C(Cl)(=O)C(Cl)=O.CS(C)=O.[OH:11][CH2:12][CH2:13][N:14]1[CH2:19][CH2:18][N:17]([C:20]([O:22][C:23]([CH3:26])([CH3:25])[CH3:24])=[O:21])[CH2:16][CH2:15]1.C(N(CC)CC)C>C(Cl)Cl>[O:11]=[CH:12][CH2:13][N:14]1[CH2:19][CH2:18][N:17]([C:20]([O:22][C:23]([CH3:26])([CH3:25])[CH3:24])=[O:21])[CH2:16][CH2:15]1
Oxalyl chloride (3.6 mL, 0.0425 mol) was dissolved in DCM (87 mL) at −78° C. Dimethyl sulfoxide (6.58 mL, 0.0927 mol) was added and the solution was held at −78° C. for 10 min. To the resultant mixture was added a solution of tert-butyl 4-(2-hydroxyethyl)piperazine-1-carboxylate (from Oakwood, 8.90 g, 0.0386 mol) in DCM (44 mL) over 15 min. The reaction was stirred at −78° C. for 1 h, then triethylamine (26.9 mL, 0.193 mol) was added. The mixture was warmed to RT over 30 minutes and then stirred at RT for another 30 min. The mixture was diluted with DCM, washed with water (2×), brine (1×), dried over sodium sulfate, and concentrated. The crude product (8.10 g, 91.8%) was used directly in next step without further purification. 1H NMR (400 MHz, CDCl3): δ 9.70 (1H, s), 3.48 (4H, m), 3.19 (2H, s), 2.47 (4H, m), 1.45 (9H, s) ppm.
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