C(Cl)(=O)C(Cl)=O.CS(C)=O.[OH:11][CH2:12][C:13]1[O:14][C:15]([C:18]([CH3:21])([CH3:20])[CH3:19])=[CH:16][N:17]=1.C(N(CC)CC)C>C(Cl)Cl>[CH:12]([C:13]1[O:14][C:15]([C:18]([CH3:21])([CH3:20])[CH3:19])=[CH:16][N:17]=1)=[O:11]To a stirred solution of oxalyl chloride (45 mL, 90 mmole) at −78 deg C. under argon was added dropwise dimethyl sulfoxide (8.80 mL, 124 mmole). The reaction mixture was stirred at −78 deg C. for 10 min., and was treated with a solution of 2-hydroxymethyl-5-t-butyloxazole (11.7 g, 75.1 mmole) in anhydrous methylene chloride (30 mL) over 20 min. The mixture was stirred at this temperature for 1 hour, then triethylamine was added slowly (31.0 mL, 222 mmole), during which the reaction mixture became a yellowish slurry. After stirring at −78 deg C. for 20 min, the reaction mixture was warmed to room temperature, added with methylene chloride (100 mL) and stirred for 1 hour. The solid was filtered off and washed with EtOAc. The filtrate was washed with 5% aqueous citric acid (100 mL) and brine (50 mL), dried over MgSO4. Concentration and column chromatography (silica gel, EtOAc/hexane 1:4) afforded 2-formyl-5-t-butyloxazole as a light yellow oil (10.1 g).
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