Iodine → (S)-Methyl 2-(tert-butoxycarbonylamino)-3-(3-oxocyclopent-1-enyl)propanoate

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A solution of (R)-methyl 2-(tert-butoxycarbonylamino)-3-iodopropanoate (32.9 g, 0.100 mol) in DMF (20 mL) was added to a mixture of Zn (19.5 g, 0.300 mol) and iodine (6.6 g, 26 mmol) in DMF (30 mL) under nitrogen protection. The mixture was stirred for 1 h at ambient temperature. Then a solution of 3-iodocyclopent-2-enone (20.8 g, 0.100 mol) in DMF (50 mL), Pd2(dba)3 (2.3 g, 2.5 mmol) and S—Phos (2.1 g, 5.0 mmol) were added successively. The reaction mixture was stirred overnight at 50° C. The mixture was cooled to ambient temperature and water (100 mL) was added. The resulting mixture was extracted with EtOAc (150 mL×3). The combined organic extracts were dried over anhydrous sodium sulfate and concentrated. The residue was purified by flash column chromatography on silica gel (petroleum ether/EtOAc=5:1 to 2:1) to afford (S)-methyl 2-(tert-butoxycarbonylamino)-3-(3-oxocyclopent-1-enyl)propanoate (17 g, 60% yield) as a pale yellow oil.

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