Dimethyl Sulfoxide → (3S)-3-(3-Oxo-1-propyl)-5-oxo-1-[(1R)-1-phenylethyl]pyrrolidine-3-carboxylic acid tert-butyl ester

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Reaction Steps

Dichloromethane (35 ml) was cooled with dry ice-methanol in a nitrogen atmosphere. Oxalyl chloride (3.45 ml, 39.5 mmol) and dimethyl sulfoxide (4.68 ml, 66.0 mmol) were added, and the mixture was stirred under cooling for 15 minutes. A solution of (3S)-3-(3-hydroxy-1-propyl)-5-oxo-1-[(1R)-1-phenylethyl]pyrrolidine-3-carboxylic acid tert-butyl ester (4.58 g, 13.2 mmol) in dichloromethane (31 mL) was added, and the mixture was stirred under cooling for one hour. Triethylamine (11.1 ml, 79.5 mmol) was added under cooling, and the mixture was stirred under cooling for one hour and then at room temperature for one hour. A saturated ammonium chloride solution (100 ml) was added to the reaction solution, followed by extraction with chloroform (100 ml×1, 80 ml×1). The organic layer was washed with brine (120 ml) and then dried over anhydrous sodium sulfate. After filtration, the filtrate was concentrated under reduced pressure. The resulting residue was purified by silica gel column chromatography (hexane:ethyl acetate=100:0→90:10→66:34→60:40→50:50→40:60→34:66→25:75) to give 4.59 g of the title compound as white crystals.

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