N-[4,5-Dihydro-5-oxo-1-(2,4,6-trichlorophenyl)-1H-pyrazol-3-yl]-N-methyl-3-aminobenzamide (8.2 g, 19.9 mmole) was dissolved in a mixture of tetrahydrofuran (100 ml) and pyridine (20 ml) and cooled in an ice bath. 2,4-Di-t-pentylphenoxyacetyl chloride (20.5 mmole) was dissolved in tetrahydrofuran (20 ml) and added dropwise to the stirred mixture. Stirring was continued for 1 hr and the mixture was then poured into stirred dilute hydrochloric acid (1.51), the oil extracted into ethyl acetate and the extract washed and dried. The solvent was removed by evaporation and replaced with ethanol (100 ml). A solution of sodium hydroxide (0.8 g, 20 mmole) in water (5 ml) was added dropwise and the mixture stirred for 15 min. The oil gradually dissolved and a solid gradually formed. The mixture was poured into dilute hydrochloric acid (11) and the pale orange solid filtered off washed and dried. The solid was chromatographed on silica gel using 1:1 60-80 petroleum ether: ethyl acetate as eluent to give the product as a white glass, 6.9 g, 50%.
