C(Cl)(=O)C(Cl)=O.CS(C)=O.[OH:11][C@@H:12]1[CH2:16][O:15][CH2:14][C@H:13]1[NH:17][C:18](=[O:24])[O:19][C:20]([CH3:23])([CH3:22])[CH3:21].C(N(CC)CC)C>C1COCC1.O>[O:11]=[C:12]1[CH2:16][O:15][CH2:14][CH:13]1[NH:17][C:18](=[O:24])[O:19][C:20]([CH3:22])([CH3:21])[CH3:23]A mixture of oxalyl chloride (3.20 mL, 36.9 mmol) in THF (137 mL) is cooled to −78° C. under nitrogen and treated dropwise with DMSO (5.24 mL, 73.8 mmol). The mixture is stirred for 20 min at −78° C., whereupon trans-tert-butyl N-[4-hydroxytetrahydrofuran-3-yl]carbamate (5.00 g, 24.6 mmol) is added. Stirring at −78° C. is continued for 1 h. Triethylamine (18.5 mL, 133 mmol) is added and the reaction is warmed to room temperature. The reaction is stirred for 16 h, then water (100 mL) is added and the reaction is concentrated in vacuo to remove THF. The mixture is extracted with EtOAc (3×70 mL), the combined organics dried over magnesium sulfate, filtered, and concentrated to give 6.4 g of crude product as an orange oil. The crude product is purified on silica gel (220 g, 15-30% EtOAc/hexanes) to give the title compound as a yellow oil (2.20 g, 44%). GC-MS m/z 201 (M)+, 143 (M-t-Bu)+.
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