C(Cl)(=O)C(Cl)=O.CS(C)=O.[CH2:11]([O:18][C:19](=[O:26])[C:20]([CH3:25])([CH3:24])[CH2:21][CH2:22][OH:23])[C:12]1[CH:17]=[CH:16][CH:15]=[CH:14][CH:13]=1.C(N(CC)CC)C>ClCCl.O>[CH2:11]([O:18][C:19](=[O:26])[C:20]([CH3:24])([CH3:25])[CH2:21][CH:22]=[O:23])[C:12]1[CH:17]=[CH:16][CH:15]=[CH:14][CH:13]=1Step C To a solution of oxalyl chloride (2.8 mL, 22 mmol) (Aldrich) in dichloromethane (40 mL) at −78° C. was added the solution of dimethyl sulfoxide (3.1 mL, 44 mmol) in dichloromethane (5 mL) dropwise. After 5 mins, the solution of 4-hydroxy-2,2-dimethyl-butyric acid benzyl ester (4.5 g, 20 mmol) in dichloromethane (5 mL) was added dropwise. The reaction mixture was stirred at −78° C. for 15 min. Triethylamine (10 mL, 72 mmol) was added and the reaction mixture was slowly warmed up to room temperature and stirred at room temperature for 45 min. Then water was added. The organic layers were separated, and the aqueous layer was extracted with dichloromethane. The organic layers were combined, washed with 10% of HCl, saturated NaHCO3, brine, dried over MgSO4, and concentrated to give 2,2-dimethyl-4-oxo-butyric acid benzyl ester as a colorless oil (Yield: 2.9 g, 66%).
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