylate (4) (2.05 g, 5.0 mmol) in THF (15 mL) was added. The resulting solution was stirred and refluxed at 80° C. overnight. HCl aquous solution (11.0M, 50 mL) was added and extracted organic layer with ethyl acetate (50 mL twice). The combined organic phase was evaporated under vacuum. The crude residue was further purified by prep HPLC to provide 0.862 g (1.86 mmol, 37%) of the title compound.
