tert-Butanol → tert-butyl (S)-3-[tert-butoxycarbonyl-[(R)-1-(naphthalen-1-yl)ethyl]amino]pyrrolidine-1-carboxylate

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To a solution of 14.9 g of triphosgene dissolved in 400 ml of methylene chloride was added dropwise a solution containing 25.68 g of tert-butyl(R)-3-[1-(naphthalen-1-yl)ethylamino]pyrrolidine-1-carboxylate (the compound obtained in the above-mentioned Reference example 1.005 (1)) and 31.5 ml of triethylamine in 100 ml of methylene chloride at −20° C. Further, 7.5 g of triphosgene was added to the same, and the mixture was stirred at room temperature for 30 minutes. Water was added to the reaction mixture, the mixture was stirred and the liquids were separated. The organic layer was dried, the solvent was evaporated, and the residue was purified by silica gel column chromatography (hexane:ethyl acetate=6:1→2:1) to obtain 10.63 g of tert-butyl(S)-3-[chlorocarbonyl-[(R)-1-(naphthalen-1-yl)ethyl]amino]pyrrolidine-1-carboxylate and 9.22 g of tert-butyl(R)-3-[chlorocarbonyl-[(R)-1-(naphthalen-1-yl)ethyl]amino]pyrrolidine-1-carboxylate shown in the following Reference example Table, respectively. (2) To 18.52 g of tert-butyl(S)-3-[chlorocarbonyl-[(R)-1-(naphthalen-1-yl)ethyl]amino]pyrrolidine-1-carboxylate was added 1.0 liter of tert-butanol, and the mixture was stirred at 60° C. for 2 days. The reaction mixture was concentrated, and then, the residue was purified by silica gel column chromatography (hexane:ethyl acetate=10:1) to obtain 9.24 g of tert-butyl(S)-3-[tert-butoxycarbonyl-[(R)-1-(naphthalen-1-yl)ethyl]amino]pyrrolidine-1-carboxylate (the following Reference example 1.006(a)).

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