[CH2:1]([N:8]([CH2:22][C:23]1[CH:28]=[CH:27][CH:26]=[CH:25][CH:24]=1)[C@H:9]([CH2:20][OH:21])[C:10]([O:12][CH2:13][C:14]1[CH:19]=[CH:18][CH:17]=[CH:16][CH:15]=1)=[O:11])[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.S([O-])([O-])(=O)=O.[Na+].[Na+].[F:36][C:37]([F:45])(S(F)(=O)=O)C(O)=O>C(#N)C>[CH2:22]([N:8]([CH2:1][C:2]1[CH:3]=[CH:4][CH:5]=[CH:6][CH:7]=1)[C@H:9]([CH2:20][O:21][CH:37]([F:45])[F:36])[C:10]([O:12][CH2:13][C:14]1[CH:15]=[CH:16][CH:17]=[CH:18][CH:19]=1)=[O:11])[C:23]1[CH:24]=[CH:25][CH:26]=[CH:27][CH:28]=1To a mixture of Benzyl (2R)-2-(dibenzylamino)-3-hydroxypropanoate (22.2 g, 59.2 mmol) and sodium sulfate (2.0 g, 14 mmol) in acetonitrile (200 mL) at 40° C., difluoro(fluorosulfonyl)acetic acid (10.5 g, 59.2 mmol) was added dropwise for 1.5 hrs. The reaction mixture was concentrated to dryness. The residue was mixed with ethyl acetate and silica gel, then concentrated again and purified by column chromatography, eluting with 1.5-2.5% ethyl acetate in hexanes to give benzyl (2R) 2-dibenzylamino-3-difluoromethoxy-propionate (3.375 g, 13.4%) as a colorless oil. 1H NMR (300 MHz, CDCl3): δ(ppm) 7.20-7.40 (m, 15H), 6.17 (wt, 1H), 5.27 (q, 2H), 4.22 (dd, 1H), 4.10 (dd, 1H), 3.88 (d, 2H), 3.74 (t, 1H) and 3.65 (d, 2H).
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