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Reference Example 55; L(-)-proline (17.0 g) was dissolved in tetrahydrofuran (350 ml) and a 1 N aqueous sodium hydroxide solution (296 ml), and then benzyl chlorocarbonate (23.2 ml) was added dropwise thereto at 0C under a nitrogen atmosphere. The resulting mixture was returned to room temperature and stirred overnight. 1 N Hydrochloric acid (296 ml) was added thereto at 0C, and the mixture was extracted with ethyl acetate. The organic layer was washed with saturated brine, and dried over magnesium sulfate. The solvent was distilled off under reduced pressure to give 1-[(benzyloxy)carbonyl]-L-proline, which was as such dissolved in tetrahydrofuran (250 ml), and then triethylamine (26.8 ml) was added thereto. To the resulting solution was added dropwise ethyl chlorocarbonate (16.9 ml) at 0C under a nitrogen atmosphere. The mixture was returned to room temperature and stirred for 1 hour, and the insolubles were removed by filtration. To the filtrate was added dropwise an aqueous sodium borohydride (11.2 g) solution (100 ml) at 0C, and the mixture was returned to room temperature and stirred for 3 hours under a nitrogen atmosphere. Next, water was added thereto, and the mixture was extracted with ethyl acetate twice. The organic layer was washed with saturated brine. The solvent was distilled off under reduced pressure, and the resulting residue was purified by silica gel column chromatography (hexane : ethyl acetate 2 : 1 ? 1 : 4) to give benzyl (2S)-2-(hydroxymethyl)pyrrolidine-1-carboxylate (25.0 g) as a colorless oily material. To a solution of oxalyl chloride (6.23 ml) in dichloromethane (70 ml) was added dropwise a solution of dimethyl sulfoxide (10.9 ml) in dichloromethane (100 ml) at -78C under an argon atmosphere. The mixture was stirred as such for 15 minutes, and then a solution of benzyl (2S)-2-(hydroxymethyl)pyrrolidine-1-carboxylate (12.0 g) in dichloromethane (80 ml) was added dropwise thereto. The mixture was stirred as such for 15 minutes, and then triethylamine (42.7 ml) was added dropwise thereto, followed by stirring as such for 20 minutes. The resulting mixture was returned to room temperature and then water was added thereto, followed by separation. The organic layer was washed with 1 N hydrochloric acid twice, an aqueous 4% sodium carbonate solution and saturated brine, respectively, and then dried over magnesium sulfate. The solvent was distilled off under reduced pressure, and the resulting residue was purified by silica gel column chromatography (hexane : ethyl acetate = 2 : 1 ? 1 : 1) to give benzyl (2S)-2-formylpyrrolidine-1-carboxylate. To [2-(1,3-dioxolan-2-yl)ethyl]triphenylphosphonium bromide (90.4 g) was added tetrahydrofuran (400 ml), further added t-butoxypotassium, and the mixture was stirred at room temperature for 1.5 hours under a nitrogen atmosphere. To the resulting mixture was added dropwise a solution of benzyl (2S)-2-formylpyrrolidine-1-carboxylate in tetrahydrofuran (200 ml), and the mixture was stirred at room temperature for 1 hour and at 50C for 3 hours under a nitrogen atmosphere. After returning to room temperature, water was added thereto and the mixture was extracted with ethyl acetate. The organic layer was washed with saturated brine, and dried over magnesium sulfate. The solvent was distilled off under reduced pressure, and the resulting residue was purified by silica gel column chromatography (hexane : ethyl acetate = 3 : 1 ? 2 : 1) to give benzyl (2S)-2-[3-(1,3-dioxolan-2-yl)-1-propenyl]pyrrolidine-1-carboxylate (15.1 g). Benzyl (2S)-2-[3-(1,3-dioxolan-2-yl)-1-propenyl]pyrrolidine-1-carboxylate (15.0 g) was dissolved in ethanol (200 ml), and then 10% palladium carbon (4.0 g, water content: 50%) was added thereto, followed by overnight stirring at room temperature under a hydrogen atmosphere. The insolubles were removed by filtration, and then the solvent was distilled off under reduced pressure. The resulting residue was dissolved in tetrahydrofuran (200 ml) and a 1 N aqueous sodium hydroxide solution (150 ml), and then benzyl chlorocarbonate (10.1 ml) was added dropwise thereto at 0C under a nitrogen atmosphere. The mixture was returned to room temperature, stirred for 3 hours and extracted with ethyl acetate. The organic layer was washed with saturated brine, and dried over magnesium sulfate. The solvent was distilled off under reduced pressure, and the resulting residue was purified by silica gel column chromatography (hexane : ethyl acetate = 7 : 1) to give benzyl (2R)-2-[3-(1,3-dioxolan-2-yl)propyl]pyrrolidine-1-carboxylate (13.6 g). Benzyl (2R)-2-[3-(1,3-dioxolan-2-yl)propyl]pyrrolidine-1-carboxylate (13.0 g) was dissolved in tetrahydrofuran (130 ml), and then 2 N hydrochloric acid (305 ml) was added thereto at 0C. After stirring the resulting mixture at room temperature for 3.5 hours, a 1 N aqueous sodium hydroxide solution (610 ml) was added thereto at 0C. The mixture was extracted with ethyl acetate, the organic layer was then washed with satura... |
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