[C:1]1([CH2:7][O:8][CH2:9][C@@H:10]([C:12]([OH:14])=[O:13])N)[CH:6]=[CH:5][CH:4]=[CH:3][CH:2]=1.[Br-:15].[Na+].N([O-])=O.[Na+]>S(=O)(=O)(O)O>[Br:15][C@@H:10]([CH2:9][O:8][CH2:7][C:1]1[CH:6]=[CH:5][CH:4]=[CH:3][CH:2]=1)[C:12]([OH:14])=[O:13]A solution of O-(phenylmethyl)-L-serine (21.6 g, 0.108 mol) in aqueous sulfuric acid (786 ml, 2.5N) containing sodium bromide (69.3 g, 6.0 eq) was cooled to 0° C. in an ice bath. Sodium nitrite (21 g, 2.7 eq) was added over 10 minutes, and the solution stirred at 0° C. for one hour. The cooling bath was removed, ether (250 ml) was added, and stirring was continued overnight at room temperature. The aqueous layer was extracted repetitively with ether (3×100 ml), and the combined extracts were dried over anhydrous magnesium sulfate and evaporated under reduced pressure to give 25 g of a crude product. The product was purified by column chromatography (83:17; petroleum ether:ethyl acetate) to yield the title compound (10.6 g).
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