Oxidation Procedure: 0.40 mL (5.6 mmol) of dimethyl sulfoxide was dissolved in 5 mL of dichloromethane and cooled to -78 °C. 0.35 mL (2.48 mmol) of trifluoroacetic anhydride was slowly added dropwise under stirring and stirring was continued for 30 minutes. Subsequently, 0.25 g (1.14 mmol) of a 2 mL solution of 1-benzyl-3,3-dimethyl-4-hydroxypiperidine in dichloromethane was added dropwise, and the reaction mixture was stirred at -78 °C for 1 hour. Then, 1.0 mL (7.2 mmol) of triethylamine was added and the reaction mixture was slowly warmed to 0°C and stirred at this temperature for 2 hours. After completion of the reaction, the mixture was poured into water and extracted with ethyl acetate. The organic phases were combined, dried over anhydrous sodium sulfate and concentrated under reduced pressure. The crude product was purified by silica gel column chromatography with the eluent being a hexane solution of 0-20% ethyl acetate. The fraction containing the target product was collected and concentrated under reduced pressure to give 0.20 g (79% yield) of 3,3-dimethyl-1-phenylmethyl-piperidin-4-one.
