Acetic Acid → 1-(6-Benzyloxycarbonylamino-hexanoyl)-4-oxo-pyrrolidine-3-carboxylic Acid Ethyl Ester

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To a suspension of potassium t-butoxide (7.12 g, 64 mmol) in toluene (150 mL) at 0° C. under nitrogen, was added diester 59 (20 g, 44 mmol) in toluene (25 mL) over a 10 min period. The solution was stirred for 30 min at 0° C. and 5 mL of glacial acetic acid was added, immediately followed by 25 g of NaH2PO4.H2O in 250 mL of ice-cold water. The resultant mixture was extracted with chloroform (3×200 mL), and the combined organic extracts were washed twice with phosphate buffer (2×25 mL, pH=7.0), dried over anhydrous sodium sulfate and evaporated to dryness. The residue was dissolved in toluene (300 mL), cooled to 0° C., and extracted with cold pH 9.5 carbonate buffer (3×150 mL). The aqueous extracts were converted to pH 3 with phosphoric acid, and extracted with chloroform (5×125 mL) which were combined, dried, and evaporated to a afford keto ester 60 (12 g, 45%).

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