ClC1C=CC(C(O)=O)=CC=1.[CH2:11]([O:13][C:14]([C@@:16]1([NH2:21])[CH2:18][C@H:17]1[CH:19]=[CH2:20])=[O:15])[CH3:12].[S:22](=[O:26])(=[O:25])([OH:24])[OH:23]>O1CCCC1>[S:22]([OH:26])([OH:25])(=[O:24])=[O:23].[CH2:11]([O:13][C:14]([C@@:16]1([NH2:21])[CH2:18][C@H:17]1[CH:19]=[CH2:20])=[O:15])[CH3:12].[NH2:21][C@:16]1([C:14]([O:13][CH2:11][CH3:12])=[O:15])[CH2:18][C@H:17]1[CH:19]=[CH2:20]Tetrahydrofuran (80 g) was poured into (1R,2S)-1-amino-2-vinylcyclopropanecarboxylic acid ethyl ester 4-chlorobenzoate (8.0 g, 25.7 mmol) obtained in Example 25. After stirring, a mixed liquid of 96% sulfuric acid (1.31 g, 12.8 mmol) and tetrahydrofuran (80 g) was added dropwise over 2.5 hours. The obtained mixture was stirred at room temperature for 1 hour, cooled to 1° C. over 2.5 hours and then filtered at the same temperature to obtain a solid. The obtained solid was washed with a mixed liquid of tetrahydrofuran (8 g) and toluene (4 g) and then dried under reduced pressure to obtain (1R,2S)-1-amino-2-vinylcyclopropanecarboxylic acid ethyl ester hemisulfate having an optical purity of more than 99% e.e. (3.98 g, 19.5 mmol). Yield: 76%.
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