General procedure for the synthesis of (S)-1-(tert-butoxycarbonyl)-4,4-difluoropiperidine-2-carboxylic acid from compound (CAS: 1352342-07-4): compound 2 (1.526 g, 5.462 mmol) was dissolved in tetrahydrofuran (11 mL), methanol (11 mL), and 1N aqueous potassium hydroxide (11 mL, 11 mmol). It was stirred at room temperature for 1.5 hours. Subsequently, 1N aqueous potassium hydroxide solution (5.5 mL, 5.5 mmol) was added and stirring was continued for 1 hour. After completion of the reaction, the mixture was concentrated to half the original volume, diluted with water and washed once with ether. The aqueous phase was acidified with 1N hydrochloric acid (20 mL) and extracted twice with ethyl acetate. The organic phases were combined, washed once with saturated brine, dried over anhydrous sodium sulfate and concentrated to give compound 3 (1.429 g, 98% yield). Mass spectrometry analysis showed [M-H]? = 264.2.
