General procedure for the synthesis of ethyl 1-benzyl-4-keto-3-pyrrolidinecarboxylate from ethyl 3-(benzyl(2-ethoxy-2-oxoethyl)amino)propanoate: 1127.324 g of the crude product, compound (c), was dissolved in anhydrous 2.5 L of toluene, and 243.028 g of potassium tert-butanolate was slowly added under ice bath conditions with continuous stirring for 2 hours. The reaction process was monitored by thin layer chromatography (TLC). Upon completion of the reaction, the reaction solution was adjusted to acidic by adding 4 M hydrochloric acid in an ice bath, followed by adjusting the pH to 8 with saturated sodium bicarbonate solution.The reaction mixture was extracted with ethyl acetate, and the organic phase was dried with anhydrous sodium sulfate, filtered, and then concentrated by rotary evaporator to give 376.7 g of the pink solid compound (d) in 98% yield.
