Hydrochloric Acid → Methyl 1-benzylpyrrolidine-3-carboxylate

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To a solution of 1-benzyl-5-oxo-pyrrolidine-3-carboxylic acid methyl ester (30 mmol, 7 g) in anhydrous tetrahydrofuran (40 ml) was added borane-tetrahydrofuran solution (1M, 50 mmol, 50 mL) at ambient temperature. When gas evolution had subsided the solution was heated under reflux for 75 min then stirred for 16 hr at ambient temperature. Hydrochloric acid (6M) was added dropwise (ca. 5 mL) and the mixture was stirred at ambient temperature for 1 hr before removing the solvent under vacuum. The residue was dissolved in dichloromethane and the solution was washed with dilute sodium hydroxide solution. The dichloromethane solution was then extracted with dilute hydrochloric acid (×3), the extracts combined, made basic by addition of sodium hydroxide and extracted with dichloromethane (×3). The combined organic extract was dried over anhydrous sodium sulfate and the solvent was removed under vacuum. The product was purified by chromatography on silica gel eluting with 5% methanol-dichloromethane to give 1-benzyl-pyrrolidine-3-carboxylic acid methyl ester (200 mg, 3%).

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