C(Cl)(=O)C(Cl)=O.CS(C)=O.[CH3:11][O:12][C:13]([CH:15]1[CH2:20][CH:19]([OH:21])[CH2:18][CH2:17][N:16]1[C:22]([O:24][C:25]([CH3:28])([CH3:27])[CH3:26])=[O:23])=[O:14].OS([O-])(=O)=O.[Na+]>C(Cl)Cl.CCN(CC)CC>[CH3:11][O:12][C:13]([CH:15]1[CH2:20][C:19](=[O:21])[CH2:18][CH2:17][N:16]1[C:22]([O:24][C:25]([CH3:28])([CH3:27])[CH3:26])=[O:23])=[O:14]To a mixture of oxalyl chloride ((15 mL, 30 mmol, 2 M dichloromethane) in CH2Cl2 (100 mL) cooled to −78° C. was added DMSO (4.5 mL, 63.4 mmol). The mixture was stirred at this temperature for 1 h, after which 4-hydroxy-piperidine-1,2-dicarboxylic acid 1-tert-butyl ester 2-methyl ester (2.0 g, 7.71 mmol dissolved in CH2Cl2) as added. The mixture stirred for a further 1 h and Et3N (20 mL) was then added and the mixture stirred for another 30 min. The mixture was then allowed to warm to −40° C. and poured into a solution of 10% NaHSO4. The reaction mixture was then extracted with ethyl acetate. The organic extract was then washed with brine and dried over MgSO4 (anhydrous) and the solvent was removed in vacuo and the crude residue was purified by silica gel flash column chromatography giving 1.75 g (88%) of the product as a yellow oil. 1H-NMR (CDCl3), δ(ppm): 4.85 (br, d, 1H), 4.02 (m, 1H), 3.61 (s, 3H), 3.58 (br, 1H), 2.75 (m, 2H), 2.44 (br, 2H), 1.43 (br, s, 9H).
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