[N-:1]=[N+:2]=[N-:3].[Na+].[CH3:5][O:6][C:7]([C@H:9]1[CH2:13][C@H:12](Br)[CH2:11][N:10]1[C:15]([O:17][C:18]([CH3:21])([CH3:20])[CH3:19])=[O:16])=[O:8]>CN(C)C=O.O>[CH3:5][O:6][C:7]([C@H:9]1[CH2:13][C@@H:12]([N:1]=[N+:2]=[N-:3])[CH2:11][N:10]1[C:15]([O:17][C:18]([CH3:21])([CH3:20])[CH3:19])=[O:16])=[O:8]Add sodium azide (157 g, 2.39 mol) to (2R,4S)-4-bromo-pyrrolidine-1,2-dicarboxylic acid 1-tert-butyl ester 2-methyl ester (370 g, 1.20 mol) in N,N-dimethylformamide (2.5 L) and heat at 70-75° C. for 16 h under nitrogen. Cool to room temperature, dilute with water (5 L), and extract with ethyl acetate (3 L). Wash with brine (2 L). Extract the brine layer with ethyl acetate (3 L), combine the organic layers, dry over sodium sulfate, filter and concentrate to obtain an oil (324.5 g). Dissolve the material in ether (2 L), wash with water (2×2 L), dry over sodium sulfate, filter, and concentrate to obtain 261.2 g of a dark yellow oil. Back-extract the aqueous layer with ether (2×2 L), dry over sodium sulfate, filter, and concentrate to obtain an additional 7.3 g of product. Overall yield 268.5 g (83%). [α]D20+39.5 (c=1.0 in methanol). 1H NMR (400 MHz, CDCl3) δ 1.40-1.41 (s, 9H), 2.09-2.13 (m, 1H), 2.40-2.44 (m, 1H), 3.37-3.45 (m, 1H), 3.61-3.65 (m, 1H), 3.67-3.69 (s, 3H), 4.09-4.15 (m, 1H), 4.25-4.38 (m, 1H).
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