General procedure for the synthesis of methyl 4-(3,4-dichlorophenyl)-2,4-dicarbonylbutyrate from dimethyl oxalate and 3,4-dichloroacetophenone: dimethyl oxalate (5.9 g, 50 mmol) was slowly added to a suspension of freshly prepared sodium methanolate (3.24 g, 60 mmol) in anhydrous toluene at 8-10 °C. Subsequently, 3,4-dichloroacetophenone (6.7 g, 50 mmol) was added dropwise over 30 min. The reaction mixture was stirred overnight at 8-10 °C and under nitrogen protection. After completion of the reaction, the yellow precipitate was obtained by filtration and washed with toluene (2 x 20 ml), then the precipitate was dissolved in water (20 mL) and acidified by adding 25 ml of 6N HCl. The organic layer was extracted with diisopropyl ether, followed by washing the organic layer with brine, drying with anhydrous sodium sulfate, and finally evaporating the solvent to give pure methyl 4-(3,4-dichlorophenyl)-2,4-dicarbonylbutyrate (8a-e) as a yellow solid in good yield.
