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At room temperature and under nitrogen, triphenylphosphine (13.0 g, 49.5 mmol), zinc dust (2.16 g, 33.0 mmol) and carbon tetrabromide (11.0 g, 33.0 mmol) were added to CH2Cl2 (80 mL). After stirring for 5 minutes, a solution of N-t-butyloxycarbonyl-(S)-prolinal (3.29 g, 16.5 mmol) in CH2Cl2 (25 mL) was added. The reaction was slightly exothermic. After stirring for 1 hour, the reaction mixture was diluted with EtOAc/hexane (1:1) and filtered through basic alumina. The filter cake was then washed with a mixture of CH2Cl2 /EtOAc/hexane (1:1:1). The filtrate was concentrated in vacua, and the residue was taken up in EtOAc/hexane (1:1). The resulting precipitate was filtered, and the filtrate was taken up in EtOAc/hexane (1:1). The resulting precipitate was filtered, and the filtrate was (1:6.5 to 1:5) as the eluant. The resultant pure solid product was isolated in 91% yield (5.31 g): mp 65-66° C.; [α]D≤ +20.1 (c 1.10, MeOH); 1H NMR (DMSO-d6, 70° C., 300 MHz) δ 6.57 (d, J=8.1 Hz, 1H), 4.26 (ddd, J=7.9, 7.9, 4.9 Hz, 1H), 3.30 (m, 2H), 2.11 (m, 1H), 1.72-1.92 (m, 2H), 1.65 (m, 1H), 1.40 (s, 9H); MS m/e 354 (M+H)+ ; Anal. Calcd for C11H17Br2NO2 : C, 37.21; H, 4.83; N, 3.95. Found: C, 37.45; H, 4.85; N, 3.97.

1. stirringAfter stirring for 1 hour
2. filtrationfiltered through basic alumina
3. washThe filter cake was then washed with a mixture of CH2Cl2 /EtOAc/hexane (1:1:1)
4. concentrationThe filtrate was concentrated in vacua
5. filtrationThe resulting precipitate was filtered
6. filtrationThe resulting precipitate was filtered
7. customThe resultant pure solid product was isolated in 91% yield (5.31 g)