[C:1]1([CH2:6][C@H:7]([NH:13][C:14](=[O:20])[O:15][C:16]([CH3:19])([CH3:18])[CH3:17])[C:8](=[O:12])[C:9]([CH3:11])=[CH2:10])[CH2:5][CH2:4][CH2:3][CH:2]=1.[OH2:21]>CN(C=O)C>[C:1]1([CH2:6][C@H:7]([NH:13][C:14](=[O:20])[O:15][C:16]([CH3:19])([CH3:18])[CH3:17])[C:8]([C@@:9]2([CH3:11])[CH2:10][O:21]2)=[O:12])[CH2:5][CH2:4][CH2:3][CH:2]=1A solution of (S)-tert-butyl (1-(cyclopent-1-en-1-yl)-4-methyl-3-oxopent-4-en-2-yl)carbamate (10.0 g, 35.6 mmol) in DMF (180 mL) was cooled to −20° C. and bleach (54.0 mL, 71.2 mmol, 10%) was added dropwise under nitrogen. The reaction mixture was warmed to 0° C. and stirred for 1.5 h. Water (200 mL) was added and the mixture was extracted with EtOAc (200 mL×2). The organic phases were combined, washed with brine (200 mL×2), dried over anhydrous sodium sulfate, and concentrated. The residue was purified by flash column chromatography on silica gel to afford tert-butyl ((S)-3-(cyclopent-1-en-1-yl)-1-((R)-2-methyloxiran-2-yl)-1-oxopropan-2-yl)carbamate as viscous oil (5.6 g, 53% yield). 1H NMR (300 MHz, CDCl3): δ 4.62 (s, 1H), 4.91 (d, J=7.5 Hz, 1H), 4.44-4.37 (m, 1H), 3.29 (d, J=4.8 Hz, 1H), 2.89 (d, J=4.8 Hz, 1H), 2.56-2.52 (m, 1H), 2.29-2.26 (m, 5H), 1.92-1.82 (m, 2H), 1.51 (s, 3H), 1.41 (s, 9H).
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