Hydrochloric Acid → HCID 70429717, compound

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(6,7-Dichloro-2-cyclopentylmethyl-2,3-dihydro-2-methyl-1-oxo-1H-inden-5-yl)acetamide (5 g., 0.0141 mole) and diethyl oxalate (2.19 g., 0.015 mole) are dissolved in dry dimethylformamide (30 ml.) and stirred in an ice bath under nitrogen for 20 minutes. Potassium t-butoxide (3.53 g., 0.0315 mole) is then added in two portions 15 minutes apart. The mixture is stirred while cooling in the ice bath for another 45 minutes, then stirred at room temperature for 18 hours and poured into ice water (500 ml.) The mixture is acidified with hydrochloric acid and extracted with ether (4×125 ml.). The combined organic extracts are washed with water and then repeatedly extracted with dilute sodium carbonate. The combined aqueous extracts are acidified with hydrochloric acid, extracted with methylene chloride and then with ether. The combined organic extracts are washed with water, dried over magnesium sulfate and concentrated under vacuum. The residue is chromatographed on silica (175 g.) with a mixture of toluene, dioxane and acetic acid (50:5:1). The appropriate product fractions are concentrated under vacuum and the residue is dissolved in ether and extracted with dilute sodium bicarbonate. The aqueous extracts are acidified with hydrochloric acid and extracted with methylene chloride and then with ether. The combined organic extracts are washed with water, dried over magnesium sulfate and concentrated under vacuum to obtain the 3-(6,7-Dichloro-2-cyclopentylmethyl-2,3 -dihydro-2-methyl-1-oxo-1H-inden-5-yl)-4-hydroxy-1H-pyrrole-2,5-dione as a foam which was then dried under high vacuum at 90° C. for 2 hours to give 3.6 g. (63%).

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